transport networks, and health services, further discourage the growth of local economies.
Solar photovoltaic (PV) systems are renewable energy sources whose application globally has been limited primarily by the intensity and duration of sunshine in the places in need (and the related availability of the land needed to set up collectors for large-scale applications). The cost and efficiency of PV cells are yet another problem. In recent years, the cost of such systems has fallen along with the cost of purified silicon, the semiconductor at the heart of a solar cell, and the efficiency of manufactured solar cells has risen, with the result that the cost of generating solar electricity is only slightly higher than the average cost of power from the grid. Solar photovoltaics may not be ready to generate electricity for the grid, but it can be the technology of choice for communities that lack access to the grid or where the grid is unreliable. A large part of Nigeria is in that category most of the time, and yet the government finds that many Nigerians do not consume enough power to justify the expense of extending the grid into rural or isolated regions. Small-scale solar PV systems may provide the solution, if it can be demonstrated that, with certain incentives, private enterprises can fulfill that need, while ensuring sustainability by making a profit and ensuring efficient use by enabling consumers to afford the cost.
Although developing countries now have a great deal of experience with the installation of solar home systems, there are few places in which an extensive residential area is illuminated for an extended period by solar PV. It is well known that most of these installed systems fail. The principal reasons are not technical, but failures of the business model and poor adaptation to local customs and capabilities. These failures include the lack of training for users, the lack of service and maintenance, and the lack of ownership felt by the users. The last is characteristic of systems that are donated by universities or nongovernment organizations (NGOs) for demonstration purposes. These systems typically are in operation for less than a year.2
Solar photovoltaic systems suitable for rural households—solar home systems—usually consist of several components (see Figure A-1 in Appendix A). They include a PV module containing the silicon cells to be mounted on the roof or another sunny spot, a battery for storing electrical energy for use at night, a charge controller, wires and structural frames, and outlets for lights and other appliances. Such a system can operate several fluorescent lamps (often four), a radio or black and white television, and perhaps a fan. The system normally operates on 12 volts, direct current. Long-lasting, deep-cycle batteries, which can discharge