Solar Pv Calc

Checkout cancelled · you have not been charged

Still deciding on the Solar Planning Pack?

• Quote comparison (XLSX)
• Bill tracker (XLSX)
• Roof survey (DOCX/PDF)
• Installer checklist (PDF/DOCX)

• Full refund within 7 days
• Instant download
• Local currency at checkout where available
• Secure checkout by Stripe

Buy now — $5.00Try a free sheet first

What stopped you? (optional, anonymous)

The priceNot sure it fits my needPayment problemJust looking for now

Free printables

Single sheets you can print right now, no sign-up. The full pack adds every sheet in one download plus the editable files.

Printable Solar Quote Comparison Sheet1 page · free PDFPrintable Electricity Bill Tracker1 page · free PDFPrintable Roof and Shade Survey1 page · free PDFPrintable Solar Installer Checklist1 page · free PDF

Browse the free printables →

How the sizing works

1. Add up a year of electricity use from your bills (or multiply a typical month by 12).
2. Decide what share to cover — 100% aims to match your annual use.
3. Find the average peak sun hours for your area: the equivalent number of hours per day of full-strength sunlight (1,000 W/m²).
4. Each kilowatt of panels then produces about sun hours × 365 × (1 − losses) kWh a year.
5. System size = the energy you want ÷ that figure.
6. Panels = system size ÷ panel wattage, rounded up.

Worked example

These are the calculator’s default inputs. Change them to your own bill, local sun hours, quotes and tariff.

Peak sun hours

Peak sun hours are not the same as daylight hours. A place with 12 hours of daylight might receive the same total energy as 4.5 hours of full-intensity sun. Sunny desert regions can average 6 or more; much of the central and eastern US and southern Europe are around 4–5; cloudier northern regions can be 2.5–3.5. National laboratories and solar agencies publish maps and calculators — for example, the US National Renewable Energy Laboratory’s PVWatts tool — that model your exact location, roof angle and direction.

System losses

A combined loss of around 14% is a common default in planning tools; shading can add a lot more. Panels also lose a little output each year — often around half a percent — which the simple estimate ignores.

Roof direction and tilt

• In the northern hemisphere, south-facing roofs produce the most; east and west roofs typically produce somewhat less over a year.
• A tilt close to your latitude maximises annual output, but most pitched roofs are close enough.
• North-facing roofs in the northern hemisphere (south-facing in the southern) produce much less.
• Avoid shade between mid-morning and mid-afternoon — even partial shading can cut output noticeably without optimisers or microinverters.

Cost and payback

Installed cost per watt varies widely by country, installer, system size and equipment, so use real quotes. Simple payback divides the net cost by yearly bill savings; it ignores financing, electricity price changes, panel degradation, maintenance and the value of exported power. Incentives, tax credits and export tariffs change frequently — check what applies in your area and year before relying on any figure.

Reducing use before sizing

Every kilowatt-hour you don’t use is one you don’t need panels for. Before sizing a system, look for easy efficiency gains: LED lighting, a smart thermostat, sealing draughts, or replacing an old fridge. If you plan to add an electric car or heat pump soon, include their expected use instead — an electric car driven 10,000 miles a year typically needs roughly 2,500–3,500 kWh, depending on the vehicle and driving.

Net metering and self-consumption

How much solar saves depends on how your electricity supplier credits power you export. Under full net metering, exported kilowatt-hours offset imported ones one-for-one, so covering 100% of annual use makes sense. Where exports earn less than you pay to import, it often pays to size the system closer to your daytime use and shift appliances such as dishwashers and car charging into sunny hours, or to add a battery.

Questions to ask installers

• What annual production do you estimate, and with what losses and shading assumptions?
• Which panels, inverter or microinverters, and what warranties?
• How will exported electricity be credited on my tariff?
• Does my roof need work before installation?
• What permits, inspections and grid connection steps are included?
• Would a battery make sense for my usage pattern?

Solar planning pack

The optional pack includes an Excel solar comparison sheet for up to five quotes (cost per watt, production per dollar, payback), a 12-month bill tracker, a roof and shading survey sheet and an installer questions checklist. The calculator above is free.

AI-assisted content

This page was drafted with AI assistance and reviewed before publishing. Results are estimates; they are not an engineering design or financial advice.