Fossil fuels comprise the accumulation of prehistoric biomass that was energised by sunlight, and formed by earth system dynamics. Fossil fuels can be conceptualized as stored energy stocks that can be readily converted to power flows, on demand. A transition from a reliance on stored energy stocks, to renewable energy flows, will require a replication of energy storage by technological devices and energy conversion methods. Most analyses of energy storage focus solely on the economic-technical properties of storage within incumbent energy systems. This book broadens the scope of the study of storage by placing it within a broader, historical, biophysical framework. The role and value of storage is examined from first principles, and framed within the contemporary context of electrical grids and markets. The energy-economic cost of electrical storage may be critical to the efficacy of high penetration renewable scenarios, and understanding the costs and benefits of storage is needed for a proper assessment of storage in energy transition studies. This book provides a starting point for engineers, scientists and energy analysts for exploring the role of storage in energy transition studies, and for gaining an appreciation of the biophysical constraints of storage.

Pumped storage is the only mature grid-scale energy storage technology. Originally developed to support nuclear base load plants due to its ability to store energy on the scale of gigawatt-hours (GWh) and rapidly respond to demand fluctuations, pumped storage is recognized as a viable option to support variable renewable sources of energy such as solar and wind. However, in the United States, environmental concerns, regulatory barriers, and high capital costs have effectively prevented the building of new pumped storage facilities for the past 30 years. Instead, developers and researchers have primarily invested their time and resources into pursuing chemical storage options, including lead-acid, lithium-ion, and sodium-sulfur (Na-S) chemistries. These alternative technologies do not have the geographic limitations of pumped storage, but suer from higher costs at grid scales, shorter lifespans, and the negative environmental impacts of mining, manufacturing, and disposing of large quantities of chemicals. Grid-scale storage needs will increase substantially as variable resources like solar and wind supply an increasing fraction of the grid's energy. To address this challenge, we propose a renewed focus on developing large-scale pumped storage facilities at sites with existing reservoirs. This approach avoids the environmental concerns associated with building new dams and reduces regulatory barriers by requiring minimal land-use changes. Retrotting existing facilities in this way converts their primary purpose to storing electricity generated from other renewable sources such as solar or wind, while still enabling hydroelectricity generation to continue. Such retrofitted systems have already been built in the United States and Europe, proving that an approach of this type is feasible. In order to match the scale of the need, however, significantly more storage capacity is required. Therefore, we propose a widespread adoption of this approach, especially as a potential alternative to chemical storage. To illustrate this concept, we explored the technical feasibility of retrotting the Big Creek hydropower system in central California (Edison International) by carrying a preliminary technical feasibility study. The Big Creek system is composed of 6 reservoirs and currently supports about 1GW of capacity. We found that by expanding the tunnel network and adding pump-turbines between two of these reservoirs, the Big Creek system could provide 75GWh of energy storage capacity and 5GW of power capacity. These values are large enough to enable complementary solar power to provide 5GW of baseload power in the summer, 25% of the baseload demand for the California Independent System Operator (CAISO). Existing infrastructure would remain untouched, enabling current hydropower generation to continue. Added infrastructure would include 4 tunnels 6m in diameter and approximately 24km in length each, 24 pump-turbines evenly distributed across the 4 powerhouse locations that lie between the reservoirs, additional powerhouses to store the pump-turbines, and 4 500kV transmission lines to transmit the power to either San Francisco or Los Angeles. A preliminary cost analysis for this project estimates costs between $2500-$4000/kW ($12.5-20 billion), in line with current standard estimates of pumped storage costs that demonstrate the superiority of pumped storage to chemical storage alternatives for grid-scale energy time-shifting applications. Future research will include a more comprehensive study of the technical and economic feasibility of adding a large scale pumped storage facility to the Big Creek system. Additionally, we will expand our analysis to cover the scale of the state of California by including other existing hydropower sites.

This paper describes the procedures and results of an investigation to evaluate potential increases in nationwide hydropower production that could be achieved by reallocation of flood control storage at existing hydropower reservoirs. One aspect of the investigation considered only the increase in energy that could be achieved by storage reallocation; a second aspect considered potential gains in both energy and capacity that could be achieved by adding to the existing installed capacity as well as storage reallocation. The investigation was performed by the Hydrologic Engineering Center of the U.S. Army Corps of Engineers, and is a component of a technical overview study which is part of the National Hydropower Study. (Author).

The Richard B. Russell Dam and Lake Project is presently under construction and is being placed in tandem between Hartwell and Clark Hill, two existing multipurpose hydropower plants on the Savannah River. System operational simulations were performed in support of a feasibility study for the installation of pump turbines at Russell, using a version of the Corps of Engineers HEC-5C computer program modified for system power and pumped storage. Information developed from the simulations include system hydropower production, pumping energy requirements, daily reservoir pool fluctuations, and reservoir elevation statistics. This information was useful in judging the effects of the addition of pumped storage on system hydropower production and reservoir recreation useability, as well as in ascertaining efficient system operational methods. (Author).