How the builder sizes a system
Every off grid system is a chain, and each link is sized from the one before it. The builder runs that chain in order rather than treating the components as separate questions.
The bus voltage suggestion follows the inverter load, because current is what costs money in copper: up to roughly 1,500 W of inverter, 12 V is workable; 1,500 to 3,000 W favours 24 V; above that, 48 V. Doubling the voltage halves the current and quarters the resistive loss for the same cable.
Where the numbers come from
Nothing here is a black box. The array figure uses the same method as the panel size calculator, the bank uses the battery bank calculator, the inverter follows the inverter size calculator, and the controller and cable come from the charge controller and wire gauge tools. Open any of them to see the formula, a worked example and the mistakes that catch people out.
Reading the result honestly
- This is a planning estimate, not a permit drawing. Confirm final designs against component datasheets and local electrical code before buying or installing.
- The worst month decides the system. If you enter an annual average sun figure, a system that works in June may empty the bank in December.
- Loads always grow. Leaving 10 to 20 percent headroom on the array and bank is cheaper than expanding later, because expansion often means matching batteries you can no longer buy.
- Heat is not an electrical problem. If your load list includes electric heating, water heating or air conditioning, propane or wood will cost a fraction of the panels and batteries those loads demand.
Frequently asked questions
What size solar system do I need to run a house off grid?
Full time off grid homes commonly land between 3,000 and 8,000 Wh of daily consumption once heating is handled by other fuels, which typically means a 1.5 to 4 kW array and a 400 to 1,000 Ah bank at 24 or 48 V. Homes that heat, cool or heat water electrically need several times that, which is why almost no off grid design does so.
Should I start with panels or batteries?
Neither. Start with the load list, because both are sized from it. Buying panels first is the most common and most expensive sequencing mistake in off grid builds.
Is my data sent anywhere?
No. Every calculation in this builder runs in your browser. Nothing is uploaded, stored or emailed, and there is no account to create.