Solar system sizing in Pakistan starts with listing all appliances, their wattage, and daily hours of use — the total daily kWh consumption divided by 4.5 peak sun hours and adjusted for system losses gives the required system size in kW.
List All Appliances and Their Wattages
| Appliance | Typical Wattage | Notes |
|---|---|---|
| Split AC 1 ton inverter | 800-1,000W | Running load; startup is higher |
| Split AC 1.5 ton inverter | 1,200-1,500W | Most common in Pakistani homes |
| Ceiling fan | 60-80W | Inverter fans use less |
| LED bulb | 7-15W | Per bulb |
| Refrigerator average | 100-200W | Runs about 50% duty cycle |
| Electric geyser | 2,000-3,000W | High wattage but infrequent use |
| Desktop PC plus monitor | 150-300W | Varies by hardware |
| LED TV 40 inch | 60-100W | Depends on brand and panel type |
Calculate Your Daily kWh Consumption
For each appliance: multiply its wattage by hours used per day, then divide by 1,000 to get daily kWh. Add all appliances for the household total. Example for a medium Pakistani house: 1.5 ton AC (1,300W x 8h = 10.4 kWh); four ceiling fans (280W x 12h = 3.4 kWh); ten LEDs (100W x 5h = 0.5 kWh); refrigerator (150W x 12h x 50% duty = 0.9 kWh); miscellaneous electronics 1.5 kWh. Daily total: approximately 16.7 kWh.
Calculate the Required System Size
Pakistan average peak sun hours: 4.5-5.5 hours per day (use 4.5h as a conservative estimate to ensure the system isn't undersized). System efficiency loss from cables, inverter, and dust: typically 20%. Formula: System size in kW = Daily consumption in kWh divided by 4.5h divided by 0.80. Using the example: 16.7 divided by 4.5 divided by 0.80 = 4.6 kW — round up to a 5 kW system.
Cross-Check Against Your Actual Electricity Bill
Your DISCO bill shows monthly Units Consumed. Divide by 30 to get the daily average. If your appliance-based calculation significantly exceeds your actual bill — for example, your calculation gives 16.7 kWh/day but your bill shows only 11 kWh/day — this means some appliances are used less often than you estimated, or your AC is more efficient than assumed. Use the lower of the two figures to avoid an unnecessarily oversized system, since oversizing wastes capital without improving output.
Installation and System Problems
Share your full appliance list with the vendor and ask them to explain the difference. Vendor recommendations sometimes undersize to reduce the proposal cost — but an undersized system leaves you with continued high electricity bills. Your own calculation is often more accurate.
Search for the specific model number on the manufacturer's website — the product specifications page lists rated power consumption. Alternatively, a plug-in watt meter device (available for Rs. 1,500-3,000 from electronics markets) measures real consumption of any plugged appliance directly.
Frequently Asked Questions
Size for summer peak consumption if your budget allows — summer is when electricity tariffs are highest for air conditioning users and solar savings are greatest. A system sized only for winter consumption will fall significantly short during the peak summer months when savings matter most.
Install the largest system your roof can accommodate in unshaded area, and design your usage to run high-consumption appliances (particularly AC) during peak generation hours. A well-optimised 5 kW system can deliver most of the savings of an 8 kW system if usage timing is aligned with solar generation.
Size for peak summer consumption if budget allows — summer is when electricity costs are highest (air conditioning) and when solar generation is also at its maximum. A system sized for winter average consumption will fall significantly short during summer peak months when your bills — and therefore your savings — are largest.
Add a 15–20% buffer above your current calculated system size if you plan to add a major appliance within 3 years — a second AC unit, an electric vehicle charger, or a water heater. It's significantly cheaper to install additional panels now than to expand the system later, which requires another installation visit, possibly a larger inverter, and additional mounting structure.
Use the 12-month average from your DISCO bill history — most DISCO portals show the last 12 months of consumption. If your bills swing between 150 units and 600 units depending on season, don't use the peak month as your sizing basis — you'd significantly oversize the system. Instead, calculate the annual total and divide by 12 for the true average daily consumption.