Power Electronics in Solar Energy Systems Part 1 – Introduction to Solar Energy I – How important is electrical energy in our modern existence? Energy is one of the most vital resources for our modern existence. Our survival depends on the availability of energy. Every day, we consume energy to perform our daily activities that are vital for our survival. Electrical energy, which is just one form of energy, is considered to be the most important form of energy in our modern world. Everything is powered by electrical energy in our modern world. We cook our food using electric stoves. We refrigerate our food using electric refrigerators. We wash our clothes using washing machines. We entertain ourselves using computers and electronic appliances. We use air-conditioners to stay comfortable during hot weather. The list just goes on and on. All of the gadgets just mentioned are powered by electrical energy. It is clear that without cheap and abundant sources of electrical energy our modern civilization will be put in jeopardy. II – Where does the electrical energy that we use come from? At present, most of the electrical energy produced by electric power companies comes from nonrenewable sources like fossil fuels (coal, gas, and oil) and nuclear sources. A very small part of it comes from renewable sources (wind, tidal, hydroelectric, geothermal, and solar). Figure 1 III – So, what is the problem with non-renewable fossil fuels? Our fossil fuel emissions have increased dramatically over the past century. The massive amount of carbon dioxide in the atmosphere has dire implications for the delicate balance of our ecosystem and could eventually lead to environmental problems. Figure 2 Back in 1956, an American geophysicist, Marion King Hubbert, stated in one of his papers that the production of oil in the USA would peak toward the end of the 1960s and, would peak worldwide in the year 2000. The theory of Hubbert states that production of fossil fuels follows a bell-shaped curve, where production begins to gradually increase, then as the technology becomes mainstream there is a sharp upturn in production, followed by a flattening off when production has to continue against rising costs. As the cost of extraction increase, production begins to plateau, and then fall—falling sharply at first, and then rapidly. Figure 3 The International Energy Agency has stated that energy production is in decline in 33 out of the 48 largest world oil producers. In the same way that production of oil has reached its limits, other fossil fuels such as gas and coal will also reach their limits. Nuclear power plants use radioactive materials (e.g. uranium) which is not only also limited but also pose as an environmental threat. IV – Why choose solar energy? Solar energy is clean, green, free, and best of all it will last as long as the sun will last. Actually, solar energy is the main energy source of our planet. Plants rely on the sun to produce their food. The wind is caused by the heat that comes from the sun. The waves in the sea are caused by the wind which is caused by the heat of the sun. The hydrological cycle depends on the sun for it to continue. The bottom line is, the sun is our main power source. V – Relationship between Solar Energy Photovoltaic Systems and Power Electronics One of the advantages of solar photovoltaic systems is the potential to provide sustainable electricity in areas not served by the conventional power grid. The growing market for renewable energy technologies such as solar photovoltaic systems has resulted in a rapid growth in the need for power electronics. Solar photovoltaic systems produce DC power and hence power electronics and control equipment are required to convert the DC into AC power. Inverters are used to convert DC to AC. There are two types of inverters for this purpose: (a) stand alone and (b) grid-connected. A stand-alone inverter is used in off-grid applications with battery storage. With back-up diesel generators (such as photovoltaic/diesel/hybrid power systems, the inverters may have additional control functions such as operating in parallel with diesel generators and bidirectional operation (battery charging and inverting). Grid interactive Inverters must follow the voltage and frequency characteristics of the utility generated power presented on the distribution line. For both types of inverters, the conversion efficiency is a very important consideration. VI – Photovoltaic Power - A solar photovoltaic device is one which takes light from the sun and turns it into electricity. In doing so, it produces no emissions or harmful waste, and does so completely silently! - The photovoltaic (pv) power technology uses semiconductor cells (wafers), generally several square centimeters in size. From the solid-state physics point of view, the cell is basically a large area p-n diode with the junction positioned close to the top surface. - The cell converts the sunlight into direct current electricity. Numerous cells are assembled in a module to generate required power. - Because much of the current pv technology uses crystalline semiconductor material similar to integrated circuit chips, the production costs have been high. However, between 1980 and 1996, the capital cost of pv modules per watt of power capacity has declined. Major advantages of the photovoltaic power are as follows: • short lead time to design, install, and start up a new plant. • highly modular, hence, the plant economy is not a strong function of size. • power output matches very well with peak load demands. • static structure, no moving parts, hence, no noise. • high power capability per unit of weight. • longer life with little maintenance because of no moving parts. • highly mobile and portable because of light weight.