Best solar estimators for technical homeowners
If you like checking the numbers, the useful question is not which interface displays the most decimal places. It is which assumptions you can inspect, change and reproduce. Production models and regional financial estimates answer different questions, so compare them carefully.
| Tool | Best fit in this guide | Access and tradeoffs |
|---|---|---|
| PVWatts | Best for inspecting and varying a documented set of production inputs. | Public web calculator; API use has separate key and usage requirements. |
| OpenSolar | Useful when you or your installer need a design and proposal workflow around the calculation. | Core platform advertised as free; external API access and connectors can have charges. |
| CleanFuture (ours) | Useful for explaining assumptions and saving the broader planning context. | Account required to save; saved AI estimates currently require an active subscription. |
What matters for technical homeowners checking production
Explicit model inputs
Record capacity, geometry, losses and location before comparing results. Two outputs are not a meaningful cross-check if the inputs differ in unobserved ways.
One change at a time
Use sensitivity scenarios to explore uncertainty. Changing tilt, system size and losses together makes it harder to explain which assumption caused a difference.
Correct units and purpose
Installed power, annual energy and avoided bills are distinct outputs. Label each quantity, its period and its model rather than treating them as interchangeable scores.
PVWatts
- Category
- Public photovoltaic production model
- Best for
- Best for inspecting and varying a documented set of production inputs.
- Access
- Public web calculator; API use has separate key and usage requirements.
PVWatts models grid-connected photovoltaic output using inputs such as capacity, tilt, azimuth and losses. Its V8 API documents monthly and hourly output options.
What to weigh before choosing
You remain responsible for whether those inputs represent the actual roof and equipment.
A modeled production result does not verify usable roof area, structural condition, electrical design or a household’s bill savings.
OpenSolar
- Category
- Professional solar design and sales software
- Best for
- Useful when you or your installer need a design and proposal workflow around the calculation.
- Access
- Core platform advertised as free; external API access and connectors can have charges.
OpenSolar provides professional design and proposal workflows, including 2D, 3D and manual design options described in its documentation.
What to weigh before choosing
This is professional software; a homeowner may get more value by reviewing the installer’s model than rebuilding it.
Imagery and design modes vary by location. A software layout is not a substitute for site verification or professional responsibility.
CleanFuture (ours)
- Category
- Conversational household planning
- Best for
- Useful for explaining assumptions and saving the broader planning context.
- Access
- Account required to save; saved AI estimates currently require an active subscription.
Discuss your energy plan in Chat, explore supporting Map and Data pages, and keep preliminary estimate versions inside My system. You can explicitly publish a limited read-only snapshot.
What to weigh before choosing
Its regional estimate is not presented as a validated PVWatts replacement or an accuracy benchmark.
Not installer bidding, professional roof design or a guaranteed savings calculation. A regional solar estimate excludes battery costs and detailed tariff modeling.
A practical next-step checklist
- Define a baseline and save its inputs and model version.
- Reproduce the installer’s assumptions as closely as the tool permits.
- Vary one uncertain input and record the effect.
- Ask the installer to explain material differences before using the output in a financial decision.
A situation to watch for
If an installer’s production estimate differs from your model, first compare the proposed capacity and array orientation. Do not infer poor workmanship or model failure from two totals alone.
This checklist is our planning advice, not a claim that any listed tool automatically performs every step.
Questions worth asking
Which model is most accurate?
This review does not establish comparative accuracy. Input quality, site conditions and model scope matter; we did not run a measured-output benchmark.
Can CleanFuture import a PVWatts model automatically?
This guide does not claim an automatic import or integration. Keep the source model and its inputs available when discussing results.
Turn the reading into a plan
Bring your questions to Chat and keep the assumptions tied to your system.
Discuss my plan in ChatYour question and this article’s context will be prefilled for you to review and send. Account required to save a system; saved AI estimates currently require an active subscription. Preliminary guidance, not an installation quote.
Sources and review method
We make CleanFuture. These are our editorial recommendations based on first-party documentation and our own product’s scope, not hands-on performance tests. We recommend other products when they fit the job better. US-focused; local availability and terms need checking.
We selected five overlapping solar workflows: quote comparison, installer research, advisor-led buying, production modeling and professional design. PVWatts and OpenSolar are adjacent tools, not equivalent homeowner services. This is a focused shortlist, not an exhaustive market survey or an objective top-five company ranking.
Recommendations weigh the task, required inputs, output, access terms and limitations. We did not test purchases, installation quality, model accuracy or response times. Product descriptions come from the linked official documentation; workflow advice and rankings by fit are our editorial judgment. We do not use numeric ratings or vendor savings claims to choose winners.
For broader whole-home electrification, also consider QuitCarbon’s planning and coaching. Solar.com is another shopping service outside this five-tool selection. Exclusion is not a negative evaluation.
Sources: PVWatts: public calculator; PVWatts V8: official model inputs and outputs; OpenSolar: professional platform; OpenSolar: first project design guide; OpenSolar: free platform and paid external access; CleanFuture: solar estimate workflow.
Capabilities and terms can change. Check the provider’s current documentation and your actual proposal before committing.