Solar PV System Components: Batteries, Charge Controllers and Inverters
Solar PV System Components: Batteries, Charge Controllers and Inverters
This domain tests battery capacity and care, charge-controller choice, and inverter sizing and output quality.
Core rules
- Battery capacity in Ah depends on the discharge rate; C10 means capacity at a 10-hour discharge. Depth of discharge (DoD) is the usable fraction.
- Lead-acid specific gravity falls as the battery discharges; a fully charged cell is about 1.265 at 25°C. Equalisation charging helps balance cells.
- PWM controllers are simple and suit small systems where array Vmp is close to battery voltage; MPPT controllers track the array's maximum power point and suit higher-voltage arrays.
- Inverter must supply continuous load plus surge; output may be square, modified sine or pure sine. Grid-tie inverters must synchronise and have anti-islanding.
Worked example
A 12 V, 100 Ah battery is used to 50% DoD, giving 50 Ah × 12 V = 600 Wh. An inverter with 90% efficiency delivers 540 Wh. A 60 W fan can run for 540/60 = 9 hours, ignoring battery ageing and temperature derating.
Traps that cost marks
Treating Ah as usable energy without voltage; discharging lead-acid below 50% regularly; choosing an inverter by VA only and ignoring surge; connecting a grid-tie inverter without anti-islanding; using a PWM controller with a high-voltage array.