Rural Solar Applications

At first, aid agencies tried to put solar to work for unelectrifed populations. In some projects, these agencies tried an approach that would have seemed intuitive at the time - they centralized the solar panels in the middle of a village, or on its outskirts, strung distribution wires to each home, and then transported the solar power to the local families or enterprises. This has since come to be known as a solar 'mini-grid', and its track record in terms of sustainability and cost-effectiveness is not a good one.

Figure 1.8 A solar mini-grid

Pakistan was one of the first countries to experiment with solar mini-grids, setting them up in eight villages in the late 1980s. However, the project failed on two counts. First, it failed in terms of maintenance: if the system is owned and used by a village, who precisely is responsible for its upkeep and for ensuring that everyone uses only their appropriate share of the power? Second, it failed in terms of cost-effectiveness: if the poles and wires to transport electricity and connect the households is the most costly part of rural electrification, then why use them with solar if you don't have to? Faced with these difficult question, the Pakistan post-evaluation study by the World Bank and UNDP concluded categorically that:

a decentralized approach for household PV systems in which individual households or buildings are powered by individual PV systems is less costly than a centralized approach in which a village is serviced by a single PV array and mini-distribution grid.11

A more decentralized approach to using solar technology has come to be known as the 'solar home system'. This approach puts the ownership of the system and the responsibility for its maintenance with the household or enterprise which buys it. The systems are bought by individual consumers (rather than at the communal level as in the case of solar mini-grids), just like generators, motorbikes or washing machines.

Figure 1.9 A solar PV module coming off the manufacturing line
Figure 1.10 Installed solar PV modules (from above and below)
Figure 1.11 A solar home in emerging markets

Perhaps a note on terminology will be helpful at this point. Because solar systems are bought by both households and commercial establishments, the title of 'solar home system' seems too restrictive for our purposes, and I instead use the term 'solar system' to apply to the decentralized applications of solar technology. And as a further point of clarification, by 'solar' I mean a solar electric system. This is different to a solar thermal system: the technology is different and the use of the sun's energy is different. In the case of a solar electric system, the technology is solar photovoltaic (PV) technology, which uses photons of light from the sun to generate electricity. In the case of a solar thermal system, the technology captures the heat of the sun, often to heat water.12

Figure 1.12 Example of a solar thermal system for heating water

How then a does a solar system work? First solar PV panels (what I will call 'solar modules') are mounted on a roof, or nearby pole, and are pointed in the direction of the equator - south if you are in the northern latitudes and north if you are in the southern. The closer you are to the equator, the more horizontal the solar module will be, as the sun spends more time directly overhead. These modules generate electricity from sunlight - photons of light that, upon hitting a solar module, displace electrons to create an electrical charge. This charge is then channelled and conducted from the solar modules through wires either direct to the 'load' (the technical term for the use of the electricity) or to a storage device - a battery - for use at a later time. Often between the solar modules and the battery is a 'charge controller', electronics that regulate the flow of electricity to protect the lifetime of the battery. Finally, because a solar panel produces direct current (DC) at 12 volts, as opposed to alternating current (AC) at 110 or 220 volts, some solar systems also have an 'inverter' to turn DC into AC electricity.13

Figure 1.13 Diagram of a typical solar system

Solar systems are ideal for producing electric light at the flip of a switch. When combined with energy-efficient compact fluorescent lights (CFLs), a 'typical' 50-watt solar system will provide a household or small business with four or five lights.14 Compared to the dim, hot light from a kerosene lantern, a cool, white light at the flip of a switch has its advantages. Moreover, the same system will normally have enough residual power for a small radio or a black and white TV that runs on 12 volt DC electricity.

Figure 1.14 Electric light at the flip of a switch
Figure 1.15 A typical solar light
Figure 1.16 Solar light in a kitchen
Figure 1.18 Comparison of (a) kerosene vs. (b) solar light in village stores

Where customers want to use a colour television, ceiling fan, blender or other appliance, they will need to use a bigger system with an AC inverter. A typical solar system that provides AC power would be about three times larger than a DC solar system - roughly 150 watts. But these are just averages. One of the virtues of solar is that it can be tailored to the precise needs and budget of the family or enterprise in question.

Figure 1.19 Larger solar system for appliances running on alternating current (AC)
Figure 1.20 Solar-powered colour TV and entertainment system
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