Home / Calculators / Solar Calculator
SOLAR PLANNING, MADE CLEAR
Solar Calculator for your site.
Explore solar capacity, energy generation and savings with assumptions you control.
Build your solar estimate.
Enter the average monthly units on your bill. One unit equals 1 kWh.
Enter only the electricity-use charge, excluding fixed charges, taxes and old dues.
Enter the energy charge per unit (kWh), not the total bill divided by units.
Enter clear, unshaded roof area in square metres. Example: 10 m × 6 m = 60 m².
Choose the share of yearly electricity use you want solar to generate. This is not the bill-saving percentage.
Enter the solar size you are considering. kWp is the rated panel capacity; roof space may limit it.
Estimate how much solar electricity you will use while it is generated. The rest is surplus.
Fine-tune the assumptions
Starting assumptions only. No location lookup, equipment quotation or subsidy is applied.
Equivalent hours of strong sunshine per day, averaged over the year. Use a local solar estimate if available.
Share of ideal output left after heat, inverter, wiring and other losses. 80% is a starting assumption.
Roof area needed for each 1 kWp, including spacing and access. Confirm the layout with an installer.
Expected installed price per 1 kWp. Replace this starting figure with your quotation.
Payment or credit per surplus unit sent to the grid. Leave zero unless your utility has confirmed a rate.
Yearly upkeep as a percentage of the initial price. This annual amount stays fixed in the projection.
Expected yearly reduction in panel output, starting from year two.
Assumed yearly rise in the energy rate. Leave zero for no increase; this is not a prediction.
Live calculations stay in this tab. Details are shared only when you request a report.
Your solar calculation, explained.
The first submission is checked on our server. Further edits update this private on-screen preview instantly.
Live preview updated from your current values. The original enquiry remains saved; these edits stay in this tab unless you email an updated PDF.
Generation through the year
kWh / monthSame daily yield across the year; month length changes the bars. Seasonal weather is not modelled.
View monthly figures
| Month | kWh |
|---|
20-year cash-flow scenario
After initial costUndiscounted; includes maintenance and generation degradation. Excludes financing, taxes, subsidy and equipment replacement.
View annual figures
| Year | kWh | Net benefit | Cumulative |
|---|
Inputs & assumptions
How this is calculated
- Size the systemAnnual consumption × generation target ÷ annual yield per kWp, rounded up to 0.1 kWp and limited by roof space. Manual capacity uses the same roof limit.
- Estimate generationkWp × peak sun hours × 365 × performance ratio.
- Value the energySelf-consumed kWh × energy tariff + surplus kWh × entered export credit. Self-consumption is capped at annual use.
- Estimate paybackInitial investment ÷ (year-one bill benefit − annual maintenance). No payback is shown if net benefit is zero or negative.
Formula version: solar-1.0. No measured interval-load or site weather data is used.
BEHIND YOUR ESTIMATE
Know what you’re estimating.
kWp describes solar capacity. kWh describes electricity generated. This tool uses annual-average solar resource and system-performance assumptions; it is not a site weather simulation.
Does a generation target mean the same bill reduction?
No. Savings depend on how much solar electricity is used on site, your variable electricity tariff and any applicable export credit. Fixed charges, taxes and demand charges are excluded. The generation target controls sizing; the use-offset indicator shows the estimated annual consumption supplied directly by solar.
Are subsidies and net metering included?
No subsidy is applied. Export credit starts at zero and only changes when you enter a rate. Eligibility, approvals, metering and settlement rules must be checked for your connection before relying on them.
Can this confirm roof suitability or backup during an outage?
No. Roof condition, structural capacity, shading and mounting layout need a site survey. A standard grid-connected solar installation does not provide backup during a grid outage without a suitable backup arrangement.
How should I use the financial projection?
Treat it as an undiscounted scenario, not a guaranteed return. It includes entered maintenance, generation degradation and optional tariff escalation. It excludes financing, taxes, subsidy and equipment replacement. Compare the assumptions with an itemised quotation.
Methodology: PVWatts production modelling · Self-consumption and export value. This independent, simplified calculator does not call PVWatts.