In this year’s Gates Foundation annual letter, Bill and Melinda lay out their 15-year roadmap for the challenges they want to solve.

The Foundation’s work is estimated to have saved at least five million lives and improved the quality of many more. One of Gates’ objectives has been to make it easy to move money for the over two billion of the world’s unbanked population. Two of his projects include bKash in Bangladesh and M-Pesa in Kenya, which make it possible to send and store money with just a mobile phone.

Join the iFX EXPO Asia and discover your gateway to the Asian Markets

As to how well digital currencies can help in this regard, Gates acknowledged to Medium that:

“There’s a lot that Bitcoin or Ripple and variants can do to make moving money between countries easier and getting fees down pretty dramatically.”

However, he continued, Bitcoin won’t be the dominant system. For a domestic economy, Bitcoin has two major shortcomings. First, in the event funds are sent to the wrong person, transactions can’t be reversed. And second, “[a traditional system] doesn’t have this huge fluctuation where the value of your account is going up and down by a factor of two.”

The software giant he founded, Microsoft, began accepting Bitcoin late last year. But like most companies taking it for payment, bitcoins are immediately converted into fiat, thereby not exposing the company to wild price fluctuations.