Bill Gates: "It Is Surprisingly Hard to Store Energy"

Yes, yes it is.
And that's why storage is the Holy Grail for VCs.*
From Mr. Gates' personal blog, Gates Notes:

Solar and wind power are great sources of low-carbon energy, but they also have their downsides. The biggest problem is that they’re not constant sources. With solar, it’s not just that the sun goes away at night; cloudy days also make it hard for some places to use solar year-round. According to this list from NOAA, my hometown of Seattle gets less sun than all but 9 cities in the United States.

When you hear about this problem with wind and solar, it is tempting to ask: Can’t we generate extra energy on days when the sun and wind are strong, and store it for those days when they’re not?

Here’s the problem: Storing energy turns out to be surprisingly hard and expensive.

For example, I wrote in this year’s Annual Letter: “If you wanted to store enough electricity to run everything in your house for a week, you would need a huge battery—and it would triple your electric bill.” Let’s break that sentence down.

“If you wanted to store enough electricity to run everything in your house for a week, you would need a huge battery …”

According to this U.S. Energy Information Administration fact sheet, in 2014 the typical U.S. household used 911 kilowatt-hours a month, which works out to roughly 210 kilowatt-hours per week (911 per month / 30 days per month x 7 days per week). The best lithium-ion batteries store less than 0.2 kilowatt-hours per kilogram.

So a lithium-ion battery large enough to store 210 kilowatt-hours would weigh at least 210 / 0.2, or 1050 kg. 1050 kg is about 2314 pounds, or more than one ton.

“…and it would triple your electric bill.”...

..MORE

Also at Gates Notes:


Try This Quiz About Time, 
Energy, and Superheroes

*Oddly enough, in 2012's "Batteries: The Venture Capitalist's Holy Grail" I mentioned a different Holy Grail:

...Microsoft famously didn't need venture capital either.
(Technology Venture Investors was the sole VC investor and got that plum only because Marquardt and Ballmer were buddies) 

That's the Holy Grail, finding a company that doesn't need you but will let you in.
The battery on the other hand....that's going to be a longer slog than the press releases would lead one to believe.

See also:

Gates, Pritzkers vs. Musk: "The $5 Billion Race to Build a Better Battery" (TSLA)

for some of our posts on batteries.