Kenyan graffiti artist Bankslave created a mural of Barack Obama. The president himself will visit Kenya on Friday. One of the president's agenda items is to promote solar power. Ben Curtis/AP hide caption

itoggle caption Ben Curtis/AP

Iran's Supreme Leader Ayatollah Ali Khamenei delivers a sermon during morning prayers for the Eid al-Fitr holiday, marking the end of the holy month of Ramadan. He signaled his approval of the nuclear agreement with Western powers but reiterated that Tehran's policy toward the "arrogant" United States would not change. Reuters/Landov hide caption

itoggle caption Reuters/Landov

"Our degree of oil dependency is our degree of vulnerability."--Rob Hopkins James Duncan Davidson/TED hide caption

itoggle caption James Duncan Davidson/TED

"We've under-priced water, we've over-exploited it, we don't regulate how people pump groundwater out of the ground.... we just use too much."--Jonathan Foley Courtesy of TEDxTC hide caption

itoggle caption Courtesy of TEDxTC

The Solar Impulse 2 landed in Hawaii in early July. The team behind the sun-powered airplane says it will be grounded until next spring. Solar Impulse | Revillard | Rezo/Solar Impulse | Revillard | Rezo hide caption

itoggle caption Solar Impulse | Revillard | Rezo/Solar Impulse | Revillard | Rezo

Stacked rigs are seen along with other idled oil drilling equipment at a depot in Dickinson, N.D., last month. The International Energy Agency forecasts a continued drop in oil prices amid overproduction and falling global demand. Andrew Cullen/Reuters/Landov hide caption

itoggle caption Andrew Cullen/Reuters/Landov