Off-grid solar system calculator
Tell us what you use. We size the panels, battery, inverter and charge controller, then price it with today’s best-value parts on Amazon. Prices as of Oct 21, 2026.
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Assumes 77% panel-to-battery efficiency, LiFePO4 at 85% usable capacity, and an inverter and charge controller sized at 125%. Picks are in-stock listings rated 4★+ with 100+ reviews, cheapest in total for the quantity needed. This is an estimate, not an engineering design. Check local code before you buy.
The rules behind the numbers
- PanelsDaily use ÷ peak sun hours ÷ 0.77 system efficiency.
- BatteryDaily use × days of backup ÷ 0.85 usable LiFePO4 capacity, at your system voltage. 12 V batteries can be wired in series to reach 24 or 48 V.
- InverterLargest load × 1.25, pure sine, one unit. Inverters are never paralleled: when one isn’t enough, raise the system voltage.
- Charge controllerPanel watts ÷ battery voltage × 1.25, MPPT, up to 4 identical units.
- PicksIn-stock Amazon listings rated 4★+ with 100+ reviews, not flagged for an unusually low price, cheapest in total for the quantity needed.
Compare every option on our price lists: panels, batteries, inverters, charge controllers and power stations.
Off-grid sizing FAQ
How big a battery bank do I need for off-grid solar?
Multiply your daily energy use by the days of backup you want without sun, then divide by the usable share of the battery. LiFePO4 batteries can safely use about 85% of their rated capacity. For example, 5 kWh a day with 2 days of backup needs 5 × 2 ÷ 0.85 ≈ 11.8 kWh of LiFePO4 batteries.
How many solar panels do I need for an off-grid system?
Divide your daily energy use by your peak sun hours and by the system efficiency (about 77% from panel to battery once wiring, charge controller and battery losses are counted). 5 kWh a day at 4.5 sun hours needs about 5,000 ÷ 4.5 ÷ 0.77 ≈ 1,440 W of panels, for example eight 200 W panels.
Should I build a 12 V, 24 V or 48 V system?
12 V suits small systems such as vans, boats and small cabins up to roughly 1-1.5 kW of inverter load. 24 V suits mid-size cabins. Above about 3 kW, 48 V is usually the better choice: the same power flows at a quarter of the current of 12 V, so cables, fuses and charge controllers are smaller and cheaper.
MPPT or PWM charge controller?
MPPT. An MPPT controller converts the higher panel voltage down to battery voltage and harvests roughly 20-30% more energy than PWM, especially in cold weather and with 24 V or 48 V banks. PWM only makes sense for very small 12 V systems with panels matched to the battery. Watch out for very cheap listings sold as "MPPT" that are really PWM; this calculator only picks controllers that list a maximum PV input voltage.
Is an all-in-one inverter better than separate parts?
An all-in-one combines the inverter, MPPT charge controller and battery charger in one box, which means less wiring and often a lower total price above about 3 kW. Separate parts let you mix brands, replace one part at a time and scale the controller independently. The calculator prices both and shows the cheaper one first.
How accurate is this estimate?
The sizing uses standard rules of thumb, and the prices are real Amazon listings as of the date shown. It is a parts estimate, not an engineering design: it does not include installation, permits, a transfer switch or a generator, and you should check panel string voltages and local electrical code before you buy.