Pumped Hydroelectric Storage: Putting Gravity to Work

by Chad Redman

Damming natural flowing rivers is an ancient and effective method for generating renewable energy. However, sufficient rivers are a scarce resource and modern dams produce an array of undesirable environmental effects. In response to the drawbacks of traditional dams, the main commercial technique for storing potential energy in water is pumped hydroelectric storage (PHS). Traditionally, these facilities use a massive pump and two reservoirs, one elevated above the other. During off-peak hours, excess energy produced from sources such as wind farms and nuclear power plants is used to power a pump which moves water into the elevated reservoir. When energy demand rises, the water is released back into the lower reservoir, spinning the pump which effectively becomes a generator. Continue reading

Storing Wind Energy on Islands is Risky, Economically


by Emil Morhardt

Electrical storage is needed to meet demand when solar and wind power become intermittent, particularly in off-grid systems like isolated oceanic islands. Both fast-response and long-term storage is needed; fast response (seconds to minutes) systems to prevent grid overload during short periods of high load (everybody on the island turns on the air conditioners at once), or of clouds passing over sun, or the wind stopping for a while. Longer-term storage (hours to days) can shift the time the power from renewables is produced to when it is really needed, or is at its highest value (more valuable than, say, the diesel generator sets that the island was previously dependent on. But at what cost? Moazeni et al. (2014) modeled the expected revenues to be gained in an isolated island environment of intermittent wind, shifting electrical loads, and a pumped storage hydroelectric system station. It turns out that optimizing the amount of storage and using it in the most economically efficient manner is no trivial matter, with the economic returns deviating as much as 29% from what might have been expected by the investors, depending on how the system is managed. What such systems operators apparently clearly need is electrical engineering modelers like these authors to figure it out for them.

Moazeni, S., Powell, W.B., Hajimiragha, A.H., 2014 (in press). Mean-Conditional Value-at-Risk Optimal Energy Storage Operation in the Presence of Transaction Costs. IEEE TRANSACTIONS ON POWER SYSTEMS  http://bit.ly/1pskjj5