Up or down, does it matter?

Pumped hydro storage is a simple technology already in wide use. Pump water up a hill when you have available energy, let it fall when you need its power.

But Riverbank Power; a new start-up is trying out a new idea. Instead of using hills for the height, it will go the other way. Down into the ground.

Their Aquabank would let gravity drop water underground to turn turbines and make hydro electricity. That electricity would be sent from underground to the grid day time. At night, when excess wind is available; wind powered electricity would gently push the water back up to replenish its surface source.

Each project would use a source of water at ground level, an excavated cavern approximately 2,000 feet below ground and four 250-MW generators in a below-ground powerhouse.

The surface footprint would be only 5 to 10 acres, mainly for the water diversion structure and transmission infrastructure. The underground footprint would be about 100 acres.

It would use about 1 billion gallons of water for six hours of electricity production. It would take eight hours to pump out the cavern. The remaining sixteen hours each day the water supply would not be diverted.

To avoid sucking up fish inadvertently, the initial intake from the river is extremely slow and filtered so that the natural flow of the river remains unaltered, unlike conventional hydro power.

Given that the water is stored underground only for a short time, the pumping does not change the quality or temperature of the water before it is returned to the river.

So is this simply a tweaking of what was already done? Down instead of up? What are the advantages of going down? For one, you don’t need hills around. What else? Write in to us.