For many developing countries, where the electricity grid is largely confined to the main urban areas, and where a substantial proportion of the rural population does not have access to most basic energy services, PV is widely regarded today as the best - and least expensive - means of providing many of the services that are lacking. Based on minimum energy requirements to provide basic energy services to every individual in the developing world, the corresponding potential for PV is estimated to be 16 GW (approximately 15 W per capita).
PV modules can be used for (see also table for examples of these applications):
- Pumping systems: to supply water to villages, for land irrigation or livestock watering
- Refrigeration systems: particularly to preserve vaccines, blood and other consumables vital to healthcare programs.
- Lighting: for homes are community buildings such as schools and health centers to enable education and income generation activities to continue after dark.
- Battery charging stations: to recharge batteries, which are used to power appliances ranging from torches and radios to televisions and lights
- Solar home systems: to provide power for domestic lighting and other DC appliances such as TVs, radios, sewing machines, etc.
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Examples of applications for PV in developing countries
| Agriculture |
• water pumping, irrigation
• electric fencing for livestock and range management |
| Community |
• water pumping, desalination and purification systems
• lighting for schools and other community buildings |
| Domestic |
• lighting, enabling studying, reading, income-producing activities and general increase in living standards
• TV, radio, and other small appliances
• water pumping |
| Healthcare |
• lighting for wards, operating theatre and staff quarters
• medical equipment
• refrigeration for vaccines
• communications (telephone, radio communications systems)
• water pumping
• security lighting |
| Small enterprises |
• lighting systems, to extend business hours and increase productivity
• power for small equipment, such as sewing machines, freezers, grain grinders, battery charging
• lighting and radio in restaurants, stores and other facilities |
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Components and maintenance
Photovoltaic power systems are exceptionally modular, which not only provides for easy transportation and rapid installation, but also enables easy expansion if power requirements increase. PV systems for stand-alone applications may comprise some or all of the following basic components:
- A PV generator and support structure (a single module or an array of several modules)
- Power conditioning equipment (Optional - typically includes inverters and control and protection equipment)
- Power storage (Optional - usually provided by batteries)
- Cables
- A load (e.g. lights, pumps, refrigerators, radio, television)
The solar PV generating equipment has no moving parts, which on the whole keeps maintenance requirements to a minimum and leads to long service lifetimes. The modules themselves are typically expected to operate for about twenty years, and should not require much more than the occasional cleaning to remove deposits of dirt. The majority of the other components - referred to as the Balance of Systems (BOS) - are generally serviceable for ten or more years if simple preventative maintenance measures are followed. Batteries, which are commonly required for most off-grid applications except water pumping, are currently the "weak-link" in the PV system and will typically need replacement every five years or so.
It is essential that storage batteries, and indeed all system components are of an acceptable quality. Where PV systems have failed in the past for technical reasons, it has generally been due to bad system design and/or poor selection of BOS components, rather than to failure of a PV module. As a result, considerable international research efforts are presently directed towards improving performance of BOS components.
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Costs and economics
In terms of average unit energy costs calculated using traditional accounting techniques, PV generated electricity cannot yet compete with efficient conventional central generating plants. Accordingly, the vast majority of PV installations to date have been for relatively low-power applications in locations, which do not have ready access to a mains electricity grid. In such cases, PV has been selected because it offers a secure and reliable power supply, and is often the cheapest power option.
Like any such commodity, the total purchase price of a PV system is based on all inherent costs of producing the individual components, transporting these to the site and installing them. There may also be associated costs of designing and engineering the system and purchasing land - particularly for large-scale or one-off projects.
However, there are many other factors to consider:
- Most PV systems manufacturers will offer some form of discount for bulk-purchase agreements
- Components imported from overseas will normally subject to some import levy
- Where systems are purchased through a local distributor there will usually be a mark-up for handling and some form of local sales tax will generally be payable.
The total price is therefore very difficult to define, varying with application, size of system and location. However, the costs of the PV array are a significant factor and will typically constitute 30%-50% of the total capital cost with the BOS contributing a similar amount.
As an example, a small domestic lighting system to power two or three fluorescent tubes would typically be in the order of 50 W, and would cost perhaps USD 500, whereas a solar photovoltaic vaccine refrigerator might require a 200 W array, bringing the total price of the system to around USD 5000.
Thus PV systems are an attractive option in rural areas where no grid-connection is available, though simple payback terms, because of its high capital costs, PV can often appear unattractive. However, using life-cycle costing, which accounts for all fuel and component replacement costs incurred over the life of the system, PV often compares favorable with the alternatives, which tend to have lower initial costs, but incur significantly greater operating costs.
Displacing conventional technologies with photovoltaic systems can bring various positive effects, which are difficult to quantify in direct financial terms, but which nonetheless offer significant economic and social benefits. For instance, in comparison to traditional kerosene lamps, PV can provide better lighting levels, enabling educational and income generating activities to continue after dark with reduced risk of fire and avoidance of noxious combustion fumes. The World Health Organization has noted that PV offers a more reliable refrigeration service than other power supply options. This has resulted in increased efficacy of stored vaccines, which in turn has helped to reduce mortality rates. Such factors must be considered when PV is compared to the alternatives even though the cost benefits are not easy to assess.
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PV-hybrid systems
Although PV systems will generally have some means of storing energy to accommodate a pre-defined period of insufficient sunshine, there may still be exceptional periods of poor weather when an alternative source is required to guarantee power production. PV-hybrid systems combine a photovoltaic generator with another power sources - typically a diesel generator, but occasionally another renewable supply such as a wing turbine. The PV generator would usually be sized to meet the base load demand, with the alternate supply being called into action only when essential. This arrangement offers all the benefits of PV in respect of low operation and maintenance costs, but additionally ensures a secure supply.
Hybrid systems can also be sensible approach in situations where occasional demand peaks are significantly higher than the base load demand. It makes little sense to size a system to be able to meet demand entirely with PV if, for example, the normal load is only 10% of the peak demand. By the same token, a diesel generator-set sized to meet the peak demand would be operating at inefficient part-load for most of the time. In such a situation a PV-diesel hybrid would be a good compromise.
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