IB Environmental systems and societies 7.2B Energy Storage Systems Notes

Energy Storage: Balancing Supply and Demand from Renewables

1. Wind and solar are intermittent: they only produce power when the wind blows or the sun shines.
2. This rarely matches the times of peak demand, so surplus energy has to be stored and released later.
3. Storage is what lets a grid run reliably on variable renewables.

Pumped Hydroelectric Storage: The Main Grid-Scale Option

1. Pumped hydro (PHS) is the most widely used form of large-scale storage and has been in operation for decades.
2. It works between two reservoirs at different heights, shifting water up or down to store or release energy.

How Pumped Hydro Works

1. Storing energy (pump mode)
   1. When demand is low or renewable output is high, surplus electricity pumps water from the lower reservoir to the upper one, storing gravitational potential energy.
2. Generating energy (discharge mode)
   1. When demand is high, water is released back down through turbines to generate electricity.

Strengths of PHS

1. Large-scale, long-duration storage
   1. It holds large amounts of energy for hours to days, ideal for smoothing peak demand.
2. Grid stabilisation
   1. It provides frequency regulation and load balancing, which matters most where variable renewables are common.
3. Efficient and durable
   1. It recovers about 70-80% of the energy put in and lasts for decades with low running costs.

Limits of PHS

1. Geographic constraints
   1. It needs a large height difference and a reliable water source, so not every region can build it.
2. High upfront cost
   1. Reservoirs and dams are expensive to build, even though they are cheap to run.
3. Environmental impact
   1. Flooding land to create reservoirs disrupts habitats and river ecosystems.