Style Guide Full Text

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Below is the full text of the Style Guide for web pages for the Office of Energy Efficiency and Renewable Energy. The guide features formatting, spelling, punctuation, capitalization, grammar, and language guidelines.

Guidelines are listed alphabetically for easy reference. You may also use the topic index to locate information covered in the guide.

A | B | C | D | E | F | G | H | I | J | K | L | M | N | O | P | Q | R | S | T | U | V | W | X | Y | Z

a and an

Use "a" before any acronym or word that begins with a consonant sound. Use "an" before any acronym or word that begins with a vowel sound. An acronym is pronounced as a word (for example, a HEPA filter); an initialism is pronounced as its letters (for example, an NGO). The first sound of the word or letters indicates whether to use "a" or "an."


  • a light-water reactor: an LWR
  • a Human Resources Office memo: an HRO memo
  • a nongovernmental organization: an NGO

abbreviations and acronyms

An abbreviation is a shortened form of a word used in place of the full word (e.g., Corp.). An acronym is a word formed from the first letters of each of the words in a phrase or name (e.g., NASA or laser). Abbreviations and acronyms are treated similarly. 

1. Using Abbreviations and Acronyms Sparingly

Avoid using a given acronym unless you use it extensively in a publication. In a short report, do not use an acronym for a phrase you use five or fewer times. In a long report, do not use an acronym for a phrase you use fewer than 10 times.

Some two-letter abbreviations and acronyms are acceptable (e.g., AC and DC, or MW). Avoid other two-letter acronyms that are less universally used (e.g., EE and RE).

If you use many acronyms in a report, add a list of acronyms at the beginning of the report.

2. Spelling out Acronyms

In general, each time you use an acronym for the first time in the body of a report or on a given web page, spell it out and put the acronym in parentheses after the full name. However, you do not need to spell out most common abbreviations and acronyms (e.g., AC, DC, cm, m, Hz, kW, MW, GW, and rpm) in most technical reports.

3. Abbreviating Measurement Units

Spell out a technical abbreviation in full in text when you use it without numerals. For example, write "a few centimeters" rather than "a few cm."

Abbreviate units of measurement when they are used with a numeral or numeric value. With a few exceptions (such as %, °, $, and ¢), use a space to separate them from numerals.

4. Abbreviating Plurals

Use a small s (no apostrophe) for plurals of most abbreviations. For plurals of units of measurement, omit the s (e.g., 15 cm, 6 m, 5 million Btu, 75 dB, 40 W).

5. Abbreviating Equations and References

You can abbreviate "equation" and "reference" when you use them with numbers, but spell them out at the beginning of a sentence.


  • See Eq. 1-1, Eq. 2-7, and Ref. 10.
  • Equation 2-1 shows the relation.
6. Abbreviating in Journals

For a journal article, consult the publisher's or professional society's guidelines for abbreviations, if they are available. For abbreviations of journal titles, please see the Web of Science website.  

academic degrees

Avoid the use of academic degrees unless it's absolutely necessary to establish credentials. If it's absolutely necessary, use the following abbreviations after a name and set it off with periods: Ph.D., B.A., M.A., and LL.D. Use them only on first reference. Also, use an apostrophe in bachelor's degree, a master's, etc., but there is no possessive in Bachelor of Arts or Master of Science, for example.

See the Associated Press Stylebook for more guidelines.


See abbreviations and acronyms.

active voice and passive voice

Try to write more active-voice sentences than passive-voice sentences. In other words, the subject of most of your sentences should be the "actor" or "agent" (who did it?) rather than the thing "acted upon."

  • Active voice: We tested the apparatus.
  • Passive voice: The apparatus was tested by us.

Research shows that active voice helps even highly educated readers absorb information more quickly. Passive voice is no longer considered to be more scholarly or scientific than active voice. Active voice also lends clarity and vigor to technical writing. But sometimes passive voice is appropriate, especially when it's more important to emphasize what was done than who did it. Passive voice can add variety to your writing, too. See also personal pronouns.


Use U.S. Postal Service abbreviations (such as CO for Colorado and DC for District of Columbia) for states in bibliographies, references, and full addresses (those that include streets or post office boxes).


  • P.O. Box 123
  • Denver, CO 80101

In text, when you refer to a state with a city or by itself (for example, "The state energy office is stepping up solar retrofit activities in Massachusetts."), spell out the name of the state in full, except for the District of Columbia (D.C.). See also states and countries.

affect and effect

"Affect" is usually a verb and "effect" is usually a noun.

  • Affect (verb): The new deposition process affected the efficiency of the device.
  • Effect (noun): We measured the effect of the new process on the efficiency of the device.

These words can be confusing, because "affect" can sometimes be a noun (when it denotes an emotion), and "effect" can be a verb (when it means "to bring about").

air conditioning

Air conditioning is two words when used as a noun and hyphenated when used as an adjective.


  • Air conditioning is energy-intensive.
  • The efficiency of the air-conditioning system can be improved.

American Recovery and Reinvestment Act of 2009

After spelling out the full name on first reference, you may use "Recovery Act" in subsequent references instead of the acronym "ARRA." But when using "Recovery Act," do not identify it in parentheses after the full name like you would with the acronym.


Ampersands can be used in acronyms, left navigation, right navigation, and in a website's top banner (but not in the heading). Ampersands can also be used as the official name of a company or initiative, for example, PG&E or Leadership in Energy & Environmental Design. Do not use “&” to mean "and" in other situations.


You can include detailed background or technical information in one or more appendices. Large, detailed tables are often placed in an appendix. If you have more than one appendix, title them with letters (Appendix A, B, C, etc.) and name figures and tables so they reflect the title (Figure A-1, Table B-2, etc.). If you have only one appendix, title it "Appendix" rather than "Appendix A."

assure, ensure, and insure

"Assure" means to guarantee. "Ensure" means to make certain. "Insure" means to obtain insurance.


  • The manufacturer assured the group the equipment would work properly.
  • Ensure the lid is fitted properly before starting the experiment.
  • The laboratory must insure the new equipment before it can be used.

author-date citations

This is the preferred style for EERE reports and papers. Do not use a comma between the author's last name and the year: (Smith 2000). See also references.

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"Bandgap" is one word.


"Baseload" is one word when used as a noun or adjective.

because and since

"Because" indicates a cause-and-effect relationship. "Since" indicates a time relationship.


  • Because the equipment malfunctioned, the experiment failed.
  • Since we began using the new procedures, there have been no more malfunctions.


A bibliography, which is different from a reference list, is a list of works that are related to your subject or publication but not cited, either by author or by number, in text. Alphabetize works in bibliographies according to the last name of the first author. Some bibliographies are titled "For Further Reading." Compile your in-text citations of literature and other sources in a list of references.


BOS stands for balance of systems (not system).

British thermal units

The abbreviation for "British thermal unit" is Btu. Btu is used for both singular and plural cases.


Bullets are printed to the left of items in a list. You must have at least two items in a bulleted list.

  • Make bulleted lists parallel in construction (that is, begin all the items in the list with the same part of speech, such as a verb or a noun).
    • Make sure items are either all phrases or all complete sentences.
    • Punctuate all items consistently.
  • Use bulleted lists sparingly to:
    • Highlight important items
    • Draw attention to main points
    • Help readers find information.
  • Use bulleted lists sparingly, in most cases, to highlight important items, draw attention to main points, or help readers find information.
  • Use numbered or lettered lists instead of bullets if you want to refer to items in a list or procedure elsewhere in the text.
  • Begin each item with a capital letter; omit ending punctuation for all but the last item, unless all items are complete sentences.

In text, the first level of bullet is indented 0.25 in., and text begins at the 0.5-in. mark. This level is bulleted with a solid dot. Second-level bullets are open dots, and third-level bullets are em dashes. Each subsequent level of bullet is sequentially indented 0.5 in. In lists of items that are more than one line, each bulleted item is followed by a 6-pt. space.

On the Web

Except for the indenting and spacing formats for reports, all of the above guidelines apply to the web. When formatting bullets on the web, there should be a space between the text above the bullets and the first bullet. To help facilitate scanning, you might also consider a space between each bulleted item when the bulleted text is long.

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  1. Capitalizing Proper Nouns

    Capitalize proper names. These include the names of government programs, official projects, formal groups, organizations, companies, titles when they precede a name (use lowercase in titles that follow the name), specific geographic areas or features, and ethnic groups.


    • the U.S. Bureau of Mines
    • Solarex Corporation
    • World Wide Web
    • President Carter
    • Christine Johnson, president and chief executive officer
    • the Southwest
    • Lake Powell
    • the Colorado River
    • African, Asian, Caucasian, Hispanic, or Native Americans

    One exception to this rule is companies and products with stylized lowercase or "camel cap" names. In these cases, use the company’s or product’s preferred capitalization.

  2. Capitalizing Taxonomic Names

    When writing about botanical and zoological divisions, capitalize the names of all divisions higher than species: genera, families, orders, classes, and phyla. Print genera, species, and varieties in italics.


    • Clostridium thermocellum
    • Escherichia coli

    After you first mention them (and spell them out), you can abbreviate most generic names followed by species names.


    • C. thermocellum
    • E. coli
  3. Capitalizing Table Titles, Headings, and Captions

    Capitalize the main words of table titles and most headings and subheadings, including the second word in a hyphenated term (e.g., PV Program Five-Year Plan). Do not capitalize articles (e.g., "a," "an," and "the") unless they begin the title or heading; conjunctions (e.g., "and," "or," "nor," and "but"); or prepositions (e.g., "for," "of," and "to"). When "to" is used in a table title or heading, it is capitalized as an infinitive and lowercase as a preposition. Verbs, including "is" and "are," are always capitalized.


    • Table 1. Number and Frequency of Defects in Six Samples
    • (May–June 1998)
    • Testing the 7.6-m Blades (subhead)
    • Results for E. coli (subhead)
    • Development of Method To Detect Anomalies (subhead)

    Capitalize only the first word and proper nouns in figure captions.


    • Figure 1. Results for the electrochromic window

    Follow the style recommended by your professional society or journal publisher regarding the word "figure" and its abbreviation ("Fig.") when you prepare a paper or an article for submission to a conference or journal. Many societies and publishers recommend lowercasing everything but the first word and proper nouns in all table titles, subheads, and captions.

  4. Capitalizing States and Titles

    Capitalize the names of states, but capitalize "state" only when it appears with the entire official name:


    • the State of Colorado; Washington State

    Capitalize titles when they precede the person's name. Lowercase titles and names of groups when they follow the name:


    • Chief Operating Officer Mark Wilson
    • Mary Jones, the president of the company
    • John Smith, the chair of the committee
  5. Capitalizing Trade Names

    Capitalize trade or brand names, and include a trademark, copyright, or other symbol only when it's part of the official name. Include the symbol the first time you use the trade name in body text; thereafter, you may omit the symbol:


Refer to the company's literature or stationery if you're not sure. See also the online database of current trademarks.

See also captions, fiscal year, geographic regions, states and countries, and tables.

Back to Top | Topic Index


All substantive photos should be accompanied by a caption. Begin figure and photo captions with a capitalized word and use lowercase thereafter, except for proper nouns and capitalized abbreviations. You don't need a period at the end of a caption unless you add a subcaption or the caption is a complete sentence.

chemical terms

Do not use a hyphen in most chemical expressions, even when the terms are used as modifiers.


  • carbon dioxide levels
  • hydrogen ion activity

Use a hyphen after prefixes when that's the standard for certain chemical formulas.


  • L(+)-2, 3-butanediol
  • trans -glycol

Use a hyphen to indicate mixtures or combinations.


  • hexane-benzene


See references for guidance on author-date and numbered citations.


"Cleantech" is spelled as one word. It is not hyphenated, and the "t" is not capitalized. The word "cleantech" is typically used in reference to investments in sustainable technologies, including renewable energy and energy efficiency. Don't use as a shortened form of "clean technology" in other references.

close-spaced sublimation

The term is "close-spaced sublimation," not "closed-space sublimation."



Colons formally introduce a list or series, a question, or an amplification. Colons often separate the parts of a ratio.


  • We test three types of collectors: flat plates, evacuated tubes, and parabolic troughs.
  • We added enough water to obtain a 3:1 dilution.

But commas, not colons, usually follow words such as "that is," "namely," or "such as." You don't need a colon after a verb or preposition that precedes or introduces a list ("includes," "to," "with," "between," etc.). Use a colon when a noun (such as "the following") introduces a list in text.


  1. When To Use Commas

    Use a comma to separate items in a series, including the next-to-last word in the series:


    • We develop solar thermal, wind, biomass, and photovoltaic energy technologies.

    Use a comma to separate the parts of a compound sentence linked by a coordinating conjunction (such as "and," "but," "or," or "nor") when each part has its own subject and verb (unless they're very short):


    • I laughed at the unintentional joke, but she frowned.

    Use commas to set off nonessential or nonrestrictive (parenthetical) words, phrases, and clauses from the rest of the sentence. In other words, the commas signal that the information between them is something extra and not essential to the meaning of the sentence


    • The subsystem, which takes a day to install, will be delivered in two weeks.

    Use commas to enclose the name of a state when it follows a city and a year when it follows the month and day.


    • The test systems in Gardner, Massachusetts, are performing well.
    • The next test sites will be in Golden, Colorado, and Chapel Hill, North Carolina.
    • On April 11, 1998, the committee members completed five of the six objectives.
  2. When Not To Use Commas

    Do not use a comma to separate compound subjects or compound verbs.


    • Theorists and nonspecialists alike agree on the importance of the discovery. (There is no comma between the two parts of this compound subject.)
    • The researchers rolled out the thin metal sheet and formed it into coils. (There is no comma between the two parts of this compound verb.)

    Do not use commas to set off words or phrases that are restrictive, that is, essential to the meaning of a sentence.


    • Only the sensors that were attached to the outer edge failed. (The words are essential to the meaning of the sentence.)
    • The system will work efficiently only if it includes storage. (The words are essential to the meaning.)

See also which and that.

compose and comprise

"Composed of" is correct; "comprised of" is incorrect.


  • The United States is composed of 50 states.
  • The parts constitute the whole.
  • The whole comprises its parts.
  • The department comprises four groups; each group is composed of five to seven scientists, technicians, and support staff.

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compound words, unit modifiers, and hyphens

  1. Verb Phrases: Verb, Noun, and Adjective Forms

    Verb phrases that contain an adverb (build up, set up, start up, break down) are usually written as two words. The noun and adjective forms of these words are either one word (no hyphen) or a hyphenated form of the words. However, there are exceptions. Refer to the dictionary for the correct spelling.


    • We observed the slow buildup of biofouling on the blades.
    • We helped with the setup.
    • The start-up costs were higher than we estimated.
    • I think I'm having another breakdown.
  2. Compound Words Containing Prefixes and Suffixes

    You don't need a hyphen between many prefixes and suffixes and the root words, unless the root word is a proper noun:

    threefold, hundredfold
    (also 100-fold)


    These prefixes usually require a hyphen: "ex," "self," and "quasi."

  3. Unit Modifiers With and Without Hyphens

    Use a hyphen to indicate that words have been combined into a unit modifier, which is a descriptive expression composed of two or more words that form one new meaning. For example, in the term "flat-plate collector," "flat-plate" is the unit modifier. Although there is a tendency in modern writing to eliminate hyphens, they help prevent ambiguity and confusion. Here are some examples of unit modifiers that usually include hyphens:

    • low-level radiation
    • last-minute addition
    • fatigue-induced wear
    • five-year plan
    • nine-story building.

    To see how adding the hyphen can prevent confusion, consider these examples:

    • The scientists tested a new defect causing gas.
    • The scientists tested a new defect-causing gas.

    In the first example, the scientists might seem to have been testing a defect; in the second example, it's clear that they have tested a gas.

    You don't need a hyphen in common unit modifiers that are not ambiguous or confusing.

    • high school students
    • solar radiation resource
    • solar thermal electric systems

    Don't use a hyphen when both words of a unit modifier are capitalized.

    • Bronze Age tools
    • Vietnam Era veterans
    • Biofuels Program objectives

    Leave out the hyphens if you rewrite a sentence so the words in the unit modifier come after the noun they describe.


    • We purchased state-of-the-art lab equipment.
    • We purchased lab equipment that reflects the state of the art.
    • They made some last-minute adjustments.
    • They made some adjustments at the last minute.

    Don't use a hyphen with a unit modifier containing an adverb ending in "-ly."


    • frequently missed deadlines
    • heavily skewed results

    When you use numbers in unit modifiers, retain all the necessary hyphens.


    • 2-in.-diameter tubes
    • 13-cm-wide substrate

    Or rewrite the sentence to omit the hyphens.


    • tubes that are 2 in. in diameter
    • a substrate that is 13 cm wide

    Use a hyphen between prefixes and proper nouns (but not common nouns) or dates, whether they're used as nouns or modifiers.


    • non-EERE
    • mid-1990s

    Use two hyphens when adding a prefix to a word that already contains a prefix, even when there is no hyphen after the prefix in the original word.


    • non-self-limiting

comprise and compose

See compose and comprise.

Congress and congressional

Capitalize "U.S. Congress" and "Congress" when referring to the U.S. Senate and House of Representatives. Lowercase "congressional" unless it is part of a proper name.


  • The U.S. Congress is reviewing congressional salaries. A full list is available in the Congressional Record.

cooperative research and development agreement

On first reference, use lowercase for "cooperative research and development agreement" because it's not a proper noun. On second reference, you can use the acronym "CRADA."


countries and states

See States and Countries.


CPV (concentrating photovoltaics) uses lenses to intensify the sunlight striking PV cells, which enhances the cells' electricity production.

criterion, datum, memorandum, phenomenon, and their plurals

"Criterion" is a singular noun (one criterion), and "criteria" is the plural (two or more criteria). "Data" is the plural of "datum." The plural of "memorandum" can be either "memoranda" or "memorandums." "Phenomenon" is singular, and "phenomena" is plural.


CSP (concentrating solar power) captures the sun's heat and uses the thermal energy to produce electricity (e.g., via a steam turbine).

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Use dashes (often called "long dashes" or "em dashes") to enclose and set off parenthetical (nonessential but often illustrative) information in a sentence. Also use dashes to set off a list of items separated by commas. Do not add spaces around the dash.


  • The polymer components of the cell walls—cellulose, hemicellulose, and lignin—provide the feedstocks for these chemicals.

Use an em dash to signal that an important point is going to be made or that a change in the construction of the sentence follows.


  • The presentation concluded with a discussion of the two project factors that concern contractors the most—cost and time.

  • The major omission in the project assessment was the delay caused by the circuit failures—everyone knew about it but no one mentioned it to the reviewers.

You can usually use commas, colons, and semicolons in place of dashes, but dashes add special emphasis.

Use shorter dashes known as "en dashes" (rather than a hyphen or em dash) to indicate a range or to substitute for the word "to."


  • 25–45 cm2
  • 2–5 runs per hour
  • See sections 3.1–3.6
  • Jan. 16–Feb. 3, 2011

In date spans, do not use "from" in conjunction with an en dash (e.g., "from Jan. 16–Feb. 3"). The correct form is "from Jan. 16 to Feb. 3" or "Jan. 16–Feb. 3."

Do not use an en dash (or hyphen) to mean "and"; the word "between" is followed by the word "and" (not "to").


  • between 25 and 30

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data in tables

Place a zero to the left of the decimal in any number less than 1 in text and tables (e.g., 0.5, 0.039). Align columns of data vertically on the decimals. When the units of measurement for the data are different, alignment is not necessary (but be sure to specify the units).


Use common month abbreviations when a full date is provided. Use cardinal numbers for the day.


  • Jan. 1, 2010
  • May 6, 1990

decision maker

degree symbol

Print the degree symbol right next to the symbol for the temperature scale.


  • 36ºC
  • 85ºF

Repeat the degree symbol in ranges.


  • 32º-36ºC

Express kelvins as K rather than as ºK; leave a space before the K.


  • 85 K

Department of Energy

See U.S. Department of Energy.


DOE requires EERE publications to include a disclaimer. The disclaimer used depends on the type of publication.


  • This report was prepared as an account of work sponsored by an agency of the United States government. Neither the United States government nor any agency thereof, nor any of their employees, makes any warranty, express or implied, or assumes any legal liability or responsibility for the accuracy, completeness, or usefulness of any information, apparatus, product, or process disclosed or represents that its use would not infringe privately owned rights. Reference herein to any specific commercial product, process, or service by trade name, trademark, manufacturer, or otherwise does not necessarily constitute or imply its endorsement, recommendation, or favoring by the United States government or any agency thereof. The views and opinions of authors expressed herein do not necessarily state or reflect those of the United States government or any agency thereof.

dish/engine systems

Use a slash rather than a hyphen.


Express thousands of dollars using a comma.


  • $5,000

Express millions and billions of dollars this way.


  • $3 million
  • $1.2 billion

In technical reports and papers, use a dollar sign to express costs less than $1.


  • $0.25
  • $0.06 per kilowatt-hour

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effect and affect

See affect and effect.


When you want to leave out part of text material you are quoting, use ellipsis marks (three dots with a space on each side) to indicate the omission.


  • A participle is "a word having the characteristics of both verb and adjective ... [that] shows such verbal features as tense and voice. ..."

If the words before the ellipses form a grammatically correct sentence, put a period at the end of the sentence and follow it by ellipses. In most cases, however, you don't have to use ellipses at the beginning or end of quotes, just within them. When you add a word or words to the quote, to make it clear, enclose the added word or words in brackets to show that it is not part of the original quotation.

When you quote whole paragraphs but omit text between any two of them, center three asterisks, with spaces between them (* * *), between the paragraphs quoted. See also quotation marks.


Acceptable in all references for "electronic mail." Use a hyphen with other e- terms: e-book, e-business, e-commerce.


  • I sent an email to everyone involved with the project.


ENERGY STAR is always in capitals. If the first instance of ENERGY STAR is in the content, use ENERGY STAR®. If the first instance is in a header, use ENERGY STAR without the superscript. In both cases, use ENERGY STAR thereafter. There is no space between the ® and ENERGY STAR.

enhanced geothermal system

The preferred term is "enhanced geothermal system" (EGS). It also sometimes referred to as an "engineered geothermal system."

ensure, insure, and assure

See assure, ensure, and insure.


Make sure that all the terms in your equations are defined and used consistently both in the text and in subsequent equations, figures, and tables.


  • The conductive heat flow equation is:
    dQ/dt = AKdT/dx,

    dQ/dt = the time rate of heat transfer
    A = the area of an end contact
    K = the thermal conductivity
    dT/dx = the thermal gradient.


Because it's vague, please use "etc." (et cetera) sparingly. Don't add it to the end of a list beginning with "for example," or the abbreviation "e.g.," because each word in your list is an example of your subject or topic, but "etc." is not, so you don't need it.

executive summary

If you include a summary in a report, place it before the contents page. If your report is brief, a summary is not usually necessary. If your report is long, or if you think some readers will want one, you can include an executive summary.

An executive summary can be up to 5% to 10% of the length of your paper and it should be written so that it can be read independently of the full report as they are frequently published as a separate document. Its content should include a brief statement of the problem or proposal covered in the report, background information, concise analysis, and the main conclusions.


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Use a capital letter with "federal" for corporate or governmental bodies that use the word as part of their formal names.


  • Federal Trade Commission, Federal Communications Commission

Use lowercase when the word is used to distinguish something from state, county, city, etc. entities.


  • federal government, federal court, federal judge


Figures can include line drawings, graphs, charts, diagrams, schematics, flow charts, illustrations, and photographs.

For print products, use an Arial font and consistent line weight in your figures. Be sure that computer-generated figures are clear and readable so they can be reproduced easily.

Use 10-pt. Arial bold for captions; capitalize only the first word and proper nouns. Number figures in a simple sequence (e.g., Figure 1, Figure 2). In long reports, papers, or book chapters, you may include section or chapter numbers in the figure numbers (e.g., Figure 1-1, Figure 1-2, Figure 2-1, and so on).

Make sure the data in your figures correspond to the data in your text and tables. The caption is placed under the illustration (see also captions).

[[{"type":"media","view_mode":"media_large","fid":"985256","field_deltas":{},"link_text":null,"attributes":{"alt":"A graphic that uses colored lines to represent numbers for generation of concentrating solar power, solar photovoltaics, biomass","height":231,"width":450,"style":"width: 450px; height: 231px;","class":"media-image caption media-element file-media-large","data-delta":"1"},"fields":{}}]]

Figure 1. Renewables as a percent of total installed capacity worldwide

No period is needed after a caption if it is an incomplete sentence. If one or more full sentences follow the incomplete sentence (as a continuing caption or subcaption), each caption (including the opening incomplete sentence) should have a period. Don’t bold subcaptions. See Figure 2-1 below for an example.

  • Figure 2-1. Photoconductivity spectra of a composite CIS thin film.
    Inset: the probable energy band diagram.

first-person pronouns

See personal pronouns.

fiscal year

Spell out "fiscal year" (e.g., Fiscal Year 2006) the first time you use it; after that, you can abbreviate it using two capitals followed by a space before the full year (e.g., FY 2001). FY01 may be used to save space in charts and graphs. On the web, always spell out "fiscal year."


You can use footnotes to place \detailed explanatory or supplementary information at the bottom of a page; use in-text references to cite others' works. Use superscript numerals for footnote numbering. You can also place explanations, details, contradictions, and examples in the text rather than in footnotes. Footnote numbers are printed outside commas and periods but inside colons, semicolons, and dashes.

The experiment took place in April,1 and it was evaluated in May.2
We discussed these three stages of writing7: prewriting, writing, and revising.

Mark the footnotes to tables in EERE reports with superscript letters: a, b, c, etc.


The foreword to a book or formal report contains introductory remarks written, and usually signed, by someone other than the author or authors. Brief introductory remarks written by authors are contained in a preface.


Use words instead of numerals for simple fractions in text.


  • a third of the way
  • one-fifth its actual size
  • three-fourths of the participants

Write out complex fractions with numerals separated by a solidus.


  • 1/64
  • 23/32
  • 5-1/2 days afterward
  • 2-1/2 times greater

Display complex, built-up fractions by centering them vertically between two parts of a paragraph.

[[{"type":"media","view_mode":"media_large","fid":"985246","field_deltas":{},"link_text":null,"attributes":{"alt":"Example of an equation centered and placed vertically between two parts of a paragraph.","height":55,"width":111,"class":"media-image caption media-element file-media-large","data-delta":"2"},"fields":{}}]]

Place a zero to the left of the decimal in fractions less than 1.


  • 0.125
  • 0.006

See also equations.

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geographic information system

Do not capitalize "geographic information system" unless used as part of a proper noun. It's also "geographic," not "geographical." Our acronym style guidelines apply as well.

geographic regions

Capitalize regions of the United States when they appear by themselves.


  • the East, the West, the North, and the South
  • the Southeast, the Northeast, the Southwest, the Pacific Northwest
  • the Midwest, the East Coast, the West Coast, the Gulf Coast

Don't capitalize words that merely describe general areas in the country or areas of a state.


  • the eastern United States
  • southwestern Nebraska
  • northern New Mexico
  • the midwestern states

geopressured geothermal resource

Geothermal Electric Technology Evaluation Model

glossaries and nomenclatures

If you use many mathematical or Greek symbols or technical terms in your report or paper, consider defining them in a glossary or nomenclature. Arrange the list alphabetically, and group Greek letters and definitions alphabetically in a separate list. Nomenclatures are usually in the front of a report, before the contents page. Glossaries usually go in the back, before the references.

Google Earth and Google Maps

When using satellite images from Google Earth and terrain images from Google Maps, include attribution to Google, which is included in Google images with copyright notices such as "© 2009 Google, Map Data © 2009 Tele Atlas." The Google logo and attribution text can be removed if they are added elsewhere within the image content.

In print, if attribution cannot be placed on the image or map, separate attribution text must be provided directly adjacent to it.

In video, attribution must appear on-screen for the duration of the time the map or image is shown; including attribution in end credits only does not suffice.

If the Google Earth image is altered (e.g., text or graphics are added), the image is legal only if Google Earth software is used to make the alteration and correct attribution is included. Any other alteration of the image using any other software is strictly prohibited.

Derivative works cannot be created. For example, EERE cannot combine multiple static map images to show a larger map.

ground-source heat pump

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heat mining

hybrid electric vehicle

This phrase contains no hyphens.


See compound words, unit modifiers, and hyphens.

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An initialism is similar to an acronym, but it is pronounced by its letters.


  • American Society for Testing and Materials (ASTM)
  • National Fire Protection Association (NFPA)
  • public utility commissions (PUCs)
  • chemical vapor deposition (CVD)
  • compact vacuum insulation (CVI)
  • chlorofluorocarbons (CFCs)

Use a small s (no apostrophe) for plurals of most initialisms (e.g., PUCs and CFCs, not PUC's or CFC's).

Avoid the use of initialisms unless they are used extensively in a document. In short reports, spell out initialisms that are used fewer than five times. In long reports, spell out initialisms that are used fewer than 10 times. If initialisms are used, spell them out on first use, and put the initialism in parentheses after the full name.

To avoid confusion, try not to use too many in any sentence or paragraph. Include a glossary or list of acronyms if your publication contains a lot of them.

On the Web

The above guidelines apply to web content as well. However, if you use an initialism, spell it out or define it the first time you use it on each web page.

insure, assure, and ensure

See assure, ensure, and insure.


Lowercase "internet."


Inverters convert direct current to alternating current.


  1. Using Italics for Emphasis

    Use italics (sparingly) to emphasize a word or phrase or bring attention to it.


    • Never operate this equipment when it has a yellow danger tag.

  2. Using Italics for Foreign Words and Phrases

    Italicize such foreign words and phrases as in situ, in vivo, and inter alia; however, if the word or phrase is commonly used in your field, you may omit the italics.

  3. Using Italics for Hyphenated Prefixes

    Italicize hyphenated prefixes (such as cis-, trans-, o-, m-, and p-) to chemical formulas.


    • trans -1, 2-dibenzoylethylene
    • trans -glycol
  4. Using Italics to Cite Published Documents

    Use italics in references, footnotes, and bibliographies for book titles and the names of journals, newspapers, and magazines.


    • Gone with the Wind
    • Applied Physics Letters
    • The Denver Post
    • Science

    But print the titles of journal and magazine articles in regular Roman type within quotation marks.


    • "Solar Chimney Theory: Basic Precepts"
  5. Using Italics in Taxonomic Names

    Unless you're discussing a genus in a general way, use italics to refer to specific genera, species, and varieties.


    • Clostridium thermocellum
    • C. thermocellum

it's and its

Even though "it's" has an apostrophe, it isn't a possessive pronoun. "It's" is a contraction, a short form of two words, like "isn't." "It's" always means "it is." "Its" is the possessive form of "it." Like "his," "hers," and "ours," the possessive "its" never needs an apostrophe.


  • It's a shame that the company lost its biggest investor.

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Kalina cycle


Kilowatt is abbreviated (kW).


Kilowatt-hour is abbreviated (kWh).

laboratory and lab

Only capitalize "laboratory" or "lab" when used with a laboratory's full name. Lowercase in all other references.


  • The National Renewable Energy Laboratory is a U.S. Department of Energy national laboratory. The laboratory is known for its research and development in renewable energy and energy efficiency.

life cycle


"Lightbulb" is spelled as one word.


You can use bulleted or numbered lists. Here's an example of a numbered list:

[[{"type":"media","view_mode":"media_energy_gov_wysiwyg_fullwidth","fid":"1038256","field_deltas":{},"link_text":null,"attributes":{"alt":"Requirements for lists. Contact the webmaster if you cannot read this image.","height":316,"width":781,"class":"media-image caption media-element file-media-energy-gov-wysiwyg-fullwidth","data-delta":"3"},"fields":{}}]]

You can also list a few items or procedures in paragraph format and number them (1) one, (2) two, (3) three, etc. See bullets for more formatting information.



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mathematical symbols

Leave a space on either side of mathematical symbols used as operation signs.


  • Tin - Tamb
  • ºC × 1.8

The solidus (a/b) or division sign is an exception. Do not leave a space between numerals and the symbols for degrees, dollars (or cents), and percent (32º, $100, 17%). (Leave a space between numerals and symbols of measurement such as cm and Å, however.) Do not leave a space between symbols such as >, <, and the numeral unless they are the operation signs in an equation.

measurement units

See units of measurement.

megawatt (MW)

megawatt-hour (MWh)

metric conversions

For quick online conversions of English units of measurement to metric units, see the Digital Dutch Unit Converter or the Internet French Property Measuring Units Converter Table.

metric system

See SI (Metric) System.


"Microgrid" is spelled as one word.

microseismic events

misplaced modifiers

Modifiers in the wrong place can make a sentence confusing.


  • After identifying the correct material, the test procedure took about 5 minutes.

In this example, it isn't clear who or what identified the correct material. This might be better: After identifying the correct material, we conducted the five-minute test procedure.


  • After being lost under a pile of old reports for 5 years, she finally found the manuscript.

What, or who, was lost—the manuscript, the woman, or the reader? Try to keep modifiers as close as possible to the people and things they describe. Strunk and White, authors of The Elements of Style, say this: "Modifiers should come, if possible, next to the word they modify." This is especially true for sentences containing introductory prepositional phrases or clauses followed by a comma.

months and years

Capitalize the months in all uses. When a month is used with a specific date, abbreviate only Jan., Feb., Aug., Sept., Oct., Nov., and Dec. (Jan. 9, 2008). Also abbreviate these months in tables; however, omit the period. Spell out months when used alone or just with the year; and omit commas when the month and year appear together (October 2001).

Use a lowercase s (no apostrophe) to show the plural of a decade expressed with numerals (e.g., the 1990s).

multijunction solar cell

This term is preferred over "tandem solar cell."

multiplication symbols

Be as consistent as possible in using multiplication symbols; as appropriate, choose one symbol (× or ·) or omit the symbol and use proximity or parentheses: ab, (ab) (cd), etc.

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Always use lowercase for the word "nation" when referring to the United States.


  • Our nation is a leader in renewable energy markets.


Spell as one word. Don't hyphenate.

noncondensable gases

nonrestrictive phrases and clauses

A nonrestrictive phrase or clause is one that adds information but is not essential to the meaning of the sentence.


  • The principal investigator, who has studied thin films for 10 years, will chair the panel discussion.

  • The passive solar features, which were suggested by EERE staff, reduced the agency's energy bills by 30%.

Nonrestrictive or nonessential phrases and clauses are enclosed between two commas when the phrase or clause is within a sentence, and they usually begin with the pronoun "which" rather than "that." See also restrictive phrases and clauses and which and that.

non-SI (English) units of measurement

Use non-SI (Systeme International d'Unites) or nonmetric units of measurement (English or Imperial units) instead of metric units only when they are the industry standard. Otherwise, state metric units first, followed by English equivalents in parentheses.


  • 38.1 m (125 ft)

noun and adjective strings

Try not to string too many noun modifiers together in a sentence. An "agency personnel communications interface display" could also be called a "display of the communications of the agency's personnel." Better yet, it could just be called the "staff bulletin board."


To give your writing more flow and vigor, try changing some of the nouns (especially those ending in –tion and –ment) to verbs (e.g., determine, complete, accomplish, achieve, measure, convert, characterize, combine) and other parts of speech. Doing this will move your readers along more quickly and make it easier for them to understand your text. In these examples, we changed some of the nouns in the first sentences to verbs and other parts of speech.


  • Contraction of the tree stems occurred with rapidity.
    The tree stems contracted rapidly.

  • The frequent result of this process is the combination of the molecules.
    This process frequently causes the molecules to combine.

  • The application of fertilizer has the result of stimulation of the yield.
    Applying fertilizer stimulates the yield.

Which sentences were easiest to read and understand?


  1. Units of Measurement and Mathematical Expressions

    Use numerals with units of measurement and time.


    • 2-1/2 hours
    • 4.5 months
    • 36 cm
    • 87 years
    • 6 liters
    • 25 kW

    With units of time, you can spell out numbers less than 10 if you do so consistently (this applies mainly to outreach products rather than technical reports and papers).


    • five-year plan
    • two-hour test
    • three-week turnaround

    Use numerals to imply arithmetical values or manipulation.


    • a factor of 3
    • multiplied by 2
    • a ratio of 4:5
    • values of 1 and 48

    Express measurement errors as: 6 nm ± 0.2 nm.

    Leave a space between the number and the unit of measurement (0.2 nm) and put spaces around the operation sign; when the measurement error appears by itself, omit the space between the sign and the number.


    • The measurement error is ±0.2 nm.

  2. Aligning Numbers

    Align numbers that share a common unit of measurement on the decimals in columns of tables. Put a zero before the decimal in numbers smaller than one.


    • 0.8
    • 2.45
    • 187.362

    If all the numbers in a column do not share the same unit of measurement, you may center the numbers in the column and specify the unit of measurement.

  3. Fractions and Decimals

    You can spell out and hyphenate simple fractions (this is preferred in text) or express them, like more complex fractions, in numerals with a solidus.


    • one-fifth or 1/5
    • 1/64 (but not 1/64th)

    Use a hyphen to separate the integral and fractional parts of a mixed number, or convert the fraction to a decimal.


    • 2-1/2 cm in diameter
    • 2.5-cm-diameter solar cell

    For numbers of 1 million or more, use the numeral (and a decimal, if necessary) and the words million, billion, etc.


    • 1.1 million households
    • 3.5 billion people
    • $2.5 million in funding
  4. Precision and Numbers

    Measurement uncertainty analysis calls for precision in measurements to a significant digit to the right of a decimal point, such as two or three digits (hundredths or thousandths). If you're not absolutely sure, check with an expert before changing the number of digits to the right of the decimal, or rounding the numbers. See also standard errors.

  5. Punctuating Numbers

    Use a comma to separate groups of three digits in numbers.


    • 5,182
    • 113,728
    • 2,225,000
  6. Ranges of Numbers

    To show ranges, use an en dash (which is a little shorter than an em or long dash) with no spaces. Alternatively, if you write out a range, make sure you use the word "to" when you use "of" or "from" before the range. To express a range between some number and another number, always use the word "and" (not "to") with the word "between."


    • 15%-25%
    • from 32º to 40ºC
    • 6-12 cm
    • from 66 to 80 V
    • 10-20 m2
    • between 8 and 12 m (not "between 8 to 12 m")
    • $3 million-$4 million

    Note that some symbols, like º and %, are repeated in a range.

  7. Scientific Notation

    Express multiples of SI (metric) units in powers of 10 with the appropriate prefixes and technical abbreviations.


    • mm (millimeters, 10-3 m)
    • MJ (megajoules, 106 J)

    Use standard scientific notation to express very small and very large numbers.


    • 2.5 × 10-3
    • 3.56 × 106

    Avoid using M to mean "thousands" and MM to mean "millions"; use a capital M for "mega," or millions, as in MW for "megawatts."

  8. Spelling out Numbers

    Except with units of measurement and time, spell out numbers less than 10.


    • eight experimental runs
    • three species of yeast

    Spell out all numbers at the beginning of a sentence.


    • Fifteen trials later, the results were the same.
    • Thirty-five participants attended the seminar.

    When a sentence contains one or more numbers greater than nine that are related to a smaller number, use numerals for all of them.


    • The results were the same in 3, 12, and 18 trials.
    • The contractor tested 8 devices in May, 12 in June, and 9 in July.

    Spell out the first of two adjacent numbers unless the first one requires three or more words.


    • ten 5-kW arrays
    • thirty-two 4-cm2 devices
    • 135 16-cm collectors

See also fractions.

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over and under

In cases involving quantity, use "more than" rather than "over" and "fewer than" or "less than" rather than "under."


  • More than 500 people attended the conference, about 100 fewer than last year.

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Use parallel construction in sentences as well as in lists. Express all similar sentence elements (subjects, verbs, verbals, objects) in a similar way.

Not Parallel Structure:
  • The lever was moved completely forward, going slightly to the right, and then it went backward halfway in order to complete the procedure.
  • We are not only responsible to our chief customer but also the taxpayers.
Parallel Structure:
  • To complete the procedure, push the lever all the way forward, slide it slightly to the right, and then pull it halfway back.
  • We are responsible not only to our chief customer but also to the taxpayers.


Use parentheses as appropriate for explanatory material in text and as shown in the examples that follow.

  1. Parentheses in Equations

    In equations, use parentheses, brackets, and braces in this sequence (which may be repeated as needed).


    • {[( )]}
  2. Parentheses With Measurements

    Use parentheses around English measurements that follow SI (metric) measurements.


    • 3.1 m/s (7 mph)
  3. Parentheses in Citations

    When you use parentheses in text, such as for author-date references or for parenthetical (added) information, place a comma after the parentheses rather than before them.


    • In earlier research (Jones 1989), we showed how quantities of lipids could be increased by this method.

  4. Nested Parentheses in Text

    In body copy, use parentheses, brackets, and braces in this sequence, which may be repeated as needed: ([{ }]).


    • (The data presented here [originally derived from Mason {1998}] should not be used for location-specific analyses.)

passive voice and active voice

See active voice and passive voice.

percent, %, and percentage

Use the symbol % with numerals; use the word "percent" when you spell out numbers at the beginning of a sentence. To determine whether "percent" or % is singular or plural, look at the noun following it. If the next noun is a plural, use a plural verb; if it's singular, use a singular verb.


  • The maximum glucose yield was 60%.
  • Six percent of the pipes were rusty.
  • More than 10% of that amount was allocated to planning.

When there is no number, use the word "percentage," unless people in your field use a different terminology, such as "percent difference."


  • This table shows the percentages of government buildings having solar roofs, by state.


Periods are used in some abbreviations (e.g., i.e., a.m., p.m.) and not in others (ac, dc, rpm). Most acronyms do not have periods. When you end a sentence with "etc." (although this is seldom necessary) or another abbreviation that already includes a period, do not add another one.


  • This paper describes the program's purpose, objectives, schedule of deliverables, etc.
  • (Better: This paper describes the program's purpose, objectives, and schedule of deliverables.)

personal pronouns

First person pronouns should generally be avoided. However, some scientific and technical associations (such as the American Institute of Physics) ask technical writers to use first-person pronouns when it is appropriate. Common first-person pronouns include "we," "our," and "us." Personal pronouns can prevent confusion by clearly and concisely showing who performed an experiment or procedure.


  • We tested several hundred isolates that were able to ferment glucose.
  • We deposited a thin film of doped cadmium on the substrate.

Which of these two sentences is easier to read and understand quickly?

  1. It was determined that the workshop was a success.
  2. We agreed that the workshop was a success.

See also active voice and passive voice.

phone numbers

Do not use parentheses around area codes in phone numbers. Parentheses previously were used to set off the three-digit code in a phone number because it wasn't always necessary when dialing the number. However, they are required in most instances now.

Use hyphens to separate the digits in phone numbers.


  • 303-275-3658
  • 1-800-555-5555


When you use an image, credit the photographer or other source for legal purposes. Provide a caption when necessary. See captions.

photovoltaics and photovoltaic

"Photovoltaics" is a singular noun. "Photovoltaic" is an adjective. The acronym "PV" can be a noun or an adjective, but do not pluralize it.


"Policymaker" and "policymaking" are both spelled as one word.


See compound words, unit modifiers, and hyphens and scientific notation.


Use the standard SI unit for pressure or stress, which is the pascal (Pa) or the bar. Non-SI units include psi (pounds per square inch), millimeters of mercury, torr, and atmospheres, and they are still in relatively widespread use.

principal and principle

"Principal" often means "chief" or "main," such as the principal investigator in a research project or the principal of a high school. "Principle" often refers to a belief, value, or rule.

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quotation marks

Use quotation marks for direct quotes and the titles of articles, papers, and reports. In print, use "curly" or "fancy" quotation marks.


  • "Let's meet again in 6 months," the chairman said, "to discuss our progress."
  • She presented a paper titled "Materials Research in Silvered Polymer Reflectors."

Place commas (and periods) inside quotation marks; place semicolons, question marks, dashes, and exclamation points outside quotation marks unless they're part of the quotation.


  • "The results are in," he said.
  • "Can you hear me?" she asked.
  • Did he really say "I don't believe you"?

Use single quotation marks to indicate a quotation within material that is already enclosed in double quotation marks.


  • "Explain what you mean by 'confidence,'" she said.

When quotations are longer than two or three lines of text, begin them on the next line and indent them on each side (block quotations). You do not need quotation marks around block quotations, and you can use standard double quotation marks for quotes within block quotations. In in-text quotations, place reference numbers, superscripts, and author-date citations outside quotation marks (but before the final punctuation of a sentence). Place them after the final punctuation of the last sentence in a block quotation.

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Rankine cycle


In general, use a colon to indicate a ratio.


  • We prepared a 3:1 dilution.

However, some industries (such as the American automotive industry) use a solidus to express a ratio.


  • The engine is designed to have an optimum air/fuel ratio.

references and citations

The references you cite in your EERE publications not only allow others to place your work in the context of the published literature but they also lend credibility to your published work.

For all EERE technical publications, use the Chicago Manual of Style when you document your references and format your citations of them. Of Chicago's two systems of source citation for documenting references, EERE prefers author-date references (e.g., Keller et al. 2016) over numbered footnotes or endnotes.

Chapter 15 of the Chicago Manual of Style outlines how to document your sources using author-date references. Chapter 14 presents Chicago's system that uses numbered footnotes or endnotes. For sample citations for various types of sources using either system, see the Chicago-Style Citations Quick Guide.

Place works that you use (but do not cite in the text) in a bibliography. If you are preparing a manuscript for a publisher other than EERE, follow that publisher's preferred reference style. 

renewable energy certificate

Don't capitalize "renewable energy certificate." It's not a proper noun. Also, this is the term preferred over "renewable energy credit" or "green tags."

renewable portfolio standard

Only capitalize "renewable portfolio standard" when a state name precedes it.

  • Renewable energy certificates have been proposed under California Renewable Portfolio Standards.

restrictive phrases and clauses

Do not use commas around restrictive phrases and clauses. They are essential to the meaning of the sentence, in contrast to nonrestrictive phrases and clauses, which simply add information that is not essential.


  • This is the house that Jack built.

See also which and that.


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scientific notation

Standard scientific notation represents a number as a factor multiplied by a power of 10; 3,560,000 is expressed as 3.56 × 106. This is useful for very large and very small numbers, especially in non-SI units. You can also use certain standard prefixes, many of which are listed here with their abbreviations.


We recommend choosing a prefix that permits the numerical value to fall between 0.1 and 1,000 (62 kW rather than 62,000 W).


Semicolons indicate a stronger or more important break in the flow of words than the break indicated by a comma. Use a semicolon in compound sentences that are NOT linked by a conjunction (such as "and," "but," "or," "nor," and "yet"). Place a semicolon before conjunctive adverbs (such as "however," "hence," "therefore," "nevertheless," "consequently") in most complex sentences containing two or more clauses. When a sentence contains items in a series, you may use a semicolon between the items if one or more of the items contains commas.

  1. Using Semicolons in Compound Sentences Without Conjunctions

    When clauses in a sentence are closely related in meaning, a semicolon is an appropriate dividing punctuation mark. Note that the words "and," "but," "or," and "nor" do not follow semicolons.


    • It was difficult to reproduce the experiment; the material Smith and Jones used was not widely available. Of the 13 samples, only one did not degrade; others deteriorated an average of 8%.

  2. Using Semicolons With Conjunctive Adverbs

    "Yet" and "so" are usually preceded by commas in a complex sentence. But use a semicolon before such conjunctive adverbs as "then," "however," "thus," "therefore," "hence," "accordingly," "moreover," "nevertheless," "consequently," "besides," "indeed," and "subsequently"; place a comma after the adverb.


    • The contractor's representative was out, so I left a message.

    • We used the Schartz-Metterklume method in the experiment; however, the problems with this method are well known.

    • Energy requirements are often expressed in quads, or quadrillion Btu; therefore, this report describes the number of quads supplied annually by each option.

    Use a semicolon before "i.e." ("that is") and "e.g." ("for example") and a comma after them when a clause (with a subject and verb) follows them; use a comma when a phrase or list follows.

  3. Using Semicolons in a Series

    When items in a series contain internal punctuation (e.g., commas) or are very long, you can separate them with semicolons. In those cases, a conjunction can follow the last semicolon.


    • The contaminants in the sample were TCE, 150 ppb; toluene, 220 ppb; and benzene, 265 ppb.

    • Promising new technologies demonstrated at the exposition included advanced wind turbines; polycrystalline, thick-film, and thin-film solar cells; fast-growing energy crops; and fuel cells.

    • The vendor assured us that the replacement parts, which were essential in this installation, were on order; that the parts would be delivered as soon as they arrived; and that the delay in shipment was unavoidable.

SI (metric) system

EERE follows national policies and those of scientific societies by using the SI (Systeme International d'Unites; International System of Units) or metric system in expressing technical measurements. English units may follow metric ones or may be used alone in special cases, when that is appropriate for a publication's audience. See also the National Institute of Standards and Technology.

since and because

See because and since.

slash (solidus)

The solidus (or slash, slant, shilling mark, or virgule) is a versatile symbol that has mathematical as well as textual functions.

  1. Using a Solidus in Fractions

    Use a solidus to express a quotient in text when you do not need to use a displayed equation.


    • These structures yield photoluminescence lifetimes that are related to bulk lifetime by the expression .

    Use a solidus in superscript and subscript fractions.


    • x1/2
  2. Using a Solidus in Text

    In text, use a solidus to indicate some junctions, interfaces, and components.


    • gas-liquid interface
    • 1-butyl acetate/acetic acid/water (3:1:1)

    With abbreviated units of measurement, the solidus stands for "per."


    • 2 g/cm2
    • 355 W/m2

    But spell out "per" when you spell out the units of measurement.


    • several cubic meters per second
    • a few cents per kilowatt-hour

Smart Grid and smart grid

Use capital letters for "Smart Grid" when referring to the overall goal or concept and lowercase letters for "smart grid" when referring to current implementations or when used as an adjective.

solar cell interfaces

Use a slash rather than a hyphen to designate solar cell interfaces or layers.


  • CdTe/CdS2
  • GaInP/GaAs2

solar conversion efficiency

Define in outreach publications as "the percentage of sunlight striking a solar cell that is converted into electricity." A definition is often unnecessary in technical publications.

Solar Decathlon

In all communication products, either physical or digital, use Solar Decathlon® on the first instance in that document or web page. Afterwards, use "Solar Decathlon" with no registered trademark symbol. There is no space between the ® and Solar Decathlon.

solar electricity

This term can be used interchangeably with "photovoltaic power," "PV power," or "PV electricity."


Include the sources of all figures and tables that were originally published by others, especially those outside EERE. If figures or tables come from a copyrighted publication, you may need permission to reproduce them. Add the source at the end of a figure caption or in a note following a table.


  • Source: Hansen, W.L.; Pearton, S.J.; Haller, E.E. (1984). Appl Phys. Lett. 44:606.


Use only one space between a period and the beginning of the next sentence.


If you can't find a word or phrase in this style guide, consult the following reference guides in this order: (1) The Associated Press Stylebook 2007 and (2) Merriam-Webster's Collegiate Dictionary, Eleventh Edition.

For spelling out numbers, see numbers.

standard errors

Express standard measurement errors as shown below.


  • 6.0 nm ± 0.2 nm

state implementation plan

Capitalize "state implementation plan" only when a state or organization name precedes it.


  • The Connecticut Department of Environmental Protection incorporated emission reduction strategies into its U.S. Environmental Protection Agency State Implementation Plan for air quality.

states and countries

  1. States

    In text, consistently spell out states' names rather than using U.S. Postal Service abbreviations.


    • California (rather than CA)
    • Colorado (rather than CO)
    • Wyoming (rather than WY)

    You may use D.C. for the District of Columbia in text, in both formal and informal publications. When you include addresses or state names in full addresses (containing streets and cities), contact lists, reference lists, and bibliographies, however, you may use the following abbreviations:

    AL, AK, AZ, AR, CA, CO, CT, DC, DE, FL, GA, HI, ID, IL, IN, IA, KS, KY, LA, ME, MD, MA, MI, MN, MS, MO, MT, NE, NV, NH, NJ, NM, NY, NC, ND, OH, OK, OR, PA, RI, SC, SD, TN, TX, UT, VT, VA, WA, WV, WI, WY (PR, VI).

  2. Countries

    Do not abbreviate the names of countries (including the United States) when they are used as nouns. Use U.S. as the adjective form.


    • the United States
    • U.S. DOE program
    • U.S. population

statistical terms

When referring to statistical or graphical terms, use a hyphen but no italics. Also, do not use capital letters.


  • p-value
  • t-test
  • y-axis

supercritical fluid

systems integrator

The correct term is "systems integrator," not "system integrator."

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taxonomic names

See capitalization and italics.


Use a degree symbol (º) with temperatures expressed in the Celsius and Fahrenheit scales but not with kelvins (just use K). Don't leave a space between the number and the letter for ºC and ºF, but leave a space between the number and K.


  • 72°F
  • 0 K

See also degree symbol.

that and which

See which and that, nonrestrictive phrases and clauses, and restrictive phrases and clauses.

III-V solar cell

This term refers to a cell composed of semiconducting materials from Group III (e.g., gallium) and Group V (e.g., arsenic) elements of the periodic table.


Use lowercase a.m. and p.m. (with periods) to denote "ante meridiem" and "post meridiem" (before and after noon). Use a colon to separate hours from minutes except for the top of the hour.

  • 11 a.m. (not 11:00 a.m.)
  • 3:30 p.m.

trademark symbols

Do not use trademark symbols (® or ™) with third-party products.

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under and over

See over and under.

unit modifiers

See compound words, unit modifiers, and hyphens.

United States and U.S.

Spell out "United States" when it is used as a noun. The abbreviation "U.S." is acceptable when it is used as an adjective.


  • The United States is a leader in renewable energy markets.
  • The global markets for renewable energy are stronger than the U.S. markets.

units of measurement

Use numerals with units of measurement and time in technical papers and reports, even when the number is less than 10. In some outreach publications, you may spell out numbers less than 10, especially with units of time. Except with $, °, and %, leave a space between the numeral and the unit.

2 kW7 cm216.8%
3 m8-hour days300 Btu
5 years$2 billion45°


Uniform resource locators, or URLs, are essentially web addresses.

On websites, URLs should be embedded in text.


In print, URLs should not be embedded in text. If a URL extends beyond one line of text, add a break at a solidus. Also, in general, you do not need to include the http:// prefix on most URLs - but test it before removing it. Shorten URLs as much as possible (e.g., remove unnecessary trailing such as /index.html) while ensuring functionality.

U.S. Department of Energy

This is the preferred term for printed and electronic outreach materials. When spelling it out, "U.S." should precede "Department of Energy" to distinguish it from other state and international departments. However, "U.S." should not be included with the acronym "DOE."

If the possessive is used with the term, the apostrophe should go after "U.S. Department of Energy" and with the "DOE" acronym as well. However, if you can write it in a way that avoids use of the possessive, that is preferred.


  • The U.S. Department of Energy's (DOE's) Office of Energy Efficiency and Renewable Energy (EERE) is in charge of the program.

"Energy Department" may be used as an alternative reference in press releases and other transient communications.

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Web terms

The following words are lowercase:

  • web
  • web page (two words)
  • webcast
  • webinar
  • webmaster
  • website.

World Wide Web is a proper noun and should be initial-capped. 

which and that

Standard American English uses "which" for nonrestrictive or nondefining phrases and clauses and "that" for restrictive or defining phrases and clauses. The word "which" usually signals the approach of added, nonessential information. When a phrase or clause is not essential to the meaning of a sentence, use the relative pronoun "which" and enclose the phrase or clause in commas. See also nonrestrictive phrases and clauses and restrictive phrases and clauses.


  • This paper, which she has been working on for three weeks, discusses string theory.

When a phrase or clause is essential to the meaning of a sentence (that is, the sentence would not make much sense without it), use "that" and leave out the commas.


  • The paper that he completed recently will be presented in New York; the paper that he finished last summer will be presented in Philadelphia.

work-for-others agreement

Use lowercase for "work-for-others agreement" because it's not a proper noun. The acronym "WFO" refers only to work for others; therefore, when using the acronym, "WFO agreement" is correct.

World Wide Web

To abbreviate World Wide Web use "the web," after writing the name out in full the first time it is mentioned.

years and months

See months and years.


For numbers less than one, place a zero before the decimal.


  • 0.5
  • 0.125
  • 0.00125

zero energy building

Use the term to indicate an energy-efficient building where, on a source energy basis, the actual annual delivered energy is less than or equal to the on-site renewable exported energy. Similar terms include zero energy campus, zero energy portfolio, and zero energy community.

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