Sun, wind, water, geo - which has biggest potential?

Recently, I have been growing an interest for renewable technologies for energy production. Therefore, I visited a lecture of Prof. Aldo Steinfeld at Zürich University, entitled: 'Global Potential of Renewable Energy Technologies'. Having a restricted beginner knowledge in this field, I benefited a lot from this presentation. Here I would like just to mention what struck me the most.

Prof. Steinfeld took a scenario (made by the oil company Shell), which predicted a global increase in demand of CO₂ free electricity of ~30 TW. (1TW =10¹²W). Two reasons for that:

* Almost doubled population
* Higher amount of energy per capita

Which technology of renewable energy production has the chance to close the energy gap?

After looking at the practical and theoretical potentials of all possible technologies - wind, hydro, biomass, geothermal and solar - the answer was given: SOLAR!

Solar energy can be the real solution to the expected 30TW gap. Currently the overall energy consumption on Earth is 1.2 x 1014 W. To satisfy that using only solar power, we will need a square area of 500 x 500 km. The theoretical potential of solar power is 120 000 TW, practically 600TW can be achieved. So it is worth discussing.

Prof. Steinfeld presented two main technologies for solar power:

PV - Photovoltaic (Solar Cell) Systems. Through this technology the light (photons) is directly converted into electricity (voltage). Here is a short explanation from http://www.renewableenergyworld.com/: 'Solar cells are made of semiconducting materials similar to those used in computer chips. When sunlight is absorbed by these materials, the solar energy knocks electrons loose from their atoms, allowing the electrons to flow through the material to produce electricity.' Typically, a solar cell has a 15% efficiency, so only 1/6th of the energy that strikes it is converted to electricity. The first solar cell was used in 1950-s and had only 4% efficiency. Today there are also some cells which can reach up to 40% effiiciency. The world growth of PV technology is 34%; European growth - 87%, half of which is in Germany.

CSP - Concentrated Solar Power. Here is a short Wiki Explanation: 'CSP use lenses or mirrors and tracking systems to focus a large area of sunlight into a small beam. The concentrated light is then used as a heat source for a conventional power plant (Rankine plant - a thermodynamic cycle, which converts heat into work. The heat is supplied externally to a closed loop, which usually uses water as the working fluid.). A wide range of concentrating technologies exists. These methods vary in the way they track the Sun and focus light. In all these systems a working fluid is heated by the concentrated sunlight, and is then used for power generation or energy storage.
'What happens when the sun sets?' - you might ask. The advantage of CSP systems is that they can use fossil fuel during the night and thus generate electricity 24 hrs. This combined system is possible due to the fact that the solar power plants work on the principle of conventional power plants. The only difference is the method of heat generation.

BUT Solar power is not competitive with other energy production methods. For this reason the governments of some countries provide a feed-in tariff (in Spain it is 0.27 EUR/kWh) for investments in solar energy. This is the estimated cost of producing solar electricity. This makes the investment in this business profitable and attracts more interest.

Important issue to consider for every investment is Energy Pay Back: the number of years that the factory must work in orer to repay the initial investment.
For PV, depending on the cells used, it can be from 1 to 3.5 years.
For CSP, only about 0.5 years.

Sounds good to me :)

Conclusion: with solar power you can claim a sustainable production of energy, which has the potential to close the energy gap between today and the year 2060.