As discussed in numerous previous posts the world will need immense amounts of energy storage to transition to 100% renewables, or anywhere close to it, and the only technology that offers any chance of obtaining it is sea water pumped hydro (SWPH) storage. Here I consider the practical aspects of SWPH and conclude that there are only three places in the world where a combination of favorable shoreline topography and minimal impacts would allow any significant amount of SWPH to be developed – Chile (discussed here), California (discussed here) and, of all places, Croatia. For the rest of the world nuclear remains the only proven decarbonization technology. (Inset, Valhalla’s proposed SWPH project in Chile.)

Note: Addendum on the SWPH potential of the Dead Sea, April 21, 2018, attached

In the last few weeks I have wandered through Google Earth looking for prime SWPH potential and have found that most of the world has none (I have not looked closely at Africa). The coastal topography in most places is too low and flat, and where it isn’t the valleys lack good dam sites, and/or are full of people, and/or the sites are too far from the sea. The sites that do exist are also often in scenic areas where significant public opposition may be expected whether there are any people there or not.

This point was forcibly brought home to me by Euan Mearn’s comments on Scottish Scientist’s Loch Ness Monster of Energy Storage guest post, which proposed a 6.8 TWh SWPH upper reservoir at Strath Dearn in the Scottish Highlands. Considered purely in terms of potential Strath Dearn is probably the best SWPH prospect in the UK, but if Euan’s reaction to the proposal is shared by others the chances it will ever get built are effectively zero:

Figure 1: The proposed 50 sq km Strath Dearn upper SWPH reservoir, located about 25km from the sea. The dam would be 2 km long and 300m high. Google Earth shows that the 650m surface elevation overtops topography by about 20m in one place, but this could be fixed with an earth berm.

The second-best site in the UK is probably this one on Exmoor, the only place where deeply-incised higher ground reaches the coast. It’s much smaller that Strath Dearn (~200 GWh, dam 600m long by 185m high) yet it would still increase the UK ‘s installed pumped hydro capacity by a factor of about seven. But could it ever be built? The combes of Exmoor are noted beauty spots, and certainly the owners of the Hunters Inn would not be amused. Neither would the residents of the villages around the periphery of the reservoir, who would watch it fill and drain probably once a day in the winter:

Figure 2: Exmoor dammed SWPH reservoir (elevation 200m when full). The red lines are Google Earth polygons that define reservoir outlines



Are there any potential SWPH sites in UK that might be developed? Yes. The abandoned china clay pits around St. Austell in Cornwall and east of Plymouth. The St. Austell pits are shown in Figure 3:

Figure 3: SWPH reservoirs in disused china clay pits west of St. Austell

In total there are about fifteen pits with capacities ranging from 1 to 6 GWh within 5-15 km of the sea. Water surface elevations are between 100m and 250m. Total storage capacity is about 50 GWh, which would more than double current UK pumped hydro capacity. The environmental damage has already been done, and flooding the pits would not affect one of the area’s main attractions – the white, conical waste dumps known as the “Cornish Alps”. Watching the water go up and down in the pits as UK electricity demand fluctuates might even turn into a tourist attraction in its own right.

I will now briefly describe the better SWPH sites I found elsewhere in the World. First Canada. Figure 4 shows three potential SWPH upper reservoir sites in dammed glacial valleys in Quebec between 40 and 130km north and east of Quebec City. They have a combined storage capacity of about 8 TWh, appear to be uninhabited, and might not pose too much in the way of environmental problems*. But why would Quebec need this capacity? The province already generates 95% of its power from hydro and sells some of it to nearby US states to provide grid balancing services. British Columbia has a number of similar SWPH sites, but BC also gets 95% of its electricity from hydro.

*Although in steep-sided glacial valleys I would be concerned about how rapid fluctuations in water level over large ranges might affect sidewall stability.

Figure 4: Three dammed SWPH reservoir sites in Quebec

Second, Norway. Figure 5 shows the SWPH reservoir sites I identified east of Stavanger, all within striking distance of fjords. They come in two varieties – three dammed glacial valleys (dams in white) and 16 high-level glacial lakes that form natural reservoirs for sea water storage without the need for dams. (There are also some in Scotland, but the storage potential is lower). The three dam sites have a combined storage capacity of about 2.5 TWh and the lakes also about 2.5 TWh assuming they are all 40m deep on average (a guesstimate from projecting elevation profiles that could be off in either direction). Would Norway allow these sites to be developed?

Figure 5: Dammed and glacial lake SWPH reservoir sites east of Stavanger, Norway

The largest SWPH potential I found in Norway is contained in four large glacial lakes at the east end of Sognefjord some 300 km to the northeast. These lakes cover an area of 115 sq km, have an average elevation of 1,040m and have a storage capacity of …. what?

Figure 6: Glacial lake SWPH reservoir sites east of Sognefjord (visible in bottom left corner)

Well, it depends how deep they are, and I can’t estimate that from Google Earth. But Lake Bygdin – the second reservoir to the east, is reportedly up to 210m deep, and the average depth of large glacial lakes in Norway calculated from the data given in this reference (you may have to paste the URL into the address block to make the link work) is 113m, so I have assumed an average depth of 100m. This gives a combined storage capacity of around 30 TWh.

But now the problems start. Unlike the glacial lakes around Stavanger these lakes are readily accessible by road and are popular recreational destinations. Lake Tyin to the west also supports an existing 386MW conventional hydro plant. And Norway already generates almost all of its electricity from conventional hydro. It could of course sell the balancing capacity to Europe, but some rather large transmission lines would be needed to wheel 30 TWh of power back and forth. And while these transfers were in progress the lakes would be going up, and down, and up, and down …..

Mountainous countries in mainland Europe outside the Balkans have little SWPH hydro potential except for some dam sites in northern Spain, which contain about 4 TWh of potential in steep-sided (and scenic) gorges. In Portugal, Italy and France the coastal topography is unsuitable and most valleys are populated and farmed. There are, however, two monster SWPH sites in Albania, where the necessary elements for a dammed SWPH reservoir (large high valleys, narrow deep drainage outlets, not too far from the coast) all come together:

Figure 7: Two SWPH reservoir sites, Albania. Dam outlines are indistinguishable at this scale (left to right is approximately 100km) and are defined by yellow dots

The two reservoir sites cover an area of 600 sq km and have a combined storage capacity of around 50 TWh. The dams are large (1,800 x 250 and 1,000 x 250m) but not excessively so. The reservoirs would flood towns and villages and agricultural land, and Albania, which imported 40% of the 8 TWh of the electricity it consumed last year, certainly couldn’t use them. Neither could its neighbor Greece, which imports ~20% of its ~50 TWh annual electricity consumption (the eastern extremities of the reservoirs are in fact in Greece). The closest country that could use this much backup capacity is Germany, 1,000 km away.

Now to the star of the show, Croatia.

Figure 8 shows a typical Croatian upper reservoir SWPH site, roughly outlined with Google Earth polygons. It’s a sinkhole in limestone “karst” terrain caused by the collapse of an underground cavern. There are, however, no recent sinkholes in the area, indicating that the sinkhole is old (possibly dating from a period of higher water tables during the last ice age) and that the ground is now stable.

Figure 8: Typical Croatian “sinkhole” SWPH reservoir site

Site details are (numbers approximate):

Distance from sea: 5 km

Surface elevation when full: 1,300m

Base elevation 1,190m

Average depth: 37m

Area: 1.5 sq km

Volume: 50 million cu m

Storage potential: 170 GWh

So with this single ready-made upper reservoir site we are looking at the storage equivalent of roughly 17 Dinorwigs.

And how many such sites are there in Croatia? Dozens of them. Figure 9 shows the main concentration – there are more elsewhere. The Figure 4 site is marked with an arrow.

Figure 9: Main concentration of Croatian SWPH reservoir sites

The 39 identified upper reservoir sites in Croatia are located at elevations of between 800m and 1,400m and have a combined storage potential of approximately 9 TWh. There are numerous smaller sinkholes that could add to this total. Moreover, over 6 TWh of the potential is in uninhabited and unused areas. Almost all of the sites are within 10km of the sea, and a coast road provides access to shoreline facilities. There should be no major environmental obstacles to using at least the unpopulated sites for seawater storage. Croatia, which like Greece imports about 20% of its electricity, can’t make use of them, but the northernmost of them is only 250km from the German border.

What of the rest of the world? I looked at China, India, Russia and Saudi Arabia, and none of them is blessed with coastal topography suitable for the large volumes of SWPH storage that would be needed to support high levels of renewables penetration in these countries. Based on their recent INDC submissions to the Paris Climate Conference, however, it seems that none of them is in any great rush to transition their electricity sector to renewables anyway.

ADDENDUM: The SWPH potential of the Dead Sea

I promised to take a look at this in comments, so I did. It’s not worth another post so I’m documenting the results briefly here.

First we will look at the area’s SWPH potential, ignoring other considerations. The Figure below outlines the area around the Dead Sea that’s below sea level in white. It covers 4,700 sq km and rivals the Gulf of Aqaba in area. (The red outline to the west shows the below-sea-level portion of the Qattara depression):

The Figure below is a north-south Google Earth elevation profile along the center of the Dead Sea trough (elevations below the Dead Sea from bathymetric data). With a surface level of -415m and a bottom level of -730m the Dead Sea (dark blue) has about 50TWh of storage capacity. Flooding the surrounding area from -415m to sea level (light blue) would add another ~2,000 TWh:

But no one is going to allow an area that many regard as one of the “cradles of civilization” to be flooded with sea water. So we can forget about the 2,000 TWh of potential above the Dead Sea itself.

And the 50 TWh of potential in the Dead Sea? Well, one problem is, how does one install massive sea water inlet pipes at the bottom without draining it?

And no one plans to drain the Dead Sea anyway – quite the opposite in fact. Diversion of inflow from the Jordan River for agricultural use is lowering Dead Sea water levels by about a meter a year, and two plans have been proposed to raise and stabilize its level about 50m higher than it is now by adding sea water either from the Mediterranean or the Gulf of Aqaba. These are sometimes referred to as Med-to-Dead:

http://deadseapower.com/project_review/#/

And Red-to-Dead:

https://en.wikipedia.org/wiki/Red_Sea%E2%80%93Dead_Sea_Water_Conveyance

I had previously assumed that these plans involved pumped hydro storage, but neither of them does. Med-to-Dead will transport sea water by gravity flow through an underground pipe to a below-sea-level reservoir (Lake Shalom) next to the Dead Sea and from there by canal to the Sea. A conventional hydro plant on the canal will generate up to 2.5 GW of electricity during peak demand periods. Red-to-Dead will transport sea water via a canal that pumps the water 230m uphill and then lets it run down to the Dead Sea ~650m below. Conventional hydro on the downstream section will generate electricity, but because the project also involves sea water desalination it will be a net consumer of energy.

In summary, the seawater pumped hydro storage capacity of the Dead Sea is immense. Its realizable capacity is zero.