A general view shows solar panels to produce renewable energy at the photovoltaic park in Les Mees, in the department of Alpes-de-Haute-Provence, southern France March 31, 2015. The solar farm of the Colle des Mees, the biggest in France, consists of 112,780 solar modules covering an area of 200 hectares of land and representing 100 MW of power. REUTERS/Jean-Paul Pelissier TPX IMAGES OF THE DAY 

U.S. President Barack Obama takes a tour of a solar power array before delivering remarks on clean energy at Hill Air Force Base, Utah April 3, 2015. Obama announced a Department of Energy initiative Friday with the goal of training 75,000 workers, especially targeting veterans, to enter the solar energy workforce by the year 2020.REUTERS/Jonathan Ernst 

A general view shows solar panels to produce renewable energy at the photovoltaic park in Les Mees, in the department of Alpes-de-Haute-Provence, southern France March 31, 2015. The solar farm of the Colle des Mees, the biggest in France, consists of 112,780 solar modules covering an area of 200 hectares of land and representing 100 MW of power. REUTERS/Jean-Paul Pelissier 

An array of solar panels is seen in the desert in Victorville, California March 13, 2015. REUTERS/Lucy Nicholson (UNITED STATES - Tags: BUSINESS ENERGY) 

The Solar Impulse 2 is seen taking off at the Mandalay international airport March 30, 2015. Pilots Bertrand Piccard and Andre Borschberg will take turns at the controls of Solar Impulse 2, which began its journey in Abu Dhabi in the United Arab Emirates on March 9, as it makes its way in the first round-the-world solar-powered flight in about 25 flight days at speeds of between 50 kph and 100 kph (30 mph to 60 mph). Picture taken with slow shutter speed. REUTERS/Soe Zeya Tun 

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) 

German test pilot Markus Scherdel lands the solar-powered Solar Impulse 2 aircraft after a training flight at its base in Payerne November 8, 2014. The aircraft, which was unveiled April 9, weighs 2.4 tons with a wingspan of 72 metres (236 ft.) and has more than 17,000 solar cells. The attempt to fly around the world in stages using only solar energy will be made from March 2015 starting from Abu Dhabi. REUTERS/Denis Balibouse (SWITZERLAND - Tags: TRANSPORT ENVIRONMENT SCIENCE TECHNOLOGY)

A worker inspects solar panels at a solar farm in Dunhuang, 950km (590 miles) northwest of Lanzhou, Gansu Province September 16, 2013. China's solar panel industry is showing signs of booming again after a prolonged downturn - raising fears of another bust when the splurge of public money that is driving a spike in demand dries up. Lured by generous power tariffs and financing support to promote renewable energy, Chinese firms are racing to develop multi-billion dollar solar generating projects in the Gobi desert and barren hills of China's vast north and northwest. Picture taken on September 16, 2013. REUTERS/Carlos Barria (CHINA - Tags: BUSINESS ENERGY) 

Solar panels are pictured at the Cobija solar photo-voltaic plant near Cobija, north of La Paz September 30, 2014. Bolivia's President Evo Morales inaugurated the first stage of the building of the plant by Spanish company ISOTRON, according to local media. REUTERS/David Mercado (BOLIVIA - Tags: ENERGY POLITICS BUSINESS TPX IMAGES OF THE DAY) 

A private security guard walks between rows of photovoltaic solar panels inside a solar power plant at Raisan village near Gandhinagar, in the western Indian state of Gujarat, February 11, 2014. India said on Tuesday it was investigating U.S. policies supporting solar panel makers, the latest move in an escalating row over renewable energy that has worsened already strained ties between the two countries. REUTERS/Amit Dave (INDIA - Tags: POLITICS BUSINESS ENERGY TPX IMAGES OF THE DAY) 

A worker inspects solar panels at a solar Dunhuang, 950km (590 miles) northwest of Lanzhou, Gansu Province September 16, 2013. China is pumping investment into wind power, which is more cost-competitive than solar energy and partly able to compete with coal and gas. China is the world's biggest producer of CO2 emissions, but is also the world's leading generator of renewable electricity. Environmental issues will be under the spotlight during a working group of the Intergovernmental Panel on Climate Change, which will meet in Stockholm from September 23-26. REUTERS/Carlos Barria (CHINA - Tags: ENERGY BUSINESS ENVIRONMENT) 

A prototype sun tracking solar panel made by Concentrix Solar collects energy from its location at the University of California San Diego February 10, 2011. Under California's new carbon trading system, big polluters will be paying through the nose for the privilege. And so will everyone else in the state. Picture taken February 10, 2011. To match Special Report CALIFORNIA/CARBON REUTERS/Mike Blake (UNITED STATES - Tags: ENERGY ENVIRONMENT BUSINESS) 

People stand on the world's largest solar-powered boat in Cancun December 8, 2010. The Turanor Planet Solar arrived in Cancun on December 6 as part of its expedition around the globe and as climate talks are underway in the beach resort. The world's governments struggled on Wednesday to break a deadlock between rich and poor nations on steps to fight global warming and avert a new, damaging setback after they failed to agree a U.N. treaty last year in Copenhagen. REUTERS/Gerardo Garcia (MEXICO - Tags: POLITICS ENVIRONMENT IMAGES OF THE DAY ENERGY BUSINESS) 

A general view shows the new PS20 solar plant, which was inaugurated last month, at "Solucar" solar park in Sanlucar La Mayor, near Seville, October 7, 2009. The solar thermal power plant uses mirrors to concentrate the sun's rays onto towers where they produce steam to drive a turbine, producing electricity. REUTERS/Marcelo del Pozo (SPAIN ENERGY ENVIRONMENT SOCIETY) 

German test pilot Markus Scherdel steers the solar-powered Solar Impulse 2 aircraft over the Lake Murten during a training flight at its base in Payerne September 27, 2014. The aircraft, which was unveiled April 9, weighs 2.4 tons with a wingspan of 72 meters (236 ft.) and has more than 17,000 solar cells. The attempt to fly around the world in stages using only solar energy will be made from March 2015 starting from Abu Dhabi. REUTERS/Denis Balibouse (SWITZERLAND - Tags: TRANSPORT ENVIRONMENT SCIENCE TECHNOLOGY) 

A worker inspects solar panels at a solar farm in Dunhuang, 950km (590 miles) northwest of Lanzhou, Gansu Province September 16, 2013. China is pumping investment into wind power, which is more cost-competitive than solar energy and partly able to compete with coal and gas. China is the world's biggest producer of CO2 emissions, but is also the world's leading generator of renewable electricity. Environmental issues will be under the spotlight during a working group of the Intergovernmental Panel on Climate Change, which will meet in Stockholm from September 23-26. REUTERS/Carlos Barria (CHINA - Tags: ENERGY BUSINESS ENVIRONMENT) 

The Turanor PlanetSolar, the world's largest solar-powered boat, travels on the Seine river next to the Eiffel tower in Paris September 10, 2013. PlanetSolar, a catamaran powered exclusively by solar energy, completed the first solar-powered trip around the world on May 4, 2012 after travelling over 60,000 km (37,282 miles) in 584 days. REUTERS/Charles Platiau (FRANCE - Tags: SOCIETY ENVIRONMENT MARITIME ENERGY SCIENCE TECHNOLOGY TPX IMAGES OF THE DAY) 

Solar panels are seen at a power plant in Amareleja, southern Portugal, May 1, 2008. The Amareleja village town hall along with private investors are building a solar power plant in southern Portugal which officials say will be the world's largest and most powerful. REUTERS/Jose Manuel Ribeiro (PORTUGAL) 

General view of the solar power station Halle Pajol during its inauguration in northern Paris April 15, 2013. The huge rehabilitated Halle Pajol is the first solar power station in Paris with 3500m2 of solar panels on its roof and the largest photovoltaic urban complex in France. The solar station is part of urban renewal projects in the French capital. REUTERS/Charles Platiau (FRANCE - Tags: ENERGY ENVIRONMENT SCIENCE TECHNOLOGY)