Design a system, end to end

Six steps that join every solar tool here into one design — and tell you plainly whether your roof or your energy use is the thing setting the size.

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1 · What are you trying to do?

You can skip the roof and the money steps entirely and still get a system size. Anything you leave out is reported as missing rather than filled in with a guess.

2 · How much electricity do you use?

Anything you plan to add

3 · How much sun does the site get?

A regional yearly average — most populated places fall between 3 and 6.
These are broad starting points, not data for your address. A published figure for your region, or better a modelled estimate from an installer, will beat any of them. This is the input the whole design rests on, so it is worth getting right.

4 · Will it fit? (optional)

Leave the area at zero to skip this step — you will get an energy-sized design instead of a roof-constrained one.

Need obstacles and several planes? Use the layout designer →

5 · Storage and money (optional)

Battery

From your battery's datasheet — nothing is assumed.
Not sure what you need? Work it out →

Money

No incentive, rebate or tax credit is assumed anywhere in this tool. If you have confirmed one applies to you, the payback calculator has a field for it.

6 · The design

Three ways to go

How the size was arrived at

What to check next

    Your data stays in this browser. Everything on this page is calculated on your own device. Your electricity use, roof dimensions, prices and equipment details are never uploaded, stored on a server, or included in analytics.
    Planning estimate — not an engineering or installation plan. Results depend on the information and assumptions you enter. Output, savings and equipment behaviour vary with weather, shading, tariffs, temperature, ageing and installation. Verify equipment limits against current manufacturer documentation. Permits, structural capacity, electrical protection, conductor sizing, grounding, rapid shutdown, fire access, utility interconnection and code compliance must be reviewed by qualified professionals and the applicable authorities.
    Educational estimate, not financial advice. No incentive eligibility, tariff or utility policy is assumed. Confirm all of it with your utility, the relevant programme and a qualified adviser.
    How this is calculated

    This tool orchestrates the same tested engines as the individual calculators on this site — it does not have its own copies of the formulas. Sizing, production, roof fit and cash flow all come from one place, so a number cannot mean one thing here and something else on another page.

    The sequence is: usage (plus anything you plan to add) → target energy → array size → panel count → roof check → production → economics. If the roof cannot hold the energy-sized array, the design is reported as roof-constrained and every downstream figure is recalculated from the smaller array rather than the one you wanted.

    Losses are applied once. Peak sun hours here means plane-of-array equivalent sun.

    Energy-sized or roof-constrained?

    These are the two ways a design gets decided, and it matters which one you are in. An energy-sized design starts from what you use and asks how much array covers it. A roof-constrained design starts from the space available and accepts whatever offset that produces. Most quotes are quietly the second while being presented as the first, which is how people end up surprised that a system covers 70% of their bill rather than all of it.

    This tool tells you which situation you are in, and if the roof is the binding constraint it recalculates everything from the array that actually fits — not the one you asked for.

    What it deliberately does not do

    It does not assume an incentive, a tariff, a net-metering arrangement or an equipment specification. It does not model hourly weather, shading through the day, inverter clipping, or the structural capacity of your roof. It will not tell you a system is a good investment — it will show you the arithmetic and the assumptions it rests on, and mark the ones that are shakiest.

    Everything runs on your device. If you press Save, the design is stored in this browser only; there is no account and nothing is uploaded.