Calculation method and assumptions for the solar plant estimate
Based on the list of consuming equipment and the selected city, it estimates the number of panels, plant capacity, inverter, battery and annual output for three packages: grid-connected, hybrid and off-grid. Calculations run in your browser. Using the calculation and report service requires signing in and confirming your email. When a report is saved, the input data and results are sent to the site server and stored in your account; a copy of the report is also sent to your confirmed email. See the privacy policy for details.
- Daily consumption: Each device's power × quantity × operating hours. Coolers and heaters are calculated month by month using that city's degree-days, and the "peak day" is the highest-consumption month of the year, not the sum of all seasons.
- City irradiance: Long-term monthly irradiance for 30 Iranian cities on the panel plane at optimal tilt, including panel temperature, dust, cable and inverter losses; the estimated system performance ratio (PR) in these cities is between 72.2 and 78.7 percent.
- Size of each package: The grid-connected package is sized on annual energy, the off-grid package on the governing month plus 2 days of storage, and the hybrid package with a half-day backup battery.
- Inverter: At least 1.25 times the simultaneous load, and for motors (coolers, pumps) enough that the starting current of the largest motor together with the rest of the load does not exceed the inverter's instantaneous capacity (2 times rated power).
- Battery: Peak-day energy × days of storage ÷ (80 percent depth of discharge × 97 percent inverter efficiency); and the bank must be able to deliver the inverter's power continuously.
Annual yield per kW of panels in several Iranian cities
| City | Annual yield per kW of panels | Estimate accuracy |
|---|---|---|
| Tehran | 1,595 kWh | ±15% |
| Mashhad | 1,626 kWh | ±10% |
| Isfahan | 1,799 kWh | ±10% |
| Shiraz | 1,839 kWh | ±10% |
| Tabriz | 1,526 kWh | ±15% |
| Ahvaz | 1,603 kWh | ±10% |
| Kerman | 1,835 kWh | ±10% |
| Yazd | 1,757 kWh | ±10% |
| Bandar Abbas | 1,712 kWh | ±10% |
| Rasht | 1,130 kWh | ±10% |
For a south-facing panel at the optimal tilt with no shading. Each city's accuracy was derived from the gap between our figure and two global irradiance references (PVGIS and Solargis); across all 30 cities, our figure is on average 2.2 percent below the median of the two references (a conservative estimate).
Frequently asked questions
How many solar panels does a house need?
It depends on consumption and city. Example: a house in Tehran with a refrigerator, two evaporative coolers, a TV and twelve LED lamps (peak day about 17.0 kWh) with a 20 percent growth margin is estimated at about 4 × 580 W panels (2.3 kW) for the grid-connected package and about 8 panels (4.6 kW) with roughly 54 kWh of battery for the off-grid package. An estimate matched to your consumption data and project location is provided through the calculator.
What is the difference between grid-connected, hybrid and off-grid plants?
A grid-connected system has no battery and feeds surplus power into the grid; it does not provide backup power when the grid fails. A hybrid system uses a battery for backup during outages. An off-grid system is independent of the grid, and its capacity is sized on the highest-consumption month and the storage needed for cloudy days.
How is solar battery capacity calculated?
Peak-day energy is multiplied by the number of storage days and divided by the allowable depth of discharge (80 percent) and inverter efficiency (97 percent); 2 days for the off-grid package and half a day for hybrid. In the example above, the hybrid battery comes to about 13.1 kWh.
Can a solar system power an evaporative or air-conditioning cooler?
Yes. Since the cooler only runs in the hot months, those months determine the off-grid array and battery size, and the inverter must handle the compressor's starting current. The calculator accounts for both factors independently; enter the cooler's operating hours for the hottest month.
How accurate is this estimate?
Next to each city's annual output, that city's accuracy is given (between ±10 and ±20 percent). Shading, roof orientation and the actual equipment can change the estimate; a reliable estimate for investment requires a site visit and study.
How much does a solar power plant cost?
Pricing depends on the selected equipment and current market conditions and is not published on this page. Send your calculation result via the WhatsApp option to receive a price proposal based on the recorded results.
Related pages
Solar Power Plant·Solar Inverter·Industrial Battery·Completed Projects·Contact us·Privacy Policy