A man speaks on the phone as he walks past solar panels at the Mohammed bin Rashid Al Maktoum Solar Park in Dubai, November 28, 2015. Dubai will spend billions of dollars on generating clean energy, the government said on Saturday, aiming to have solar panels installed on the roofs of all buildings by 2030. The fast-growing desert city state of 2.4 million, located in one of the hottest regions of the world, uses huge amounts of energy to air-condition its skyscrapers and provide water supplies through desalination. The Dubai government will encourage building owners to place solar panels on their roofs and link them to a network of the local power utility, Dubai's ruler Sheikh Mohammed bin Rashid al-Maktoum said in a statement. All Dubai buildings would have solar cells by 2030. REUTERS/Stringer TPX IMAGES OF THE DAY

A farmer plants wheat with his tractor next to the Abengoa solar plant at the "Solucar" solar park in Sanlucar la Mayor, near the Andalusian capital of Seville, southern Spain November 25, 2015. REUTERS/Marcelo del Pozo 

A farmer plants wheat with his tractor next to the Abengoa solar plant at the "Solucar" solar park in Sanlucar la Mayor, near the Andalusian capital of Seville, southern Spain November 25, 2015. REUTERS/Marcelo del Pozo 

Farmers work a wheat field with their tractors next to the Abengoa solar plant at the "Solucar" solar park in Sanlucar la Mayor, near the Andalusian capital of Seville, southern Spain November 25, 2015. Spain's Abengoa started insolvency proceedings on Wednesday which could lead to Spain's largest bankruptcy on record, after a potential investor said it would not inject fresh capital into the engineering and renewables company. REUTERS/Marcelo del Pozo 

A tower belonging to the Abengoa solar plant is seen at the "Solucar" solar park in Sanlucar la Mayor, near the Andalusian capital of Seville, southern Spain November 25, 2015. Spain's Abengoa started insolvency proceedings on Wednesday which could lead to Spain's largest bankruptcy on record, after a potential investor said it would not inject fresh capital into the engineering and renewables company. REUTERS/Marcelo del Pozo 

A tower belonging to the Abengoa solar plant is seen at the "Solucar" solar park in Sanlucar la Mayor, near the Andalusian capital of Seville, southern Spain November 25, 2015. Spain's Abengoa started insolvency proceedings on Wednesday which could lead to Spain's largest bankruptcy on record, after a potential investor said it would not inject fresh capital into the engineering and renewables company. REUTERS/Marcelo del Pozo 

A tower belonging to the Abengoa solar plant is seen at the "Solucar" solar park in Sanlucar la Mayor, near the Andalusian capital of Seville, southern Spain November 25, 2015. Spain's Abengoa started insolvency proceedings on Wednesday which could lead to Spain's largest bankruptcy on record, after a potential investor said it would not inject fresh capital into the engineering and renewables company. REUTERS/Marcelo del Pozo 

A tower belonging to the Abengoa solar plant is seen at the "Solucar" solar park in Sanlucar la Mayor, near the Andalusian capital of Seville, southern Spain November 25, 2015. Spain's Abengoa started insolvency proceedings on Wednesday which could lead to Spain's largest bankruptcy on record, after a potential investor said it would not inject fresh capital into the engineering and renewables company. REUTERS/Marcelo del Pozo

A tower belonging to the Abengoa solar plant is seen at the "Solucar" solar park in Sanlucar la Mayor, near the Andalusian capital of Seville, southern Spain November 25, 2015. Spain's Abengoa started insolvency proceedings on Wednesday which could lead to Spain's largest bankruptcy on record, after a potential investor said it would not inject fresh capital into the engineering and renewables company. REUTERS/Marcelo del Pozo 

A tower belonging to the Abengoa solar plant is seen at the "Solucar" solar park in Sanlucar la Mayor, near the Andalusian capital of Seville, southern Spain November 25, 2015. Spain's Abengoa started insolvency proceedings on Wednesday which could lead to Spain's largest bankruptcy on record, after a potential investor said it would not inject fresh capital into the engineering and renewables company. REUTERS/Marcelo del Pozo 

A tower belonging to the Abengoa solar plant is seen at the "Solucar" solar park in Sanlucar la Mayor, near the Andalusian capital of Seville, southern Spain November 25, 2015. Spain's Abengoa started insolvency proceedings on Wednesday which could lead to Spain's largest bankruptcy on record, after a potential investor said it would not inject fresh capital into the engineering and renewables company. REUTERS/Marcelo del Pozo 

A tower of Abengoa solar plant at "Solucar" solar park is pictured in Sanlucar la Mayor, near the Andalusian capital of Seville, southern Spain November 13, 2015. REUTERS/Marcelo del Pozo TPX IMAGES OF THE DAY

The sun reflects off a solar collector assembly during sunset at the Andasol solar power station near Guadix, southern Spain June 30, 2015. The plant is the biggest solar farm in the world and provides electricity for up to about 500,000 people. The 620,000 curved mirrors harness the sun's power even after dark, and the glass alone would cover 1.5 square km (0.6 square miles) - the size of about 210 soccer pitches. REUTERS/Marcelo del PozoPICTURE 22 OF 25 FOR WIDER IMAGE STORY "EARTHPRINTS: ANDASOL SOLAR POWER STATION"SEARCH "MARCELO ANDASOL" FOR ALL IMAGES 

The main pipe of a power block at the Andasol solar power station is pictured near Guadix, southern Spain June 29, 2015. The plant is the biggest solar farm in the world and provides electricity for up to about 500,000 people. The 620,000 curved mirrors harness the sun's power even after dark, and the glass alone would cover 1.5 square km (0.6 square miles) - the size of about 210 soccer pitches. REUTERS/Marcelo del PozoPICTURE 21 OF 25 FOR WIDER IMAGE STORY "EARTHPRINTS: ANDASOL SOLAR POWER STATION"SEARCH "MARCELO ANDASOL" FOR ALL IMAGES 

A part of a power block at the Andasol solar power station is pictured near Guadix, southern Spain June 29, 2015. The plant is the biggest solar farm in the world and provides electricity for up to about 500,000 people. The 620,000 curved mirrors harness the sun's power even after dark, and the glass alone would cover 1.5 square km (0.6 square miles) - the size of about 210 soccer pitches. REUTERS/Marcelo del PozoPICTURE 20 OF 25 FOR WIDER IMAGE STORY "EARTHPRINTS: ANDASOL SOLAR POWER STATION"SEARCH "MARCELO ANDASOL" FOR ALL IMAGES 

Staff check a solar collector assembly at the Andasol solar power station near Guadix, southern Spain August 11, 2015. The plant is the biggest solar farm in the world and provides electricity for up to about 500,000 people. The 620,000 curved mirrors harness the sun's power even after dark, and the glass alone would cover 1.5 square km (0.6 square miles) - the size of about 210 soccer pitches. REUTERS/Marcelo del PozoPICTURE 18 OF 25 FOR WIDER IMAGE STORY "EARTHPRINTS: ANDASOL SOLAR POWER STATION"SEARCH "MARCELO ANDASOL" FOR ALL IMAGES

Solar collector assemblies are seen behind flowers at the Andasol solar power station near Guadix, southern Spain August 10, 2015. The plant is the biggest solar farm in the world and provides electricity for up to about 500,000 people. The 620,000 curved mirrors harness the sun's power even after dark, and the glass alone would cover 1.5 square km (0.6 square miles) - the size of about 210 soccer pitches. REUTERS/Marcelo del PozoPICTURE 17 OF 25 FOR WIDER IMAGE STORY "EARTHPRINTS: ANDASOL SOLAR POWER STATION"SEARCH "MARCELO ANDASOL" FOR ALL IMAGES 

The sun reflects off a solar collector assembly during sunset at the Andasol solar power station near Guadix, southern Spain June 30, 2015. The plant is the biggest solar farm in the world and provides electricity for up to about 500,000 people. The 620,000 curved mirrors harness the sun's power even after dark, and the glass alone would cover 1.5 square km (0.6 square miles) - the size of about 210 soccer pitches. REUTERS/Marcelo del PozoPICTURE 19 OF 25 FOR WIDER IMAGE STORY "EARTHPRINTS: ANDASOL SOLAR POWER STATION"SEARCH "MARCELO ANDASOL" FOR ALL IMAGES 

The moon is seen between reflector panels of a solar collector assembly at the Andasol solar power station near Guadix, southern Spain June 30, 2015. The plant is the biggest solar farm in the world and provides electricity for up to about 500,000 people. The 620,000 curved mirrors harness the sun's power even after dark, and the glass alone would cover 1.5 square km (0.6 square miles) - the size of about 210 soccer pitches. REUTERS/Marcelo del Pozo TPX IMAGES OF THE DAYPICTURE 15 OF 25 FOR WIDER IMAGE STORY "EARTHPRINTS: ANDASOL SOLAR POWER STATION"SEARCH "MARCELO ANDASOL" FOR ALL IMAGES

A worker drives among solar collector assemblies at the Andasol solar power station near Guadix, southern Spain July 1, 2015. The plant is the biggest solar farm in the world and provides electricity for up to about 500,000 people. The 620,000 curved mirrors harness the sun's power even after dark, and the glass alone would cover 1.5 square km (0.6 square miles) - the size of about 210 soccer pitches. REUTERS/Marcelo del PozoPICTURE 16 OF 25 FOR WIDER IMAGE STORY "EARTHPRINTS: ANDASOL SOLAR POWER STATION"SEARCH "MARCELO ANDASOL" FOR ALL IMAGES 

Pipes are seen in front of solar collector assemblies at the Andasol solar power station near Guadix, southern Spain August 10, 2015. The plant is the biggest solar farm in the world and provides electricity for up to about 500,000 people. The 620,000 curved mirrors harness the sun's power even after dark, and the glass alone would cover 1.5 square km (0.6 square miles) - the size of about 210 soccer pitches. REUTERS/Marcelo del PozoPICTURE 14 OF 25 FOR WIDER IMAGE STORY "EARTHPRINTS: ANDASOL SOLAR POWER STATION"SEARCH "MARCELO ANDASOL" FOR ALL IMAGES 

Staff walk behind solar collector assemblies at the Andasol solar power station near Guadix, southern Spain August 11, 2015. The plant is the biggest solar farm in the world and provides electricity for up to about 500,000 people. The 620,000 curved mirrors harness the sun's power even after dark, and the glass alone would cover 1.5 square km (0.6 square miles) - the size of about 210 soccer pitches. REUTERS/Marcelo del PozoPICTURE 13 OF 25 FOR WIDER IMAGE STORY "EARTHRPINTS: ANDASOL SOLAR POWER STATION"SEARCH "MARCELO ANDASOL" FOR ALL IMAGES 

An aerial view of a solar field at the Andasol solar power station near Guadix, southern Spain June 30, 2015. The plant is the biggest solar farm in the world and provides electricity for up to about 500,000 people. The 620,000 curved mirrors harness the sun's power even after dark, and the glass alone would cover 1.5 square km (0.6 square miles) - the size of about 210 soccer pitches. REUTERS/Marcelo del PozoPICTURE 10 OF 25 FOR WIDER IMAGE STORY "EARTHPRINTS: ANDASOL SOLAR POWER STATION"SEARCH "MARCELO ANDASOL" FOR ALL IMAGES 

An aerial view of the Andasol solar power station near Guadix, southern Spain June 30, 2015. The plant is the biggest solar farm in the world and provides electricity for up to about 500,000 people. The 620,000 curved mirrors harness the sun's power even after dark, and the glass alone would cover 1.5 square km (0.6 square miles) - the size of about 210 soccer pitches. REUTERS/Marcelo del PozoPICTURE 11 OF 25 FOR WIDER IMAGE STORY "EARTHPRINTS: ANDASOL SOLAR POWER STATION"SEARCH "MARCELO ANDASOL" FOR ALL IMAGES 

A worker checks solar collector assemblies at the Andasol solar power station near Guadix, southern Spain June 30, 2015. The plant is the biggest solar farm in the world and provides electricity for up to about 500,000 people. The 620,000 curved mirrors harness the sun's power even after dark, and the glass alone would cover 1.5 square km (0.6 square miles) - the size of about 210 soccer pitches. REUTERS/Marcelo del PozoPICTURE 7 OF 25 FOR WIDER IMAGE STORY "EARTHPRINTS: ANDASOL SOLAR POWER STATION"SEARCH "MARCELO ANDASOL" FOR ALL IMAGES 

Pigeons fly over a solar collector assembly at the Andasol solar power station near Guadix, southern Spain August 10, 2015. The plant is the biggest solar farm in the world and provides electricity for up to about 500,000 people. The 620,000 curved mirrors harness the sun's power even after dark, and the glass alone would cover 1.5 square km (0.6 square miles) - the size of about 210 soccer pitches. REUTERS/Marcelo del Pozo TPX IMAGES OF THE DAYPICTURE 8 OF 25 FOR WIDER IMAGE STORY "EARTHPRINTS: ANDASOL SOLAR POWER STATION"SEARCH "MARCELO ANDASOL" FOR ALL IMAGES

Solar collector assemblies are seen in front of electricity pylons at the Andasol solar power station near Guadix, southern Spain June 30, 2015. The plant is the biggest solar farm in the world and provides electricity for up to about 500,000 people. The 620,000 curved mirrors harness the sun's power even after dark, and the glass alone would cover 1.5 square km (0.6 square miles) - the size of about 210 soccer pitches. REUTERS/Marcelo del PozoPICTURE 6 OF 25 FOR WIDER IMAGE STORY "EARTHPRINTS: ANDASOL SOLAR POWER STATION"SEARCH "MARCELO ANDASOL" FOR ALL IMAGES 

An aerial view of Andasol solar power station near Guadix, southern Spain August 8, 2015. The plant is the biggest solar farm in the world and provides electricity for up to about 500,000 people. The 620,000 curved mirrors harness the sun's power even after dark, and the glass alone would cover 1.5 square km (0.6 square miles) - the size of about 210 soccer pitches. REUTERS/Marcelo del PozoPICTURE 9 OF 25 FOR WIDER IMAGE STORY "EARTHPRINTS: ANDASOL SOLAR POWER STATION"SEARCH "MARCELO ANDASOL" FOR ALL IMAGES 

Wind turbines are seen near the Andasol solar power station near Guadix, southern Spain August 10, 2015. The plant is the biggest solar farm in the world and provides electricity for up to about 500,000 people. The 620,000 curved mirrors harness the sun's power even after dark, and the glass alone would cover 1.5 square km (0.6 square miles) - the size of about 210 soccer pitches. REUTERS/Marcelo del PozoPICTURE 12 OF 25 FOR WIDER IMAGE STORY "EARTHRPINTS: ANDASOL SOLAR POWER STATION"SEARCH "MARCELO ANDASOL" FOR ALL IMAGES

Solar collector assemblies are seen behind flowers at the Andasol solar power station near Guadix, southern Spain June 30, 2015. The plant is the biggest solar farm in the world and provides electricity for up to about 500,000 people. The 620,000 curved mirrors harness the sun's power even after dark, and the glass alone would cover 1.5 square km (0.6 square miles) - the size of about 210 soccer pitches. REUTERS/Marcelo del PozoPICTURE 3 OF 25 FOR WIDER IMAGE STORY "EARTHPRINTS: ANDASOL SOLAR POWER STATION"SEARCH "MARCELO ANDASOL" FOR ALL IMAGES 

A general view of the Andasol solar power station near Guadix, southern Spain August 10, 2015. The plant is the biggest solar farm in the world and provides electricity for up to about 500,000 people. The 620,000 curved mirrors harness the sun's power even after dark, and the glass alone would cover 1.5 square km (0.6 square miles) - the size of about 210 soccer pitches. REUTERS/Marcelo del PozoPICTURE 1 OF 25 FOR WIDER IMAGE STORY "EARTHPRINTS: ANDASOL SOLAR POWER STATION"SEARCH "MARCELO ANDASOL" FOR ALL IMAGES

The sun shines through reflector panels of a solar collector assembly at the Andasol solar power station near Guadix, southern Spain June 29, 2015. The plant is the biggest solar farm in the world and provides electricity for up to about 500,000 people. The 620,000 curved mirrors harness the sun's power even after dark, and the glass alone would cover 1.5 square km (0.6 square miles) - the size of about 210 soccer pitches. REUTERS/Marcelo del Pozo TPX IMAGES OF THE DAYPICTURE 4 OF 25 FOR WIDER IMAGE STORY "EARTHPRINTS: ANDASOL SOLAR POWER STATION"SEARCH "MARCELO ANDASOL" FOR ALL IMAGES

A view of a solar field at the Andasol solar power station near Guadix, southern Spain July 1, 2015. The plant is the biggest solar farm in the world and provides electricity for up to about 500,000 people. The 620,000 curved mirrors harness the sun's power even after dark, and the glass alone would cover 1.5 square km (0.6 square miles) - the size of about 210 soccer pitches. REUTERS/Marcelo del PozoPICTURE 2 OF 25 FOR WIDER IMAGE STORY "EARTHPRINTS: ANDASOL SOLAR POWER STATION"SEARCH "MARCELO ANDASOL" FOR ALL IMAGES

A worker walks through solar collector assemblies at the Andasol solar power station near Guadix, southern Spain August 10, 2015. The plant is the biggest solar farm in the world and provides electricity for up to about 500,000 people. The 620,000 curved mirrors harness the sun's power even after dark, and the glass alone would cover 1.5 square km (0.6 square miles) - the size of about 210 soccer pitches. REUTERS/Marcelo del PozoPICTURE 5 OF 25 FOR WIDER IMAGE STORY "EARTHPRINTS: ANDASOL SOLAR POWER STATION"SEARCH "MARCELO ANDASOL" FOR ALL IMAGES

A general view shows solar panels used to produce renewable energy at the photovoltaic park in Cestas, southwestern France, June 19, 2015. The solar farm of Cestas, the biggest in Europe, consists of 1 Million solar modules covering an area of 2,5 km2 of land and representing 300 MW of power. REUTERS/Regis Duvignau

Solar panels are seen in the Palm Springs area, California April 13, 2015. Picture taken April 13, 2015. REUTERS/Lucy Nicholson 

Solar panels are seen next to a Southern California Edison electricity station in Carson, California March 4, 2015. REUTERS/Lucy Nicholson (UNITED STATES - Tags: ENERGY ENVIRONMENT BUSINESS) 

Solar panels are seen next to a Southern California Edison electricity station in Carson, California March 4, 2015. REUTERS/Lucy Nicholson (UNITED STATES - Tags: ENERGY ENVIRONMENT BUSINESS) 

An aerial view of solar panels at the Cobija solar photo-voltaic plant near Cobija, north of La Paz, February 27, 2015. The solar photo-voltaic plant was built by Spanish company Isotron. REUTERS/David Mercado (BOLIVIA - Tags: BUSINESS ENERGY) 

Solar panels are seen at PetroChina's solar-powered Yizhuang gas station in Beijing, January 9, 2015. Picture taken January 9, 2015. REUTERS/Kim Kyung-Hoon (CHINA - Tags: TRANSPORT BUSINESS COMMODITIES ENERGY SOCIETY SCIENCE TECHNOLOGY)

Solar panels are seen at PetroChina's solar-powered Yizhuang gas station in Beijing, January 9, 2015. Reuters photographers from Mali to Mexico have shot a series of pictures of fuel stations. Whether it is plastic bottles by the roadside in Malaysia or a futuristic forecourt in Los Angeles, fuel stations help define our world. Oil prices steadied above $48 a barrel on Tuesday, recovering from earlier losses as the dollar weakened against the euro. Oil prices have dropped nearly 60 percent since peaking in June 2014 on ample global supplies from the U.S. shale oil boom and a decision by OPEC to keep its production quotas unchanged. REUTERS/Kim Kyung-Hoon (CHINA - Tags: BUSINESS COMMODITIES ENERGY SCIENCE TECHNOLOGY)

ATTENTION EDITORS: PICTURE 12 OF 26 FOR WIDER IMAGE PACKAGE 'AT THE PUMP - THE WORLD FILLS UP'

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Fuel prices are seen displayed on a fuel pump at PetroChina's solar-powered Yizhuang gas station in Beijing January 9, 2015. Reuters photographers from Mali to Mexico have shot a series of pictures of fuel stations. Whether it is plastic bottles by the roadside in Malaysia or a futuristic forecourt in Los Angeles, fuel stations help define our world. Oil prices steadied above $48 a barrel on Tuesday, recovering from earlier losses as the dollar weakened against the euro. Oil prices have dropped nearly 60 percent since peaking in June 2014 on ample global supplies from the U.S. shale oil boom and a decision by OPEC to keep its production quotas unchanged. REUTERS/Kim Kyung-Hoon (CHINA - Tags: BUSINESS COMMODITIES ENERGY SCIENCE TECHNOLOGY)

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Batteries saving electricity produced by solar power is seen at PetroChina's Yizhuang gas station which has solar power system in Beijing January 9, 2015. The gas station, equipped with a total of 804 solar panels, can produce average 375 kW electricity per a day and the electricity is used for the operation of the gas station. The gas stand is the only filling station installing its own solar energy system in China, the company said. REUTERS/Kim Kyung-Hoon (CHINA - Tags: ENERGY BUSINESS COMMODITIES ENVIRONMENT) 

A manager of PetroChina's Yizhuang gas station, which has a solar power system, checks a machine converting solar energy into electricity at the gas station in Beijing January 9, 2015. The gas station, equipped with a total of 804 solar panels, can produce average 375 kW electricity per a day and the electricity is used for the operation of the gas station. The gas stand is the only filling station installing its own solar energy system in China, the company said. REUTERS/Kim Kyung-Hoon (CHINA - Tags: ENERGY BUSINESS COMMODITIES ENVIRONMENT) 

A customer refuels his car at PetroChina's Yizhuang gas station, which uses a solar power system, in Beijing January 9, 2015. The gas station, equipped with a total of 804 solar panels, can produce average 375 kW electricity per a day and the electricity is used for the operation of the gas station. The gas stand is the only filling station installing its own solar energy system in China, the company said. REUTERS/Kim Kyung-Hoon (CHINA - Tags: ENERGY BUSINESS COMMODITIES ENVIRONMENT) 

Solar panels are seen at PetroChina's Yizhuang gas station which has solar power system in Beijing January 9, 2015. The gas station, equipped with a total of 804 solar panels, can produce average 375 kW electricity per a day and the electricity is used for the operation of the gas station. The gas stand is the only filling station installing its own solar energy system in China, the company said. REUTERS/Kim Kyung-Hoon (CHINA - Tags: ENERGY BUSINESS COMMODITIES ENVIRONMENT) 

A gas station attendant fuels a customer's car at PetroChina's Yizhuang gas station, which uses a solar power system, in Beijing January 9, 2015. The gas station, equipped with a total of 804 solar panels, can produce average 375 kW electricity per a day and the electricity is used for the operation of the gas station. The gas stand is the only filling station installing its own solar energy system in China, the company said. REUTERS/Kim Kyung-Hoon (CHINA - Tags: ENERGY POLITICS SCIENCE TECHNOLOGY BUSINESS COMMODITIES) 

A Tenderloin Pit Stop portable toilet trailer is seen in the Tenderloin District in San Francisco, California December 30, 2014. Operated by the San Francisco Department of Public Works, the solar-powered toilets are part of a six-month pilot project aimed to provide clean and secure portable toilets, used needle disposal and dog waste stations throughout the Tenderloin District in an effort to alleviate the problem of human feces on the streets. REUTERS/Stephen Lam (UNITED STATES - Tags: HEALTH SOCIETY) 

A visitor enters a portable toilet facility held open by an attendant in the Tenderloin District in San Francisco, California December 30, 2014. Operated by the San Francisco Department of Public Works, the solar-powered toilets are part of a six-month pilot project aimed to provide clean and secure portable toilets, used needle disposal and dog waste stations throughout the Tenderloin District in an effort to alleviate the problem of human feces on the streets. REUTERS/Stephen Lam (UNITED STATES - Tags: HEALTH SOCIETY) 

An attendant (L) speaks with a visitor as he unlocks the door to a toilet in the Tenderloin District in San Francisco, California December 30, 2014. Operated by the San Francisco Department of Public Works, the solar-powered toilets are part of a six-month pilot project aimed to provide clean and secure portable toilets, used needle disposal and dog waste stations throughout the Tenderloin District in an effort to alleviate the problem of human feces on the streets. REUTERS/Stephen Lam (UNITED STATES - Tags: HEALTH SOCIETY) 

An attendant opens a door to a toilet for a visitor in the Tenderloin District in San Francisco, California December 30, 2014. Operated by the San Francisco Department of Public Works, the solar-powered toilets are part of a six-month pilot project aimed to provide clean and secure portable toilets, used needle disposal and dog waste stations throughout the Tenderloin District in an effort to alleviate the problem of human feces on the streets. REUTERS/Stephen Lam (UNITED STATES - Tags: HEALTH SOCIETY) 

Vehicles drive past a Tenderloin Pit Stop station in the Tenderloin District in San Francisco, California December 30, 2014. Operated by the San Francisco Department of Public Works, the solar-powered toilets are part of a six-month pilot project aimed to provide clean and secure portable toilets, used needle disposal and dog waste stations throughout the Tenderloin District in an effort to alleviate the problem of human feces on the streets. REUTERS/Stephen Lam (UNITED STATES - Tags: HEALTH SOCIETY) 

A used needle disposal receptacle is seen next to two portable toilets in the Tenderloin District in San Francisco, California December 30, 2014. Operated by the San Francisco Department of Public Works, the solar-powered toilets are part of a six-month pilot project aimed to provide clean and secure portable toilets, used needle disposal and dog waste stations throughout the Tenderloin District in an effort to alleviate the problem of human feces on the streets. REUTERS/Stephen Lam (UNITED STATES - Tags: DRUGS SOCIETY HEALTH) 

An attendant stands outside two portable toilets in the Tenderloin District in San Francisco, California December 30, 2014. Operated by the San Francisco Department of Public Works, the solar-powered toilets are part of a six-month pilot project aimed to provide clean and secure portable toilets, used needle disposal and dog waste stations throughout the Tenderloin District in an effort to alleviate the problem of human feces on the streets. REUTERS/Stephen Lam (UNITED STATES - Tags: HEALTH SOCIETY) 

A tower at Abengoa solar plant at "Solucar" solar park is seen in Sanlucar la Mayor, near the Andalusian capital of Seville November 17, 2014. Shares in Spanish renewable energy and engineering firm Abengoa rebounded on Monday - after falling sharply last week - after the company gave details of how it accounted for debt and set new leverage targets for 2014 and 2015. REUTERS/Marcelo del Pozo (SPAIN - Tags: BUSINESS ENERGY TPX IMAGES OF THE DAY) 

A tower at Abengoa solar plant at "Solucar" solar park is seen in Sanlucar la Mayor, near the Andalusian capital of Seville November 17, 2014. Shares in Spanish renewable energy and engineering firm Abengoa rebounded on Monday - after falling sharply last week - after the company gave details of how it accounted for debt and set new leverage targets for 2014 and 2015. REUTERS/Marcelo del Pozo (SPAIN - Tags: BUSINESS ENERGY TPX IMAGES OF THE DAY) 

A worker stands next to parabolic mirrors tracking the sun at the research site of solar power company Brenmiller Energy in Israel's Negev desert, near the town of Dimona September, 9, 2014. Brenmiller Energy says it has developed a new, more efficient way to store heat from the sun that could give a boost to the thermal solar power industry by enabling plants to run at full capacity night and day. Picture taken September 9, 2014. REUTERS/ Nir Elias (ISRAEL - Tags: SCIENCE TECHNOLOGY ENERGY) 

Workers carry solar panels as they work at a solar power plant which is under construction on a hill in Wuhu, Anhui province September 16, 2014. China's factory output grew at the weakest pace in nearly six years in August while growth in other key sectors also cooled, raising fears the world's second-largest economy may be at risk of a sharp slowdown unless Beijing takes fresh stimulus measures. REUTERS/Stringer (CHINA - Tags: ENERGY ENVIRONMENT BUSINESS) 

A solar powered re-charge station for mobile devices is seen at the underground media center of the Arena de Sao Paulo stadium in Sao Paulo one day before the opening match between Brazil and Croatia June 11, 2014. In a project called 'On The Sidelines' Reuters photographers share pictures showing their own quirky and creative view of the 2014 World Cup in Brazil. REUTERS/Kai Pfaffenbach (BRAZIL - Tags: SPORT SOCCER WORLD CUP SOCIETY SCIENCE TECHNOLOGY)