Renewable energy

Renewable energy is derived from natural processes that are regularly replenished. Renewable energy sources and technologies include solar power, wind power, hydropower, geothermal energy, biomass, and biofuels. Each of these has unique characteristics which influence how and where they are used.

About 18% of global final energy consumption comes from renewables, with 13% from traditional biomass (which is mainly used for heating) and 3% from hydroelectric power. The share of renewables in electricity generation is around 18%, with 15% of global electricity coming from hydroelectricity and 3.4% from new renewable energy sources.

According to the International Energy Agency (IEA), renewable energy technologies can play an important role in addressing the challenges of moving towards clean, reliable, secure and competitive energy supply. Many countries have made progress in promoting renewables in their energy mix, but obstacles remain and, says the IEA, greater efforts are needed.

Rationale for renewable energy

Renewable energy technologies are essential contributors to the energy supply portfolio, as they contribute to world energy security, reduce dependency on fossil fuels, and provide opportunities for mitigating greenhouse gas emissions (namely carbon dioxide). The fuels that produce the most emissions of carbon dioxide are fossil fuels and they can be replaced by renewable sources of energy that produce much lower carbon dioxide emissions.

The International Energy Agency estimates that nearly 50% of global electricity supplies will need to come from renewable energy sources in order to halve carbon dioxide emissions by 2050.

Renewable energy development

The term renewable energy covers a number of sources and technologies at different stages of commercialization. The International Energy Agency (IEA) has defined three generations of renewable energy technologies, reaching back over 100 years:

• First-generation technologies emerged from the industrial revolution at the end of the 19th century and include hydropower, biomass power, and geothermal power and heat. These technologies are quite widely used.

• Second-generation technologies include solar heating and cooling, wind power, modern forms of bioenergy, and solar photovoltaics. These are now entering markets as a result of research, development and demonstration (RD&D) investments since the 1980s. Initial investment was prompted by energy security concerns linked to the oil crises of the 1970s but the primary appeal of these technologies is due, at least in part, to environmental benefits. Many of the technologies reflect significant advancements in materials of construction.

• Third-generation technologies are still under development and include advanced biomass gasification, biorefinery technologies, concentrating solar thermal power, hot dry rock (HDR) geothermal power, and ocean energy. Advances in nanotechnology may also play a major role.

First-generation technologies are well established, second-generation technologies are emerging technologies, and third-generation technologies heavily depend on long-term R&D commitments, where the public sector has a role to play.

First-generation technologies

First-generation technologies are widely used in locations with an abundance of the appropriate natural resources. Their future use depends on the exploration of the remaining resource potential, particularly in developing countries, and on overcoming challenges related to the environment and social acceptance.

Biomass

Biomass commonly refers to renewable organic materials such as wood, wood waste, straw, sugar cane, algae, and many other byproducts derived from a variety of agricultural and forestry production as well as other sources. Since biomass is derived from plants which were generated by utilizing solar energy in the photosynthesis process, it can also be defined as the organic material on Earth that has stored solar energy in the chemical bonds of the organic material.

The use of biomass for producing heat and electric power is a fully mature technology which offers a ready disposal mechanism for municipal, agricultural, and industrial organic wastes. However, the use of biomass remained relatively stagnant over the period of 1997 to 2007, even though demand for biomass (mostly wood) continues to grow in many developing countries. One of the problems of biomass is that material directly combusted in cook stoves produces pollutants, leading to health and environmental consequences, although improved cook stove programs are alleviating some of these effects. First-generation biomass technologies can be economically competitive, but may still require gaining public acceptance and overcoming small-scale issues.

Hydroelectricity

(CC) Photo: Eric Sollien
Hydroelectric power Three Gorges Dam on Yangtze river in China

Hydroelectric power plants have the advantage of being long-lived and many existing plants have operated for more than 100 years. Hydropower is also an extremely flexible technology from the perspective of power grid operation. Large hydropower provides one of the lowest cost options in today’s energy market, even compared to fossil fuels and there are no harmful emissions associated with plant operation.

Hydroelectric power is currently the world’s largest installed renewable source of electricity, supplying about 17% of total electricity in 2005. China is the world's largest producer of hydroelectric power in the world, followed by Canada.

However, there are several significant social and environmental disadvantages of large-scale hydroelectric power systems: dislocation of people living where the reservoirs are planned and disruption of aquatic ecosystems and birdlife. Hydroelectric power is now more difficult to site in developed nations because most major sites within these nations are either already being used or may be unavailable for environmental reasons. The areas of greatest hydroelectric growth are the growing economies of Asia. India and China are the development leaders; however, other Asian nations are also expanding hydropower.

There is a strong consensus now that countries should adopt an integrated approach towards managing water resources, which would involve planning hydropower development in co-operation with other water-using sectors.

Geothermal power and heat

(PD) Photo: Gretar Ívarsson
Geothermal power plant in Iceland

Geothermal power plants can operate 24 hours per day, providing baseload capacity. Estimates for the world potential capacity for geothermal power generation vary widely, ranging from 40 GW by 2020 to as much as 6,000 GW.

Geothermal power capacity grew from around 1 GW in 1975 to almost 10 GW in 2008. The United States is the world leader in terms of installed capacity, representing 3.1 GW. Other countries with significant installed capacity include the Philippines (1.9 GW), Indonesia (1.2 GW), Mexico (1.0 GW), Italy (0.8 GW), Iceland (0.6 GW), Japan (0.5 GW), and New Zealand (0.5 GW). In some countries, geothermal power accounts for a significant share of the total electricity supply, such as in the Philippines, where geothermal represented 17 percent of the total power mix at the end of 2008.

Geothermal ground source heat pumps represented an estimated 30 gigawatts-thermal (GWth) of installed capacity at the end of 2008, with other direct uses of geothermal heat (i.e., for space heating, agricultural drying and other uses) reaching an estimated 15 GWth. As of 2008, at least 76 countries use geothermal energy in some form.

Second-generation technologies

Markets for second-generation technologies have been strong and growing over the past decade, and these technologies have gone from being a passion for the dedicated few to a major economic sector in countries such as Germany, Spain, the United States, and Japan. Many large industrial companies and financial institutions are involved and the challenge is to broaden the market base for continued growth worldwide.

Solar Heating

Solar heating systems are a well known second-generation technology and generally consist of solar thermal collectors, a fluid system to move the heat from the collector to its point of usage, and a reservoir or tank for heat storage. The systems may be used to heat domestic hot water, swimming pools, or homes and businesses. The heat can also be used for industrial process applications or as an energy input for other uses such as solar assisted air conditioning.

In many warmer climates, a solar heating system can provide a very high percentage (50 to 75%) of domestic hot water energy. As of 2009, China has 27 million rooftop solar water heaters.

Solar thermal power stations

(PD) Drawing: Milton Beychok
Schematic flow diagram of the SEGS solar power plants

Solar thermal power stations include the 354 MW Solar Energy Generating Systems power complex in the USA, Nevada Solar One (USA, 64 MW), Andasol 1 (Spain, 50 MW) and the PS10 solar power tower (Spain, 11 MW). Many other plants are under construction or planned, mainly in Spain and the USA. In developing countries, three World Bank projects for integrated solar thermal and combined cycle gas turbine power plants in Egypt, Mexico, and Morocco have been approved.

(PD) Photo: National Oceanic and Atmospheric Administration Parabolic trough mirrors in solar power plants

(PD) Photo: Sandia National Laboratory Fields of parabolic trough mirrors at the SEGS solar power plants in the Mojave Desert

Photovoltaics

Photovoltaic (PV) cells, also called solar cells, convert light into electricity. In the 1980s and early 1990s, most photovoltaic modules were used to provide small, stand-alone power systems in areas with no electricity distribution system. However, from around 1995, industry efforts have focused increasingly on developing building-integrated photovoltaics and photovoltaic power plants for grid-connected applications.

As of October 2009, the largest photovoltaic (PV) power plants in the world are the Olmedilla Photovoltaic Park (Spain, 60 MW), the Puertollano Photovoltaic Park (Spain, 50 MW), the Moura Photovoltaic Power Plant (Portugal, 46 MW), and the Waldpolenz Solar Park (Germany, 40 MW). The largest photovoltaic power plant in North America is the 25 MW DeSoto Next Generation Solar Energy Center in Florida. The plant consists of over 90,000 solar panels.

At the end of 2008, the cumulative global PV installations reached 15,200 MW. Photovoltaic production has been doubling every two years, increasing by an average of 48 percent each year since 2002, making it the world’s fastest-growing energy technology. The top five photovoltaic producing countries are Japan, China, Germany, Taiwan, and the United States.

Wind power

(CC) Photo: Natalie Meister
Wind farm turbines in San Gorgonio Pass, Southern California

Some of the second-generation renewables, such as wind power, have high potential and have already realized relatively low production costs. At the end of 2009, worldwide wind power plant capacity was 157,900 MW, representing an increase of 31 percent during the year, and wind power supplied some 1.3% of global electricity consumption. Wind power is widely used in European countries, and more recently in the United States and in Asia. Wind power accounts for approximately 19% of electricity generation in Denmark, 11% in Spain and Portugal, and 9% in the Republic of Ireland. These are some of the largest "wind farms" in the world, as of January 2010:

Wind farm	Installed capacity (MW)	Country
Capricorn Ridge Wind Farm	662	United States
Fowler Ridge Wind Farm	750	United States
Horse Hollow Wind Energy Center	736	United States
Roscoe Wind Farm	781	United States
San Gorgonio Pass Wind Farm	619	United States
Tehachapi Pass Wind Farm	690	United States

Modern forms of bioenergy

Global ethanol (C₂H₅OH) production for transport fuel tripled between 2000 and 2007 from 17 billion to more than 52 billion litres, while biodiesel expanded more than ten-fold from less than 1 billion to almost 11 billion litres. Biofuels provide 1.8% of the world’s transport fuel and recent estimates indicate a continued high growth. The main producing countries for transport biofuels are the United States, Brazil, and the European Union.

The growing ethanol and biodiesel industries are providing jobs in plant construction, operations, and maintenance, mostly in rural communities. According to the Renewable Fuels Association, the ethanol industry created almost 154,000 U.S. jobs in 2005 alone, boosting household income by $5.7 billion. It also contributed about $3.5 billion in tax revenues at the local, state, and federal levels.

Ethanol

Brazil has one of the largest renewable energy programs in the world, involving production of ethanol fuel from sugar cane, and ethanol now provides 18 percent of the country's automotive fuel. As a result of this and the exploitation of domestic deep water oil sources, Brazil, which for years had to import a large share of the petroleum needed for domestic consumption, recently reached complete self-sufficiency in liquid fuels.

Most cars on the road today in the United States can run on blends of up to 10% ethanol, and motor vehicle manufacturers already produce vehicles designed to run on much higher ethanol blends. Ford, DaimlerChrysler, and General Motors are among the automobile companies that sell flexible-fuel cars, trucks, and minivans that can use gasoline and ethanol blends ranging containing up to 85% ethanol (E85). By mid-2006, there were approximately six million E85-compatible vehicles on U.S. roads. The challenge is to expand the market for biofuels beyond the farm states where they have been most popular. Flexible-fuel vehicles are assisting in this transition because they allow drivers to choose different fuels based on price and availability. The Energy Policy Act of 2005, which calls for 7.5 billion gallons of biofuels to be used annually by 2012, will also help to expand the market.

Biodiesel

Existing diesel engines often can use, without modification, up to 20% biodiesel blends. Other engines can use 100% biodiesel.

Biodiesel is biodegradable, while petroleum diesel is not. Emissions from biodiesel are said to have less environmental impact.

Recent growth of renewables

From the end of 2004 to the end of 2008, solar photovoltaic (PV) capacity increased sixfold to more than 16 gigawatts (GW), wind power capacity increased 250 percent to 121 GW, and total power capacity from new renewables increased 75 percent to 280 GW. During the same period, solar heating capacity doubled to 145 gigawatts-thermal (GWth), while biodiesel production increased sixfold to 12 billion liters per year and ethanol production doubled to 67 billion liters per year.

Selected renewable energy indicators

Selected global indicators	2004	2005	2006	2007	2008
Annual investment in new renewable capacity	30	38	63	104	120 billion USD
Existing renewables power capacity, including large-scale hydro	895	930	1,020	1,070	1,140 GWe
Existing renewables power capacity, excluding large hydro	160	182	207	240	280 GWe
Wind power capacity (existing)	48	59	74	94	121 GWe
Biomass heating					~250 GWth
Solar hot water/ Space heating	77	88	105	126	145 GWth
Geothermal heating					~50 GWth
Ethanol production (annual)	30.5	33	39	50	67 billion liters
Number of countries with policy targets for renewable energy use	45	49		66	73

Annual percentage growth for 2008 was significant. Wind power grew by 29 percent and grid-connected solar PV by 70 percent. The capacity of utility-scale solar PV plants (larger than 200 kilowatts) tripled during 2008, to 3 GW. Solar hot water grew by 15 percent, and annual ethanol and biodiesel production both grew by 34 percent. Heat and power from biomass and geothermal sources continued to grow, and small hydroelectric power sources increased by about 8 percent.

In 2008, for the first time, more renewable energy than conventional power capacity was added in both the European Union and United States, demonstrating a "fundamental transition" of the world's energy markets towards renewables, according to a report released by REN21, a global renewable energy policy network based in Paris.