We need to store the huge quantities of excess electricity generated by variable renewables. But what’s the best way? Currently, over 99% of large-scale electricity storage uses pumped hydro dams. But geography severely limits where you can build one. And the growth of grid-scale batteries is limited by raw material costs and short lifecycles. Antoine Koen and Pau Farres Antunez at Cambridge University review an important alternative, Pumped Thermal Electricity Storage. It’s still in the development stage, but the technologies it uses – heat exchangers, compressors, turbines, electrical generators – are commonplace and proven in the power and processing industries. Units can be installed anywhere. They are compact: 1kg of water stored at 100°C can release ten times more electricity than 1kg stored at a height of 500 metres by a pumped hydro plant. The components last for decades, unlike batteries. The heat is stored in cheap and plentiful materials: gravel, molten salt, water. The downside is their energy conversion efficiency. At 50-70%, its well below 80-90% for lithium-ion batteries or 70-85% for pumped hydro storage. But who cares if, as expected, costs decline as the prototypes move to commercialisation, and costs continue to decline for variable wind and solar.
Energy Post 5th March 2020 read more »