About Solar & Off-Grid Calculators
Solar and off-grid power design is one of those engineering problems where the numbers either line up or the system disappoints: a battery bank that runs flat by 3 a.m., an inverter that trips on the well pump’s startup surge, panels that produce a third of their nameplate rating because of a single shaded corner, or a generator that drinks far more fuel than the spec sheet promised. The AllCalculators Solar hub gathers the math that homeowners going off-grid, cabin owners, van and RV builders, marine systems integrators, and small solar installers reach for at every stage of a build. Load auditing comes first: a realistic watt-hour-per-day total for every device on the system, derated for inverter efficiency and parasitic draws, is the foundation everything else sits on: undercount it and the rest of the design is wrong by the same percentage.
Array sizing converts that daily load into the panel wattage required at your latitude and worst-month sun hours, with a healthy multiplier for cloudy stretches and panel degradation. Battery bank sizing turns the load into amp-hours at a chosen system voltage and a target depth-of-discharge (lithium tolerates 80–90% DoD, lead-acid only 50% if you want it to last) then multiplied by days of autonomy for the cloud streak you actually want to ride through. Charge-controller sizing matches array voltage and current to an MPPT or PWM controller without exceeding the controller’s input ceiling, and inverter sizing handles both the continuous load and the surge demand of motors, compressors, and well pumps that pull 3–7× their running watts at startup.
Panel-tilt and azimuth math returns the angle that maximizes annual production at your latitude (roughly latitude minus 15° for summer-biased loads, plus 15° for winter-biased ones). Output-by-irradiance estimates real production for a given site’s solar resource map. Shading-loss quantifies what a single chimney, vent stack, or tree branch costs across a string, and it is usually more than people guess, because bypass-diode behavior makes shading non-linear.
Net-metering math compares grid-tied production against utility tariffs to see whether the meter spins backward or forward across a billing cycle. Generator fuel sizing pairs runtime, load, and fuel type into a tank-and-jerrycan plan for the days the sun does not show up. Loan-vs-cash compares financed against paid-up systems on a true lifetime-cost basis, including interest, federal credit, and degradation. Done up front, this math is the difference between a system you love for fifteen years and one you keep apologizing for.
When to Use a Solar & Off-Grid Calculator
- Auditing daily watt-hour loads before sizing any panels, batteries, or inverter
- Sizing a battery bank in amp-hours from daily load, system voltage, depth-of-discharge, and days of autonomy
- Choosing an MPPT or PWM charge controller that matches array voltage and current without exceeding its input ceiling
- Sizing an inverter for both continuous load and the surge draw of well pumps, compressors, and AC startup
- Setting panel tilt and azimuth to maximize annual or seasonal production at your latitude
- Quantifying shading loss from a chimney, vent stack, or tree before committing to an array layout
- Comparing financed vs. cash purchase of a system on a true lifetime-cost basis including degradation and credits
Frequently Asked Questions
Why does my off-grid system run out of power even though the panels match my daily load on paper?
Because the on-paper match almost always ignores real-world losses. Inverter efficiency (typically 88–94%), battery round-trip efficiency (85% for lead-acid, 95% for lithium), charge-controller losses, wiring losses, panel temperature derate (hot panels make less power), and the difference between nameplate and worst-month sun hours together strip 30–40% out of the headline number. Add a few cloudy days in a row and a bank sized for one day of autonomy goes flat by morning. The correct sequence is load audit first, then a panel array sized to your worst-month sun hours with a generous multiplier, then a bank sized for several days of autonomy at a safe depth-of-discharge.
How much depth-of-discharge can I actually use on my battery bank?
It depends on chemistry. Quality LiFePO₄ batteries are happy at 80–90% DoD daily and will deliver 3,000–6,000 cycles to that depth. Sealed lead-acid (AGM, gel) batteries only deliver their rated life if you stay around 50% DoD; going deeper roughly halves cycle life every additional 10%. Flooded lead-acid is similar. That means a 200 Ah lead-acid bank gives you about 100 Ah of usable energy, while a 200 Ah lithium bank gives you about 170 Ah and lasts several times longer. The autonomy calculator lets you set the DoD ceiling per chemistry so the usable capacity number is honest.
How much does shading really cost on a solar array?
Far more than the shaded area would suggest, because traditional string inverters and series-wired panels behave non-linearly under partial shade: a single shaded cell can drag down the entire string until a bypass diode kicks in, and even then the affected panel may contribute almost nothing. A chimney shadow across one corner of one panel in a 10-panel string can cost 10–25% of the string’s output during that window, not 1%. Microinverters and DC optimizers reduce the penalty by isolating each panel, but the right answer is still to design the array layout to avoid shade during peak production hours. The shading-loss calculator estimates the daily and annual cost so you can decide whether to move panels, trim trees, or accept the hit.
Is a generator still worth it when I have a big solar array and battery bank?
For most off-grid systems, yes. Sizing a purely solar system to cover the worst week of weather in December at high latitudes is wildly expensive: you end up with an array that is two or three times larger than you need from March through October just to ride out a few bad winter weeks. A modestly sized propane or diesel generator paired with an automatic transfer switch and a battery-charger handles those edge cases for a fraction of the cost. The generator-fuel calculator pairs runtime, load, and fuel type into a tank-and-jerrycan plan so you know what reserve to keep on hand for extended cloudy stretches.