Your solar load is the watts of everything you want to run, added up. Four fans, eight LED bulbs, a fridge, a 1.5 ton inverter AC, a TV, a router and a 1 hp water motor come to 2,406 W, and at normal hours they use about 16.7 units a day. In Lahore that load needs about 4.7 kW of panels, a 4 kW inverter and, to run the night part on batteries, about 6.5 kWh of lithium storage.
Edit the list with your own appliances, quantities and hours. Put the hours each one runs while the sun is up and at night separately: day use comes straight from the panels, night use has to come from batteries or the grid.
How the load is worked out
- Load in watts. Watts of each appliance × how many. The total is the most your wiring and inverter would carry if everything ran at once.
- Units a day. Watts × hours ÷ 1,000 for each appliance, day and night separately. One unit on your bill is one kWh.
- Inverter. Load running at the same time × 1.25, rounded up to a standard size, and never smaller than the panels ÷ 1.3.
- Panels. Units a day ÷ what 1 kW of panels makes a day in your city (peak sun hours × 78% after 22% losses).
- Battery. Night units ÷ 0.9 usable share of a lithium battery (0.5 for tubular) ÷ 0.9 inverter efficiency.
Worked example (the list above, Lahore)
- Load: 320 + 96 + 150 + 1,000 + 80 + 10 + 750 = 2,406 W
- Daylight units 11.39, night units 5.30, total 16.69 units a day (about 508 a month)
- 1 kW of panels in Lahore makes 5.08 × 0.78 = 3.96 units a day, so 16.69 ÷ 3.96 = 4.21 kW, which is 8 panels of 585 W (4.68 kW)
- Inverter: 2,406 × 1.25 = 3,008 W, and 4.68 ÷ 1.3 = 3.6 kW, so 4 kW
- Battery: 5.30 ÷ 0.9 ÷ 0.9 = 6.54 kWh, two 51.2 V 100 Ah lithium packs
The same home in Karachi needs 3.6 kW of panels (7 panels), because a kilowatt there makes 4.63 units a day.
What 1 kW of panels makes in each city
Yearly average sunlight on panels at the best fixed tilt, from Global Solar Atlas long-term data, after 22% losses.
| City | Peak sun hours | Units a day per kW of panels | Panels for 10 units a day |
|---|---|---|---|
| Lahore | 5.08 | 3.96 | 2.52 kW |
| Karachi | 5.94 | 4.63 | 2.16 kW |
| Islamabad and Rawalpindi | 5.38 | 4.20 | 2.38 kW |
| Peshawar | 5.21 | 4.06 | 2.46 kW |
| Quetta | 6.78 | 5.28 | 1.89 kW |
| Multan | 5.65 | 4.41 | 2.27 kW |
| Faisalabad | 5.22 | 4.07 | 2.46 kW |
| Gujranwala | 5.10 | 3.98 | 2.51 kW |
| Bahawalpur | 5.80 | 4.52 | 2.21 kW |
| Hyderabad | 6.21 | 4.85 | 2.06 kW |
| Sukkur | 6.06 | 4.72 | 2.12 kW |
Winter output is lower: in Lahore, January gives about three quarters of the monthly average. The solar system calculator shows each month, the cost and the payback.
Typical watts of home appliances
Running watts used as starting values in the calculator. Rating plates vary, so replace them with the figure on your own appliance where you can.
| Appliance | Typical watts | Units for 8 hours | Starting surge |
|---|---|---|---|
| Ceiling fan | 80 W | 0.64 | - |
| DC inverter fan | 35 W | 0.28 | - |
| LED bulb | 12 W | 0.10 | - |
| LED tube light | 20 W | 0.16 | - |
| Refrigerator (average) | 150 W | 1.20 | Yes, motor or compressor |
| Deep freezer (average) | 200 W | 1.60 | Yes, motor or compressor |
| Inverter AC 1 ton | 700 W | 5.60 | - |
| Inverter AC 1.5 ton | 1,000 W | 8.00 | - |
| Non-inverter AC 1.5 ton | 1,800 W | 14.40 | Yes, motor or compressor |
| LED TV | 80 W | 0.64 | - |
| Laptop | 50 W | 0.40 | - |
| Desktop computer | 150 W | 1.20 | - |
| Wi-Fi router | 10 W | 0.08 | - |
| Water motor 1 hp | 750 W | 6.00 | Yes, motor or compressor |
| Iron | 1,000 W | 8.00 | - |
| Washing machine | 400 W | 3.20 | Yes, motor or compressor |
| Microwave oven | 1,200 W | 9.60 | - |
| Air cooler | 150 W | 1.20 | Yes, motor or compressor |
A fridge or freezer compressor cycles on and off, so its figure here is an average over the day, not its running watts. For an AC use the AC size calculator to check the tonnage first.
Running load, starting surge and the inverter
The watts on a rating plate are running watts. Appliances with a motor or compressor, such as a water motor, fridge, deep freezer, washing machine or a non-inverter AC, draw several times that for a moment when they start. An inverter AC starts slowly and does not have this jump.
That is why the inverter is sized at 1.25 times the running load and why the calculator flags motor loads. Before you buy, compare the inverter's surge or peak rating with your largest motor, and do not switch on the water motor and the AC at the same moment.
If not everything runs together, lower Load running at the same time. The inverter still has to handle the full output of the panels.
Day load and night load
Panels only produce while the sun is up. Anything that runs in daylight can be powered directly; anything at night needs stored energy or the grid.
- On-grid system, no batteries. Size panels for your whole daily use. Daytime surplus goes to the grid under net billing, and night use comes back from it. Choose No batteries.
- Hybrid system. Panels charge batteries in the day for the night load. The battery here is sized for your night units only, so a family that runs fans and lights at night but the AC only in the day needs a much smaller bank.
To check how long a battery lasts during loadshedding with a fixed load, use the UPS backup calculator.
Questions people ask
How do I calculate the load for a solar system?
Add the watts of every appliance you will run, multiplied by how many you have. That is the load in watts, which sizes the inverter. Then multiply each appliance's watts by its hours a day and divide by 1,000 to get units a day, which sizes the panels and battery.
What size inverter do I need for a 1.5 ton inverter AC?
A 1.5 ton inverter AC draws about 1,000 W while running. With four fans, eight LED bulbs, a fridge, a TV and a router the load is 1,656 W, and 1,656 × 1.25 = 2,070 W, so a 3 kW inverter carries it. A 3 kW inverter suits up to 3.9 kW of panels; with more panels, or a 1 hp water motor on top, choose 4 kW.
How many solar panels do I need for 10 units a day?
About 2.5 kW in Lahore, 2.2 kW in Karachi and 1.9 kW in Quetta, after 22% losses. With 585 W panels that is five panels in Lahore and four in Karachi or Quetta. Winter months give less, so allow a margin if winter use matters to you.
What is the difference between load and units?
Load is power, in watts: how much the appliances draw at one moment. Units are energy, in kWh: load × hours ÷ 1,000. A 1,000 W AC running for 6 hours uses 6 units. Your inverter follows the load; your panels, battery and bill follow the units.
How big a battery do I need for night load?
Divide your night units by the usable share of the battery and by the inverter efficiency. For 5.3 night units on lithium that is 5.3 ÷ 0.9 ÷ 0.9 = 6.5 kWh, two 51.2 V 100 Ah packs. Tubular batteries should only be drained halfway, so they need almost twice the capacity.
Last reviewed 30 September 2026. Results are estimates; official notices always take precedence.