The number of solar panels or the size of solar system depends on your:
A) Electricity Bill
B) Geographical Location
C) Configuration of roof
D) Type of solar panels
Electricity Bill
It is one of the most important factors that determine the size of solar system you need. A 1kWp solar system generates about 120 units a month. Therefore, Approximate size of solar system you need (in kWp) = Average monthly consumption in units / 120 Utilities provide monthly consumption units (kWh or kVAh) in your electricity bill. Average can be calculated by using units from the last 12 months bills. Accurate estimation of the size of the solar system depends on the remaining three factors.
Location
Certain states/areas within a state in India receive more solar radiation compared to other areas. Therefore, a 1 kWp solar system generates different units based on location. For example, a 1 kWp solar system generating 120 units in Delhi may generate 130 units in Tamil Nadu. Therefore, the size of the solar system varies based on location.
The table below gives expected units for 1 kWp solar plant:
| Name of State | Monthly Average Generation (Units/kWp) |
|---|---|
| Punjab | 1500 |
| Haryana | 1500 |
| West Bengal | 1509 |
| Rajasthan | 1557 |
| Maharashtra | 1605 |
| Telangana | 1647 |
| Tamil Nadu | 1613 |
Configuration of Your Roof
Third important factor that determines the size of solar system is the configuration of your roof. Shadow-free space is required to get maximum generation from solar panels. For 1 kWp solar PV system, you need approximately 10 Square meters or 100 Square feet of shadow-free space. For understanding more on space requirements (Read: How Much Area do I Need For Setting Up a Solar Plant?). Roofs generally have utilities like water tanks, AC exhausts, chillers, small rooms etc. They cast shadow, reduce radiation on roof and increase the area required to capture required energy.
Type of Solar Panels
There are different types of Solar panels (Click Here to See Different Types of Solar Panels Available) available in the market. They differ in efficiency but are largely the same in size/area. The type of panels does not impact the kWp size of system you need. They will impact the number of panels you need. If you choose a more efficient panel, you would need less number of panels or less space for the same capacity according to the table below.
| S. No. | Technology | Standard Size (Wp) | Efficiency (%) | No. of panels for 10kWp system |
|---|---|---|---|---|
| 1 | Poly crystalline- 72cells | 330 | 17.0 | 31 |
| 2 | Mono crystalline(PERC)- 72cells | 360 | 18.5 | 28 |
| 3 | Poly crystalline(PERC)-144cells | 360 | 18.2 | 28 |
| 4 | Mono crystalline(PERC)- 144cells | 380 | 19.2 | 27 |
Wondering how much the solar panels would cost? Click here to check if you qualify for a subsidy on solar panels or not. Approximate capacity calculations based on electricity bill and location can be done without technical expertise. For accurate estimations considering roof configuration, the technology of panels etc., you may need the help of professional designers like Prodah Solutions. Prodah Solutions provides the report free of cost.