Written by CH Cheah
Saturday, 14 June 2008 22:42
Our world today is in a critical energy crisis. One of our major sources of energy today is based on fossil fuels, a source which is depleting, non-renewable and a major source of pollution to our environment. For countries in the tropics such as India, South East Asia, Mexico, and parts of the America Continent, our sun may offer an alternative energy source which is clean, renewable and able to sustain our energy needs for today, tomorrow and into our future. These countries typically enjoy 300 sunny days a year out of the total 365 - harnessing the power of our sun is a real and present possibility.
Constant Energy Source
The sun is a constant energy source of us. In some tropical countries like India (according to the Journal of Solar Energy Society of India), average solar radiation over one square meter of the land area is recorded in the range of 4-7 kWh a day. To put this into perspective, the solar energy incident on a mere one meter square of land is enough to power a typical family refrigerator for 36 hours, the total typical household lighting needs for 27 hours or a single 1 horsepower air conditioner or heater for 18 hours. Assuming we collect and harness the total solar energy incidence on our typical house rooftop (which will be significantly more than a mere square meter in area typically!) each house-hold should theoretically be self-sufficient in terms of energy needs.
Although the above scenario looks good, there is a flaw. We are assuming that there is a perfect conversion of incident solar energy to the form of energy that we can use. There are currently two major issues with solar energy utilization today - conversion efficiency and storage. Today, most of the household appliances and tools run on electricity and not directly from solar. Hence we need a method to efficiently convert solar energy into electricity. The second problem is that the sun is not a consistent source of energy. The amount of energy received from the sun fluctuates throughout the day and at night it is practically zero. Hence we also need to have a way to efficiently store the energy collected for usage at night or when the energy production is lower than requirements.
Energy Conversion and Storage
For a typical Photo-Voltaic (PV - conversion of solar energy into electricity) based on a single junction of a-Si cells, the conversion efficiency (source: Journal of Solar Energy Society of India) is currently at about 12%. Research and development are also underway to fabricate solar cells based on cadmium telluride, copper indium diselenide (CIS) and silicon thin films are also in progress. A research in Bangalore, India has reported around 13.5% efficiency on a gallium doped copper indium diselenide solar cells. Current research points to a new type of solar panel based on a multi-junction solar cell promising up to 40% of efficiency. The efficiency numbers still have potential to grow as new materials and methods are discovered. However with the current conversion efficiency, a 5 x 2 meter (area) of solar panel (cells) will still fulfill the typical household electrical energy needs.
Energy storage is the other major factor in the success of solar energy as a mainstream energy source. As solar energy production is not always consistent (the amount of sunlight received varies throughout the day) we need to efficiently store the energy collected for use when the sun's intensity is on the low side. Current technology for static installation uses lead-acid type of batteries similar to those used in your car but specified for deeper discharge cycles for solar energy storage. A typical 12 volts lead-acid battery (8-D battery rated at a capacity of 225Ah and assuming discharge to 20% capacity) will store enough power to power two 60 watts light bulbs for about fourteen hours. Since your typical household will need more than just enough energy for two light bulbs you will need a bank of such batteries. A bank of 8 or more of these cells may be needed to support your household electricity needs at night and when there is a lack of sunlight during the day (based on a 700W daily constant power requirement).
A more practical installation would be batteries combined with a gas or diesel generators as a backup. However if you are living within reach of your national (electricity) grid, you can use that as a backup when your in-house electric generation is exhausted. These hybrid systems point to a practical centralized-decentralized system where the primary power source is a local home solar energy system with auxiliary power from the national grid when necessary.
Harnessing Solar Energy from Space
According to a 2007 report by Pentagon's National Security Space Office, America is very interested in the concept of solar power harnessing direct from space. The concept argues that a single kilometer-wide band of geosynchronous earth orbit experiences enough solar flux in one year to nearly equal the amount of energy contained within all known recoverable conventional oil reserves on Earth today. Russia, China and the European Union are also interested in such a venture. The idea is to harvest this solar energy in space and beam it down as microwave radiation to ground based receivers and converted to usable electricity.
The concept of harnessing solar power from space is not new, according to an April 2000 article in the Electric Power Research Institute (EPRI) Journal, photovoltaic arrays in a geostationary Earth orbit (at an altitude of 22,300 miles) would receive, on average, eight times as much sunlight as they would on Earth's surface. Such arrays would be unaffected by cloud cover, atmospheric dust or by the Earth's day-night cycle.
According to a recent report from India's Ministry of Non-Conventional Energy Sources (MNES), harnessing the energy of the sun has reached a stage of commercial viability and their exports are also rising. The cumulative Photo Voltaic products (PV - conversion of solar energy into electricity) production in India is estimated at 133MWp of which 62MWp of PV products have been exported. There is a total of 71MWp of PV systems deployed in India making in the forth largest PV producers in the world. The technology for a practical implantation and commercialization of solar energy is definitely here today.
Future research will find better materials and technique for efficient conversion of solar energy to our primary energy form - electricity. The results of these will drive down cost per watts-hour of electricity harnessed from the sun from the current estimate of USD2.10 per watt using current technology.
Our environment is degrading rapidly each day and energy costs are skyrocketing. This may be a call for us to seriously consider solar energy as a major contributor to our energy needs.
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