Solar Generation Calculator
Estimate how much electricity a solar panel system will generate daily, monthly and yearly.
What this tool does
A solar generation calculator estimates how much electricity a solar panel system will produce over time. Enter the system size in kilowatts, the peak sun hours for your location, and the system efficiency (which accounts for inverter losses, wiring, temperature and soiling). The calculator multiplies system size by peak sun hours by efficiency to get daily generation in kWh, then scales to monthly and yearly totals. It can compare the result against average household consumption to show what fraction of demand the system covers.
Estimates daily, monthly and annual solar generation in kWh from system size in kW, peak sun hours and system efficiency.
Shows the effect of each variable - panel wattage, sun hours and system efficiency - so the estimate can be tuned.
Compares the result against average household consumption to show what fraction of demand it covers.
Recalculates instantly as you adjust system size, sun hours or efficiency.
How to use it
- Enter the solar system size in kilowatts.
- Enter the peak sun hours for your location.
- Enter the system efficiency as a percentage (typical values are 75% to 85%).
- Optionally enter your monthly electricity consumption to see coverage.
- Read the daily, monthly and yearly generation in kWh.
Why use this calculator
Shows the effect of each variable - panel wattage, sun hours and system efficiency - so the estimate can be tuned, because a single output number hides the assumptions behind it. Two systems of the same size can produce very different amounts of energy depending on location, shading and equipment quality. By exposing each input, this calculator lets you see how sensitive the result is to each one and make informed decisions about panel quality, inverter selection and system design.
Why we built it
We built the solar generation calculator to work in the opposite direction from the solar panel system size calculator, which finds the size you need from your usage. This tool takes a given system size and tells you how much it will produce. The solar savings calculator then converts that generation into money saved on your electricity bill.
If your task goes further, try the electricity bill calculator to see what you currently pay, and the energy consumption calculator to break down where your electricity goes.
Who this tool is for
- Homeowners who already have solar and want to check the system is performing as expected
- Buyers considering a quoted system size and wanting to know the output
- Solar installers providing estimates to customers
- Students learning about solar energy and capacity factors
When to use it
- Estimating the output of a proposed solar system.
- Checking whether an existing system is generating what it should.
- Comparing the output of different system sizes or locations.
- Estimating how much of a home's electricity demand solar can cover.
How it is calculated
Daily generation in kWh = system size in kW × peak sun hours × system efficiency. Monthly = daily × 30. Yearly = daily × 365.
Worked example: a 6 kW system in a location with 4.5 peak sun hours and 80% system efficiency. Daily generation = 6 × 4.5 × 0.80 = 21.6 kWh. Monthly = 21.6 × 30 = 648 kWh. Yearly = 21.6 × 365 = 7,884 kWh. Against a household using 900 kWh per month, this system covers about 72% of demand.
System efficiency of 80% means 20% of the panel's rated output is lost to the inverter, wiring, temperature and dirt. A high-quality installation in a cool climate may achieve 85%; a poor installation in a hot climate may only manage 70%.
What you enter, and what you get back
| Item | Details |
|---|---|
| System size | The solar array size in kilowatts. |
| Peak sun hours | The equivalent hours of full-power sunlight per day for your location. |
| System efficiency | The percentage of rated output that reaches your home. |
| Monthly consumption | Optional, to show what fraction of demand is covered. |
| Result | Daily, monthly and yearly generation in kWh. |
Issues you may run into
| What you see | Why it happens | What to do |
|---|---|---|
| Estimate is higher than actual output | Shading, panel degradation or a lower efficiency than assumed. | Check for shading and use a lower efficiency. |
| Peak sun hours unknown | They vary by location and season. | Use a solar irradiance database for your area. |
| System size in panels, not kW | Panels are counted, not sized in kW. | Multiply panel count by panel wattage and divide by 1,000. |
A worked example
These are the values the calculator opens with, so you can see exactly what it does with them. Change any value on the page and the result updates; the figures below come from the same calculation.
| Input | Value |
|---|---|
| System size | 6 kW |
| Peak sun hours | 4.5 hours |
| System efficiency | 80% |
| Monthly consumption | 900 kWh |
With those inputs, the calculator returns:
- Daily generation: 21.6 kWh
- Monthly generation: 648 kWh
- Yearly generation: 7,884 kWh
- Coverage: about 72% of a 900 kWh monthly demand
Assumptions and limitations
- Uses average peak sun hours; real generation varies day to day and season to season.
- Does not model shading, panel orientation or tilt.
- System efficiency is an assumption; real efficiency depends on equipment quality and installation.
- Panel degradation over time (typically 0.5% to 1% per year) is not included.
- An estimate, not a performance guarantee.
Frequently asked questions
How much electricity does a solar panel produce per day?
A single 400-watt panel in a location with 4.5 peak sun hours and 80% system efficiency produces about 1.44 kWh per day (0.4 × 4.5 × 0.80). A typical 6 kW system of 15 such panels produces about 21.6 kWh per day.
What is a good capacity factor for solar?
Solar capacity factors range from about 10% in northern cloudy regions to 25% in sunny desert regions. A capacity factor of 15% to 20% is typical for most populated areas. It is the ratio of actual annual output to the theoretical maximum if the system ran at full power 24 hours a day.
How does shading affect solar generation?
Shading even a small part of one panel can disproportionately reduce the output of a whole string of panels, because panels in a series string are limited by the weakest panel. The calculator cannot model shading, so if your roof is shaded, real output will be lower than the estimate.
What is the difference between kW and kWh for solar?
Kilowatts (kW) measure the size of the system - its maximum power output under ideal conditions. Kilowatt-hours (kWh) measure the energy it produces over time. A 6 kW system might produce 21.6 kWh in a day. kW is the capacity; kWh is the production.
How many peak sun hours do I get?
Peak sun hours depend on your location, ranging from about 3 hours per day in northern Europe to over 6 hours per day in parts of Australia, the southwestern US and desert regions. Use a solar irradiance database or your local solar installer for an accurate figure.
Does solar work in winter?
Yes, solar panels work in winter and actually perform better in cooler temperatures. However, shorter days and lower sun angles mean winter generation is typically 30% to 50% lower than summer generation in temperate climates. Annual estimates use average peak sun hours to account for this variation.