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A note on the utilization of solar energy

Posted by Syeilendra Pramuditya on December 12, 2010

Our planet receives an extremely gigantic amount of energy from the sun, in fact, of total energy flux entering the Earth’s surface, about 99.978% comes from the sun. For the whole Earth, the total solar energy rate is 174E+15 W. This 174 PW is the total rate of solar energy received by the Earth’s atmosphere, oceans, and land masses; about half, 89 PW, reaches the Earth’s surface.

According to 2005 data, the world primary energy consumption rate is about 15 TW (15E+12 W), with 86.5% derived from the combustion of fossil fuels. According to one research, with current fossil fuels reserve and energy consumption rate, then oil will be still available up to 43 years, gas 167 years, and coal 417 years. Some important issues with fossil fuels utilization are about pollution, climate change, energy security, and development sustainability, which are the reason why we should start to develop and utilize the renewable energies very soon, in particular solar energy. If we compare our current energy consumption rate with that of 89 PW of solar energy, we can see that solar energy is about 6,000 times more than those 15 TW of average power consumed by humans today. Hence, theoretically solar energy alone is much more than enough to supply our global energy consumption rate.

Considering those data mentioned above, it seems that the energy from the sun is one very promising renewable energy source for the future. This solar energy can be applied in many ways, including to generate electricity using photovoltaic solar cells/PV, concentrated solar power/solar thermal plant, and solar power satellites; to generate hydrogen using photo-electrochemical cells; to heat buildings, water, air, food; and many more.

Of all those kind of applications, probably the most popular to utilize solar energy are Photovoltaic cell (PV) and Solar Thermal Plant (STP). In PV cell, solar energy is converted directly into electricity, with average energy conversion efficiency available commercially on the market today, is between 12% and 18%. However, PV cell efficiency as high as 42% has been achieved at the University of Delaware. On the other hand, solar thermal plant work in a very different way, it works in a similar principle as a conventional heat engine. In STP, solar radiation is concentrated by using array of mirrors to heat and evaporate fluid, and this high pressure vaporized fluid finally will drive turbine to produce electricity. STP has average energy conversion efficiency from 19% to as high as 31.25% at the SandiaLab (SNL) testing facility.

Some advantages of solar technology are, no “fuel” is needed, pollution free during use, can operate with little maintenance after initial setup, extremely low operating costs (compared to existing power technologies), and additionally, solar electric generation has the highest power density (global mean of 170 W/m²) among renewable energies. On the other hand, some disadvantages are, solar electricity is often initially more expensive than electricity generated by other sources, solar cells produce DC which must be converted to AC when used in currently existing distribution grids, this cause an energy loss of 4-12%, and also, solar power technology is an intermittent power source, that may be uncontrollably variable than conventional power sources, and it is not available at night and is less available in cloudy weather.

A research about possibility of replacing all conventional energy sources by solar energy only has been conducted by Dr. M. Loster from UC Berkeley. In his research, he identified 6 areas worldwide (2 in America, 2 in Asia, 1 in Africa, and 1 in Australia), that are very suitable and optimal for installation of solar power systems. In this scenario, very vast solar farms will be built on these areas, each will cover an area of about 130,000 km2 to 180,000 km2, and the total area will be about 900,000 km2. He said that these only 6 solar farms (assuming a conversion efficiency of only 8%) could provide a little more than the world’s current total primary energy demand. That is, all energy currently consumed, including heat, electricity, fossil fuels, etc., would be produced in the form of electricity by PV cells.

Anyway, in my opinion, although solar energy looks so promising, still diversification of energy sources is always a wise decision, don’t ever to rely on only one single energy source, no matter how abundant, how make sense, and how easily-to-use that particular energy source. All kind of energy sources have their own advantages and disadvantages, all of them will raise some issues (and maybe problems), and I believe that there is no perfect energy source. Concerning the energy security issue, I think all we have to do is to find the optimal scheme of energy sources diversification, I mean we must find a “good enough” (instead of “correct”) formula to combine those various type of energy sources.

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