Off-Grid Solar Basics: Panels, Battery, Inverter and Charge Controller

Going off-grid, or adding solar to a cabin, shop, or well house, is easier to plan once you understand what each component does and how they connect. This guide covers the four building blocks, how to size them, and the mistakes that cause the most trouble.

The four building blocks

1. Solar panels

Panels convert sunlight to DC electricity. Output is rated in watts under standard test conditions, and real output is lower because of heat, angle, shade, and wiring losses. Panels are wired in series (raising voltage) or parallel (raising current), and the arrangement must match your charge controller or inverter input. Mounting, orientation toward the sun, and keeping panels free of shade matter as much as the wattage on the label. Shade on part of a string can pull down the whole string, which is why some installers add module-level electronics such as Tigo optimizers. Browse our solar panels for portable and fixed options.

2. Charge controller

The U.S. Department of Energy describes charge controllers as devices that regulate the flow of electricity from the generation source to the battery and load, prevent overcharging, and stop power flow when batteries are depleted to extend battery life. There are two main types:

• PWM (pulse width modulation): simple and low-cost, best when panel voltage and battery voltage are closely matched.
• MPPT (maximum power point tracking): adjusts for the panel's best operating point and typically harvests more energy, especially with higher-voltage panel strings, cold weather, or longer wire runs. Most modern systems use MPPT.

Make sure the controller's maximum input voltage and current ratings exceed what your panel array can produce, including cold-weather voltage rise. MidNite Solar is a respected name in controllers and system protection, and many all-in-one inverters from SunGoldPower and Growatt include a built-in MPPT controller.

3. Battery bank

Batteries store energy so you can use it after dark and through cloudy stretches. The Department of Energy notes that stand-alone batteries should be sized based on anticipated cloudy weather or low-wind periods, that deep-cycle lead-acid batteries typically used in small systems last 5 to 10 years, and that batteries can discharge up to 80 percent of capacity repeatedly without damage in the lead-acid case it describes. Lithium iron phosphate (LiFePO4) batteries are now common in off-grid systems because they generally allow deeper regular discharge and need less maintenance, but always follow the specific battery manufacturer's depth-of-discharge and charging specifications. Batteries should be installed in a well-ventilated space as the manufacturer directs. See our energy storage collection.

4. Inverter

The inverter converts battery DC to 60 Hz AC for household appliances. Choose a pure sine wave inverter for sensitive electronics and motors. Size the continuous rating to your largest simultaneous load and the surge rating to your motor starts, such as a well pump or air compressor. The DOE also notes that it can make sense to buy more inverter capacity than you currently need for future expansion. Many off-grid owners choose an all-in-one or hybrid inverter that combines the inverter, charge controller, and optional generator or grid input, such as products from Sol-Ark, Growatt, and SunGoldPower. Browse power inverters to compare.

How the pieces connect

How to size an off-grid system

1. Total your daily watt-hours. List every load, multiply watts by hours of use, and add them. Our sizing guide for solar generators shows the arithmetic.
2. Choose the days of autonomy. Decide how many cloudy days the battery should carry without sun. More days means a bigger battery.
3. Size the battery. Daily watt-hours x days of autonomy, divided by the usable fraction of the battery (its allowed depth of discharge), plus inverter losses.
4. Size the panels. The array should be able to refill a day's usage in one good sun day, and have enough surplus to recover after cloudy weather. Use panel watts x peak sun hours x about 0.75 as a planning estimate.
5. Choose the system voltage. Higher voltage (24 or 48 V) means lower current, thinner cable, and better efficiency as loads grow. Small cabins may use 12 V; larger systems generally use 48 V.
6. Size the inverter and controller for your peak load and array, with room to grow.

Backup power sources

Off-grid homes often keep a generator or a second source for long storms. Some owners add a wind turbine to cover winter nights. Whether that makes sense depends on your average wind speed; we cover it in wind versus solar for home power.

Common off-grid mistakes

• Undersized wire and missing overcurrent protection. DC current is high and can start fires. Use correctly rated cable, fuses, and disconnects, and follow code.
• Mismatched voltages. Panel strings, controller, battery, and inverter must agree.
• Ignoring temperature. Cold raises panel voltage and slows some batteries; heat shortens battery life.
• Skipping monitoring. A battery monitor shows state of charge and tells you when loads are too heavy.
• Underestimating loads. Heating and cooling appliances can be the largest draws.

When to bring in a professional

Small portable systems are straightforward. Anything connected to a home's wiring, a transfer switch, or a permitted installation should be designed and installed in line with local code and by a qualified electrician. OmniNova can help you choose components and review your plan. If you only need portable power, start with portable power stations; for a permanent build, browse off-grid solutions.

Frequently asked questions

What do I need for a basic off-grid solar system?

Solar panels, a charge controller, a battery bank, and an inverter, plus wiring, fuses or breakers, disconnects, and mounting hardware. Many all-in-one inverters combine several of these functions.

Do I need a charge controller?

Yes. The U.S. Department of Energy notes that charge controllers regulate the flow of electricity to the battery and prevent overcharging. Some all-in-one inverters have one built in.

Is MPPT better than PWM?

MPPT controllers typically harvest more energy and handle higher-voltage panel strings, so they are the usual choice for larger systems. PWM can work for small, closely matched 12 V setups.

How big should my battery bank be?

Multiply your daily watt-hours by the days of autonomy you want, then divide by the battery's usable depth of discharge and allow for inverter losses.

Can I install an off-grid system myself?

Small portable systems are DIY-friendly. A system tied into a building's wiring should follow local code and be installed by a qualified electrician.

Sources

• U.S. Department of Energy: balance-of-system equipment (batteries, charge controllers, inverters)