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If batteries are a weak link in the solar chain. Why not use water?  RSS feed

 
Chael Givan
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I'm not here offering answers but rather I'm here asking questions. I've read that solar systems are expensive, in large part, because of their battery needs to power things when there is no sun out. Why aren't people using panels to pump copious amounts of water into holding tanks, thereby storing potential energy, for use later via outlet gates and water wheels or turbines?

This methodology would apply to metal springs also. It seems to me that a solar system could be broken down into a few motors, springs and solar panels or alternatively, solar panels, a water pump, holding tanks and a water wheel with attached motor. Perhaps it's all just pie in the sky optimism and not practical. I'm asking here to see what others think.
 
John Elliott
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Well yes, there are better ways to store energy than in chemical batteries. The hydrogen fuel cell is a very promising technology: use solar power to break water into hydrogen and oxygen, collect the hydrogen and burn it later to get the energy back.

The only problem with mechanical ways of storing energy (springs, motors, lifting water, etc.) is that they are not as efficient on the energy return as hydrogen. Usually you only want to use these methods when their mechanical feature is an essential part of the energy use in the first place.
 
Chael Givan
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The hydrogen idea is interesting and sounds like a solid technology if it gets to the commercial stage. My own guess is that the methods I mentioned simply don't have the efficiency of a battery system but might surpass the battery system for longevity and/or cost.

Ideally, I'm praying that I have a small running body of water or enough wind/sun to let me tinker at my next home.
 
Ken Peavey
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The Laws of Thermodynamics dictate that when energy is converted from one form to another, there is an energy loss, usually in the form of heat. This loss is unrecoverable. Examples of this conversion is sunlight to electricity, kinetic (motion) to potential (stored), or potential back to kinetic.

Energy can be stored in many ways, but the energy that comes out of storage will always be less than the energy going in. Some forms of storage are more efficient, some more practical for the intended use of the extracted energy, some are cheap but inefficient, others are highly efficient but very expensive.

Converting sunlight to stored water in a high tank is far less efficient than storing a battery. It is a means of storing energy, and when batteries are not available, it can do the job, but the energy that can be drawn out of such a system will be far less than a battery storage system.


 
William Bronson
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I like to think of these things in war time terms. During WWII lots of "inefficient " things were done, because there alternatives were worse, or unavailable.
If the real costs of fossil fuels were included in their prices, even the least efficient solar would win hands down.
Right now fossil fuels are like the septic tank company that can charge a fraction of the competitors rates because they dump their trucks into the drinking water supply instead of paying to have it sanitized.
 
r john
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In Uk pumped storage is very important to cope with peak demand

http://www.fhc.co.uk/dinorwig.htm

Capable of going from 0 to 1320 mw in 12 seconds
 
Manfred Eidelloth
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In Germany we have some big pump storages, too.
They had been designed to store the energy from nuclear and coal plants at night and provide for peak consumption during the day.
Now they are mostly used to store the peaks of solar and wind energy, but are hardly profitable any more, as the price difference during the day is too low and the use too irregular.

For small uses it is a problem of size and transformation efficiency.
At an overall efficiency of 50%, to store 1 kWh you would need to lift a weight of 740 tons to a height of 1 meter, or 74 tons to 10 meters, or 7.4 tons to 100 meters.
You need a big tank, an efficient pump and an efficient turbine.
You can buy a lot of battery capacity for that kind of money...
 
R Scott
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In theory, yes. In practice, it is less efficient than batteries.

If you can get away with only converting once, then it is more feasible. Like pumping water into a water tower so gravity supplies the pressure. The farm I grew up on had an old cistern three fourths the way up the hill from the house, just high enough to give the right pressure from gravity and not so high that the windmill couldn't pump to it.

But today that system would cost 10x more than a set of batteries and a pressure tank.
 
Kevin EarthSoul
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Since we're having a discussion of alterative ways of storing solar power...

IMO, the best way to store solar energy is chemical--- in the cellulose bonds of woody plants. Call this "the old fashioned way"... you grow it.

Yes, photosynthesis of plant matter is a relatively inefficient conversion, on an energy per unit of area measure, but since plants essentially grow themselves, the costs of manufacture and installation of the systems are greatly reduced from that of PV cells. As for converting that energy into useful forms of energy, a Combined Heat/Power wood-gas generator seems to be the most efficient. Converting chips of wood into natural gas that can be burned in a generator, and the heat used to power water-heaters and hydronic heating systems is pretty efficient. Trees can be coppiced or pollarded instead of cut down completely, with a set of trees being rotated through several years' rotation. Fast growing, high BTU trees can be useful for other purposes, as well. black locust, Osage Orange, and Red Mulberry, for example, are all useful for other purposes. One more thing... a "waste" product of wood-gas stoves is char, which is very valuable as a soil additive, sequestering carbon in the soil.

Kevin
 
Marcos Buenijo
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Chael Givan wrote:I'm not here offering answers but rather I'm here asking questions. I've read that solar systems are expensive, in large part, because of their battery needs to power things when there is no sun out. Why aren't people using panels to pump copious amounts of water into holding tanks, thereby storing potential energy, for use later via outlet gates and water wheels or turbines?

This methodology would apply to metal springs also. It seems to me that a solar system could be broken down into a few motors, springs and solar panels or alternatively, solar panels, a water pump, holding tanks and a water wheel with attached motor. Perhaps it's all just pie in the sky optimism and not practical. I'm asking here to see what others think.


The problem with these prospects is low energy density and high cost. A conventional deep cycle lead acid storage battery weighing about 70 pounds and costing on the order of $120 can deliver about 1 KWh of electricity when fully charged. This represents about 2 million foot pounds of energy. Therefore, when one considers the losses in energy conversion, storing 1 KWh of electricity in the form of water in elevated storage tanks would require a set up that represents about 3 million foot pounds of energy. If the elevation is 10 feet, then one requires about 4800 cubic feet of water. If the elevation is 100 feet, then about 480 cubic feet of water is necessary. In short, this is why a lead acid battery is used in lieu of pumping copious amounts of water into storage tanks.

What I think is that batteries are by far the most practical means to store solar energy in the micro scale, and assuming electricity. Even when used in tandem with a heat engine (such as a wood gas engine system), then a battery is very useful to store energy for low power electrical loads. Now, if the desire is to store thermal energy, then water is a brilliant choice. Also, if the scale is larger, then water is also a brilliant choice even for electricity generation - but I'm not referring to the way you might think. Consider the work of Terrajoule (see http://www.terrajoulecorp.com/). In this case, photovoltaics is not used, but the overall efficiency is higher than conventional PV with battery storage, and a lot less expensive.
 
r john
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Hydraulic energy densities can be far higher than batteries see below.

http://www.diva-portal.org/smash/get/diva2:373607/FULLTEXT01.pdf

Theres no reason why apart from expense that the same technology could not be developed for the domestic market.
 
Manfred Eidelloth
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@r_john:

(Edit: The posting I am referring to seems to have been deleted?)

We were talking about potential energy storage.
Hydraulic pressure storage is a different thing.
And I do not know about any available electric to electric pressure storage system in household size.
You link shows high power short term storage systems for automotive applications.
Even if you would turn this into a bigger long term storage system and develop a small high efficiency hydraulic generator, you would still be far away from the 94% (mechanic energy to mechanic energy) cycle efficiency shown in your link due to 2 (or at least 1) more energy conversions and the energy loss in the storage due to compressed gas cooling down during a longer storage time.
And you would have extra costs for technical inspection every year, as pressure vessel regulations do apply, especially to a bigger long term storage system. You would not like to see one of these go off…

There are some interesting developments in compressed air storage systems, too, combined with heat storage, to avoid the energy loss by cooling of the compressed air. But again I do not know of any household size system available now.

I think all these options (potential energy, hydraulic- or gas pressure) are too complex to make them cost effective for single households.
But I can well imagine they will once be used in medium size as peripheral storage systems for whole villages or for bigger wind engines and photovoltaic plants, allowing these plants to deliver energy on demand.
 
r john
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Manfred

Off the shelf hydraulic solutions already exist and are used on oil rigs to give back up supply to generators instead of battery banks a typical small hydraulic generator below

http://www.eaton.com/Eaton/ProductsServices/Aerospace/Hydraulics/PCT_249145


Also mini power packs with 12V or 24V DC input suitable for solar applications

http://www.hydraproducts.co.uk/hydraulic-power-packs/mini-power-pack.aspx
 
Marcos Buenijo
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r john wrote:Hydraulic energy densities can be far higher than batteries see below.

http://www.diva-portal.org/smash/get/diva2:373607/FULLTEXT01.pdf


Hydraulics show very nigh POWER DENSITY, not high energy density. Solar energy storage needs high energy density.
 
Samantha Langlois
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I like this idea. I believe it is energy storage that is harder to achieve than capturing the actual energy.

Your idea of using pumps, water, a holding system and gravity makes a lot of sense. I'm just not sure if it scales.

In a way it reminds me of the use of gravity in this thread on permies: http://www.permies.com/t/33200//Gravity-Light-light-source-gravity
 
Chael Givan
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Samantha Langlois wrote:I like this idea. I believe it is energy storage that is harder to achieve than capturing the actual energy.

Your idea of using pumps, water, a holding system and gravity makes a lot of sense. I'm just not sure if it scales.

In a way it reminds me of the use of gravity in this thread on permies: http://www.permies.com/t/33200//Gravity-Light-light-source-gravity


It is funny that you mention the gravity light thread. That is what initially triggered the thoughts which led to this post
 
r john
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Marcos Buenijo wrote:
r john wrote:Hydraulic energy densities can be far higher than batteries see below.

http://www.diva-portal.org/smash/get/diva2:373607/FULLTEXT01.pdf


Hydraulics show very nigh POWER DENSITY, not high energy density. Solar energy storage needs high energy density.


Energy density is totally irrelevant. Pumped storage is already commercially viable for storage of renewable energy in UK and Germany using gravity alone. Energy densities are increased many times by using a weighted accumulator. On a local level it could be the weight of the house used as the accumulator but on a country scale this German proposal seems a reasonable proposal given the marble cutting technology used in Italy.

http://blogs.worldwatch.org/revolt/unconventional-“hydraulic-hydro-storage”-system-offers-energy-storage-for-the-grid-on-a-grand-scale/
 
Marcos Buenijo
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r john wrote:

Energy density is totally irrelevant. Pumped storage is already commercially viable for storage of renewable energy in UK and Germany using gravity alone. Energy densities are increased many times by using a weighted accumulator. On a local level it could be the weight of the house used as the accumulator but on a country scale this German proposal seems a reasonable proposal given the marble cutting technology used in Italy.

http://blogs.worldwatch.org/revolt/unconventional-“hydraulic-hydro-storage”-system-offers-energy-storage-for-the-grid-on-a-grand-scale/


"On a Grand Scale". Exactly.
 
Dale Hodgins
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I expect that most electricity used at my place during the summer, will be used to lift water for irrigation and other uses. Elevated storage is a simple way for me to use solar electrical output without batteries. I may not need water for several days and then I may wish to use more than what is available in the upper storage. The storage water at 20 ft. above ground level, could be run through a jet pump. There are areas to be irrigated which lie only about 5 ft. above the big lower pond. High pressure water from the upper storage should be able to deliver a greater quantity of low pressure water to the land surrounding the pond which would contain the jet pump. No need to convert back to electricity, since the pump uses kinetic energy.
 
Chris Olson
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The title of this thread is what caught my eye. Some of the discussion is rather far out there.

Batteries are not, IMO, the "weak link" in an off-grid power system. They do what they do at very low cost and very high reliability compared to any other alternative. There are few to none other systems that can store solar energy as electricity with no moving parts. We have stored the electricity for our home in batteries for well over a decade. And as most other off-grid folks that have at least five years experience will attest, batteries are not the "weak link" that people that have zero experience make them out to be. Sure, they are expensive but they do something no other device on earth can do at 85-90% efficiency.
 
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