Designing a reliable off-grid solar system requires coordinating six distinct engineering calculations. This toolkit brings them all together on one page, with data flowing automatically between tools — your location's peak sun hours feed directly into the yield calculator, which then informs the charge time and cost analysis.
Calculates how long it takes your solar panels to fully recharge a depleted battery bank, based on panel wattage, battery capacity, and system efficiency.
Uses your geolocation or a manual address to retrieve real-world average daily peak sun hours (PSH) from the Open-Meteo solar API for accurate yield calculations.
Estimates daily, monthly, and annual energy output in kWh for your solar array, using your PSH data and a realistic 80% system efficiency factor.
Selects the correct AWG wire gauge for any conductor run, calculating voltage drop for each gauge and flagging those that meet the NEC 3% maximum voltage drop limit.
Add household and off-grid appliances from a prebuilt library, input daily usage hours, and get a precise total daily Wh load automatically populated into the battery calculator.
Generates a live schematic diagram showing series and parallel configurations for your battery bank and solar array, illustrating how voltage and capacity combine in each topology.
Peak sun hours (PSH) is not the same as daylight hours. A peak sun hour is defined as one hour during which solar irradiance averages 1,000 watts per square meter (W/m²) — the standard test condition (STC) used to rate solar panel wattage. If your location receives 5 PSH per day, it means the total solar energy received equals five hours of full-intensity sunshine, even if the sun is actually out for 10 or 12 hours.
PSH varies significantly by geography, season, and weather. The US Southwest (Arizona, New Mexico, Southern California) averages 5.5–7.5 PSH/day in summer. The Pacific Northwest and upper Midwest may average only 3–4 PSH/day annually. This difference has a direct 1:1 multiplier effect on your system's power output.
The 80% system efficiency factor accounts for real-world losses: wire resistance, charge controller inefficiency, battery round-trip losses, panel temperature derating, and soiling. This is the industry-standard derate factor used by the NREL PVWatts calculator.
Undersized wiring is one of the most common — and most dangerous — mistakes in DIY solar installations. Wire that is too thin generates excessive heat (I²R losses), causes voltage drop that starves your inverter, and can pose a fire hazard. The NEC recommends keeping voltage drop to 3% or less for branch circuits and 5% or less for combined feeder and branch circuits.
All calculations are estimated configurations for educational reference only. Always consult a licensed electrician before installation.
Understanding how to wire solar panels and batteries in series vs. parallel is fundamental to designing your system correctly. The wiring diagram tool on this page visualizes both configurations, but here is the electrical theory behind each:
Connecting components in series — positive terminal of one to the negative terminal of the next — adds their voltages together while keeping the amperage (Ah) constant. Three 12V/100Ah batteries wired in series produces a 36V/100Ah bank. Use series wiring to increase system voltage to match your inverter or charge controller.
Connecting components in parallel — positive to positive, negative to negative — keeps voltage constant while adding the Ah ratings together. Three 12V/100Ah batteries wired in parallel produces a 12V/300Ah bank. Use parallel wiring to increase capacity while maintaining system voltage.
Most large systems use series-parallel combinations. For a 48V/400Ah bank using 12V/100Ah batteries: wire four batteries in series to get 48V/100Ah, then connect four such strings in parallel to reach 48V/400Ah — requiring 16 batteries total. The wiring visualizer automatically generates the correct schematic for any combination you specify.