Addressing the intermittency challenge: massive energy storage in a sustainable future

Abstract

The storage of power line frequency electrical energy as electrical energy is limited to capacitors and inductors, and neither has proven particularly practical where massive amounts of energy are involved. When electric power is needed, the stored energy is back-converted to electricity and returned to the grid. These conversions, however, are not ideally efficient, and each process is characterized by a figure of merit called the cycle efficiency, defined as the ratio of the total joules delivered to the grid over a suitable study period divided by the total joules received from the grid during the same period. As the number of grid-connected CSP farms increases, the resulting spatial diversity provides opportunity for averaging out the intermittency. Also, if CSP farms are connected across several time zones, and even across seasonal boundaries, the need for storage is lessened. It makes little sense to convert electricity to heat to store it because of the low efficiency of back conversion.