What Size Solar System Do I Need? 3kW, 5kW and 10kW Compared
The most common sizing mistake is starting with the roof. Roof space is a limit, not a specification. What you need follows what you actually use.
Start with the bill, not the building
Find the kWh number on your electricity bill, not the peso amount. Take twelve months if you can and average them. One summer bill will oversize your system; one December bill will undersize it.
Then apply the rule of thumb: 1 kW of panels makes roughly 4 kWh a day, so about 120 kWh a month in Philippine conditions. Deliberately conservative.
A house using 600 kWh a month would need around 5kW to cover all of it. Though covering all of it often isn't the goal, for reasons below.
The three sizes people ask about
| Size | Roughly per month | Usually suits |
|---|---|---|
| 3kW | ~360 kWh | Lights, fans, fridge, TV, aircon now and then |
| 5kW | ~600 kWh | Family home with one or two aircon running regularly |
| 10kW | ~1,200 kWh | Large house, or a shop, clinic, small office, café |
Past 10kW you're into commercial territory, where demand charges and three-phase supply enter the conversation and the design changes shape.
Why bigger isn't automatically better
Once your system makes more than you use during daylight, the surplus leaves at the net metering credit rate rather than offsetting your retail tariff. That extra capacity still earns. Just about half as much per kilowatt-hour.
So the efficient size is usually the one where most output gets consumed on site. "Cover the whole bill" sounds appealing and often means paying full price for capacity that earns at half rate.
The things that cap it anyway
Roof area
Allow roughly 5 to 7 square metres of usable, unshaded roof per kW. A 5kW array wants somewhere around 25 to 35 m². Pitch, orientation and obstructions all eat into that number.
Which way it faces, and what's shading it
East and west roofs work fine here, they just produce a different daily shape. East peaks in the morning, west in the afternoon. Shade is the real enemy. One tree, or a neighbour's water tank throwing a shadow across part of the array for two hours, costs more output than a mediocre angle does.
Your service connection
Single-phase supply and your existing main breaker put a ceiling on things. Going past it means upgrading the service, which is its own cost and its own paperwork.
The net metering ceiling
RA 9513 covers systems up to 100kW. Irrelevant for a house, relevant for a larger commercial project.
Backup is a separate sizing question
If you want power through a brownout, two numbers get sized, not one.
- The array in kW, sized against consumption as above.
- The battery in kWh, sized against what you want to keep running and for how long.
Work out the essential load first. Lights, fans, a fridge and a router might total a few hundred watts. Add an aircon and it multiplies fast. Four hours of essentials is a normal system. The whole house overnight is a very different quote.
We read the real kWh off your bill rather than estimating from the size of the house. If you want to check the money side, the payback walkthrough is the companion to this.
We'd rather size it than guess it
Every rule of thumb on this page is a starting point. The right answer comes from twelve months of your own kWh figures and a proper look at your roof.
If you're interested in going solar, message us with your monthly consumption or call and we'll come back with a size, an itemized price, and the reasoning behind both. You can also visit the shop in Concordia, Bolinao and we'll sit down with your bill.