An overview of various sustainable energy sources such as hydroelectric, solar, wind and other sources,

The generally known sustainable energy sources are from hydropower, solar power, wind power, wave power, geothermal power and tidal power.

Hydropower is one of the most commonly used energy sources throughout the world. It has several advantages. At the beginning of the new Millennium, this energy source constitutes about 20% (2600 TWh/year) of the electricity world consumption (12900 TWh/year. Of 175 countries, more than 150 have hydropower resources. For 65 of them, hydro produces more than 50% of electricity; for 24, more than 90% and for 10, practically the total.

According to the Hydropower & Dams Atlas (H & D, 1999), world hydro potential is as follow:

 Gross hydro potential: 40,500 TWh/year
 Technically feasible: 14,300 TWh/year
 Economically feasible: 8,100 TWh/year

The installed capacity is about 700 GW (corresponding to the 2600 TWh/year). The remaining exploitable capacity represents 1500 GW (producing 5500 TWh/year). It is estimated that by the middle of this century, the consumption of electricity in the world will be multiplied by a factor of 2.5 to 3.0. Hydropower, a renewable and clean energy, will contribute largely to this development. The main advantages of hydroelectricity is that it is a reliable technology, proven by one century of construction and operation. It is easily accessible, particularly for developing countries. In addition, it plays a major role in reducing greenhouse gas emissions in terms of avoided generation by fossil fuels. It is competitive and the kWh cost does not depend on variations in combustible costs and on international economic politics. It is an important factor in providing energy independence for a country. Most importantly, hydropower stations are very often integrated within multipurpose schemes, which satisfy other fundamental human needs (irrigation, domestic and industrial water supply, flood protection) and hydropower can help finance these other functions.

Wind power is an equally important sustainable energy source. The low cost of wind power, makes it particularly important compared to other renewables. Wind turbines in different countries are basically available at comparable prices based on normal market conditions, but the trend everywhere is the same - wind energy is getting cheaper. Within the last decade, the cost of wind power has dropped between two and three times, and this trend is expected to continue, with the cost of 1KW installed predicted to drop from 1000 EURO in 1998 to around 500 EURO in 2020. There are various reasons for this. Wind turbines themselves cost less as technology improves and the number being manufactured increases. The newer designs are also more efficient, so more electricity is produced from more cost-effective turbines. The size of wind turbines is also increasing - from around 100 kW in the mid 80's, to around 200 kW in the late 80's, 500 kW in the early 90's, through to 1-2 MW now. 4-5 MW wind turbines can be expected in the future which, for logistical reasons, will mostly be for offshore applications. The industry has been characterised by short development periods of 2-3 years to double individual wind turbine capacity. This has all reduced infrastructure costs, as fewer turbines are needed for the same output. Wind power development started in the late 70's, and was stimulated in the mid 80's by the Californian market. This collapsed a few years later, to be replaced by strong market development in western Europe, notably in Denmark, Germany and Spain, with these three countries accounting for 80% of the total installed wind power in Europe. These countries are not leaders due to superior wind resources, but due to their market policy of fixed minimum prices, which seems to be sufficient guarantee for investors to move into this new sector. To illustrate the importance of appropriate policies and attitudes to new clean energy solutions, we can compare the situation in different countries. Netherlands (370 MW installed) and UK (350 MW installed), which have bidding systems where electricity is purchased from limited numbers of wind schemes selected on the basis of price competition, have less than one quarter the installed capacity of Denmark (1700 MW). In the month of November 1999, Germany installed as much as half of the total installed capacity in the UK (350 MW), in spite of the fact that Germany has wind resources inferior to the UK.

Solar Energy is the most promising sustainable energy source. The sun radiates about 10'000 times the energy we presently need on Earth, some of it being reflected back into space, a lot being absorbed by water surfaces, mountains and clouds, but the irradiation variations are also moving winds and waves and evaporating water for useful precipitations for the growth of biomass and the river motions by gravity. A logic solar harvesting concept offers all the roof surfaces on Earth, where energy is needed for heat and electricity, since buildings and their inhabitants consume about 1/3 of all energy. Even if we assume only one m2 useable roof space per inhabitant and only 10 % average PV and thermal efficiency, there are now over 6 Billion m2 or 6 TW (Terawatt, i.e. 6'000 GW) peak power at disposal at noon, or annually around 6 PWh solar energy in the form of heat and/or electricity available. This roof program alone would provide 5 % of the world energy needs - clean, sustainable and eternally available without energy cost, and providing many more jobs than with the resource intensive conventional systems. Solar thermal energy can be directly used for hot water production from solar collectors of different types for different heat levels or be converted into electricity by different types of concentrator systems. Hybrid solar roof systems or cogeneration with solar power systems allow the simultaneous production of electricity and heat. Once solar systems are mass produced like conventional, fossil energy systems, and integrated into buildings, thus replacing conventional roofs and facades they will become competitive and even more so if the external cost of polluting systems are fully taken into account. The solar electricity production can be enhanced by solar electricity exchange pools with the utilities, which already operate successfully in several countries.There are also systems available for the daily and seasonal storage of solar heat and cold, combined with heat pumps, which can make buildings practically independent and pollution-free from conventional energy supplies.

Wave Power is yet another sustainable energy source which has tremendous potential in modern world. Wind passing over the surface of water gradually passes some of its energy into the water to create waves. If the wind has a reasonable velocity and persists for a long time across a long stretch of water then the resulting waves will be large and powerful. This is why certain locations around the World enjoy healthy wave climates: for them the predominant winds have travelled across several thousand kilometres of ocean and in so doing have generated annual average wave power levels of around 50 kW per metre of crest length. Other sites do not have such high power densities but are still potentially valuable. The World wave power resource is estimated at 2'000 GW, largely to be found in deep water locations. This is in depths of 40m or more. A great deal of technical progress has been achieved over the last 25 years of wave power development. Many of the prototype schemes are shore mounted and incorporate an Oscillating Water Column driving a self rectifying air turbine. These schemes have few moving parts, and with judicious choice of the structural size and geometry, and the turbine, the overall performance can be impressive. The shoreline resource, although easier to exploit, has lower power density (typically around 20 kW/m) than the deep water.

Biomass as the energy source is not fully explored for its potential. In spite of the large world-wide biomass resource potential and the optimistic long-term, contribution (World: 7'800 MTOE/y- E.U. 400 MTOE/y), it can be stated that commercial bio-energy production is not yet initiated, with the exception of the heat production, mainly concentrated in Scandinavia and Austria (biofuel contribution ~18% of total primary energy). Terrestrial biomass production is estimated at 60 Billion TOE/yr. with an average world-wide photosynthetic efficiency of 0.3%. The introduction of well developed bio-energy dedicated crops like S.R.F. (annual yield:~5 TOE/ha) and especially high productivity C-4 crops (annual yield:~10 TOE/ha) in marginal agricultural and semi-arid lands could supply huge amounts of sustainable, modern, low-nox emissions energy. As far as the improvement of crop productivity is concerned, we are still at an early stage compared with agricultural crops.

Geothermal energy and its relative technology is well known for many years. At present, there are records of geothermal utilization in more than fifty countries in the world. Geothermal energy is used both directly as heat and for the generation of electricity.

A number of other sustainable energy sources such as heat pump, muscle energy etc are being commonly referred. A lot more must be explored in order to extract the full potential of any of these sources.
(Source: http://www.uniseo.org" ISEO, Ganeva)