Pumped Storage

Source: ZE

The interconnected network that delivers electricity from producers to consumers, known as the “electric grid,” is facing new changes. Mandatory renewable energy targets are being adopted worldwide, meaning electricity suppliers are required to obtain a specific percentage of their total electricity from intermittent renewable energy sources. Wherever intermittent power sources reach high levels of grid penetration, energy storage becomes one of the options to provide reliable energy supplies.

Stability vs. Sustainability

At the heart of the renewables debate has always been their irregular nature – solar and wind power are both time- and weather-dependent and therefore unreliable. According to a recent article in the Irish Examiner, “The quality of British electricity is falling because unreliable renewable generation is becoming an increasingly large component in the power supply, causing more flickering in households and potentially triggering outages.”

Power grids need to maintain a stable current in order to provide quality electricity supplies. Because of this, the high costs associated with powering down and because of the unpredictability of renewable energy, it makes more sense that when power demand drops, the excess energy is stored for later use. National Grid, which operates Britain’s power transmission system, said “that developing storage technology would help stabilize the grid” (Irish Examiner).  In recent years there has been growing interest in energy storage technologies and focus has centered on advanced batteries, compressed air storage, and the most widely-used on power grids today, pumped hydro storage.

Pumped-Storage Hydropower

According to the Electric Power Research Institute (ERPI) and Germany’s Fraunhofer Institute, pumped-storage hydropower currently accounts for more than 99% of installed storage capacity for electrical energy worldwide, equaling around 127 GW (International Electrotechnical Commission). So, how does it work? Using electricity that would normally be wasted, a pumped storage facility uses that excess off-peak power to pump water uphill from a lower reservoir to a higher reservoir. When demand is high, the water can be released back to the lower reservoir through a turbine to generate electricity, which is then fed to the grid.

There are several key benefits associated with pumped storage. The plants reduce electricity costs by using electricity at off-peak times when prices are lower, making them highly cost-effective. The plants have low operation and maintenance costs and are characterized by a long asset life of at least 50 years. While capital costs are location-dependent, given that a large space with varying altitudes is typically required, the extended lifetime of this storage system makes it an attractive long-term investment. Pumped storage also helps to balance out fluctuating renewable sources and improves power quality, frequency, and voltage with its ability to kick in when it is most needed (International Electrotechnical Commission).

As noted in an article on Thinkprogress.org, “A facility that can supply extra power when demand spikes, as well as usefully take in extra power when supply stays high while demand drops is extremely helpful.”

Issues and Concerns

While pumped storage has been thrust under the spotlight as the storage solution for a renewable energy future, it does raise some concerns. Sean Fridley, the Station Manager at The Bath County Hydro Pumped Storage Facility, the largest facility of its kind in the world, discussed how drought conditions can be detrimental to power output, putting it simply: “If there’s no water, you can’t make electricity” (thinkprogress.org). It has also been noted that since energy is lost in the pump turbine unit, the plant will need to buy power more cheaply than it sells it in order to work economically. Environmental and operational challenges also need to be addressed so that the technology is not always limited to mountainous terrain.

Some efforts have been undertaken to combat the technology and location barriers, with one UK company planning to turn abandoned quarries and mines into energy storage facilities (Bloomberg).  As the conversation on climate change continues to be at the forefront of the renewable energy debate, and the amount of uncertainty in demand forecasting increases with its incorporation into the grid, perhaps we will see a shift in the market, with more room being made for pumped storage.