The shortcut answer
Household electricity use varies enormously — both between regions and within them. A small flat in a mild climate might use 5 kWh a day; a typical family home 15–25; a larger household with electric heating, cooling, or an EV can push past 40. Usage is the main driver of system size, which is why there’s no useful global rule of thumb. The calculator above takes your country and your actual numbers and returns a recommended range.
For a sense of scale before you open it, here’s how much solar a home like that typically needs:
- Modest household with little daytime load: a 3–5 kW solar system, roughly 7–12 panels.
- Typical family home with daytime use: 6–8 kW, roughly 15–20 panels.
- Larger household with an EV or heat pump: 8–12 kW or more, 20–30+ panels.
These are rough orientation markers for system size — the calculator above turns them into something specific for your home.
What affects the right size
Four factors drive the answer.
Your total electricity usage
The single biggest driver. You’ll find yours on a recent electricity bill, usually shown as a daily or monthly kWh total. Use a figure that reflects a full year if you can — winter and summer bills can differ by 30–50% depending on whether you heat or cool with electricity.
When you use electricity
Solar generates during the day, so the value you get from each kW depends heavily on when you actually use electricity at home. A home that runs the dishwasher, hot water, a pool pump, or EV charging during daylight gets more value per kW of solar, because that electricity offsets retail-priced grid power. A home that sits empty during the day exports most of its solar to the grid at the feed-in tariff, which is almost always a much lower rate than what you pay to buy power back — sometimes a third of retail, sometimes zero.
Three things raise your share of daytime use: smart appliances on timers, small habit shifts (running laundry mid-day instead of evening), and a battery, which stores daytime solar for evening use and effectively converts exported solar into self-used solar. If a battery is in your plans, size the solar generously — enough to cover your daytime load and fully charge the battery on an average day.
Future energy needs
Solar systems last 20+ years, so size for the home you’ll have in 3–5 years, not just today. Electrification is trending upward in most markets: EVs, heat pumps, and induction cooktops all shift household demand higher. A typical EV driven ~15,000 km a year adds roughly as much consumption as a small-to-medium household uses for everything else. A heat pump for water or space heating materially lifts winter consumption. If any of these are on your horizon — or if the household is likely to grow — size up now rather than later.
Roof constraints
Sometimes the roof caps system size before the maths does. Shaded areas, obstructions, and fire-code setbacks all reduce usable area. Our panel placement tool helps you see how many panels actually fit.
Common sizing mistakes
A few patterns come up repeatedly:
- Sizing for summer, under-sizing for winter. Generation varies seasonally; a full-year average is the fairer benchmark.
- Ignoring an incoming EV. An EV driven ~15,000 km a year uses roughly as much electricity as a small household adds to its bill. It changes the ideal system size materially.
- Over-sizing with no plan behind it. Some oversizing is usually smart — panels are cheap and demand trends up. A reasonable upper bound for most homes is around 20–50% above today’s usage; see the FAQs below for why. Sizing for 3–4× today’s usage with no EV, battery, or electrification plan locks in panels that will mostly export at low rates, which slows overall payback.
- Under-sizing to hit a lower upfront price. Chasing the cheapest quote usually means fewer panels, and the short-term saving disappears in forgone bill reduction over the next 20+ years. Before you settle on a size, use our savings calculator to compare the long-term returns of different sizes side by side — it’s usually a much bigger number than the extra few panels cost.
Sizing for future you, not today
Solar systems have a 20-plus-year life. If you’re planning an EV, going electric-everything, or expecting your household to grow, size for the home you’ll be in five years — not today. The inverse applies too: if you’re within a few years of downsizing, don’t over-size. Batteries are easier to retrofit than panels, so if you’re undecided on a battery, it’s usually fine to leave that decision for later and size the solar first.
