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Solar Photovoltaics

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Community Involvement in a Solar Energy Project in Brazil


Introduction
Photovoltaic power offers a proven and reliable source of electrical power for remote, small-scale ICT facilities. PV systems turn sunlight directly into electricity for use by communications devices, computers and other kinds of equipment. Since there are typically no moving parts in PV systems, they require minimal maintenance. While often more expensive than other renewable technologies, the modularity of PV systems and the broad availability of the solar resource, sunlight, often make PV the most technically and economically feasible power generation option for small installations in remote areas.

The initial investment in a PV system typically accounts for most of its lifetime acquisition, operation and maintenance costs. Careful selection, planning and management of ICT loads are critical to controlling this upfront cost. The cost of a PV system rises in direct proportion to the total size of the loads. Experience has shown that failure to specify the size of the ICT load when requesting quotations for PV systems can result in proposals that are grossly oversized and cost tens of thousands of dollars more than necessary. This is not ordinarily due to any attempt by suppliers to take advantage of the situation; it simply reflects the fact that when the equipment power consumption is not specified in a request for quotes, system engineers will tend to err on the side of caution.

Resource

The solar resource is available all over the world. Insolation, or the rate at which solar energy is received over a period of time, is measured by the number of peak sun hours (PSH) per day. The number of PSHs is very important when sizing the PV system because it tells how much energy can be “harvested” from the sun in a specific location.

Insolation tends to be higher around the equator, in tropical zones, in deserts and in semi-arid regions, but is also affected by factors such as cloudiness and altitude. The fewer cloudy days an area experiences during a year, the better the system will perform. Average insolation in Cairo, Egypt is approximately 5.68 PSH, while insolation far to the north in Goose Bay, Canada is only 2.78 PSH. Although the city of Quito, Ecuador is situated only 25 km from the equator, its location high in the Andes mountains and long rainy season result in average insolation of only 3.82 PSH. Average annual insolation levels around the world tend to range between 3 PSH and 6 PSH (see map).

Since PV energy is only produced when the sun is up, most systems require batteries to support loads during nighttime and periods of cloudy weather. The battery bank is sized to provide power over the course of a given number of days of autonomy, or the maximum length of time the facility can be powered from the batteries without recharging. Battery storage adds to the cost and complexity of the system, but increases the availability of power at sunless times of the day and year.

Components

Typical components of a solar PV system include PV modules, controllers, inverters, battery banks, and BOS (see diagram below). A PV module, also called a solar panel, is a set of PV cells that are electrically interconnected, sealed together in a casing and weatherproofed. The type of PV cell technology used can affect the design of the system, but has little, if any, impact on the functioning of the system. Since there are no moving parts, modules are very reliable and durable.


Components of a Photovoltaic System



Modules come in several different sizes. The most common size for a module is 50W nominal power, although modules are produced in sizes ranging from 10W to 300W nominal power. There are different types of modules that vary in longevity, from 15 to more than 25 years.

Two or more modules connected together form an array. The energy output of an array is dependent on the rated power of each module, the number of modules in the array, and the number of hours of direct sunlight received. You will get twice the energy from two modules as from one. Very large arrays can have several hundred modules.

PV arrays, like batteries, output electrical energy in the form of direct current. In some PV system designs, such as the one illustrated in Figure 2, there is an inverter to convert the electrical energy to AC. In other designs there is a DC-DC converter to produce the appropriate DC voltage for the loads.

Location

Due to energy losses when transporting electricity over distances, especially at the low voltages typical of small PV projects, PV systems should be located within a reasonable distance of the point of energy use. Fortunately, PV modules can be placed anywhere the sun shines, including the roof of a building. Care must be taken to secure the modules in areas of high winds to prevent loss or damage. PV modules are very sensitive to shading. The shading of 5% to 10% of the surface area of a module can lead to a drop in power output of 30% to 50% or more.

Operation and Maintenance (O&M)

The minimal O&M requirements of a PV system make this technology well suited for isolated locations and rural applications where assistance may be infrequently available. Preventive maintenance, such as routine system cleaning and inspection, are always recommended. The most common maintenance required for typical PV systems is the periodic addition of distilled water to the batteries when flooded batteries are used. More expensive systems, using sealed batteries, can run for extended periods (months) without user intervention.

When PV systems are used and managed by community organizations or system owners, there is a critical ongoing need for training and/or assistance in system maintenance and troubleshooting. Sometimes the malfunctioning of a small fuse can be the reason for a system failure. In this case, a routine inspection by an experienced technician could reveal what caused the original problem that burned the fuse.

Environmental Impacts

A PV system produces negligible pollutants during normal operation. The main environmental impact associated with PV systems comes from the failure to properly dispose of batteries used in conjunction with the arrays.

Costs

The cost of a standalone PV system varies greatly depending on local market conditions and the quality of the equipment used. While the PV modules themselves may cost US$4.00 to US$7.00 per Watt, the total upfront investment cost of a PV system, including batteries, inverter, installation, etc., typically ranges between US$12.00 and US$20.00 per Watt installed. Costs per installed Watt depend on system size, the installation site and component quality. Smaller systems (less than 1 kW) tend to be at the higher end of the cost range. Additional factors that influence overall costs include government subsidies, the scale of the equipment procurement (with larger volume orders benefiting from lower per-unit costs), and the competitiveness of the local PV market.

The initial cost of a small-scale PV energy system typically rises by about US$640 (+/- $160) (Ref) for every additional 100 Watt hours (Wh) of energy that the system must supply on a daily basis. This is about the amount of energy needed to run a 17” CRT computer monitor for an hour a day. A 17" LCD monitor of the same size consumes only about 35 Wh of energy each hour, thus necessitating an additional capital investment of only $224 (+/- $56) in the photovoltaic system.

O&M costs for small-scale PV systems are generally low, at less than 1% of initial investment costs annually. If poor quality BOS components are used, these may fail and lead to higher costs to diagnose the problem and replace the faulty components.

Viability

The PV option is most likely to be competitive when tens or hundreds of peak Watts are required in remote or hard-to-reach areas. Depending on the situation, PV may also be competitive when only a few kilowatts of energy are needed. In many rural areas, diesel or gas generators and PV systems are the only viable alternatives. Unlike generator sets, PV systems are quiet and do not generate pollution. With proper design, installation and maintenance practices, PV systems can be more reliable and longer lasting than generators.

The modularity of PV systems enables systems to be well matched to the demand. When there are multiple small sites requiring electrification, PV is best installed in the form of independent systems sized to match each individual load.

PV systems are more likely to fail in areas that lack the commercial and technical infrastructures needed to ensure long-term sustainability. This infrastructure includes PV markets that are active enough to sustain the field over time, including suppliers of warranted PV system components, installers and maintenance technicians. Another key requirement is end-user acceptance of the technology, both in terms of the solar PV energy system and the ICT services being implemented. If the end-user does not share part of the responsibility for the cost, installation, maintenance and supervision of the system, the project is unlikely to survive.

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