Hybrid systems combine solar electric, generators and, occasionally, other renewable energy systems to increase energy availability. In hybrid PV systems, the solar array charges the batteries and supplies primary daily power requirements. A generator is used to charge batteries when there is not enough sunshine (or wind), to run battery equalization and to power specific large loads that the PV system cannot power. Hybrid systems are best used in remote locations where solar or wind resource is variable and where there is occasionally a need for large amounts of power. Most are PV-diesel hybrid systems.
In general, stand-alone PV systems are economically viable without gensets when energy requirements are less than about 5kWh per day and there is good constant sunshine. As energy needs increase, hybrid systems with diesel gensets and/or wind generators begin to look more attractive. Hybrid systems allow more flexibility in energy end-use because they ensure that power is available from a variety of sources. For example, during cloudy periods, a system operator can use wind or diesel generators to charge batteries and not be 100 per cent reliant on PV.
Cost is not the only factor to be considered when designing a PV system and there are other questions customers should ask:
• How far must fuel be carried and how often must trips be made to get it?
• Do people want to deal with the noise and fumes of petroleum generators?
• Is self-sufficiency or ‘eco-friendliness’ a consideration?
• How reliable are the alternatives?