Medium Off-Grid AC System

Here all the loads are run on AC using an inverter to convert power stored in the battery bank to 230 VAC. This simplifies wiring since low cost readily available cable, switches, outlets and fittings can be used, together with standard appliances.

Normally, the battery bank voltage will be 24 or 48 VDC instead of 12 VDC to reduce cable sizes.

The charge in the battery bank is then maintained using a PV array connected to the battery via a solar charge controller.

Good solar resources are important in order for the energy demand to be satisfied even when weather conditions are poor.

• The solar PV array must be sized so it is able to put sufficient power into the batteries to maintain demand at all times of the year.
• The inverter must be sized to meet the maximum electrical load that is needed i.e. to run all appliances that might be on at the same time.
• Often fuels other than electricity are used for heating and cooking.

Adding a wind turbine can provide more consistent year-round generation.

Including a diesel or LPG generator as back-up for times of poor weather or to power peak loads can be an economical alternative since the other system components do not need to be sized to suit worst case conditions.

In these systems the inverter also works as a charger (inverter charger) this means AC power from the diesel generator can be converted back to DC to charge the batteries.

• Generator charges battery and runs loads when batteries become low.
• Generator can also run peak loads - giving savings in inverter cost and allowing a smaller battery bank to be utilised.
• Generator can be automatically started and stopped using the inverter/charger.

Adding a petrol, LPG or diesel generator can be economical since you don't have to size the rest of the system for worst case weather conditions.

Often for places without any mains electricity a generator will be the existing source of power so adding a battery store with inverter/charger and additional wind and/or solar generation is the perfect way to reduce fuel costs and to make 24/7 power available without running the generator continually.