TechBlog

The recent energy crisis and soaring oil prices have compelled the human race to look for alternate energy sources, such solar, wind, geothermal, nuclear and bio fuels. Harnessing of nuclear power is getting new impetus.

In the following article we will look at different aspects of solar power. There are different approaches to harness the solar power, such as, conversion to electricity and focusing the sun rays from very wide area to a very narrow spot for getting very high power densities. This concentrated radiation energy can be used to produce steam very efficiently to drive turbines.

In the following article we shall discuss the production of electricity with the help of solar cell. What then is a solar cell and how does solar power work? Here you will find a simple introduction to the technology for the uninitiated.

What is a Solar Cell?

A solar cell or photovoltaic cell is a device which generates electricity directly from visible light by means of the photovoltaic effect. In order to generate useful power, it is necessary to connect a number of cells together to form a solar panel, also known as a photovoltaic module. There are different types of solar cells.

Two typical types of solar cells are described below;

Amorphous Solar Cells

Amorphous technology is most often seen in small solar panels, such as those in calculators or garden lamps, although amorphous panels are increasingly used in larger applications. They are made by depositing a thin film of silicon onto a sheet of another material such as steel. The panel is formed as one piece and the individual cells are not as visible as in other types. The efficiency of amorphous solar panels is not as high as those made from individual solar cells, although this has improved over recent years to the point where they can be seen as a practical alternative to panels made with crystalline cells.

Crystalline Solar Cells

Crystalline solar cells are wired in series to produce solar panels. As each cell produces a voltage of between 0.5 and 0.6 Volts, 36 cells are needed to produce an open-circuit voltage of about 20 Volts. This is sufficient to charge a 12 Volt battery under most conditions. Although the theoretical efficiency of monocrystalline cells is slightly higher than that of polycrystalline cells, there is little practical difference in performance.

here. The nominal output voltage of a solar panel is usually 12 Volts, and they may be used singly or wired together into an array. The number and size required is determined by the available light and the amount of energy required.

We Can Store the Solar Power

The amount of power generated by solar cells is determined by the amount of light falling on them, which is in turn determined by the weather and time of day. In the majority of cases some form of energy storage will be necessary. It is possible to connect an array of solar panels to the mains to assist when the power required is greater than that being generated. The cost of this is offset by selling surplus power back to the electricity company when it is available.

This site, however, is concerned with self-contained systems where this is not possible. In this type of system the usual choice for energy storage is the lead-acid battery. The number and type of batteries is dependent on the amount of energy storage needed.

Power Control

No matter what, sometimes there will be too much power. Other times there won’t be enough. The battery will be damaged if it is allowed to be overcharged or over discharged, so a controller is needed to protect it. How charge is stored is explained below;

Charge Controllers and Controller Types

Most solar power systems will need a charge controller. The purpose of this is to ensure that the battery is never overcharged, by diverting power away from it once it is fully charged. Only if a very small solar panel such as a battery saver is used to charge a large battery is it possible to do without a controller. Most charge controllers also incorporate a low-voltage disconnect function, which prevents the battery from being damaged by being completely discharged. It does this by switching off any DC appliances when the battery voltage falls dangerously low.

Solar charge controllers are specified by the system voltage they are designed to operate on and the maximum current they can handle. The system voltage is usually 12 or 24 Volts, or occasionally 48 Volts. The maximum current is determined by the number and size of solar panels used. A single panel would need a controller of between 4 and 6 Amps rating, while larger arrays may need controllers of 40 Amps or more. Different settings are needed if sealed batteries are used. The controller shown is available with ratings of 8, 12, 20 and 30 Amps, and automatically selects between 12 and 24 Volts.

How Charge Controller Works

The principle behind a solar charge controller is simple. There is a circuit to measure the battery voltage, which operates a switch to divert power away from the battery when it is fully charged. Because solar cells are not damged by being short or open-circuits, either of these methods can be used to stop power reaching the battery. A controller which short-circuits the panel is known as a shunt regulator, and that which opens the circuit as a series regulator. Optionally there may also be a switch to disconnect the power from the appliances or loads when the battery voltage falls dangerously low.

The smallest systems may have only a few 12 Volt lights, but in bigger systems 230 Volts will probably be needed. An inverter is used to transform the low voltage DC generated by the solar panels into mains voltage AC.

The recent load sheddings in many under developed countries have introduced this device to previlaged class of citiens

Inverters

Many different types of inverter can be used in a solar power system. There are dedicated inverters for solar power available, but what’s important is that the correct inverter is used for the job it has to do. This job is converting a certain amount of power from low voltage DC to 230 Volts AC to power mains appliances. The right inverter will deliver enough power but will be no bigger than necessary, and will have the right output waveform.

How it Works

Most people are familiar with the idea of a transformer. A transformer is a device that converts one voltage into another, so why do we need an inverter? Well the problem with a transformer is that it can only work with alternating current or AC. The power from the battery in a solar power system is direct current or DC. Roughly, what an inverter does is to turn this DC into AC by rapid transistorised switching, and then use a transformer to convert it to the correct AC voltage. Depending on how this is done, the result can be either a sine wave like the mains or a modified sine wave which approximates to the mains.

Inverter Types

Inverters come in many different sizes. The smallest and cheapest, like the one shown, are basic modified sine wave devices designed to be plugged into a lighter socket. The top end of the market provides inverters rated at many kilowatts, with a sine wave output and additional features such as generator control. As a rule, a smaller system will use a small inverter to power exceptional loads, whereas a larger system may have everything powered from the inverter. The choice of waveform is dependent on the loads; a modified sine wave inverter is likely to be cheaper and more efficient, so a sine wave inverter would be chosen only if mains-quality power is specifically needed, for example for a high-quality sound system.

Harnessing of Solar Energy

The sun’s heat and light provide an abundant source of energy that can be harnessed in many ways. There are a variety of technologies that have been developed to take advantage of solar energy. These include concentrating solar power systems, passive solar heating and daylighting, photovoltaic systems, solar hot water, and solar process heat and space heating and cooling.

Solar power can be used in both large-scale applications and in smaller systems for the home. Businesses and industry can diversify their energy sources, improve efficiency, and save money by choosing solar technologies for heating and cooling, industrial processes, electricity, and water heating. Homeowners can also use solar technologies for heating and cooling and water heating, and may even be able to produce enough electricity to operate “off-grid” or to sell the extra electricity to the utilities, depending on local programs. The use of passive solar heating and daylighting design strategies can help both homes and commercial buildings operate more efficiently and make them more pleasant and comfortable places in which to live and work.

Beyond the localized uses of solar power, utilities and power plants are also taking advantage of the sun’s abundant energy resource and offering the benefits to their customers. Concentrating solar power systems allow power plants to produce electricity from the sun on a larger scale, which in turn allows consumers to take advantage of solar power without making the investment in personal solar technology systems.

Solar power technologies, from individual home systems to large-scale concentrating solar power systems, have the potential to help meet growing energy needs and provide diversity and reliability in energy supplies.

NREL performs research to develop and advance all of these technologies:

• Concentrating solar power systems — Using the sun’s heat to produce electricity.
• Passive solar heating and daylighting — Using solar energy to heat and light buildings.
• Photovoltaic (solar cell) systems — Producing electricity directly from sunlight.
• Solar hot water — Heating water with solar energy.
• Solar process heat and space heating and cooling — Industrial and commercial uses of the sun’s heat.

Due to the explosive demand for solar energy, El Segundo, Calif.-based market research company iSuppli Corp is predicting that worldwide investments in the production of photovoltaic (PV) cells will rise to the same level as those for semiconductor manufacturing by 2010.

The company expects global production of PV cells to rise to as much as 12 Gigawatts (GW) by 2010, up from 3.5GW in 2007.

Also by 2010, iSuppli predicts that there will be as many as 400 global production lines that can produce at least 1 Megawatt (MW) of PV cells per year, which would be a four-fold increase from the approximate 90 to 100 production lines running in 2007.

Factories capable of 1GW of annual PV production will be established with the aim of ensuring continued strong delivery of PV cells to the market, the company noted.

“The market for PV cells is estimated to grow by 40% annually until 2010, and 20% beyond. Nearly all market participants plan to increase their sales by a Compound Annual Growth Rate (CAGR) of 40 to 50% during the next few years,” explained Dr. Henning Wicht, senior director and principal analyst for MEMS and photovoltaics at iSuppli, in a statement.

Heavy investments will be required to finance the expansion of PV cell production with each PV factory requiring an investment of $500 million and more, employing as many as 1,000 workers per site, and generating annual revenue of $1 billion per year or more, putting them into the size, cost and employment range of semiconductor fabs, Wicht also noted.

Growth of PV market driven by several factors

While the high price of oil and surging energy prices fuel demand for solar power in the short term, demand will not wane in the years to come, Wicht believes, particularly given that projections show the world will need 3 to 4 times more electrical power over the next 50 years to support continued growth in population and economic output.

And according to the German Advisory Council On Global Change, by 2100, 80% of energy must be generated from renewable sources, he pointed out.

In addition, PV cell makers have affirmed that PV cell production will become cheaper in time, as PV cell makers Q-Cells AG and REC Group said they expect a reduction in PV system costs by 40% from 2006 to 2010.

iSuppli believes that with these cost reductions, many regions in the world will soon reach grid parity, which is the point when PV electricity costs the same or less than power derived from the electrical grid. PV grid parity is expected beginning 2012 in nations where sunshine is plentiful and constant, and 2018 in areas of the world with adequate or medium sun exposure, the market research company concluded.

To be sure, solar is such a hot area for development these days, even major semiconductor players are not being left behind. Just last week, both Intel and IBM separately made moves in the solar energy market.