"What size solar system do I need?" is the question behind almost every solar project — and the honest answer is that it's not one number, it's a chain of connected calculations. Each component depends on the ones before it, so getting the order right is what separates a balanced system from an expensive mismatch. This guide walks through every sizing decision and points you to the exact calculator for each.
Start with your energy needs
Before sizing any hardware, you need one number: how much energy you use, in kilowatt-hours. Everything downstream scales from it. Guess this and every other figure inherits the error, which is why the very first step is an honest tally of your consumption. From there, the sizing chain flows naturally through each component below.
The six sizing steps
Work through these in order — each card links to the calculator that does the math for that stage:
Why the order matters
Each step feeds the next. Your energy usage sizes the solar array; the array and your overnight needs size the battery; your peak load sizes the inverter; the array's current sizes the charge controller; and the whole layout determines your string configuration and cable sizes. Jump around and the numbers won't line up. Follow the chain and every component is matched to the rest.
Check your production and payback
Once the system is sized, two questions remain: how much energy will it actually produce, and is it worth it? The energy production calculator estimates daily, monthly, and yearly output from your system size and sun hours, while the ROI calculator and bill savings calculator show the payback period and the money you'll save.
Verify before you commit
Sizing on paper is step one; confirming it in the real install is step two. If you already have a cable in mind, the voltage drop calculator checks it stays within limits, and to understand how battery runtime changes with load, the battery runtime calculator shows how long your bank lasts. For a guided walk-through of a full off-grid build, see our off-grid solar system guide.
Frequently asked questions
How do I size a solar power system?
Work out your energy needs, then size the array to meet them, the battery to store overnight energy, the inverter for your peak load, the charge controller to match the array, and the cables to carry current safely. Each has a dedicated calculator above; do them in order.
What size solar system do I need?
It depends on your electricity usage and local sun hours. Instead of guessing a round number, start from your kilowatt-hours and let the panel calculator turn that plus your location into an exact array size.
Should I size the panels or the battery first?
Size your energy needs first, then the battery, then the panels. They depend on each other, so always start from a solid daily-consumption figure.