The honest answer is: enough to cover the electricity you use while the sun is up, plus whatever a battery will carry into the evening. Panels sized to your whole monthly bill will produce more than you can use during the day, and without a battery or an export arrangement that extra output is wasted.
The rule of thumb
Across Kenya, each kW of panels produces about 3.8 kWh a day on average, after losses from heat, dust, wiring and the inverter. A modern 620 W panel therefore produces about 2.4 kWh a day.
Your monthly use in kWh is printed on your KPLC bill or token receipts. Divide by 30 for a daily figure, then estimate how much of it happens in daylight.
Panels by monthly use
This table assumes half of the home's use happens between morning and late afternoon, which is typical for a family with someone at home during the day. It uses Kenya's average monthly sun and the all-in domestic rate.
| Monthly use | Monthly bill (about) | Panels (620 W) | Array | Roof area | Savings per year |
|---|---|---|---|---|---|
| 100 kWh | KES 2,600 | 1 | 0.6 kW | about 3 m² | about KES 15,000 |
| 200 kWh | KES 5,700 | 2 | 1.2 kW | about 6 m² | about KES 34,000 |
| 300 kWh | KES 8,500 | 3 | 1.9 kW | about 8 m² | about KES 51,000 |
| 500 kWh | KES 14,200 | 4 | 2.5 kW | about 11 m² | about KES 83,000 |
| 800 kWh | KES 22,600 | 6 | 3.7 kW | about 17 m² | about KES 130,000 |
| 1,500 kWh | KES 42,500 | 11 | 6.8 kW | about 31 m² | about KES 243,000 |
Bills are at the all-in DC2 rate of KES 28.30 per kWh, or KES 25.79 for the 100 kWh home on DC1. Roof area allows for spacing around each panel. Most homes start with a 3 kW inverter or larger, even for one or two panels, so they can add panels later.
If you want the evening covered too
Solar alone covers only daytime use. To use solar after dark, add a battery and more panels to fill it. For the 500 kWh home, adding a battery that carries 5 kWh into the evening raises the array to six panels (3.7 kW) and the savings to about KES 130,000 a year. The battery also keeps essentials running during outages; our battery backup guide shows how to size it.
Three things that change the answer
- When you use power. If the house is empty all day, fewer panels make sense, or a battery becomes essential. If you can run the washing machine, water pump and ironing in the middle of the day, the same panels save more.
- Where you live. Northern and eastern counties get noticeably more sun than the national average, and some highland areas less, especially from June to August. The solar by county pages give the monthly figures for your area.
- Your tariff band. If solar takes your grid use below 100 kWh a month, you may move to the cheaper DC1 rate, which slightly reduces the value of each unit saved.
A note on the cloudy months
July is Kenya's weakest solar month on average, with about 30% less output than the yearly average. A system sized for the average will cover less of the daytime load in June to August. That is usually fine for a grid-connected home, which simply buys more from KPLC in those months; an off-grid home needs to size for July instead.
Work out your own number
- Enter your bill in the free solar calculator to get panels, inverter, battery and savings for your home.
- Before you buy, read how to compare solar quotes and how to calculate payback honestly.