How to Calculate Your Daily Power Consumption for Off-Grid Solar
The foundation of every off-grid solar system is an accurate calculation of how much energy you use each day. Overestimate and you waste money on oversized equipment. Underestimate and your batteries drain too fast, shortening their life and leaving you without power. Here is how to do it right.
Step 1: List Every Appliance
Walk through your home or facility and write down every electrical device, its wattage rating (found on the nameplate or in the manual), and how many hours per day you use it.
Step 2: Calculate Watt-Hours Per Day
For each appliance: Wh/day = Watts x Hours/day
Typical UAE / Middle East Household
| Appliance | Qty | Watts Each | Hours/Day | Wh/Day |
|---|---|---|---|---|
| LED ceiling lights | 8 | 10 | 6 | 480 |
| Refrigerator | 1 | 150 | 12 | 1,800 |
| Ceiling fans | 4 | 75 | 8 | 2,400 |
| Split AC (1.5 ton) | 1 | 1,500 | 6 | 9,000 |
| TV (55-inch) | 1 | 80 | 4 | 320 |
| Wi-Fi router | 1 | 12 | 24 | 288 |
| Phone chargers | 4 | 10 | 3 | 120 |
| Washing machine | 1 | 500 | 1 | 500 |
| Water pump | 1 | 750 | 1 | 750 |
| Total | 15,658 Wh |
This household uses approximately 15.7 kWh per day.
Typical Rural African Home
| Appliance | Qty | Watts Each | Hours/Day | Wh/Day |
|---|---|---|---|---|
| LED lights | 4 | 7 | 6 | 168 |
| Small refrigerator | 1 | 80 | 12 | 960 |
| Phone chargers | 3 | 10 | 3 | 90 |
| Radio | 1 | 15 | 6 | 90 |
| TV (32-inch) | 1 | 40 | 4 | 160 |
| Fan | 1 | 50 | 8 | 400 |
| Total | 1,868 Wh |
This home uses approximately 1.9 kWh per day — a much smaller system is needed.
Step 3: Add System Losses
Real systems have losses from the inverter, charge controller, wiring, and battery charging. Add 25-30% to your total:
Adjusted daily consumption = Total Wh x 1.25 to 1.30
UAE example: 15,658 x 1.25 = 19,573 Wh (19.6 kWh)
African example: 1,868 x 1.25 = 2,335 Wh (2.3 kWh)
Step 4: Size Your Solar Array
Divide adjusted consumption by your location's peak sun hours:
- UAE: 5.5-6.5 peak sun hours
- Saudi Arabia: 5.5-7.0 peak sun hours
- Nigeria: 4.0-5.5 peak sun hours
- Kenya: 4.5-6.0 peak sun hours
UAE example: 19,573 Wh / 6 hours = 3,262W of solar panels needed
Step 5: Size Your Battery Bank
For 2 days of autonomy with LiFePO4 at 80% DoD:
19,573 Wh x 2 / 0.80 = 48,933 Wh = 48.9 kWh battery bank
At 48V: 48,933 / 48 = 1,019 Ah at 48V
Step 6: Size Your Inverter
Add up the maximum watts you will run simultaneously (not total daily). In our UAE example, if the AC, refrigerator, fans, and lights run at once: 1,500 + 150 + 300 + 80 = 2,030W continuous. With a 30% safety margin: 2,030 x 1.3 = 2,639W minimum inverter. A Felicity IVPS 3.5kVA or 5kVA would be appropriate.
Common Mistakes
- Forgetting standby power: Many devices draw 5-15W even when "off"
- Underestimating AC usage: Air conditioning is often 40-60% of total consumption in the Gulf
- Ignoring seasonal variation: Summer AC use can triple winter consumption
- Not measuring — guessing: Use a plug-in power meter for accurate readings
Frequently Asked Questions
How many kWh does a typical house use per day in the UAE?
A typical UAE villa with one air conditioner, refrigerator, fans, lighting, and common electronics uses 12-20 kWh per day. During summer with heavy AC use, this can increase to 25-40 kWh. An energy audit is essential for accurate sizing.
What is the easiest way to measure my power consumption?
Use a plug-in power meter (available for under $20) on each appliance for 24 hours to measure actual consumption. Many appliances draw less than their nameplate rating during normal use. For whole-house measurement, a clamp meter on your main breaker provides total consumption data.
Do I need to include appliances I only use occasionally?
Yes, include them if they will be used on the same day as your regular loads. Calculate their daily contribution by multiplying watts by average hours of use per day. A washing machine used 3 times per week averages about 0.43 hours per day (3 hours total / 7 days).
