Converted Volvo diesel engines to help tackle renewable energy's biggest problem

A university project could transform air-polluting diesel engines into key components in future renewable energy infrastructure.

Researchers at the University of Nottingham will convert donated Volvo Truck engines into machines that compress air using renewable energy. The air can then be expanded to generate energy when needed.

The machines could charge electric bus and lorry fleets, said lead investigator Professor Seamus Garvey. Widespread deployment of the machines – 200,000 converted engines – could help contribute to 50GW of nationwide renewable energy storage after 2030, he added.  

“What can be done with end-of-life engines is an open question,” he said. “One option is to melt them down to recycle the steel, but we propose to explore another possibility.”

He added: “Power is increasingly being generated from renewable sources that are intermittent by nature – chiefly, the sun and wind. How to store that off-grid energy for use when needed, and not just when generated, is a pressing issue to solve.”

The team will repurpose engine blocks, crankshafts, connecting rods, pistons and crankshaft bearings into reversible compressor–expander machines. The devices will form the low-pressure stage of a three-stage 250kW train.

If the target efficiency of at least 85% is met for compression and expansion then the turnaround efficiency for the overall system could be better than 70%, Garvey told Professional Engineering. 

"The real question is what we will have to do to achieve that," he added. "Because the speeds of these machines performing as compressors/expanders will be lower than their normal speeds as engines, the main sources of loss will be associated with sealing. We have some interesting concepts which can reduce the leakage losses across pistons, without causing undue increases in the piston friction losses."

The project will run at the University of Nottingham's High-Performance Compression and Expansion Laboratory until August 2019. The work is a key element of the £60m Energy Research Accelerator, also involving the Universities of Birmingham, Warwick, Leicester, Loughborough and Aston, as well as the British Geological Survey.