Solar Generation Calculator

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Estimate daily, monthly and annual solar output for any PV size, including common 1 kW, 2 kW, 3 kW, 5 kW and 10 kW rooftop systems, using peak sun hours and performance ratio.

Inputs

Calculation mode

Mode B computes each month separately from its own irradiation and PR

PV DC capacity (kWp)

Sum of module nameplate power at STC

Average peak sun hours (h/day)

Daily irradiation ÷ 1 kW/m². Drives the quick estimate only.

Performance ratio source

Soiling loss (%)

Shading loss (%)

Mismatch loss (%)

DC wiring loss (%)

Inverter conversion loss (%)

AC wiring + transformer loss (%)

Plant availability (%)

Module power temperature coefficient γ (%/°C)

Datasheet value — normally negative, e.g. −0.35 %/°C. The sign is used as entered.

Average operating cell temperature (°C)

Energy-weighted cell temperature; drives the thermal term of the loss chain

Annual degradation (%/yr)

Analysis period (years)

Electricity tariff (per kWh)

Grid emission factor (kg CO₂/kWh)

Must match your local grid — 0.71 India (CEA), ~0.25 EU

How to use this calculator: Solar Generation Calculator

Estimate daily, monthly and annual solar output for any PV size, including common 1 kW, 2 kW, 3 kW, 5 kW and 10 kW rooftop systems, using peak sun hours and performance ratio. The example below is calculated by this page's real engine from the displayed inputs.

1Confirm that the Solar Generation Calculator matches the quantity or design check you need.
2Enter PV DC capacity, Average peak sun hours, and Soiling loss using the units printed beside each field.
3Select the applicable Calculation mode and Performance ratio source options; these choices change the calculation method or factors.
4Calculate, then follow the substituted equations in the worked example and compare the result with any stated limit.
5Read the assumptions, warnings and cited references before using the result for a financial, medical or engineering decision.

Input guide and example values

Use values from the same measurement basis and time period. Conditional fields appear only when the related option is selected.

Input	Example value	Why it matters
Calculation mode	A — Quick preliminary estimate (PSH × PR)	Mode B computes each month separately from its own irradiation and PR
PV DC capacity	5 kWp	Sum of module nameplate power at STC
Average peak sun hours	5 h/day	Daily irradiation ÷ 1 kW/m². Drives the quick estimate only.
Performance ratio source	Derive from the loss chain (IEC 61724-1)	Select the option that matches the real installation or scenario.
Soiling loss	3 %	Measured or known soiling loss used by the calculation engine.
Shading loss	2 %	Measured or known shading loss used by the calculation engine.
Mismatch loss	2 %	Measured or known mismatch loss used by the calculation engine.
DC wiring loss	1.5 %	Measured or known dc wiring loss used by the calculation engine.
Inverter conversion loss	2.2 %	Measured or known inverter conversion loss used by the calculation engine.
AC wiring + transformer loss	1 %	Measured or known ac wiring + transformer loss used by the calculation engine.
Plant availability	99 %	Measured or known plant availability used by the calculation engine.
Module power temperature coefficient γ	-0.35 %/°C	Datasheet value — normally negative, e.g. −0.35 %/°C. The sign is used as entered.
Average operating cell temperature	45 °C	Energy-weighted cell temperature; drives the thermal term of the loss chain
Annual degradation	0.6 %/yr	Measured or known annual degradation used by the calculation engine.
Analysis period	25 years	Measured or known analysis period used by the calculation engine.
Electricity tariff	8 per kWh	Measured or known electricity tariff used by the calculation engine.
Grid emission factor	0.71 kg CO₂/kWh	Must match your local grid — 0.71 India (CEA), ~0.25 EU

Formula inputs & variables for Solar Generation Calculator

These are the named quantities used by this calculator. When the source formula does not define a mathematical symbol, OneCalcApp keeps the real input label instead of inventing one.

Variable / input	Unit	Meaning in this calculation
Calculation mode	—	Mode B computes each month separately from its own irradiation and PR
PV DC capacity	kWp	Sum of module nameplate power at STC
Average peak sun hours	h/day	Daily irradiation ÷ 1 kW/m². Drives the quick estimate only.
Irradiation entered as	—	GHI is transposed to the array plane using the factor below
GHI → POA transposition factor	—	Ratio of tilted to horizontal irradiation for your tilt and latitude
Performance ratio source	—	Select the option that matches the real installation or scenario.
Performance ratio	%	Measured or assumed PR for the whole system
Soiling loss	%	Measured or known soiling loss used by the calculation engine.

Formula, derivation and worked example

Peak sun hours express the day's irradiation as equivalent hours at 1000 W/m². The performance ratio then removes real losses. Each loss is applied multiplicatively so nothing is counted twice, and the thermal term uses your module's own signed temperature coefficient rather than a fixed allowance. Mode B repeats the whole chain month by month, which is what actually determines seasonal cash flow, self-consumption and battery sizing.

Mode A: E_day = P_DC × PSH × PR; E_annual = P_DC × PSH × 365 × PR

Mode B: E_month = P_DC × H_POA,month × d_month × PR_month

PR = (1−soil)(1−shade)(1−mismatch)(1−DC)(1−inv)(1−AC)(1−unavail)(1 + γ·ΔT_cell)

Specific yield = E_annual / P_DC; Capacity factor = E_annual / (P_DC × 8760)

E_year n = E_year 1 × (1 − d)^(n−1)

Substitution steps

1. Thermal factor
1 + γ × (T_cell − 25)
= 0.93 (γ = -0.35 %/°C)
2. Loss chain PR
Π(1 − loss) × availability × thermal
= 81.8 %
3. Daily energy
P_DC × PSH × PR
= 20.45 kWh
4. Annual energy
daily × 365
= 7,464 kWh
5. Specific yield
E_annual / P_DC
= 1,493 kWh/kWp
6. Capacity factor
E_annual / (P_DC × 8760)
= 17.04 %
7. Lifetime energy
Σ E₁ × (1 − d)ⁿ, n = 0…24
= 173,768 kWh

Computed example results

Daily generation: 20.45 kWh; PR 81.8% (derived loss chain)
Monthly average: 622 kWh
Annual generation: 7,464 kWh
Best month: Jan — 634 kWh; 8.5% of the year
Worst month: Feb — 573 kWh; 7.7% of the year
Specific yield: 1,493 kWh/kWp/yr
Capacity factor: 17.04 %
Energy lost to system losses: 1,661 kWh; 18.2% of the ideal 9,125 kWh
Year 25 generation: 6,460 kWh; 0.6%/yr degradation
25-year generation: 173,768 kWh
Annual bill saving: 59,714
CO₂ avoided per year: 5,300 kg; emission factor 0.71 kg/kWh — edit it to match your grid

Understanding the result

Read the main result together with supporting checks, assumptions, limits and intermediate values.

For a manual check, repeat the first equation, confirm the units and change one input at a time.

Common mistakes when using Solar Generation Calculator

Do not mix units for PV DC capacity (kWp), Average peak sun hours (h/day), Soiling loss (%). A unit mismatch changes the input magnitude even when the typed number looks reasonable.
Do not leave Calculation mode on the default choice unless that choice matches the real scenario; the selected option can change the calculation path or factor.
Do not replace the displayed Mode A: E_day = P_DC × PSH × PR; E_annual = P_DC × PSH × 365 × PR relationship with a different convention without also changing the underlying assumptions; compare like-for-like methods when checking the result.
Do not treat Daily generation = 20.45 kWh from the worked example as a universal answer. It belongs to the displayed example inputs and must be recalculated for the actual case.

Next logical calculator

Continue with Battery Backup Calculator

Battery Backup Calculator is directly connected from Solar Generation Calculator as a source-defined continuation or comparison.

Open Battery Backup Calculator

Standards, source trail and limitations

References show the method used. Check the current local edition, amendments and project specification before a regulated decision.

How many units will 1 kW, 2 kW, 3 kW, 5 kW or 10 kW solar generate?

Solar energy output depends on the site's solar resource and the real system losses, not only the nameplate kW. A practical first estimate is daily energy = DC system size × peak sun hours × performance ratio. At 5 peak-sun-hours and a 78% performance ratio, each 1 kW of PV produces about 3.9 kWh (units) per day before year-to-year weather variation.

On that same assumption, a 3 kW system is about 11.7 units/day, 5 kW about 19.5 units/day and 10 kW about 39 units/day. Use your location-specific irradiation or monthly mode above for a better estimate; shaded roofs, high temperature, soiling, clipping, downtime and cable losses can materially change the result.

3 kW rooftop solar system: generation planning

A 3 kW rooftop system at 5 peak-sun-hours and 78% PR gives about 11.7 kWh/day, around 351 kWh in a 30-day month and roughly 4,270 kWh in a 365-day year. These are planning values rather than a guaranteed bill saving because self-consumption, export rules and seasonal irradiation affect the financial outcome.

For roof planning, panel count depends on the module wattage actually selected. Divide the target DC watts by module watts and round up, then verify the final DC/AC ratio, usable roof area, setbacks, access paths, shading and structural capacity with the relevant OneCalcApp solar design tools.

Panel count, roof area, inverter and battery are separate design checks

Generation in kWh is only one part of rooftop sizing. Panel count depends on module wattage and the actual DC capacity; roof area depends on module dimensions, tilt, orientation, maintenance access and fire or electrical clearances. Inverter selection depends on AC rating, MPPT voltage/current limits and the chosen DC/AC ratio.

Battery sizing should be based on the loads that need backup, backup duration, usable depth of discharge, efficiency and the battery voltage/system architecture. Use the linked mounting, inverter and battery calculators rather than assuming that every 3 kW or 5 kW PV array needs the same hardware.

Why actual rooftop solar output changes month to month

Monsoon cloud, seasonal sun angle, module temperature and local shading cause monthly energy to move even when system size is unchanged. Soiling can also build up between cleaning cycles. The monthly engineering mode lets you enter separate irradiation values instead of forcing one annual average onto every month.

For an investment or final engineering design, compare the estimate with a bankable irradiation source and a detailed PV simulation. Keep the performance ratio assumptions traceable so measured plant performance can later be compared with the design basis.

Formula

Mode A: E_day = P_DC × PSH × PR; E_annual = P_DC × PSH × 365 × PR
Mode B: E_month = P_DC × H_POA,month × d_month × PR_month
PR = (1−soil)(1−shade)(1−mismatch)(1−DC)(1−inv)(1−AC)(1−unavail)(1 + γ·ΔT_cell)
Specific yield = E_annual / P_DC; Capacity factor = E_annual / (P_DC × 8760)
E_year n = E_year 1 × (1 − d)^(n−1)

Rooftop solar output chart by system size

Example only: 5 peak sun hours/day and 78% performance ratio. Actual output varies with location, season, orientation, temperature, shading, soiling, clipping and downtime.

PV system size	Approx. daily output	30-day month	Approx. annual output
1 kW	3.9 kWh/day	117 kWh	1,424 kWh/year
2 kW	7.8 kWh/day	234 kWh	2,847 kWh/year
3 kW	11.7 kWh/day	351 kWh	4,271 kWh/year
5 kW	19.5 kWh/day	585 kWh	7,118 kWh/year
10 kW	39.0 kWh/day	1,170 kWh	14,235 kWh/year

3 kW quick output at 5 PSH / 78% PR

About 11.7 kWh/day, 351 kWh per 30-day month and 4,270 kWh/year before site-specific seasonal and operational differences.

5 kW quick output at 5 PSH / 78% PR

About 19.5 kWh/day, 585 kWh per 30-day month and 7,118 kWh/year on the same planning assumptions.

10 kW quick output at 5 PSH / 78% PR

About 39 kWh/day, 1,170 kWh per 30-day month and 14,235 kWh/year on the same planning assumptions.

Solar mounting structure & roof planning

Check module layout, mounting geometry and structural planning inputs.

Battery backup calculator

Size backup energy from load, duration, efficiency and usable battery capacity.

Inverter sizing calculator

Cross-check inverter capacity and PV system sizing assumptions.

Worked example

15 kWp, 5 PSH, loss chain giving PR 0.781.
2Daily = 5 × 5 × 0.781 = 19.5 kWh; annual ≈ 7 127 kWh; specific yield 1 425 kWh/kWp.

Assumptions

Irradiation values represent long-term monthly averages for the array plane.
PR is applied to DC nameplate power at STC (1000 W/m², 25 °C, AM1.5).
Degradation is applied uniformly from year 2 onwards.

Tips

Use site-specific irradiation from PVGIS, NASA POWER or Meteonorm — national averages hide 10–15% differences.
If you have measured data, enter PR directly and compare it with the derived loss chain to locate the gap.

Warnings

A PR above 88% for a fixed-tilt system usually means the irradiation source or the meter is wrong, not that the plant is exceptional.
Do not equate sunshine duration (hours of visible sun) with peak sun hours.

Standards & references

IEC 61724-1 (performance monitoring)
IEC 61853
IEC 62548

Frequently asked questions

How many units does a 1 kW solar system generate per day?

About 3.9 kWh in a 5 PSH location at a 78% performance ratio, which is roughly 1 425 kWh per year.

What is a good performance ratio?

75–80% for rooftop and 80–84% for a well-engineered ground-mount plant. Below 70% points to shading, soiling or clipping.

Why model month by month?

Because irradiation, cell temperature and load all move seasonally; an annual average hides the worst month, which is what off-grid and self-consumption designs must survive.

How many units does a 3 kW solar system generate per day?

At 5 peak sun hours and 78% performance ratio, a 3 kW system produces about 11.7 kWh (units) per day. Actual daily output changes with location, season, shading, temperature, soiling and system availability.

How many units does a 5 kW solar system generate per month?

Using 5 peak sun hours and 78% PR, a 5 kW system is about 19.5 kWh/day or roughly 585 kWh in a 30-day month. Use local monthly irradiation for a more realistic estimate.

How many units does a 10 kW solar system generate per day?

On the same 5 PSH and 78% PR planning basis, 10 kW gives about 39 kWh/day. This is an estimate, not a guaranteed production figure.

How many solar panels are needed for a 3 kW system?

Divide the target DC watts by the selected module wattage and round up. For example, module wattage changes the panel count, so confirm the final installed DC capacity, inverter limits, roof area and string design rather than using one fixed panel count for every 3 kW system.

Does a 3 kW solar system always need the same inverter and battery?

No. Inverter sizing depends on DC/AC ratio, MPPT limits and grid design; battery sizing depends on backup load, duration, efficiency and usable depth of discharge. Size those items separately.

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