The conventional power grid supplies 240 volt AC (Alternating Current) to the average household. Around 12,000 homesteads in Australia do not have access to a centralised electricity grid. Even when connection is physically possible, costs of the order of $10,000 per kilometre are prohibitive. Many of these consumers are dependent on diesel or petrol generators with occasional battery storage and/or renewable energy systems added. Others may depend mostly on renewable energy systems with possibly a petrol, LPG or diesel generator with a battery charging facility as a backup. These systems may have a conventional AC type of supply and/or a DC (Direct Current) battery supply.

Types of Systems
There are three basic types of stand alone renewable power systems. All of these systems may incorporate any combination of solar, wind and hydro as the primary energy sources.

1. DC Only System used in vehicles, boats, sheds, caravans, cottages etc to power lighting and low voltage appliances. The power is usually stored in a battery bank (usually 12 volt) which is regularly or intermittently recharged. This system should incorporate meters to monitor and fuses to protect the system. It may or may not include a charge regulator.
2. Combined DC and AC System is as above except that it contains a DC to AC (eg 12 volt to 240 volt) inverter to enable the use of commonly available 240 volt appliances. The inverter should be carefully matched to the loads (see Inverter section).
3. AC Only System where all the loads are run on AC via an inverter. This type of system is inherently more costly, less efficient and more prone to failure (eg no lights if inverter fails) than the above systems.

If you are charging a low voltage battery bank to meet your power requirements, we do not recommend that you then run your house as a conventional 240 volt AC household through an inverter (an AC Only System) as this would necessitate a much larger and more costly installation as would otherwise be the case. It would dictate a substantial battery bank powering an appropriately sized inverter to cope with everything being on at the same time. It would also require a substantially larger charging source (eg solar panels) to put back into the battery what the inverter is taking out.

If you refer to the graph, we have presented a fairly typical performance curve of a very typical battery bank to 240 volt AC inverter. You will notice from this that at its peak you may expect 85% efficiency from a modern solid state inverter. The further the wattage rating of the appliance is from this peak, the more inefficiently the inverter will deliver that power.

If you look at the type of appliance that you may wish to have in your home you may find some electronic appliances dependant on getting their power supply via a transformer. The transformer uses the high voltage to generate a much lower voltage. We may be able to operate these directly by the low voltage DC power supply without needing the transformer or inverter.

One of the more annoying aspects of some inverters, particularly inverters which are either square wave or stepped wave, is that they can produce an annoying hum on your stereo equipment. With some effort this can be minimised or filtered out, but at the same time introducing another level of inefficiency. If you can run the sound system directly from a low voltage DC supply or from a sine wave inverter you shouldn't get any hum.

Low Voltage Motors
It is generally recognised that low voltage motors have more torque than a 240 volt motor of the same wattage rating (power consumption).