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Calculate how many solar panels you need based on your electricity consumption, roof space, and local sun hours. Estimate daily and annual energy production, potential savings, and payback period for your solar installation.
Solar photovoltaic (PV) technology has undergone a dramatic cost reduction — panel prices fell over 90% between 2010 and 2023. Today, solar is often the cheapest source of new electricity generation globally. Accurately calculating the required system size ensures you generate enough energy to meet needs without significantly over-investing in excess capacity.
Calculating the right solar panel system size requires knowing your electricity consumption, local peak sun hours (solar irradiance), panel efficiency, and system losses. A properly sized system covers your needs without significant over or under-production.
Peak sun hours (PSH) is the number of hours per day when solar irradiance averages 1,000 W/m² (the standard test condition for solar panels). PSH varies by location: Arizona (7-8 PSH), California (5-6 PSH), UK (2.5-3.5 PSH), Germany (3-4 PSH), Pakistan (5-6 PSH), India (4.5-6 PSH). Higher PSH = more energy per panel per day.
Real-world solar systems produce less than rated output due to: inverter efficiency (~96%), cable losses (~2%), temperature derating (~10-15%, panels lose ~0.5%/°C above 25°C), soiling/shading (~5%), and panel degradation (~0.5%/year). Total system efficiency: typically 75-85% of nameplate rating.
| Configuration | Daily Output | Annual Output |
|---|---|---|
| 100W panel, 5 PSH, 80% eff. | 0.4 kWh/day | 146 kWh/year |
| 300W panel, 5 PSH, 80% eff. | 1.2 kWh/day | 438 kWh/year |
| 400W panel, 5 PSH, 80% eff. | 1.6 kWh/day | 584 kWh/year |
| 400W panel, 7 PSH, 80% eff. | 2.24 kWh/day | 818 kWh/year |
A complete solar installation requires more than just panels. The inverter, battery storage, charge controller, wiring, and mounting all affect system performance and cost. Understanding these components helps make informed decisions and avoid costly mistakes.
Solar panels are connected in series (strings) to reach inverter input voltage requirements. A 48V battery system uses 2-4 panels in series (Voc ~180-370V). MPPT (Maximum Power Point Tracking) charge controllers continuously find the optimal operating point on the I-V curve, extracting 10-30% more energy than older PWM controllers — especially valuable on partly cloudy days.
Battery storage = Daily consumption × Days of autonomy / DoD. For 10 kWh/day, 2 days autonomy, 80% DoD (lithium): 10 × 2 / 0.8 = 25 kWh of battery storage. Lead-acid DoD is only 50%, requiring 40 kWh for the same result. Lithium (LiFePO4) batteries cost more upfront but last 3-5× longer with deeper cycling.
Grid-tied systems export excess power to the utility and draw from the grid when needed — no batteries required, lower cost. Off-grid systems are fully independent — require battery storage, larger panel arrays, and diesel generator backup. Hybrid systems (grid-tied with battery backup) provide energy independence while maintaining grid connection for reliability.