Building performance
Solar PV yield estimator
Estimate annual and monthly PV output from capacity and a regional or documented specific yield, with savings and simple payback.
Loading the local tool…
What the solar PV yield estimator calculates
A solar panel output calculator estimates how much electricity a PV system produces in a year: annual output = system size in kWp × specific yield in kWh/kWp/year. This tool does that multiplication, applies extra losses if your yield figure does not already include them, and shows the daily average and the effective specific yield.
Specific yield is the number that carries the location, tilt, orientation, shading and system losses. You can start from a preset: a small offline table of typical yields for US cities and a few international ones, rounded from NREL PVWatts and PVGIS runs for an equator-facing array at near-latitude tilt, with a rule-of-thumb factor for other tilts and orientations. For anything you will rely on, look the yield up for your own site in PVWatts or PVGIS, enter it as a custom value and record where it came from.
The tool also spreads the annual figure across the months using a clear-sky shape for the latitude and tilt, splits generation into self-consumed and exported electricity, and works out first-year savings and a simple payback from the system cost, electricity price and export tariff. It uses no live weather data, so the result is only as good as the yield you enter or confirm.
How to use the solar PV yield estimator
- Enter the DC system capacity in kWp: the sum of the module nameplate ratings. Twenty 400 W modules make 8 kWp.
- Pick a specific-yield preset for a nearby city, or keep Custom and enter the specific yield in kWh/kWp/year and the site latitude from your own PVWatts or PVGIS run.
- Set the yield assumption. Choose Net if your yield already includes system losses. Choose Before additional losses to show an additional losses (%) field and apply it.
- Choose the array orientation and tilt. Keep Apply typical tilt/orientation factor when using a preset; choose Yield already reflects tilt and orientation when your custom yield was modelled for this roof. The tilt also sets the monthly profile shape.
- Enter the self-consumed share, electricity price, export tariff and, optionally, the installed system cost for a simple payback. Record the yield source, location, tilt and orientation; it is printed with the results.
- Read the annual generation, daily equivalent, effective specific yield, the factor applied, self-consumed and exported kWh, annual savings and payback, then the month-by-month table and bar chart. Download a PDF, CSV or SVG, copy the result, or save your inputs.
Worked example
A 5 kWp system at an assumed net yield of 1,200 kWh/kWp/year produces an estimated 6,000 kWh/year.
What is specific yield (kWh/kWp)?
Specific yield is the energy a PV system produces in a year per kilowatt of rated DC capacity. A 5 kWp system that generates 6,000 kWh in a year has a specific yield of 1,200 kWh/kWp. Because it is normalized by size, it lets you compare sites and roof orientations regardless of system size.
It depends on how much sunlight reaches the modules (climate, latitude, tilt, orientation and shading) and how much is lost turning it into usable AC power (temperature, wiring, inverter, soiling and downtime). One rough way to see the link: specific yield ≈ peak sun hours per day × 365 × performance ratio. With an illustrative 4.5 peak sun hours and a performance ratio of 0.8, that is about 1,314 kWh/kWp/year.
Very broadly, and only as an illustration, well-oriented systems range from under 1,000 kWh/kWp/year in cloudy, high-latitude climates to more than 1,600 in sunny, dry, lower-latitude regions. Do not use a range like that for a real estimate. Get a site-specific figure from PVWatts, PVGIS or your installer's modeling software.
Typical specific yields by region (preset table)
These are the preset values the tool offers, rounded to the nearest 50 kWh/kWp/year from PVWatts and PVGIS runs for a fixed, equator-facing array at near-latitude tilt with default system losses. Treat them as typical to within about ±10 %: microclimate, module temperature, soiling and shading all move a real site. Run PVWatts or PVGIS for the address before quoting a number.
| Location | Typical yield (kWh/kWp/yr) | Latitude |
|---|---|---|
| Phoenix, AZ / Las Vegas, NV | 1,750 | 33–36° N |
| Los Angeles, CA | 1,600 | 34° N |
| Denver, CO / Salt Lake City, UT | 1,550 | 40–41° N |
| Austin, TX / Miami, FL | 1,450 | 26–30° N |
| Atlanta, GA | 1,400 | 34° N |
| Washington, DC | 1,350 | 39° N |
| Chicago, IL / New York, NY / Boston, MA | 1,300 | 41–42° N |
| Seattle, WA | 1,100 | 48° N |
| Madrid, Spain | 1,600 | 40° N |
| Rome, Italy | 1,450 | 42° N |
| Berlin, Germany / Amsterdam, Netherlands | 1,000 | 52° N |
| London, UK | 950 | 52° N |
| Sydney, Australia | 1,450 | 34° S |
| Auckland, New Zealand | 1,250 | 37° S |
Tilt and orientation: how much a non-ideal roof loses
The presets assume the best fixed position: facing the equator (south in the northern hemisphere) at a tilt near the latitude. Other roofs produce less, and the tool applies a typical multiplier from the table below when you keep the tilt/orientation factor on. The multipliers are rule-of-thumb values for mid-latitude sites, consistent with how PVWatts and PVGIS outputs respond to tilt and azimuth, and are accurate to roughly ±5–10 %. Flat roofs lose little to orientation but more to soiling; vertical facades lose the most in summer.
| Tilt | Toward the equator | SE / SW (45° off) | E / W (90° off) |
|---|---|---|---|
| Near latitude (20–40°) | 1.00 | 0.95 | 0.85 |
| Flat / low (0–10°) | 0.90 | 0.90 | 0.90 |
| Steep (50–60°) | 0.95 | 0.90 | 0.80 |
| Vertical (90°) | 0.70 | 0.65 | 0.55 |
Solar output by system size and specific yield
The table is arithmetic only: capacity × yield for annual output, and yield ÷ 8,760 hours for capacity factor. The yields are example values across a broad range, not predictions for any location.
| Specific yield (kWh/kWp/yr) | Capacity factor | 5 kWp system (kWh/yr) | 8 kWp system (kWh/yr) | Daily average per kWp (kWh) |
|---|---|---|---|---|
| 800 | 9.1% | 4,000 | 6,400 | 2.19 |
| 1,000 | 11.4% | 5,000 | 8,000 | 2.74 |
| 1,200 | 13.7% | 6,000 | 9,600 | 3.29 |
| 1,400 | 16.0% | 7,000 | 11,200 | 3.84 |
| 1,600 | 18.3% | 8,000 | 12,800 | 4.38 |
| 1,800 | 20.5% | 9,000 | 14,400 | 4.93 |
Net vs gross yield: apply losses once
Some sources give a yield before system losses; others already include them. PVWatts and PVGIS both ask for a system loss percentage and report output after it, so their results are normally net. Apply the tool's additional losses only when your yield figure leaves them out.
Example: a 5 kWp system with a gross yield of 1,400 kWh/kWp/year and the tool's example 14% additional losses gives 1,400 × 0.86 = 1,204 kWh/kWp/year, or 6,020 kWh/year. If you entered a net yield of 1,200 and then applied 14% losses as well, you would get 5,160 kWh/year, an underestimate of 14% caused by counting losses twice.
Worked example: how many kWp to cover annual use?
The tool works forward from system size, but the same formula runs backward. Suppose a household uses 10,800 kWh a year (an illustrative figure; use twelve months of bills) and a PVWatts run gives a net yield of 1,300 kWh/kWp/year for the roof (also illustrative).
- Required capacity = 10,800 ÷ 1,300 = 8.31 kWp.
- With 400 W modules, 8.31 ÷ 0.4 = 20.8, so 21 modules, or 8.4 kWp.
- Check in the tool: 8.4 kWp × 1,300 = 10,920 kWh/year, about 29.9 kWh/day on average.
- Confirm the roof has room for 21 modules, clear of shade, before going further. The roof pitch calculator gives the sloping area of each roof plane.
- Annual balance is not hourly balance. Output peaks around midday and in summer; the monthly table shows the seasonal swing, and the self-consumed share you enter (not a measured value) decides how much of the output offsets the bill rather than being exported.
Who it is for and when to use it
Early feasibility for a roof array
Turn a roof's likely capacity and a sourced yield into an annual kWh figure for a design report or client meeting.
Checking an installer's quote
Divide the quoted annual kWh by the system kWp to see the specific yield being assumed, then compare it with PVWatts or PVGIS for the same site.
Comparing roof planes
Run the same capacity with the orientation set to equator-facing and then to E / W to see the typical difference, or enter yields for each roof plane from your modeling source for a site-specific answer.
Documenting assumptions
Export a PDF that states the capacity, the yield, its source and the loss basis, so the estimate can be checked later.
Method, formulas & assumptions
Annual output = DC system capacity (kWp) × specific yield (kWh/kWp/year, from a regional preset or your source) × tilt/orientation factor (typical table, optional) × (1 − additional losses) only when the yield is before losses. Monthly shares follow a clear-sky model for the latitude and tilt. Savings = self-consumed kWh × electricity price + exported kWh × export tariff; simple payback = system cost ÷ annual savings.
Common mistakes to avoid
- Applying losses twice to a yield that is already net of system losses.
- Entering the inverter's AC rating instead of the DC module capacity. Specific yield here is per kWp of DC nameplate.
- Treating a regional preset as a site figure. The presets are typical values for an ideal fixed array; look the yield up for the actual site and roof plane before relying on it.
- Applying the tilt/orientation factor to a yield that was already modelled for your roof. Choose Yield already reflects tilt and orientation in that case.
- Ignoring shade from trees, chimneys and neighboring buildings, which a generic yield does not include. The sun path diagram generator shows where the sun is through the year.
- Reading the daily average as a daily forecast. Winter days produce much less than summer days; the figure is annual output ÷ 365.
- Treating a first-year estimate as lifetime output. Module output declines slowly over the years, and this tool does not model degradation.
Scope & limits
No live weather or irradiance data. Regional yields and tilt factors are typical values (about ±10 %) to confirm with PVWatts or PVGIS. The monthly profile is a clear-sky shape, not a forecast. Payback ignores degradation, price changes, maintenance and financing. This is not hourly output or system design.
Frequently asked questions
How much electricity does a 5 kW solar system produce?
Multiply 5 by the specific yield for your site. At an illustrative 1,200 kWh/kWp/year that is 6,000 kWh a year, about 16.4 kWh a day on average; look up your actual yield in PVWatts or PVGIS.
What does kWp mean?
Kilowatt-peak is a PV system's DC rated power under standard test conditions of 1,000 W/m² irradiance and 25 °C cell temperature. It is the sum of the module nameplate ratings.
What is a good specific yield for solar?
It depends on location, tilt and orientation. As a broad illustration, well-oriented systems range from under 1,000 kWh/kWp/year in cloudy high-latitude climates to over 1,600 in sunny low-latitude ones, so compare your figure with a site model rather than a general benchmark.
How do I find the specific yield for my location?
Use a PV modeling tool such as NREL's PVWatts or the European Commission's PVGIS. Enter your location, tilt, azimuth and losses, then divide the annual AC output by the system's kWp.
What is the capacity factor of a solar system?
Annual output divided by what the system would produce at full rated power all year. Specific yield ÷ 8,760 gives it directly, so 1,200 kWh/kWp/year is a 13.7% capacity factor.
Should I include system losses?
Only if your yield figure does not already include them. Outputs from PVWatts and PVGIS already reflect the system loss percentage you entered there.
How many solar panels do I need?
Divide annual electricity use by the specific yield to get kWp, then divide by the module wattage. 10,800 kWh at 1,300 kWh/kWp needs about 8.31 kWp, or 21 modules of 400 W.
Does this estimate monthly output or payback?
Yes, in a simple form. Monthly figures spread the annual total using a clear-sky shape for the latitude and tilt, so they show the seasonal pattern rather than any month's real weather. Payback is the installed cost divided by first-year savings (self-consumed kWh × electricity price + exported kWh × export tariff), with no degradation, price escalation, maintenance or financing.
Do I need an account to download the result?
No. All calculations, local file processing and exports on this page are free, without an account.
Where are my inputs stored?
The tool keeps inputs in this browser tab. It does not upload them or create a cloud copy. Save or download anything you want to keep before leaving the page. Standard site analytics may operate independently of the tool.
Further reading
- Solar altitude and azimuth explained
- Solar data by location
- All building performance tools
- All free architecture & construction tools
- Harth resource library
In this category
Keep developing your project in Harth.
Bring your ideas, models and project research into one workspace. Downloaded results are yours to take with you.