--- title: "PVWatts typical-year weather and production estimate limits" description: "Separate PVWatts typical weather, dataset vintage, report dates, and measured operating years. Use a synthetic comparison and an assumption worksheet." canonical: "https://scalewithsearch.com/articles/pvwatts-typical-weather-year-production-estimate-limits" --- ## Site navigation - [Scale With Search](https://scalewithsearch.com/) - Services - Services - [AI systems](https://scalewithsearch.com/ai-systems) - [Site build](https://scalewithsearch.com/work#site-build) - [Whole website fix](https://scalewithsearch.com/work#whole-website-fix) - [Content library with SEO](https://scalewithsearch.com/work#content-library) - [Working session](https://scalewithsearch.com/audit) - Start here - [Send your brief](https://scalewithsearch.com/work#send-your-brief) - [Example scope](https://scalewithsearch.com/work#review-the-example-scope) - [Prices and terms](https://scalewithsearch.com/work#prices-and-terms) - Industries - Real estate - [Real estate agents and teams](https://scalewithsearch.com/for/real-estate) - [Platforms, ownership, and IDX](https://scalewithsearch.com/for/real-estate/real-estate-website-platforms-ownership-idx) - [Search, content, and AI](https://scalewithsearch.com/for/real-estate/real-estate-search-content-ai) - [Inquiries, campaigns, and handoffs](https://scalewithsearch.com/for/real-estate/real-estate-website-inquiries-campaigns-handoffs) - [Buyer, seller, and local pages](https://scalewithsearch.com/for/real-estate/real-estate-buyer-seller-local-resources) - [Rules, privacy, and trust](https://scalewithsearch.com/for/real-estate/real-estate-website-rules-privacy-trust) - Browse by business - [Trades and home services](https://scalewithsearch.com/for/#group-trades) - [Health, wellness, and animal care](https://scalewithsearch.com/for/#group-practices) - [Law, finance, and IT](https://scalewithsearch.com/for/#group-professional) - [Marketing and SEO agencies](https://scalewithsearch.com/for/#group-agencies) - [Shops and manufacturers](https://scalewithsearch.com/for/#group-manufacturing) - [Restaurants, shops, studios, and nonprofits](https://scalewithsearch.com/for/#group-local-services) - Chiropractic practices - [Chiropractic and wellness practices](https://scalewithsearch.com/for/chiropractic-and-wellness-practices) - [Chiropractic and physical therapy clinics](https://scalewithsearch.com/for/chiropractic-and-physical-therapy-clinics) - [All industries](https://scalewithsearch.com/for/) - Resources - Free tools - [AI readiness check](https://scalewithsearch.com/check) - [Free tools](https://scalewithsearch.com/tools/) - [Free Starter Kit](https://scalewithsearch.com/kit/business-memory-starter-kit.zip) - Guides - [AI-native library](https://scalewithsearch.com/ai-native) - [Industry intelligence](https://scalewithsearch.com/intelligence) - [Office job guides](https://scalewithsearch.com/guides/) - [Business memory](https://scalewithsearch.com/articles/business-memory-for-ai-agents-guide) - [Agent governance](https://scalewithsearch.com/articles/ai-agent-governance-guide-small-business) - [Migration and ownership](https://scalewithsearch.com/articles/leaving-vendor-ai-memory-guide) - Articles - [All articles](https://scalewithsearch.com/articles/) - [What changed](https://scalewithsearch.com/changes/) - About - Evidence - [Proof](https://scalewithsearch.com/proof) - Scale With Search - [About](https://scalewithsearch.com/about) - [How it works](https://scalewithsearch.com/how-it-works) # PVWatts weather data: explain a typical year without promising next year's production A report prepared today can use a representative weather year assembled from historical conditions. Its preparation date does not turn the estimate into a forecast for the following year. Before a buyer compares production figures, explain what the weather record represents. Give the buyer a short basis statement and keep the detailed assumptions behind it. State the weather source, selected model version, and period represented by each comparison. Leave unresolved conditions visible rather than filling them with a reassuring explanation. The [solar installation page](/for/solar-installation) covers work around approved job information. This guide focuses on the weather basis of a production estimate and the evidence needed before comparing it with operating results. ## What a typical year represents The [SAM Typical and Single Year documentation](https://samrepo.nlr.gov/help/weather_typical_single.html) explains that a typical year represents conditions across a longer period. Its twelve months can come from different historical years. Single-year weather instead describes one specified year. That distinction controls the explanation you give a buyer. A typical-year January and February need not form a historical sequence from one observed calendar year. Displaying them in calendar order makes the modeled year readable; it does not establish a forecast sequence. Use a simple teaching illustration. Imagine an invented representative file containing January selected from Year A and February selected from Year B. The labels A and B are placeholders. They describe no actual dataset selection and no PVWatts simulation. If a reviewer asks, “What happened immediately after that January?”, the assembled file cannot answer the historical question as posed. It contains a selected February for the representative sequence. The original historical record would be a separate source. Keep the explanation concise in a proposal. A useful structure is: “This estimate uses a representative weather file. The file's identity and model assumptions are recorded with the report.” Then identify the exact evidence available for the specific estimate. ## Separate four kinds of dates Create separate fields for the report date, weather dataset identity, modeled sequence, and operating observation period. These fields serve different review questions. Combining them under a heading called “Year” leaves the reader to infer the relationship. The report date answers when the estimate was prepared. It should identify the report revision being discussed. A later preparation date alone does not show that the preparer changed the weather file or technical inputs. The dataset identity answers which weather resource the model used. Preserve its full label and file identifier when available. A shortened label such as “current weather” removes information that another reviewer may need. The modeled sequence answers how the estimate's time series should be interpreted. Identify whether it uses typical-year or single-year data. Do not infer that choice from a date printed in the page footer. The observation period answers when the operating measurements were collected. Record the beginning, end, and any gaps. An installation's first partial year should not silently occupy a worksheet cell labeled “full annual production.” These date fields are a proposed record structure. They do not establish what any particular installer supplied. Complete them from the report and its supporting evidence before writing the customer explanation. ## Read the selected source instead of assuming one weather vintage The [PVWatts V8 documentation](https://developer.nlr.gov/docs/solar/pvwatts/v8/) lists multiple weather datasets. Its returned station information includes the solar resource filename, weather data source, and distance. Record the actual returned identity instead of assuming every V8 estimate uses one identical weather product. Preserve the original source label without interpreting a year-like suffix as an observed operating year. If its meaning is unclear, ask the preparer for the selected dataset documentation. The label should lead to a definition, rather than become a substitute for one. For example, a reviewer might receive a report dated October 2026 and a weather filename containing another year. Those labels alone do not establish a contradiction. First ask what each date describes and whether the report identifies the selected weather basis. Do not change the weather label to match the proposal date. Retain the source identifier and add a plain-language explanation. This lets a later reviewer distinguish a documentation clarification from a new estimate. If the report contains only a screenshot, request the associated settings and weather-source record. A screenshot may help locate the question, but it should not force the technical reviewer to reconstruct missing assumptions from appearance. ## Compare a synthetic estimate with an observation Consider an invented report showing annual AC energy of 9,000 kWh under a typical-year basis. A separate invented operating record totals 8,100 kWh over a stated twelve-month period. These numbers illustrate a review method. They represent no property or model run. Subtract the modeled value from the observation: 8,100 minus 9,000 equals negative 900 kWh. Divide that difference by the modeled value of 9,000. The observation is 10 percent below the estimate on this chosen comparison basis. Name the denominator. Dividing 900 by the observation of 8,100 would answer a different percentage question, approximately 11.1 percent. Without a named reference value, two reviewers can produce different percentages from the same pair of numbers. | Synthetic comparison field | Recorded value or condition | | --- | --- | | Modeled annual energy | 9,000 kWh AC, typical-year basis | | Observed energy | 8,100 kWh, supplied twelve-month record | | Arithmetic difference | Observation minus estimate: negative 900 kWh | | Percentage basis | Difference divided by modeled energy: negative 10 percent | | Weather for observation period | Unresolved | | Measurement boundary | Requires confirmation | | Missing intervals and downtime | Requires confirmation | | Cause of difference | Undetermined | The arithmetic is complete while the explanation remains open. Keep both states in the record. A completed subtraction does not resolve weather, measurement boundaries, or operating conditions. Before presenting the comparison, confirm that both totals cover the intended system and period. Ask whether the observation comes from a production meter, inverter export, or another record. Preserve its definition with the value. ## Do not assign the gap to weather without evidence PVWatts' [results interpretation guidance](https://pvwatts.nlr.gov/docs/en/help_results_interpret.php) describes modeled weather as representative of longer-term conditions. It also identifies system design and operating conditions as relevant to interpretation. The worksheet therefore needs more than a statement that one observed year was “different.” For the synthetic example, list competing questions without deciding their answers. Did the measurement cover a complete operating year? Were any intervals missing? Did the installed configuration match the report? Were outages or changes documented? Ask the responsible reviewer which evidence could resolve each question. An operating log might address a recorded interruption. A settings record might address a configuration change. Weather attribution requires an appropriate weather comparison and a defined technical method. Do not assign arbitrary portions of the 900 kWh difference to separate causes. A plausible explanation is still a hypothesis until supported. Use “unresolved” in the worksheet when the relevant evidence has not been checked. Also avoid treating published variability discussion as a project-specific guarantee or acceptance threshold. This guide assigns no passing percentage to the synthetic difference. Any contractual threshold needs its own controlling terms and responsible review. ## Use single-year analysis for a clearly defined question SAM's [weather guidance](https://samrepo.nlr.gov/help/weather_typical_single.html) identifies single-year data as suitable for studying performance in a particular year. That provides a different analytical basis from a typical-year estimate. It does not make every historical measurement comparable automatically. If a technical reviewer proposes a single-year analysis, write the question first. For example: “Compare the documented configuration under weather for the operating period.” Then specify the configuration evidence, selected weather source, and observation coverage. Keep that analysis separate from the original proposal estimate. Give it its own identity and explanation. Otherwise, replacing the typical-year result can make it unclear which estimate the buyer originally reviewed. Change one identified assumption at a time when the review method requires attribution. If the reviewer changes weather, capacity, and losses together, ask how the analysis separates their effects. Do not infer a causal breakdown from the final total alone. This article does not perform that analysis. It describes the evidence request that should precede it. The technical owner chooses the appropriate method and records what the resulting comparison can support. ## Build a reproducible assumption record Use the following worksheet as an editorial starting point. Save it with the report and original measurement export. A later reviewer should be able to identify both records without relying on the preparer's memory. | Record section | Evidence to retain | | --- | --- | | Estimate identity | Report version, preparation date, and preparer | | Weather basis | Typical or single year, exact source label, and file identity | | Model basis | Selected version and supporting settings record | | System assumptions | Capacity, orientation, losses, and documented changes | | Observation basis | Source, measurement boundary, dates, and interval coverage | | Comparison method | Selected totals, conversions, reference denominator, and rounding | | Open questions | Missing evidence, assigned owner, and next review action | | Approved explanation | Exact wording, reviewer, and the records it describes | Keep “not supplied” separate from “checked and unchanged.” Those states require different follow-up actions. The first requests evidence; the second records a completed comparison against an identified prior version. Record corrections as new decisions with dates. For example, if a preparer clarifies the measurement period, preserve the earlier period and explain the correction. Do not overwrite the comparison silently and leave the buyer's previous explanation untraceable. Set a stopping point for the office reviewer. If the measurement boundary or weather identity remains unresolved, request technical clarification. The office worksheet should preserve the question rather than manufacture an engineering conclusion. ## Prepare the explanation for a proposal meeting For the synthetic case, a careful meeting note would state the 9,000 kWh modeled basis and the separate 8,100 kWh observation. It would name the percentage calculation and list the unresolved comparison conditions. It would assign no cause and promise no future production. Ask the reviewer to confirm that the explanation matches the available report. Keep technical assumptions in the attached record, with a short explanation in the proposal. The buyer should be able to find the basis without deciphering an unlabeled export. For the units behind those totals, read [DC capacity, AC power, and energy outputs](/articles/pvwatts-dc-capacity-ac-power-energy-output-review). For a different evidence task, the [solar intelligence overview](/intelligence/solar-installation) introduces public project comparisons. The [business memory guide](/articles/business-memory-for-ai-agents-guide) explains the owned record behind repeatable document work. Keep weather identities, report revisions, reviewer decisions, and corrections together so later questions start from the same evidence. Scale With Search can scope that document record around your existing proposal and technical review process. Start with the approved source files, unresolved fields, and named review responsibilities. [Discuss the scope](/work) Continue the website review: [AI-native solar installation: the first functions to build](/articles/ai-native-solar-installation-first-functions); [NYSERDA pipeline projects: compare application age before reading completion rates](/articles/nyserda-pipeline-age-completion-cohorts); [NYSERDA project costs: compare reported dollars per DC watt with a solar quote](/articles/nyserda-project-cost-dollars-per-dc-watt); [PVWatts capacity and energy outputs: keep DC size, AC power, and kilowatt-hours separate](/articles/pvwatts-dc-capacity-ac-power-energy-output-review); [Solar brochure PDFs: decide what search should find](/articles/solar-brochure-pdf-search-indexing); [Solar installation AI rules: data, approvals, and spend](/articles/solar-installation-ai-data-approval-spend-rules); [Solar project pages: separate installed work from estimates](/articles/solar-installation-project-case-study-page); [Solar installer review requests: keep the wording neutral](/articles/solar-installer-google-review-request-process); [Solar installer local SEO: connect coverage to real proof](/articles/solar-installer-local-seo); [Solar installer videos: give each useful clip a page](/articles/solar-installer-video-website-search); [Solar installer credentials: make website claims precise](/articles/solar-installer-website-certification-claims); [Solar website FAQs: publish answers you can maintain](/articles/solar-installer-website-faq-content); [Solar installer quote form: ask for the first useful facts](/articles/solar-installer-website-quote-form); [Solar website savings claims: show the assumptions](/articles/solar-installer-website-savings-claims); [Solar website warranty page: name the actual coverage](/articles/solar-installer-website-warranty-page); [Solar repair page: separate service from installation](/articles/solar-maintenance-repair-website-page). [solar installers](/for/solar-installation): website and search resources. ## Related: solar installers - [Solar brochure PDFs: decide what search should find](/articles/solar-brochure-pdf-search-indexing) - [Solar installation AI rules: data, approvals, and spend](/articles/solar-installation-ai-data-approval-spend-rules) - [Solar project pages: separate installed work from estimates](/articles/solar-installation-project-case-study-page) ---- ```text .|########||. .|########||. .|########||. |##||. .||##|. |##||. .||##|. |##||. .||##|. |#|. .|#|. |#|. .|#|. |#|. .|#|. |#| |#| |#| |#| |#| |#| .#| |#. .#| |#. .#| |#. .#. .#| .#. .#| .#. .#| |#. .#| |#. .#| |#. .#| |# ...... #| |# ...... #| |# ...... #| .# ||#########| #| .# ||#########| #| .# ||#########| #| .#. |######||######|. .#. .#. |######||######|. .#. .#. |######||######|. .#. #. .##|###|##|#|######| .# #. .##|###|##|#|######| .# #. .##|###|##|#|######| .# || |##|#||||||||||||#||#| || || |##|#||||||||||||#||#| || || |##|#||||||||||||#||#| || # |#||||||||||||||||||||#| #. # |#||||||||||||||||||||#| #. # |#||||||||||||||||||||#| #. || |#||||||||||||||||||||||#| || || |#||||||||||||||||||||||#| || || |#||||||||||||||||||||||#| || # .#||||||||||||||||||||||||#| # # .#||||||||||||||||||||||||#| # # .#||||||||||||||||||||||||#| # || ....|||#||||||##|#|||#|#||##||||....|. || || ....|||#||||||##|#|||#|#||##||||....|. || || ....|||#||||||##|#|||#|#||##||||....|. || #. . ....|# ....#||| ||| .#||| ....#. .# #. . ....|# ....#||| ||| .#||| ....#. .# #. . ....|# ....#||| ||| .#||| ....#. .# # . ||||#| .#####|| . .#| .#||| ||||# #. # . ||||#| .#####|| . .#| .#||| ||||# #. # . ||||#| .#####|| . .#| .#||| ||||# #. .| ||||| #. |#|||||. || #. |#||. .||||| || .| ||||| #. |#|||||. || #. |#||. .||||| || .| ||||| #. |#|||||. || #. |#||. .||||| || || |.... #. ....|#. |. ...|. ....|| || || |.... #. ....|#. |. ...|. ....|| || || |.... #. ....|#. |. ...|. ....|| || #. .||||||##||||||##||####|||||||#||||||#| .# #. .||||||##||||||##||####|||||||#||||||#| .# #. .||||||##||||||##||####|||||||#||||||#| .# # .||####|###########################|. # # .||####|###########################|. # # .||####|###########################|. # # .#||||||.#.|| # |. ..# #| #|||||#| # # .#||||||.#.|| # |. ..# #| #|||||#| # # .#||||||.#.|| # |. ..# #| #|||||#| # # .#|||||| .. |# ## |#| ...#|#|||#| # # .#|||||| .. |# ## |#| ...#|#|||#| # # .#|||||| .. |# ## |#| ...#|#|||#| # # .#|||#|# .# .#| #| ##|.#..#|||||#| # # .#|||#|# .# .#| #| ##|.#..#|||||#| # # .#|||#|# .# .#| #| ##|.#..#|||||#| # # .#||||||############|######|||||#| # # .#||||||############|######|||||#| # # .#||||||############|######|||||#| # # |...||#||||||#||||#|#||||||#|||||#||| |.| # # |...||#||||||#||||#|#||||||#|||||#||| |.| # # |...||#||||||#||||#|#||||||#|||||#||| |.| # #. .. ||||# .|||##|. |#| .|| || .|||#. #| # .# #. .. ||||# .|||##|. |#| .|| || .|||#. #| # .# #. .. ||||# .|||##|. |#| .|| || .|||#. #| # .# || | ...|| ...##| | #| .|. |. ##### .. .| || || | ...|| ...##| | #| .|. |. ##### .. .| || || | ...|| ...##| | #| .|. |. ##### .. .| || || ||||| || ||||#| . |. |. |#. ||||| |#| || || || ||||| || ||||#| . |. |. |#. ||||| |#| || || || ||||| || ||||#| . |. |. |#. ||||| |#| || || .# |.....#|....|#.||||.|||##.|#|....||.#||.#. #. .# |.....#|....|#.||||.|||##.|#|....||.#||.#. #. .# |.....#|....|#.||||.|||##.|#|....||.#||.#. #. #.|||||||#############################| ||| .# #.|||||||#############################| ||| .# #.|||||||#############################| ||| .# || ##||#||#||||||#||#||#||#||##. || || ##||#||#||||||#||#||#||#||##. || || ##||#||#||||||#||#||#||#||##. || # .#|||||||||#||#|||||||||||#| # # .#|||||||||#||#|||||||||||#| # # .#|||||||||#||#|||||||||||#| # || |#||||||||||||||||||||||#| || || |#||||||||||||||||||||||#| || || |#||||||||||||||||||||||#| || .# |#||||||||||||||||||||#| #. .# |#||||||||||||||||||||#| #. .# |#||||||||||||||||||||#| #. || |#||||||||||||||||||#| || || |#||||||||||||||||||#| || || |#||||||||||||||||||#| || #. .######|#|#########| .# #. .######|#|#########| .# #. .######|#|#########| .# .#. |#####||||#####| .#. .#. |#####||||#####| .#. .#. |#####||||#####| .#. |# ||########|| #. |# ||########|| #. |# ||########|| #. |# ...... #| |# ...... #| |# ...... #| |#. .#| |#. .#| |#. .#| |#. .#. |#. .#. |#. .#. .#| |#. .#| |#. .#| |#. |#| |#| |#| |#| |#| |#| .|#|. .|#|. .|#|. .|#|. .|#|. .|#|. |##||. .||##| |##||. .||##| |##||. .||##| .||########||. .||########||. .||########||. 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