( This isn't a sponsored video, but I am massively grateful to all the team at SSE! Go look: http://sse.com/whatwedo/ourprojectsan... , and pull down the description for more. ) As the world switches to renewable energy - and we are switching - there's a problem you might not expect: balancing the grid. Rotational mass and system inertia are the things that keep your lights from flickering: and they only appear in big, old, traditional power stations. Here's why that's a problem, and how we're likely going to fix it. CORRECTION: I say that turbines spin thousands of times "per second" when it should be "per minute".