Store excess energy in resevior and release as hydroelectric

EdOfTheMountain — Mon, 08 Sep 2008 13:43:32 GMT

As an energy storage method, why not use solar to pump and store water in an uphill reservoir and use it to generate hydroelectric at night?

This could be done if solar (or wind) can generate excess capacity. I expect your first reaction is to laugh and obviously some energy will be lost pumping water uphill but the economics make sense.

Conventional power plants are doing this now except they do the opposite; they pump and store water at night during off peak and use it to generate hydroelectric during day-time on-peak hours.

http://www.nationmaster.com/encyclopedia/Taum-Sauk-pumped-storage-plant http://maps.google.com/maps?ie=UTF8&q=Taum+Sauk+Trail,+Lesterville,+Reynolds,+Missouri+63654,+United+States&hl=en&cd=1&geocode=FQbjPAIdqsqV-g&sll=37.0625,-95.677068&sspn=23.875,57.630033&ll=37.533143,-90.8217&spn=0.013987,0.02738&t=h&z=16

RE: Store excess energy in resevior and release as hydroelectric

tonygs — Tue, 09 Sep 2008 19:30:50 GMT

Well, you're working against a couple of things, but this also begs a question. Why do the generation at night when power usage is low?

So, first thing to think about is the law of conservation (physics is your friend, and gravity sucks, therefore you need to figure out what the loss will be and if at all possible how to compensate), that being you can't get more power out than what's put in. You can do things with the power generated, such as take the basic output voltage and convert it from DC to AC, then step on the current to raise the voltage or reverse and raise the current. First though, you need to figure out how much power it takes to pump the water up hill, to get an idea (an approximate) of how much power this will generate. Back to law of conservation, if it takes 50kv per hour to pump the water up the hill, your output wont be any greater than 50kv.

This leads to my second question, if you're using wind and solar for generating power to run the pump, why not just expand the solar and wind farms and use the energy generated to supplement the power plant? Cut's out several points of failure, and, engineering issues.

RE: Store excess energy in resevior and release as hydroelectric

EdOfTheMountain — Tue, 09 Sep 2008 19:42:53 GMT

Yes, there are losses but depite them it is economical. My point was the same energy storage method could be applied to *excess capacity* of wind or solar generation.

"This powerplant was a net consumer of electricity; the laws of thermodynamics dictate that more power is consumed pumping the water up the mountain than is generated when it comes down. However, the plant was still economical to operate – the reservoir was filled at night when the electrical generation system is running at baseline capacity, and the power used for pump-back would otherwise be wasted."

I think thermodynamics will also prevent you from idling a big power plant and bringing it back up to efficient capacity overnight.

Here's an overview of "Pumped-storage hydroelectricity":

http://en.wikipedia.org/wiki/Pumped_storage_hydroelectricity

"Pumped storage is the largest-capacity form of grid energy storage now available."

"Taking into account evaporation losses from the exposed water surface and conversion losses, approximately 70% to 85% of the electrical energy used to pump the water into the elevated reservoir can be regained."

-Ed

RE: Store excess energy in resevior and release as hydroelectric

tonygs — Tue, 09 Sep 2008 21:30:37 GMT

Ed,

Thanks for pointing out the "excess capacity" part, I didn't give it consideration in my answer. Of course, I'm curious about what excess your referring too. Now you've added another layer, since generally power plants are run above capacity but with no capturing of the reserves not used. This would mean that to store the energy until you needed it, you would need some form of battery or very large capacitor type setup. You've now added a layer of cost that reduces your ability to make this economical even further. All the equipment needs to be taken into account when determining what is economical or cost effective.

From my point of view, and I think this is a big part of where we diverge, something is economical when it can produce a significant savings. Personally, when it comes to power consumption I don't consider 70 - 85% to be economical, because you're expending almost a third more in the amount of energy required to produce the savings, so you're actually working at a loss of anwhere from 15 - 30%, not including the infrastructer that needs to be built to make this project work.

Rather than look at hydrology, why not consider a combination of solar and wind to supplement the power station? Turn things around a bit more, and use the daytime juice, or a portion of it to pump liquid out of the ground, and place a well at the same or lower level than the source. This would be a big boost in terms of energy savings, and place it all above the power station so gravity now does all the work. Then in the evening, release the water from the well to create your hydro-electric generated power. Again, increasing the value by using a less effecient source when energy demands are much less.

This does make me thing of another quest though, once the water has traveled through the turbine, what do you do with it? You've changed the local ecology, and I would imagine from that you don't want to contribute negative actions to the local environment.