People who may be familiar with me know that in the current global climate change crisis, I mostly favor those forms of GHG free energy that have proved to work on scale, which more or less limits me to favoring nuclear, wind - and to the very limited extent it is available - geothermal energy. I also believe that solar concentrator plants - which are thermal plants - are worth some serious development in certain locales where they work well.
One of the big drawbacks to wind energy is the necessity for maintaining - at great expense - a back up capacity for when the wind doesn't blow and for solar plants, the inability to work on demand or to create energy reserves.
Still, like many people, I have my share of crazy ideas about energy and for what it's worth, I thought I'd share them here.
East northeast of San Diego, in California, is the Imperial Valley - called the "salad bowl" of the United States because it provides much of the lettuce and tomatoes that appear on American tables in winter. The Imperial Valley is actually a desert and as is often the case out west, the large agricultural output of the Valley is a total function of irrigation. California uses part of its share (and as it turns out the shares of other states) of Colorado River water to irrigate salad growing fields.
Many people may be aware that the Imperial Valley, like Death Valley, is actually below sea level. As California is being geologically ripped apart in the unstoppable adventure of plate tectonics, some areas between large faults, in this case the southern end of the San Andreas and the San Jacinto and Elsinore faults, are actually sinking. The Imperial Valley is actually part of the Salton Trough, a huge sunken block of rock that once defined the upper end of the gulf of California. Deposits of debris from the Colorado delta has actually shut off the northern end of the Gulf from the Southern end. Ultimately the isolated portion of the Gulf, which is subject to little rainfall, dried out, forming a huge sub-sea level basin. Many times in the last several millennia, the Colorado has drained into the basin, filling a huge inland lake, but as the river meandered the lake alternately dried and reformed. Several thousand years ago, the valley dried yet again, and up until the early twentieth century, the valley was completely dry, with a huge dry lake basin on its northern most end.
Today one can drive through the valley and see whimsical lines drawn on high up on silos and other structures marking sea level.
In 1905 an irrigation system designed to irrigate the valley - to create the state of affairs that we now have with a huge agricultural industry there - failed during flooding and began to fill the Imperial Valley completely. It took two years, and a herculean engineering effort to staunch the flow. Thereafter a new inland sea was formed, the Salton Sea. The Sea did not evaporate completely as it's previous natural incarnations had, but has been maintained since by the inflow of agricultural runoff water, all of which has been derived from Colorado River water - almost none of which ever makes it Mexico or to the gulf of Mexico in modern times.
The sea takes in about 1.6 billion cubic meters of water per year, which is more or less exactly counterbalanced by evaporation. The relative rates vary, and the sea shore is not completely stabilized. One can see old resorts that are now in the sea and not at its shoreline. The surface of the sea is more than 70 meters below sea level. If, instead of Colorado River water, the sea were balanced by seawater coming in from an outlet to the sea, this evaporation rate would produce about 1.1 petajoules of energy (1 petajoule = 10^15J) or weighted over a year of average power, a relatively modest 35 MW. However if recovered, this would all be solar energy. Although the energy output is trivial on the scale of coal plants, this would actually represent a rather large solar plant, since, in spite of much crowing and carrying on, only a tiny fraction of solar plants are actually this large. (Some of this energy - though certainly not all of it - may already be recovered through the coupling of small hydroelectric plants to the irrigation system. I have no idea if this is the case.)
Interestingly enough, because of the geological activity associated with being on the boundary between the North American (tectonic) Plate and the Pacific Plate, the the Salton basin actually contains significant geothermal resources. (These are real geothermal resources - not heat pumping schemes involving stored heat in ground water that are sometimes sold as "geothermal" resources.) The entire Salton basin enjoys this resource. The Mexican city of Mexicali uses the Cerro Prieto geothermal field to produce 630 MWe of power to supply its population of almost 1 million people. The heat is transferred using brines, which have a higher heat capacity than fresh water, the brines evaporating off leaving a residual of salt and silica.
In the American portion of the basin (initially Mexican territory that was militarily occupied by the United States in 1846 and never returned) a number of geothermal fields also operate. These currently produce 326 MWe from 10 facilities. Another facility is proposed that will produce 185 MWe, using 361,000 cubic meters of
fresh water provided from the Colorado River by the Imperial Valley Irrigation district.
We see from this link discussing Salton Sea Geothermal district
http://www.energy.ca.gov/sitingcases/saltonsea/ that the Salton Sea Known Geothermal Resource Area comprises almost 101,000 acres (excuse the English units) and will be, upon completion of the new project, only 10% developed. From the figures from the link we can see two things. One is that the geothermal potential of the area amounts to about 5,000 MWe, the equivalent of about four or five nuclear plants. The other is that the production of this power would require about 10 million cubic meters of water, since from the figures provided for the new plant, we can see that each megawatt of power consumes through evaporation, about 2000 cubic meters of water. In other words, if this water were obtained from the Salton Sea itself the evaporation rate could be increased by 0.6%, a small, but significant number.
The evaporation of water from the Salton Sea has an interesting consequence. The Colorado River is important to continental salt flows. The existence of fresh water on continents depends very much on the transports of salt from weathered rock to the sea and like all rivers, the Colorado is a large part of this process. In fact one mechanism for desertification of productive agricultural land involves the long term use of irrigation. "Fresh" water sprayed on fields carry small amounts of salts, which are concentrated by evaporation/transpiration. Ultimately the land itself becomes quite saline and the possibility of growing anything there becomes important. Everything dies, and the salts and topsoil are blown away never to recover. (This process is thought to have played a role in North Africa, which was once the granary of the Roman Empire.) Since the Salton Sea has no outlet, the continental salts formerly brought to the sea in the Gulf of California now end up in the Salton Sea. The salinity of the sea is rising rapidly and is now 25% greater than that of the Pacific Ocean. The Salton Sea has been stocked with various kinds of ocean going fish, notably Tilipia. The opportunity for commercial fishing there was historically rather large. However the increases in the salinity of sea, coupled it is believed with the consequences of chemistry of agricultural run-off, has lead to huge amounts of die-off of fish and the birds who feed on them.
This is somewhat tragic because the destruction of wetlands in California in service to its huge population of hominid apes has made the Salton Sea one of the most important stops for migratory birds. It is believed that the elimination of the sea will have rather dramatic negative consequences on the bird population. About half of the species of birds known in North America can be seen in the Salton Sea area.
Several methods, evaporation ponds and the like, have been sought to deal with the salinity issue - but most of these proposals are very expensive and would involve 100's of millions of dollars. Even though if these proposals were funded, they would involve the output of considerable energy. The salt would have to be removed either by truck or rail or else placed in a huge salt landfill. The United States currently produces about 43 million metric tons of salt for various purposes - most of which involve the chemical industry, road salt and the like. Almost the entire salt industry could be provided by evaporation of an amount equivalent to the evaporation of 1 billion cubic meters of the salton sea - if the transport and economics allowed - which probably it doesn't.
Besides it's geothermal and salt resources, the area around the Salton Sea - as anyone who has been to the Southern California desert can tell - there are considerable wind resources in the area. Wind farms do indeed exist in the area, but again the potential is not fully realized. Moreover, as is always the case with wind, as already mentioned, this power is not always available at peak moments.
Also, the valley has considerable solar resources inasmuch as the weather is almost eternally sunny. To my knowledge, few solar thermal plants exist in the area, even though the Salton sea waters may provide a rather large heat sink for raising the efficiency of solar collector plants, and an opportunity to provide further opportunities for evaporation.
However there is no assurance that the sea can in fact survive. The water wars of the West have just begun. California takes more water than it is allocated from the Colorado, because other states have not called for their "fair" share. The water demands of California's urban hominids, those who inhabit San Diego and LA - and who represent huge voting blocks - does not bode well for the agricultural interests of the Imperial Valley - broad American interest in salads notwithstanding.
Suppose though that some of the off peak wind energy, off peak geothermal, and excess solar were stored by pumping water
out of the Salton Sea to locations at higher altitudes? In fact, suppose one were to pump the water is a series of (saline) dams and reservoirs right over the mountains with an outlet draining into either the California Coast or the Gulf of California? The salinity problem of the Salton sea would of course be solved, offset by some energy losses owing to the evaporation from these salt water reservoirs. But what if at the same time sea water pumped out were matched by sea water that came in? Under these conditions, one could obtain energy timed precisely for the moments of peak demand. The salt balance of the Sea could be re-established close to the value of ocean water.
Moreover if the water removed from the sea were not
pumped out, but rather
sucked out, a side product would be desalination. A column of water at normal atmospheric pressure can be made to rise about 10 meters, after which it boils at reduced pressure, lowering its temperature. It is possible to imagine a series of compressors/vacuum pumps that store energy in the form of compressed air (removed from the portion of air soluble in sea water) and
fresh water. The compressed air could be used to pump water (compressed air will drive water more than 10 meters up against a vacuum) when desired, or to run air compressor driven generators, and the
fresh water that condenses in the tank (under pressure and cooling) could be separated and spread on agricultural fields
below sea level, where it will evaporate, producing yet more energy. Moreover the waste heat of compression could in theory be used to enhance evaporation of the brines - recovering even more energy. The cooled brines obtained from the sea water could either be evaporated at geothermal sites (where the low temperatures would give an efficiency boost) or pumped to the sea at moments of low energy demand, providing for stored energy (in the form of gravitational potential from inflowing seawater that can be later accommodated in the sea).
The depth of the sea, and the location of the shoreline could be managed, restoring a recreation industry that has been problematic because of fish die offs, flooding, and retreat of the shoreline.
How would we bring sea water in though? Two possibilities suggest themselves, one less crazy than the other. The first is simply to bring water in through Mexico from the Gulf of California in a series of canals coupled to hydroelectric facilities. Every kg of water that evaporates once at the Salton Basin floor would represent a solar energy boost, including that of desalinated water used for irrigation, sprayed on the fields and evaporated through transpiration. Another (crazier) possibility is to drill a tunnel under the mountains connecting the sea to the Pacific Ocean. On could, under these circumstances, build a series of inland seas, controlled by dams and hydroelectric stations. Since the area is a major earthquake zone, one could create a safety valve for cases of dam failure represented by a few siphons, wherein the tunnel would be constructed to rise in a few places, a few meters
above sea level. One could break the siphons simply by introducing air, and re-establish them by pumping the siphon breaking air out. The cost of such a tunnel can be estimated by the cost of drilling the Chunnel that now connects France and the UK. This passage cost about $10 billion dollars. This is a large investment, but one certainly imagines that it could be recouped as well as the cost of any power facility can. A side product would be a number of reservoirs in which sea food or other sea products could be grown. In addition, a chemical industry could be created via access to the salts, including sodium chloride but various other elements as well. Indeed one could use this system to store energy from anywhere else it is produced in the grid. The nuclear facilities of Arizona, wind farms in Northern California, solar plants in Palm Springs.
This is, then, my crazy idea which I envision as a win-win-win-win, if improbable. I just felt like sharing it.
Printer-friendly format
Email this thread to a friend
Bookmark this thread
(1000+ posts)
Send PM |
Profile |
Ignore
