plants

But even then, the storage is often allowing those plants to run at their optimally efficient design capacity.

The pollution gets shifted to the power plants, but the greenhouse gas emissions from power plants are often better than those from cars.

The net effect of this is that electricity originally generated by nuclear plants and other fossil fuel plants gets 'converted' into (more expensive!) 'green' energy.

Pumping upward typically happens when the renewables are overproducing and the (controllably) variable power plants are idling.

You bundle all the small plants up into 10MW packages and sell their potential output via www.nordpoolspot.com.

Coal-burning power plants, on the other hand, produce more than 4 million metric tons per power plant, per year.

The overall carbon dioxide output of coal-fired electric power plants exceeded gasoline by more than 30 percent in 2010.

Many plants are able to burn either ones, and will switch fuel sources based on the markets.

Different kind of power plants have different timelines that it takes to power them up and down.

One alway could just switch wind/solar plants off, if there were really no other way to deal with the electricity.

So on the whole, re-generation from pumped storage is going to be greener than the baseline plants, and definitely greener than other types of adjustable peak load power plants, like natural gas turbines.

These are typically 2MW plants that can ramp up in 20 minutes or so, and they are scattered through out Denmark.

And we are talking about millions of ICEs in cars vs orders of magnitude fewer "engines" at power plants.

Rooftop solar (more generally, "distributed generation") is growing rapidly and is expected to be a much larger electricity source than utility scale photovoltaic plants fairly soon, say by 2020 or even earlier.