The enormous air raid bunker in Wilhelmsburg, Germany, was once part of the Nazi war machine. During World War II, it sheltered 30,000 Hamburg residents a night as Allied bombs fell, and men shot from “flak towers” on the roof.
These days, however, it’s a bunker of a different sort–one to store energy. And its role isn’t so much to fend against incoming fire as to protect against grid failure.
Opened last year, the Energy Bunker is an example of the infrastructure Germany is using as it shifts towards more renewable sources of power. The building contains a half-million-gallon water tank that stores heat from a solar thermal plant, a unit that burns wood chips and recycles waste heat from a nearby industrial plant. A combined heat and power system burns biogas to produce more heat, as well as electricity. And a south-facing solar array produces yet more power.
The bunker supplies enough heat for 3,000 homes as part of a local heating network. Residents of Wilhelmsburg, an island on the River Elbe, don’t generate heat in their homes as most of us do. Instead, they take in heat from the network, and send it back when they have enough. Their homes therefore waste far less energy than is typical.
Though the Bunker is connected to the main power grid, it’s effectively a “virtual power plant” that combines several smaller, decentralized generation sources together. That offers a buffer to the mainstream grid, which needs to balance demand and supply, and flexibility to managers who can decide on the best mix of heat energy and electricity (if the sun isn’t shining, more heat can be converted to power). The bunker itself normally supplies enough electricity for about 1,000 homes.
The Bunker is part of a wider project in Wilhelmsburg to go 100% carbon neutral by 2050. Engineers are now looking at integrating wind farms from Northern Germany. That will allow the grid to store more energy when winds are blowing hard, saving reserves for when the weather is less co-operative.
In 1947, British experts almost demolished the Bunker as they tried to put a permanent end to German war capacity. Thankfully, they only got as far as destroying six of the eight floors inside. The 10-foot-thick concrete walls are now ideal for their purpose.