Winter energy in Europe
With its northerly latitude, winter solar availability in Europe is poor. In winter, a decarbonized Europe will rely mostly on solar energy generated in the south and wind energy in the north. Large-scale long-duration energy storage is needed to ride through days or even weeks of poor solar and wind availability.
Fortunately, Europe has unlimited, low-cost, off-the-shelf, low-environmental-impact, long-duration, off-river pumped hydro energy storage (PHES), that requires tiny amounts of land and water and does not require new dams on rivers.
Pumped hydro-energy storage
PHES provides about 95% of global long-duration (hours-days) energy storage (GWh). Batteries provide short-term storage (a few hours) with high-power (GW). Together, PHES and batteries solve energy storage.
The global pumped hydro atlas lists 820,000 sites in the size range of 2-5000 GWh with a combined storage of 86 million Gigawatt-hours. This is equivalent to 2 trillion electric vehicle batteries.
The atlas includes premium sites (cost-class AAA and AA), and lower quality sites (cost classes A, B, C, D and E). Premium PHES sites are characterized by large head (>500m), low-volume dam walls, short pressure tunnels, large-scale (>40 GWh) and long duration (>100 hours).
Europe has over 6000 premium PHES sites with a combined storage of about 1100 terawatt hours, which is about 40 times more storage than required for a fully electrified and decarbonized Europe. There are also many lower-quality sites (classes A-E).
The capital cost of premium-quality long-duration PHES is in the range of $8-25 per kWh. For example, Snowy 2.0 PHES in Australia (class AA) costs about A$12 billion for 350 GWh of energy storage and 2.2 GW of storage power (160 hours duration). This corresponds to US$22/kWh, which is far lower than batteries for a system that will last 100 years.
Clean hydrogen has been considered for long-duration energy storage. This is inhibited by the low round trip efficiency of electricity-hydrogen-electricity, and the high cost of electrolysis. However, large volumes of clean hydrogen are required to produce chemicals and synthetic aviation fuel, which can effectively store energy within themselves.
Unlimited PHES
Most studies of European 100% renewable energy overlook PHES, for the following (incorrect) reasons: there are few PHES sites; more dams on rivers are required; large areas of land are flooded; large amounts of water are required; there is a heavy environmental cost; and the capital cost of PHES is high. All these perceptions are wrong.
No new dams on rivers: PHES has traditionally been associated with dams on rivers. However, most PHES sites are located away from rivers (“off-river”), for the simple reason that most of the landscape is not near a river.
Europe has excellent PHES potential in Norway, in the Alps, and in the south. However, northern Europe lacks good sites. Fortunately, high-voltage transmission allows the sharing of both energy and storage across Europe. Strong transmission networks smooth out the effects of local weather and thus reduce storage requirements.
Image: ISES
Land requirements for PHES are very small. The figure below shows a synthetic image of a 5000 GWh site with pop-up information boxes containing 26 items of information. This single site has enough storage for 100 million fully electrified and decarbonized people and is equivalent to 100 million electric vehicle batteries. Five such sites can provide all the storage that Europe needs.
The combined flooded area is 60 km2 (0.6 m2 per person) which is 100X smaller than the area occupied by the solar farms that the storage supports and is 20X smaller than the parking area occupied by 100 million vehicles.
The capital cost of this system is about €100 billion and represents an enormous local economic opportunity. This equates to only €1000 per person for 100-year-lifetime storage.
Image: ISES
Water requirements for PHES are small because the same water goes up and down between the reservoirs for 100 years. In dry areas, small amounts of water may be required to replace evaporation. The amount of water required for the initial infill and to replace evaporation amounts to a few liters per person per day, which is equivalent to 20 seconds of a morning shower.
Environmental Impact of PHES is low because of the lack of new dams on significant rivers, the small land and water requirements, the absence of electrochemicals, the long lifetime (100 years), and the abundant choice of off-river sites (allowing avoidance of sensitive sites).
Hybrid energy systems
PHES is far cheaper than batteries for energy storage (GWh). However, batteries are cheaper than PHES for storage power (GW). Hybrid PHES and battery systems deliver very cheap energy storage and cheap storage power, by allowing storage to trickle-charge storage when energy prices are high or negative.
Global solar and wind capacity is being installed six times faster than everything else combined. Electrification of transport, heating and industry will double or triple electricity demand. Fortunately, solar, wind, PHES, batteries and transmission are available off-the-shelf to decarbonize Europe at affordable cost.
Authors: Prof. Ricardo Rüther (UFSC), Prof. Andrew Blakers /ANU
ISES, the International Solar Energy Society is a UN-accredited membership NGO founded in 1954 working towards a world with 100% renewable energy for all, used efficiently and wisely.
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