An Off-grid system is not connected to an external electricity supply and is often in a remote location or is mobile. Medium off-grid systems offer an alternative to bringing in mains electricity.
How it works:
Here all the loads are run on AC using an inverter to convert power stored in the battery bank to 230VAC. This simplifies wiring since low cost readily available cable, switches, outlets and fittings can be used. Good wind/solar resources are important in order for the energy demand to be satisfied even when weather conditions are poor. The renewables must be sized so they are able to
put sufficient power into the batteries to maintain demand at all times. 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. In these systems the inverter also works as a charger (inverter charger) this means AC power from generation sources like solar or diesel can be converted back to DC to charge the batteries. The inverter charger controls and monitors everything connected to it. The inverter charger effectively creates a 'mini-grid' for your property.
Solar PV panels or other generation sources are connected to the system as if it was a grid connect system. This is the most efficient method of connecting the generation, as it allows the generation to first power loads and additional power will charge the batteries. Alternatively generation sources can be connected directly to the battery but in order to power loads the energy must pass through the battery incurring a large loss of energy.
Adding a generator:
Adding a petrol, LPG or diesel generating set can be economical since you do not have to be size the rest of the system for worst case weather conditions. A can be connected to the inverter charger to provide additional power when you have had a period of low generation or it can be used to power high power loads. The generator can normally be automatically started by the inverter charger, when and for what reason can be configured in the settings of the inverter charger. The generator can also power peak loads, giving savings in inverter cost and allowing a smaller battery bank to be used. 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.
What can it power:
This sort of system could comfortably power everything you would expect in a standard house, office or small industrial unit.Different sizes of inverter charges can be chosen to meet your requirements, several can be used in parallel for bigger applications or multiples of three can be used for three phase.
Items you can expect to need in a small off grid system:
1. Diesel generator (recommended)
2. SMA/victron inverter charger
4. consumer unit
5. wiring for the AC side (circuits)
6. Solar photovoltaic panels
7. DC isolation
8. SMA solar inverter
9. AC isolation
10. Kwh meter for your feed in tarriff.