This is an OPINION page. Every week, a different intellectual writes a FOCUS on a pertinent issue! PV POWER SYSTEMS An Answer to Yemen’s Energy Needs? [Archives:1997/43/Focus]
By: Ahmed Zabara
Background: With two decades of history in remote applications, Photo-Voltaic (PV) systems are solidly established as a cost-effective, reliable energy source at sites where grid (main) power is un-available. The uses are now expanding rapidly beyond those “standard” applications as PV prices fall, and the environmental costs of conventional power generation become more obvious. Other determining characteristics such as silent operation, freedom from fuel and pollution, and minimal maintenance have also drawn architects and builders to photovoltaics. Going beyond the technology’s purely technical characteristics, industry leaders are exploiting the future-oriented and aesthetic advantages, using stand-alone and grid-interactive PV systems to promote it as environmentally responsive, by participating in energy conservation and pollution mitigation programs.
What are Photovoltaics: Photovoltaics are solid state semiconductor devices that convert sunlight directly into electricity. They are usually made of silicon with traces of other elements and are first cousins to transistors, LED’s and other electronic devices. A Photovoltaic device (generally called a solar cell) consists of layers or semiconductor materials with different electronic properties. In a typical poly-crystalline cell, the bulk of the material is silicon doped with a small quantity of boron to give it a positive or p-type character. A thin layer on the front of the cell is doped with phosphorous to give it a negative or n-type character. The interface between these two layers contains an electric field and is called a junction. Light consists of particles called photons. When light hits the solar cell, some of the photons are absorbed in the region of the junction, freeing electrons in the silicon crystal. If the photons have enough energy, the electrons will be able to overcome the electric field at the junction and are free to move through the external circuit they give up their energy as useful work (turning motors, lighting lamps, etc…) and return to the solar cell. Thus, virtually any electric power need can be met by an appropriate designed PV power system. This includes power for lighting, pumping, refrigeration, radio transmission, etc. The only limitation is the cost of the equipment and occasionally the size of the PV array. The PV process is completely solid state and self-contained. There are no moving parts and no materials are consumed or emitted.
Is PV Difficult to Use? In a word, no. Although making PV cells and modules requires advanced technology, they are very simple to use. PV modules are generally low voltage DC devices (although arrays of PV modules can be wired for higher voltages) with no moving or wearing parts. Once installed, a PV array generally requires no maintenance other than an occasional cleaning. Most PV systems do contain storage batteries which do require some watering and maintenance similar to the battery in a car.
The Environmental Edge Photovoltaics are probably the most benign method of power generation known today. They are silent, produce no emission, and no fuel (other than sunlight) is required. The production of photovoltaics, of course, varies among manufactures. Some make extensive use of recycled materials and even use wastes from other industries as raw materials. While some hazardous materials (primarily strong inorganic acids and bases) are used in solar cell manufacturing, these substances are not released into the environment.
What Laws Cover PV Use? While the laws of different countries vary, PV systems are generally subject to the same electrical, building, and fire safety codes which govern the installation of electrical wiring and equipment in residential, commercial and industrial buildings. In the Republic of Yemen, there is no specific law or regulation governing PV use. However, it is safe to say that the authorities are generally supportive of this industry and application.
Is PV Economical? It is common knowledge that the Republic of Yemen has a shortage of electric supply. This explains the regulated black-outs. In addition, expanding the grid system to cover small remote villages scattered all over the landscape is a costly endeavor which will not see light in the near future. Therefore, PV offers an alternative. Over 6 million people in Yemen have no access to electricity, today. For these people, PV is probably the most economical power source. In addition, as the price per kilowatt of electricity rises, many city dwellers and small commercial users frustrated by blackouts, may find it more and more attractive to consider PV systems. Therefore, I expect PV users to grow rapidly. Even at a worldwide level, PV has started to compete with traditional power sources even in countries with extensive electrical infrastructures. It is expected that by the turn of the century, PV will be economically viable in a number of grid-connected applications.
The Lost Decade? Solar energy seemed popular about fifteen years ago, then disappeared. What happened? The oil crises of the 1970’s promoted an intense interest in finding alternative sources. At that time, oil was expensive ($40/barrel) and the Western governments were supporting PV and other alternative energy sources. This resulted in substantial investment and growth in the PV industry and dramatic growth in the solar thermal industry. By the mid 1980’s however, in spite of these factors there was still some reserve about using solar energy. Oil was cheap, falling to as low as $10/barrel, at some stage. Budgetary deficits in Western governments forced the slashing of R&D funding. The number of systems was dramatically reduced and the industry shrank accordingly – 90% of the solar thermal manufacturers went out of business. The net effect was a flat period for PV. During the 1980’s, the PV industry made dramatic cost improvements. PV modules today cost a fraction of what they sold for ten years ago. They also developed a variety of economic applications. At the same time, the 1990’s brought a renewed awareness of the environment impact of energy production. These factors have combined to create an expanding market for PV and a greater interest in the technology.
Does PV Work in Cloudy weather? The Republic of Yemen is endowed with plenty of sunshine, thus making it ideal for solar energy generation. Even in cloudy weather, PVs do generate electricity, although their output is diminished. In general the output varies linearly down to about 10% of the normal full sun- light intensity. Since flat plate PVs respond to a 180ø window, they do not need direct sun and can even generate 50-70% of their rated output under a bright overcast.
What Are PV Modules? Although a PV system can be as simple as a module and supply power to equipment such as a direct driven fans, most PV systems are designed to supply power whenever it is needed and so must include batteries to store the energy generated by the PV array. Systems with batteries also need electronic devices to control their charging or limit the discharging of the batteries. Since PVs and batteries are inherently DC devices, larger systems usually include DC/AC converters to supply AC power in standard voltages and frequencies. This enables the use of standard appliances in the system. On the electrical side, protective devices such as diode fuses, circuit breakers, safety switches and grounds are required to meet electric code safety standards. In general, PV systems also require mounting hardware to support and elevate the PV modules and wiring to connect the PV modules and other components together.
Is PV Effective for Residential Use? This is really a matter of the application. In general, the PV system can supply energy to all kinds of household uses, ranging from water heating, to appliances, to cooling/warming temperature. In situations where there is no grid supplied electricity in the home (remote villages, etc.), PV can be used for most common electrical needs.
PV System Duration: In general, the PV modules are the longest lived component of a PV system. Top quality modules are designed to last at least 20. They are designed to withstand all of environmental hazards including Arctic cold, desert heat, tropical humidity, winds in excess of 125 mph (200kph), and 1 inch (25mm) hail at terminal velocity. Batteries will last about 5 years, although smaller sealed units will typically last 3 years. Automotive batteries are poorly matched to the characteristics of PV systems and will generally only last 12 to 18 months in PV service. In any event, this will depend on the maintenance guarantees provided by the agency.
What Things to Look for when Purchasing a PV Module? An informed buyer will look at a number of items when buying a PV module. First, ask the seller what outside agencies have tested, qualified, or otherwise approved the module. Next check out the module. Pick it up. Does it have a solid feel? Or does the frame easily twist. Look at the solar cells. Are they perilously close to the module frame (which can lead to electrical breakdown and premature failure)? Are the module bus bars open and well isolated or are they folded behind the cells where they can cause electrical shorts or delimitation?
Conclusion: I want to come back to the original point. The Republic of Yemen has an energy shortage which is likely to remain with us for some time. Buying small generators that make all kinds of noise and break down so fast is not the answer. Installing giant batteries fed from the electric grid is not the answer is either. I believe tapping the warmth of the sun is the answer. We have plenty of it. It is free and is a good environmental choice. Go for it. __________________ Ahmed Zabarah sells PVs for a living.