Who doesn’t like a bit of sun in their lives…and gradually we are getting it into our homes too. All thanks to solar power. From the beginning of time itself the sun has been one of the reasons for life itself. A plant synthesizes for itself using solar energy. And in a roundabout way we also get it through the food produced. But we as an organic species always failed to directly harness this immense power until photovoltaic cells came about.
Today, we have a superfluity of options to choose from to get the sun’s energy – from active and passive thermal heating to the more experimental ones. But the most prevalent one remains the photovoltaic cell.
The sun plays its part by hitting the Earth with 174 petawatts (PW) of solar radiation. Nearly one third gets reflected back into space but the rest falls onto the Earth. Digest this – This energy is so huge in quantity that in one year it is almost double that we will ever get from all of the Earth’s non-renewable resources of coal, oil, natural gas, and mined uranium combined. That’s a warm thought but the problem has always been to effectively capture, store and use it.
Power in a slice of silicon…
Should we thank Heinrich Rudolf Hertz for the photoelectric effect or Charles Fritts for giving us the solar cell? The photoelectric effect discovered the effect of electrons being charged by application of radiation (light) on matter and the solar cell was the application of it. From theory to real world application development on photovoltaic’s continued. The space race and the oil crisis in the 70′s speeded up the development of solar cells. Economies of mass production brought down the prices to reasonable levels and its use in a wide array of applications. The first use of solar cells was as a back-up power source to the chemical batteries of the Vanguard I satellite. Today, we see it in calculators and watches.
Simply speaking, solar cells are nothing but slices of silicon protected in a casing. Silicon is one of the most abundant materials found on Earth as sand. Solar panels are made from silicon. Silicon is super heated and then formed into very thin wafer looking cells arranged in an array called a panel. Panels are configured to various sizes depending on the use. A 10cm square panel can power an emergency telephone while a house might require something considerably larger.
Solar cells produce direct current electricity from the incident sunlight. When the sunlight falls on the solar cells, the energy contained in the light dislodges the electrons in silicon. The energy transfer from sunlight to the loose electrons causes the electron particles to ‘flow’. And electricity is nothing but the flow of these electrons. The current thus generated can be used to power equipment or to recharge a battery. The current can be passed through a connected inverter to convert it into alternating current to power equipment in our homes. Solar cells are solid state devices. As there are no moving parts very little maintenance is required. And it is a silent operation too. A typical PV cell has longevity up to 40 years with no work but an annual clean.
Today’s use of solar power allows for storage through rechargeable batteries. Using batteries power also becomes available during sunlight and periods of low light. In many systems tied to the main electrical grid, excess power generated is transferred to the grid for local/regional consumption.
PV plants have become a focus area for a lot of governments. For example, 120,000 solar panels bunched into 200 photovoltaic arrays makes the solar park at Jumilla, Murcia (Spain) the world’s largest PV solar plant. It generates 23 MW and is estimated to reduce CO2 emissions by 42,000 tons a year. By 2011, Arizona will outdo that with the Solana power plant. The proposed plant will generate 280 MW and light up 70,000 homes. Many countries are in the race to build their own versions of the ‘world’s largest solar plant’.
Here’s some data –
- Photovoltaic manufacture is doubling every two years.
- Since 2002 it has leapfrogged by an average of 48 percent each year.
- By the end of 2007 total power production by PV systems was 12,400 megawatts.
Besides the well known photovoltaic’s let me also put in a mention of the other methods used.
Solar Concentrating technologies use parabolic dishes and reflectors to concentrate rays of the sun and generate power. Home solar cookers also work pretty much on the same principle.
Many exploratory technologies like solar updraft towers (Solar chimneys) using heated air collected over an area to drive turbines and create electricity have been tried out. They try to combine the best of solar and wind power. In 1982, a small scale prototype was tried out for eight years. The tests showed that for an output of 100MW, a 1000 m tower and an area 20 km square km would be required. A 750 meter tower is in the offing at Ciudad Real, Spain.
Thermogenerators which work on the principle of temperature difference between two materials to generate electricity is also viewed as an experimental area. NASA used it in some of its deep space venturing satellites.
Thermochemical and photochemical process utilize the heat of the sun to generate electric potential. Though not in the public domain they are used for some industrial processes.
Developments continue to increase efficiency and decrease costs. It is clean…it is limitless…and if harnessed economically it could put fossil fuels in the shade.