A small off-grid solar system has four main parts: the panels, the charge controller, the battery and, if you need 240V AC, an inverter.
This lesson explains what each part does and how they need to be matched.
1. The basic layout
Solar panel → charge controller → battery → loads (12V DC directly, or 240V AC through an inverter)
Each connection needs suitable cable, overcurrent protection and isolation, sized to the equipment and the applicable requirements.
2. Solar panels
A solar panel turns sunlight into DC electricity. Its label lists several ratings:
- Rated power (W): output under standard test conditions. Real-world output is usually lower.
- Open-circuit voltage (Voc): the voltage with nothing connected. This is the highest voltage the panel normally produces, and it rises in cold weather.
- Short-circuit current (Isc): the current if the output is shorted.
- Voltage and current at maximum power (Vmp, Imp): where the panel produces the most power.
Shading, heat, dirt and panel angle all reduce output. Even partial shade on one panel can noticeably cut a system's output.
3. Charge controllers
A charge controller sits between the panels and the battery. It controls charging so the battery is charged correctly and not overcharged.
- PWM controllers are simpler and cheaper. They work best when the panel voltage is a close match to the battery voltage.
- MPPT controllers convert higher panel voltage into charging current more efficiently, and usually harvest more energy, especially in cold weather or with higher-voltage panels.
Check two limits on any controller:
- Maximum PV input voltage: the panels' combined Voc, including the cold-weather rise, must stay below it.
- Maximum charge current: the controller must suit the array size and battery.
Exceeding a controller's maximum input voltage, even briefly on a cold morning, can damage it. Use the panel and controller manufacturers' figures.
4. The battery
The battery stores energy for when the sun isn't shining. Set the charge controller's profile to match the battery chemistry. See the LiFePO4 vs AGM lesson for how the main types compare.
5. Inverters
An inverter converts the battery's DC into 240V AC for household-style appliances.
- Pure sine wave inverters produce power suitable for most appliances and electronics.
- Modified sine wave inverters are cheaper but can cause some appliances, chargers and motors to run poorly or hot.
- Check both the continuous rating and the surge rating. Motors and compressors can draw several times their running power at startup.
Inverters draw high DC current. A 1,000W load on a 12V inverter can draw roughly 90A or more from the battery once inverter losses are included. That needs heavy cable and a correctly rated fuse close to the battery.
6. Sizing the system
Start with the loads, not the panels:
- List each device with its watts and hours of use per day.
- Add up the watt-hours per day.
- Choose battery capacity for the usable energy and number of cloudy days you want to cover.
- Choose panels and a controller that can replace that energy in your location and season, with a margin.
7. Common beginner mistakes
- Buying panels first and working out the loads later.
- Ignoring the cold-weather rise in panel voltage.
- Using undersized cable between the battery and inverter.
- Expecting a panel's rated watts every hour of the day.
- Leaving out fuses or isolators on the panel, battery or inverter circuits.
8. Safety boundaries
Solar panels produce voltage whenever light falls on them. They can't simply be switched off at the panel.
Inverter output is 240V AC and can kill. Treat it with the same care as mains power.
In Australia, connecting to household wiring or the grid, and installing systems above extra-low voltage, must be done by appropriately licensed and accredited people. Fixed installations must meet the applicable standards.
When the design or installation is beyond your competence, get advice from a suitably qualified professional.
9. The main lesson
Panels make it. The controller manages it. The battery stores it. The inverter converts it. Size from the loads up, and protect every connection.
Handy gear
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Revival Academy 101 shares practical tutorials to help you understand electrical systems and make informed decisions.
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Technical note: This is general educational information, not a substitute for a design calculation, manufacturer instructions or applicable Australian standards.