Ellen Williams said battery systems could transform America's electrical grid.
In 2016, there are billionaires spread over 67 countries, against last year's 70 countries.
Microsoft founder Bill Gates held onto his position as the richest person in the world.
Apple compared the order to a pharma firm being forced to produce lethal injection drugs.
Only a handful have played the iconic name in technology on the big screen. Here's a list of them...
Microsoft pioneer takes different approach to Google, Facebook and Twitter by siding with the FBI.
The world's wealthiest foundation has helped make great strides against diseases.
Gates also revealed the ebbs and flows of his rivalry with Jobs, who died in 2011
Many billionaires bettered millions of lives by investing money - raising productivity and living standards.
George Osborne will go to Liverpool with the tycoon to announce the programme to eradicate the disease.
Some of the world's richest people have teamed up in the fight against famine.
Bill Gates, Carlos Slim, Warren Buffett, Amancio Ortega and Larry Ellison are among the top five.
"What the f**k is you doing, Bill Gates? Fix your s**t, man."
The technology giants will invest in a new start-up.
Trio labelled 'alarmists' for touting an artificial intelligence apocalypse.
Republican candidate Donald Trump asks Bill Gates to 'close the internet' to stop terror attacks
The US, UK, China and India to double budget for clean energy development over next five years.
Millennials have voted for the leaders that inspire them the most with Nelson Mandela coming out as a favourite.
Spaniard Ortega, who founded the Inditex Group, owns fashion brands such as Zara and Massimo Dutti.
We should embrace AI, not fear it, despite Stephen Hawking's warnings.
Gates Foundation Trust claims loss runs into millions of dollars.
Surge in Facebook's stock value has taken the internet entrepreneur past Ikea owner Ingvar Kamprad.