Step 1: start from your bill
Your Kenya Power bill tells you how many units (kWh) you use a month. If you only have the shilling amount, divide it by your cost per unit; our guide to reading your Kenya Power bill shows how. As a rough rule, a KSh 15,000 bill at about KSh 29 a unit is roughly 500 units a month.
Look at several months, not one. A bill from a month with visitors, a broken geyser thermostat or a big order at the workshop will mislead you. We ask for twelve months at survey for exactly this reason.
Step 2: when do you use power?
This matters as much as how much. Power you use in daylight comes straight off the panels. Power you use after dark has to come out of the battery, and a battery holds less than a full day's generation.
- Daytime-heavy users such as shops, salons, workshops, schools and offices get the most from solar, because generation and use line up.
- Evening-heavy homes, where most power is used between 7pm and 11pm, still save well, but the battery limits how much of the evening load solar can carry. They see a smaller saving from the same system.
This is why two properties with identical bills can need different systems.
Step 3: count your load
For a more accurate answer, list what you run. Every appliance has a rating plate showing its power in watts (W). Multiply the watts by the hours you use it each day to get watt-hours (Wh). Add them up and divide by 1,000 to get units (kWh) per day.
| Appliance (typical) | Power | Hours a day | Units a day |
|---|---|---|---|
| 10 LED bulbs | 10 W each | 6 | 0.6 |
| Television | 100 W | 5 | 0.5 |
| Fridge | 150 W, cycling on and off | about 8 hours running | 1.2 |
| Electric shower | 3,000 W | 0.5 | 1.5 |
| Laptop and phone charging | 80 W | 5 | 0.4 |
These are typical figures for illustration only. Read the rating plates on your own appliances, because they vary widely.
The example above comes to about 4.2 units a day, or roughly 126 units a month. Multiply your daily total by 30 to compare with your bill. If the two are far apart, something is using more than you think. Old fridges, water heaters and pumps are the usual culprits.
Step 4: check your biggest appliances
A system has two sizes. The battery, in kWh, is how much energy it can store: the tank. The inverter, in kW, is how much power it can deliver at once: the tap. A big battery with a small inverter cannot run an electric shower and a borehole pump at the same time.
List the appliances that might run together at your busiest moment and add their watts. That total needs to sit comfortably under the inverter rating. Motors such as pumps and compressors draw several times their running power for a moment when they start, so allow headroom for them.
Step 5: match it to a system
Our four standard systems, with the modelled monthly generation of each:
| System | Panels and inverter | Generates about | Our calculator usually suggests it for bills of |
|---|---|---|---|
| 5 kWh | 4 × 610W panels, 5 kW inverter | 254 units a month | up to about KSh 10,000 |
| 7.5 kWh (most popular) | 6 × 610W panels, 6 kW inverter | 381 units a month | about KSh 10,000 to 15,500 |
| 10 kWh | 8 × 610W panels, 8 kW inverter | 508 units a month | about KSh 15,500 to 23,500 |
| 15 kWh | 12 × 610W panels, 12 kW inverter | 762 units a month | above about KSh 23,500 |
Generation figures are modelled from array size, Nairobi peak sun hours and a standard derate factor, and are confirmed at commissioning by a metered reading. Bill ranges assume KSh 29.19 a unit and pick the system with the fastest payback. They are a starting point, not a quotation.
The savings calculator does this matching for you and shows the payback on each option. Full prices are on our solar prices page.
Why bigger is not better
A system that generates more than you can use does not save you more. Solar you cannot use or store is simply not captured, and you have paid for panels and battery capacity that sit idle. The payback stretches and the investment looks worse.
That is why our calculator picks the system with the fastest payback, not the biggest one. It is also why we tell customers with very small bills that solar is not yet worth it for them. Below a bill of roughly KSh 8,000 a month, even our smallest system generates more than you would use, and the payback runs past four years. If your use is about to rise, with a new machine, an extension or a borehole, tell us and we will size for that instead.
Common questions
What size solar system do I need for my house in Kenya?
Start from your monthly units on your Kenya Power bill and when you use them. As a rough guide, our 5 kWh system generates about 254 units a month, the 7.5 kWh about 381, the 10 kWh about 508 and the 15 kWh about 762. Most family homes fit the 7.5 kWh system. A survey of your actual load gives the final answer.
What is the difference between kW and kWh?
A kW is how much power can be delivered at once, like the size of a tap. A kWh, or unit, is how much energy is used or stored, like the water in a tank. Inverters are rated in kW and batteries in kWh.
Is a bigger solar system always better?
No. Solar you cannot use or store is not captured, so an oversized system costs more without saving more, and the payback gets longer. The right size is the one with the fastest payback on your actual use.