Solar Power Guide & Frequently Asked Questions
Solar Generation Math & Formulas
Solar systems generate electricity based on geographical location (sunlight strength), panel count, and panel efficiency:
- Annual Production Formula: System Size (kW) × Peak Sun Hours × 365 Days × Efficiency factor (typically ~75% to account for heat/inverter losses).
- System Sizing: Monthly consumption (kWh) / (Peak Sun Hours × 30 days × 0.75 efficiency). For 900 kWh/mo in a region with 4 peak sun hours: 900 / (4 × 30 × 0.75) = 10 kW system.
- Physical Footprint: Standard residential solar panels are about 400W each and take up roughly 20 sq. ft. A 10 kW system requires 25 panels and 500 sq. ft. of clear roof space.
Net Metering & Grid Connections
Connecting your system to the utility grid allows you to feed excess generation back into the grid:
- Net Metering (NEM): You receive billing credits for surplus electricity sent back to the grid. In NEM 1:1, credits are valued at retail electric rates. In newer policies (like NEM 3.0), credit rates are lower.
- Battery Storage (e.g. Tesla Powerwall): Essential if net metering credits are low, or if grid power is unstable. Batteries store daylight generation for night consumption.
- Grid-Tied vs. Off-Grid: Grid-tied systems shut off during blackouts for safety reasons. To run during outages, systems need battery backups and islanding inverters.
Frequently Asked Questions
Even minor shading can significantly reduce a solar panel system's overall output. In a traditional string inverter setup, panels are connected in series; if one panel's output drops due to shade, the current of the entire string drops to match it. Using microinverters or DC power optimizers on each panel helps isolate shaded panels so the rest of the array can run at maximum capacity.
In the Northern Hemisphere (US, UK, India), panels should face true South to receive the most direct sunlight throughout the day. In the Southern Hemisphere, they should face true North. The ideal angle/pitch generally matches your latitude (e.g. around 30° to 35° for mid-US/India). A steeper tilt (45°+) optimizes winter sun capture, while a flatter tilt (15°-20°) optimizes summer capture.
Peak Sun Hours are not just hours of daylight. One Peak Sun Hour is defined as one hour during which solar irradiance averages 1,000 watts of sunlight per square meter. Most regions get between 3 to 6 Peak Sun Hours per day, even if the sun is up for 12 hours. The calculator uses county-specific historical weather data to average this value.
Many governments offer tax credits to incentivize solar installations. For example, in the US, the federal Residential Clean Energy Credit (ITC) allows you to deduct 30% of the total installation cost directly from your federal taxes. In India, PM-Surya Ghar Muft Bijli Yojana provides direct capital subsidies for systems up to 3kW. These incentives drastically shorten the payback period.