Solar system calculator.

A quick, free estimate of the panels, batteries, inverter and generator your home needs, using the U.S. government's solar data (NREL) for your ZIP code. When you're ready to buy, get a detailed system recommendation: the detailed calculator, reviewed by Patrick, with the exact equipment to order.

Start the free estimate

1 Where the panels will go

ZIP code

Enter your ZIP code to load the sun data for your address.

2 What kind of system

Grid-tiedPanels feed the house and the grid. No batteries. Lowest cost per kWh, but no power in an outage. Grid-tied with battery backupLike grid-tied, plus batteries that keep the essentials running when the power goes out. Off-gridNo utility at all. Panels, batteries and usually a generator for the dark weeks of winter.

How much of your bill to cover

3 How much power you use

Your bill shows "kWh used". An average month is enough; all twelve is better, because Michigan use swings with the seasons.

Average kWh per month Enter each month

Add what you'll run. For battery backup, tick Backup on what must keep running in an outage. Tick Together on what can be on at the same moment: that sizes the inverter.

Appliance	Watts	Hours a day	How many	When	Backup	Together	Remove

4 Batteries and generator

Generator Fuel you have at the house

Your system, roughly

0 kW of panels

A quick estimate. Sun data: NREL PVWatts (or PVGIS when NREL is unavailable) for your ZIP code with 14% system losses and typical Michigan shade and snow. Questions first? Email Patrick.

How it works it out

What's behind the numbers.

Panels

Your yearly use, divided by what one kilowatt of panels makes at your address in a year. For off-grid, it's sized to the hardest month you chose to cover, because a Michigan December makes about a third of what June does.

Batteries

Daily use times the days you want to run with no sun, divided by how deep that battery type can safely discharge: about 90% for lithium iron phosphate, 50% for lead-acid.

Inverter

Everything you marked "Together", plus a 25% margin, with enough surge to start the biggest motor, like a well pump. Any 240-volt appliance means a split-phase inverter.

Generator

Big enough to run the house and charge the batteries at once. Its hours and fuel come from the months when the panels fall short.

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