Electricity from Sunlight, 2nd Edition

5Stand‐Alone PV Systems

5.1 Remote and Independent

Imagine living in a remote farmhouse, supplied with electricity by an elderly diesel generator and a long way from the nearest electrical grid. The generator needs replacing—but you dislike polluting fumes—the cost of diesel fuel always seems to be rising, and the local electricity utility has just quoted a large sum to connect you to the grid network. How about photovoltaics (PV) as an alternative? What are the possibilities and pitfalls if you decide on a completely independent stand‐alone system?

Figure 5.1 shows a possible scheme. The farmhouse roof faces east–west, making it unsuitable for mounting a PV array, so the modules (1) are placed on an adjacent field, south‐facing and tilted at an optimum angle. They are interconnected at the array and the DC electricity flows via an underground cable into the farmhouse. The site is windy and exposed so it is decided to include a wind generator (2) in the system. The PV array and wind generator have separate charge controllers (3) to regulate the flow of current into a battery bank (4) that acts as an energy store. This is essential because the energy generated by wind and PV is variable and does not coincide with household demand (especially at night in the case of PV!). The battery bank voltage is normally 12 or 24 V DC, but may be higher in a large system. An inverter (5), connected to the battery bank, produces AC at the national supply voltage and frequency (e.g., 220 V at ...