Rooftop solar and electric cars are a natural pair in Pakistan. But "how many panels do I need?" confuses many people, mostly because kW and units get mixed up. This guide clears that up with worked examples from the ChargeNest solar calculator.
kW vs units: the one idea to get right
- kWp (kilowatt-peak) is the size of a solar system. Ten 550-watt panels make roughly a 5.5 kWp system.
- kWh, or "units", is the energy produced or used. Your bill and your car's battery are measured in units.
A solar system's size (kWp) decides how many units it makes per day. In our calculator we assume each 1 kWp produces about 4.5 units a day on average, then subtract about 15% for losses (heat, dust, wiring, inverter). Real output changes with your city, season, roof angle and shading.
How many units does an EV use?
Daily use is simple: kilometres driven × the car's consumption, plus a little charging loss.
For example, 40 km a day in a car that uses 17 kWh per 100 km needs about 6.8 units in the battery. With around 90% charging efficiency, that is roughly 7.6 units from the wall per day. You can look up your car's consumption in our EV database.
On-grid vs hybrid systems
On-grid (net metering)
An on-grid system exports extra solar to your DISCO's grid and imports when panels fall short, recorded on a two-way meter. With no batteries, it gives no backup during load-shedding.
Hybrid
A hybrid inverter works with the grid and batteries. It can keep selected loads (fans, lights, fridge, internet) running when the grid is off. Batteries add significant cost and need replacing eventually.
Net-metering rules and buy-back rates in Pakistan have been under review and can change, so check the latest NEPRA and DISCO policy before you decide.
Why a 7 kW charger doesn't need 7 kW of panels
This is the most common misunderstanding. A 7 kW home charger draws 7 kW while it is running, but your car only needs about 7.6 units a day in our example. At 7 kW that takes just over 1 hour of charging.
So you have two choices:
- Size by daily energy (with the grid's help). Panels make enough units across the day; while the car charges quickly, the grid (via net metering) or a battery fills the gap. This is the normal, cost-effective approach.
- Size by charger speed (sun only). Panels must produce the full 7 kW at the same moment the car charges. That needs a much bigger system and only works in strong midday sun.
Our calculator shows both. In the example below, running a 7 kW charger at full speed from sunshine alone needs about 9.3 kWp, while covering the same car's daily energy needs only about 2 kWp.
Worked examples (rough estimates)
All examples use the calculator's default assumptions: Rs 60 per unit, 4.5 units per kWp per day, 15% system losses, 550 W panels, 90% charging efficiency, a 7 kW charger, and an assumed system cost of Rs 110,000 per kW. These are rough estimates, not quotes. Prices and tariffs change.
| Scenario | System size | Panels | Inverter | Roof area | Rough system cost |
|---|---|---|---|---|---|
| EV only (40 km/day) | 2 kWp | 4 | 3 kW | ~10 m² | ~Rs 220,000 |
| EV + home (10 units/day) | 4.6 kWp | 9 | 4 kW | ~23 m² | ~Rs 506,000 |
| EV + home, hybrid with battery | 4.6 kWp | 9 | 4 kW | ~23 m² | ~Rs 1,120,400 total |
| EV + home, charger at full speed from sun | 9.3 kWp | 17 | 8 kW | ~44 m² | ~Rs 1,023,000 |
Example 1: covering just the car
40 km a day uses about 7.6 units, or around 227 units a month. A 2 kWp system (four 550 W panels) produces about 229 units a month. If each of those units replaces a Rs 60 grid unit, that is roughly Rs 13,600 a month saved.
Example 2: car plus home
Add 10 units a day of household use and the total becomes about 17.6 units a day (around 527 a month). The calculator suggests 4.6 kWp, nine panels and a 4 kW inverter, producing about 528 units a month. Estimated savings are around Rs 31,600 a month, with a simple payback of roughly 1.3 years. Treat that payback as optimistic: it assumes every solar unit is worth a full Rs 60, which may not hold if you export a lot at a lower buy-back rate.
Example 3: hybrid with backup
Same home, but with a hybrid inverter and 4 hours of backup for a 1.5 kW load. The calculator adds about 10.24 kWh of batteries (two modules). At an assumed Rs 60,000 per kWh, batteries alone are about Rs 614,400, bringing the total to roughly Rs 1.12 million and the payback to around 3 years.
Choosing the inverter
- Match the panels. The inverter is usually sized close to the panel array. A slightly smaller inverter than the panel kWp is common because panels rarely hit full rating.
- Check your peak home load. If you run several ACs at once, the inverter may need to be sized for that load instead.
- Single or three-phase. Bigger systems and big loads may need a three-phase inverter and connection. An installer should confirm this.
- Hybrid features. Check battery compatibility and which circuits stay powered during outages.
Batteries: do you need them?
If load-shedding is rare and net metering is available, many owners skip batteries and let daytime solar balance evening charging. If outages are frequent, a hybrid adds comfort at a much higher cost. An EV drains home batteries quickly, so most hybrid owners still charge the car with grid support.
Next steps
- Run your own numbers on the solar calculator.
- Check running costs on the charging cost calculator and home charging page.
- Get site surveys and quotes from installers through our partners page.
Always have panels, inverters and chargers installed by qualified, licensed professionals.
FAQ
How many solar panels do I need to charge an EV?
For about 40 km a day, the calculator suggests around 2 kWp, or four 550 W panels. Your answer depends on your daily distance, your car's consumption and your location.
Can I charge my EV directly from solar at night?
No, panels make nothing at night. With on-grid solar you charge from the grid at night and your daytime export balances it out, subject to your DISCO's net-metering terms.
Does a 7 kW charger need a 7 kW solar system?
No. The car needs units over the day, not 7 kW of sunshine at the same moment. With grid support, a much smaller system can cover the daily energy.
Is a hybrid inverter worth it?
It is worth it if you need backup during load-shedding. If outages are rare, an on-grid system is usually cheaper and pays back faster.