Off-grid power calculators
An off-grid system for a van, RV, boat or cabin is a chain: what you use each day sets the batteries, the batteries and the sun set the panels, and the current in the wires decides their size. Get the first link wrong and every one after it is wrong too.
The system builder runs the whole chain at once from a list of your loads. The calculators after it take one link each, in more detail, and add the parts the builder leaves out: the charge controller, the series and parallel wiring, and what a power station can run. Each one shows a chart of the result, such as the battery charge over a day or the voltage falling along a wire, so you can see whether a choice leaves room to spare.
Use this first
Off-grid solar system builderList what you run and get the battery bank, solar panels, inverter and main cable together, with an energy-flow diagram and the battery’s charge through a typical day and a winter one.Plan the whole system
- Off-grid solar system builderUse it when you are starting from scratch and want every part sized from the same list of loads.
Store and make the energy
- Battery bank size calculatorUse it when you know your daily use and want the amp-hours, the number of batteries and a 24-hour charge chart.
- Solar panel size calculatorUse it when you want the panel watts for your daily use and the sun where you are, including a bad winter day.
- Amp-hour and battery runtime calculatorUse it when you have a battery already and want to know how long it runs a given load.
Connect the panels and batteries
- Solar charge controller size calculatorUse it when you know your panels and battery and need the controller’s amp rating, MPPT or PWM, and the voltage it must take on a cold morning.
- Series and parallel wiring calculatorUse it when you are wiring batteries or panels together and want the voltage, capacity and current, with a diagram of the connections.
Deliver it safely
- Inverter size calculatorUse it when you are choosing an inverter and need both its continuous and its surge rating, plus the battery current.
- DC wire size and voltage drop calculatorUse it when you are choosing cable for a 12, 24 or 48 V run and want the voltage drop and the fuse range.
Or buy a power station
- Power station runtime calculatorUse it when you are choosing a portable power station and want to know whether it will run your fridge, and for how long.
Battery banks can deliver hundreds of amps into a short circuit. Fuse every circuit, follow the manufacturer’s instructions and your local electrical code, and have a qualified person check the installation before you switch it on. The calculators give estimates, not a wiring plan.
Every calculator lists the sources it was checked against, and how we test explains the process. Your inputs stay in your browser.