Getting your solar system sized correctly is the most important technical decision you will make. An undersized system leaves you without power at night; an oversized system wastes money on capacity you will never use. This step-by-step guide uses real numbers relevant to Uganda so you can do the basic sizing yourself — or verify that a supplier's quote makes sense.
Step 1: List Your Appliances and Daily Usage
Write down every electrical load you want to power and how many hours per day you use it. For each appliance, multiply its wattage by the daily hours to get watt-hours (Wh) per day. Then add them all up.
Example — typical 3-bedroom Ugandan home:
- 5 × LED bulbs (10 W each) × 6 hours/day = 300 Wh
- 1 × 32-inch LED TV (80 W) × 5 hours/day = 400 Wh
- 1 × fridge (100 W average, running ~12 h/day equivalent) = 1,200 Wh
- 3 × phone chargers (5 W each) × 4 hours/day = 60 Wh
- 1 × ceiling fan (50 W) × 4 hours/day = 200 Wh
Total daily consumption: ~2,160 Wh ≈ 2.2 kWh/day
If you want to add a water pump, electric cooker, or other high-wattage loads, add those separately — they require significantly larger systems.
Step 2: Find Your Region's Peak Sun Hours (PSH)
Peak sun hours measure how much usable solar energy your location receives per day, expressed as equivalent hours at 1,000 W/m². Uganda is well-positioned geographically — close to the equator — and has good solar resources across the whole country.
- Kampala and central Uganda: ~5.0 PSH/day
- Northern Uganda (Gulu, Lira, Kitgum): ~5.5 PSH/day
- Eastern Uganda (Jinja, Mbale, Soroti): ~5.2 PSH/day
- Western Uganda (Mbarara, Kasese): ~5.0 PSH/day
- South-western highlands (Kabale): ~4.5 PSH/day (more cloud cover)
Use the PSH value for your region in the panel sizing calculation below. When in doubt, use 4.5 as a conservative figure to avoid undersizing.
Step 3: Size Your Solar Panels
Solar panels do not convert sunlight at 100% efficiency — cable losses, dust, heat, and inverter inefficiency reduce real-world output. Apply a derating factor of 0.80 (80% efficiency overall) to account for this.
Formula: Required panel capacity (W) = Daily kWh ÷ PSH ÷ 0.80
Example: 2.2 kWh ÷ 5.0 PSH ÷ 0.80 = 550 W of panels
Round up to the nearest standard panel configuration — in this case, 2 × 300 W panels (600 W total) is a practical, commonly available size in Uganda.
Step 4: Size Your Battery Bank
Your battery must store enough energy to power your loads through the night and provide backup during overcast days. Key inputs are:
- Daily kWh: 2.2 kWh in our example.
- Autonomy days: How many days of backup you want without sun. For most Ugandan homes, 1–2 days is sufficient. Use 1.5 as a practical middle ground.
- Depth of Discharge (DoD): How deeply you can discharge the battery without damaging it. Lithium (LiFePO4): 80% DoD. AGM/gel: 50% DoD.
Formula: Battery capacity (kWh) = Daily kWh × Autonomy days ÷ DoD
Example (lithium): 2.2 × 1.5 ÷ 0.80 = 4.1 kWh of battery → a 100 Ah 48 V lithium battery (4.8 kWh) is a close match.
Example (AGM): 2.2 × 1.5 ÷ 0.50 = 6.6 kWh of battery → much larger (heavier, more expensive per kWh) for the same autonomy.
Step 5: Size Your Inverter
Your inverter must handle the peak load — the maximum wattage all your appliances could draw simultaneously. Add up the wattage of all loads you might run at the same time, then apply a 1.25 safety margin.
Example peak load: Fridge motor start surge (~300 W surge + 100 W running) + TV (80 W) + 5 lights (50 W) + fan (50 W) = ~580 W running, but with the fridge surge, peak can hit ~800 W.
800 W × 1.25 = 1,000 W minimum inverter rating → a 1 kVA or 1.5 kVA inverter is appropriate. For future expansion or appliance additions, a 2 kVA inverter gives headroom without a significant price premium.
Use Our Free Calculator
You can do this sizing automatically using SolarMarket's free solar sizing calculator at /calculator/. Enter your appliances and location, and the calculator recommends a panel, battery, and inverter configuration — which you can then use as the basis of an RFQ at /rfq/create.
