Post by David B. Benson on Oct 21, 2017 16:54:09 GMT 9.5
When there is no site for a pumped hydro storage installation, dig a hole in competent rock; gravity storage: www.heindl-energy.com/
As this is similar to pumped hydro, expect about 75--80% efficiency and likely higher construction costs. Still, a potentially reasonable solution for Saudi Arabia and then similar flat locations with exposures of competent rock.
Post by Roger Clifton on Oct 22, 2017 10:39:53 GMT 9.5
The rock weight seems unnecessary, as it can much more easily be replaced by about 2.7 times its volume of water.
Pumped storage schemes offer a tantalising hope of being able to create something resembling baseload from renewables. However they usually fail to take account of the running cost of continuously topping up with fresh water during the dry season. Consider the arithmetic…
The minimum useful amount of storage to supply into the grid is about one gigawatt-week, enough backup for an intermittent windfarm averaging one gigawatt output. That comes out to 605 terajoules. Equating that to MgH and setting H, the minimum head of water, to 20 m (that's already a hell of a lot of digging), I get M, then the volume, then an area of 302 km². That much area wouldn't likely be appropriated from the productive farmland near the powerlines. More likely it would be out back in the dry grazing land, where water is precious and such as does appear evaporates in a few days.
Both the upper tank and the water in the hole are exposed to wind and sun. Many parts of Australia have an evaporation power of 10 m per year. Most productive agricultural land has a dry season of similar ferocity, say 5 m per year. That much multiplied by the above area gives the water demand at 1.504 km³ per year. However there is just not that amount of fresh water to spare, in a country where the biggest river often evaporates entirely before it reaches the sea.
Post by singletonengineer on Oct 22, 2017 17:10:34 GMT 9.5
Net evaporation rates along much of the eastern seabord of Australia lie between 1.5 and 2 metres per annum. By that I mean total evaporation minus rainfall. No runoff inflow allowed for.
For an idea of what this means at scale, the water storages of AGL Macquarie, ie dams associated with operation of Bayswater and Liddell Power Stations, lose about 10Gl/year due to net evaporation. Total water use for other purposes is over 50Gl => 60Gl all up extracted from the Hunter River.
10m/year or even 5 m/y seems to be a gross over-estimate based on my experience. One on-line estimation for numerous Californian dams yields evap estimates of 2 to 7 mm/d, ie 700 to 2500mm. www.researchgate.net/file.PostFileLoader.html.
My best guess? Of the order of 1.5 to 2 metres per annum, after allowing for 700mm of rainfall inflow, so 2.2 to 2.7 metres before allowing for rain inflows, in coastal Eastern Australian conditions.
Very shallow evaporation pans exposed to the wind, in dry (desert) conditions would of course be much thirstier.
If crops/vegetation are involved, the correct term is evapotranspiration, to allow for water loss through plant leaves and stems.
A certain Canberran researcher suggests that H=200m and envisions 2200 sites around Australia for pairs of pumped hydro dams. I think he is mistaken.
Post by Roger Clifton on Oct 22, 2017 19:20:48 GMT 9.5
(SE – welcome back!)
Converting into the same units for comparison: 1500 GL per year of water would be lost in areas of 5 m evaporation per year. 600 GL per year would be lost in areas of 2 m evaporation per year.
That is the water loss from 300 km² of open water needed for an operation of only 20 m minimum head. The scenario was of holes being dug in open flat ground. I doubt if the scheme would be able to buy that much of the expensive land on Australia's narrow eastern coastal strip.
If the unnamed professor really can find 2200 unprotected wild river valleys with 200 m of fall in them, he would only need one 10th of that area (per GW-week). But he would still need one 10th of that water supply to be taken out of the environment. And one 10th of far, far too much is still far too much water wasted.
My figures were for the first GW-week. If Australia went 100% wind-plus-storage tomorrow, we would need about 25 GW-weeks. Soon or later we will be going all-electric, needing perhaps 50 GW-weeks of storage. If we multiply all of the above by that factor of 50, we go back to saying, "far, far too much".
There is zero chance of these crackpot schemes providing the non-carbon power required for our future. The fact must be well known to the spruikers. Instead, they prey upon our credularity, our concern for the future, our desperate willingness to believe in a hey-presto solution.
Post by Roger Clifton on Oct 23, 2017 10:31:53 GMT 9.5
SE says that 2 m evaporation would be closer to the mark for the East Coast of Australia, rather than the 5 m that I had guessed. Here is a map of Australia's pan evaporation, showing he is right. Pan evaporation is more than lake evaporation, which is lower than of evapotranspiration.
To be fair, pumped storage is more likely to be happening in hilly country, which attracts orographic rain and raises the humidity above what it would have been.
A distinct advantage of excavated storage is that it could be placed anywhere. In particular, it could be placed on the site of a wind farm, or a solar farm. But where there is optimal sun or wind, there may not be excess fresh water available.
Post by David B. Benson on Oct 23, 2017 13:25:56 GMT 9.5
The gravity storage scheme does not require fresh water. With the right placement the holding basin could be the ocean. Of course the active basin, under the rock cover, suffers no evaporation whatsoever.
Nevertheless, I opine that there are few locations in Australia with an appropriate combination of geography and geology for this gravity storage scheme. A bit player, perhaps.