May 2008

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« Gravity Battery | Main | Youth in Asia »

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cky625

Three 150kw generator is able power that 80% pool for individuals.

Azi

Dave: why should leftish/anti-leftish leanings have any impact on smartness?

velkairiwyth

Well, look at it this way - I shall make up some figures that may be miles off - some are estimates from whats in my head at the time of typing. Small dams generate about 10Mw of electricity - think of the size of them. Perhaps it is possible to just use something similar to a watertower and have one in each neighbourhood - powering maybe 20-30 houses - and it will only be used at night. (or a tower sticking out of your roof some 50ft up - doesnt sound safe or cheap to me though :p)

The energy generated is from a form of pressure called "head" and the only variable is the height at which it descends from - producing force which spins a generator.

Im not 100% clear on the functioning or how much energy is needed - this is something I did study at college some 5 years ago though.

Nuclear power plants are used to pump water back up Dams at night when they are producing an excess of energy that is not being used - basically using the Dams as a big battery, I believe this is what you are theorizing here and it will work - provided you can get solar cells efficient enough that there is excess energy left over that can be used to pump the water.

Theoretically - lets say your solar panel generated 2Mw of energy (thats a hell of a lot but its just a random number)

say 50% of this was used that leaves 1Mw

your pump is not likely to be more than say 50% efficient so thats 0.5Mw that is required. Your generator would then be say 50% efficient again, thats 0.25Mw - minus losses from the lines and any other parts involved lets call that 0.2Mw - thats 10% efficient.

One way of looking at it is over the course of a 10 hour period where the solar panels are just being used to store this water energy - you get 1 hour use when required.

Anyway, ill end my rant there - please note most of these figures are made up or approximations from memory - I like the idea though :)

There are other possible solutions such as using the panels to heat up some items that contain their energy for a long time, or for charging up simple battery cells - such as a prius battery - that should be enough to light your house for a night if your up surely?

rant over. Im late for work now :p

Alex

I know a scientist who's working on energy reclamation (specifically, recovering energy from wasted heat in smoke stacks). He says that the most promising current method of short-term energy storage is paraffin wax. Solar energy or any form of heat energy melts the wax, and energy can be reclaimed as the wax melts.

The Wikipedia entry on "Solar Energy" discusses wax briefly. I'm not entirely sure how long the wax takes to cool completely, but you I would imagine that a giant hunk of wax being heated all day would stay hot for quite a while...

Wax seems like a great solution because:
a - it's probably dirt cheap
b - it contains no moving parts
c - it lasts a very long time

I haven't really researched it in depth, but it's probably worth looking into.

Martin

Forget compressed air.
The efficiensi of compressed air is only a few percent.
run a compressor with 6kWh and you you could take out at most 600 Wh from a generator. you lose a shit lode of energy to heat.
And as for water i think it would be to bulky.

Rob Landley

Yeah, about the compressed air thing:

UT has been trying to find ways to store the energy from windmills and solar for years. (Austin has hippies and a big university. The reason we've got such a big software industry in this city in the first place is the hippies aggressively recruited software development companies back in the early 1980's because that industry doesn't pollute. Who knew there was _money_ in it? The money attracted republicans the way sugar attracts ants, and now we have toll roads everywhere. Oh well.)

Anyway, we've been doing alternative energy stuff here for decades, and they've tried a bunch of things to store electricity, or mitigate the need for it. (The biggest electricity user in the summer in texas is air conditioning, but they couldn't get the land to freeze a lake to run a cooling loop through downtown. The terrain around here's all wrong for it, and land prices are way too high.)

But one thing Texas _does_ have is old empty oil wells. And those are under granite around here, sealed airtight bedrock. (If it wasn't, the oil would have leaked up to the surface millions of years ago.)

So several years ago they put lots and lots of compressed air down one of these an old oil well, so they could let it out again to spin a turbine. And they forgot about Boyle's law: compressing the air squeezed all the heat out of it, and when it got really hot all the heat leached into the bedrock (50 degrees farenheit or so once you get a few hundred feet down). Then when they let the air out, as it expanded again it got cold. Really cold. In fact it turned liquid.

Somewhat disappointed when liquid air came out of their pilot hole. Couldn't spin the turbine with that. They ended up burning it 50/50 with natural gas in the pilot project to heat it back up to a gas to spin the turbine, but I haven't heard of them trying it again since.

Lifting water to store energy might work, but good luck finding enough water. (Heck, if you've got that much, electrolyze it to produce hydrogen and put it into a fuel cell to get the electricity back. Lots and lots of work going on that. Only problem is that water's turning into a limiting factor. No, you don't want to electrolyze salt water, chlorine gas is not much fun.)

Lyon

You wouldn't want to vaporize the water in order to elevate it, since that would take even more energy than simply pumping the water up would. Water has a higher specific heat than just about any substance. (specific heat is the amount of energy required to raise one gram of a substance one degree Centigrade). Plus you'd have to re-condense it afterwords.

Daniel Von Fange

We've got a pair pumped storage plants in my area:

http://www.duke-energy.com/power-plants/pumped-storage-hydro/bad-creek.asp

wkwillis

Graphite block. Carbon doesn't melt till 4000 degrees, you can run some of your solar cells (4000 degrees is infrared radiation that matches your solar cell pretty well) on the heat all night. Heat it up again in the morning. When all your solar cells are working.
You lose 80% of the power round trip, though.
Sometimes nuclear makes sense. Night is one of those times.

chat

Thanks

Nicevil

Space Based Solar Power FTW. :D

kls

Some good inputs, but and here's one more point of view - it's helpful to think about all the reasons you need to store energy at night.

To have hot water on tap? Why not heat some extra water during the daytime (like in a batch solar heater), effectively using the thermal mass of the water as energy storage?

For heating or air conditioning? After doing a proper job of insulation and isolation, can you heat or cool some other thermal mass during the day and release the energy as needed?

Those are usually the two biggies, and most the rest are lighting and electrical appliances, for which you need some non-solar source of nighttime energy, like wind or geothermal, or finally storage, like batteries, potential energy of elevated water or flywheels or compressed air.


burt

i wish i was as smart as most of you people...

its always sunny somewhere right? why not have everyone connected by a wire. or maybe train some gerbils. but seriously, nuclear energy is amazing. Everyone is talking about some miracle substance that produces an enormous amount of energy. why not this?

damn russians and their chernobyl

burt (clueless) trub

Mike D

Wow, Scott, you live a life isolated from reality, don't you?

geopax

If you are looking for efficient mechanical energy storage, why not consider a large flywheel? One or more high-mass, high-rpm flywheels with a low-friction mountings connected to motor/generators could store and release energy efficiently. They could take up less space than water reservoirs and would not be plagued with problems associated with pumping and storing water (corrosion, leaks, evaporation, etc.)

Jeremy Miles

No one seems to have mentioned this yet:
http://en.wikipedia.org/wiki/Pumped_storage

JimG

If you limit the discussion to household use, then how much power do you need anyway? A standard deep cycle lead acid (automobile) battery with an inverter would provide all of the lighting I would need from sunset to bedtime (except on party nights - then I might use candles anyway). If I didn't raid the refrigerator at night it could probably be off until morning. Refrigeration including AC are the two biggest power hogs for home use. Why not tackle the problem directly? Use intense insulation so that neither AC or refrigeration are required to consume power at night. At present, I'll still need about 10kW to comfortably air condition my house during the day plus use all of my "accessories". I would need to spend $15,000 to $30,000 and wouldn't get an even pay back for 10-15 years - not much of a motivator.

Albert

Why not chill a substance during they day and then use the thermoelectric effect to generate electricity at night?

Albert

Why not chill a substance during they day and then use the thermoelectric effect to generate electricity at night?

Dave

>I have the smartest readers in the world.

As far as I can tell, your readers are either hardcore leftists like yourself, and people who like to mock hardcore leftists.

The smartness of these people varies widely.

Joshua Jacobsen

Weird. When I looked up the average American Household Energy Consumption, I found the number to be 40 kwh per day. Everyone else seems to be using a number half as big. I forgot to take into account that it was only night-time hours that need to be accommodated by this type of energy storage... so... half an olympic pool 6 meters above a second.

Brad K.

It looks like the more height the better - but then you get into friction of the water against the side of the pipe, and turbulence effects on higher water speeds through the pipe to the turbine - which reduce efficiency and mean more water.

I remember that people that used solar power to pre-heat the water into the water tank saw the most savings. Combine your reservoir with solar to preheat (or vaporize water to be lifted?) water to be used for heating, and you might lower the kwatts needed enough to pay off.

The other thing to remember is that you wouldn't have to replace the entire day's electricity to pay off - even 20% would likely pay out in time. Plus, if you restrict clothes washing and drying to night time, and much of cooking, you can reduce your day time requirements further.

People worried about inefficient pumps and generators need to recall the premise - that we pump when when rates are low, and generate when rates go up. In 1998 west of Phoenix, the day rate from 9 am to 9pm was 14.4 cents/kwh, 4.4 cents at night. That kind of rate difference will cover a lot of inefficiency.

DWH

Forget the water,which evaporates and is becoming scarce.Just hook all your alternate energy sources to flywheels.

Josh Powell

One of the best things about solar is that it produces power when power is most needed, during the day. Most energy is consumed during the day, much less at night. Houses use very little power at night, so a very small battery system can easily supply that power, while excess electricity created during the day can be sold on the grid, offsetting any costs needed at night.

Another thing I've noticed when these questions come up is that people are always looking for a single energy solution, when multiple means could work better. For example, on cars why not have solar/plug in/gasoline/hydrogen/ethanol power. Car runs first on electricity generated from solar because it is the cheapest fuel and doesn't lose energy for storage, next it pulls energy from the battery where solar or plugin charges it. Next, it pulls energy from hydrogen because it is the next cleanest solution, and finally from ethanol/gasoline.

For houses it could mean a solar/hydrogen/wind/gravity/grid combination. I know, each one of these adds more cost to the equation, so pick your favorite three.

Basil

There are cheaper, cleaner, less complicated ways to store energy. If you're dead set on storing potential kinetic energy (as in with the pool), a flywheel is far more efficient. If you're willing to store electrical energy, you can either use batteries (like the ones in a hybrid) or capacitors (like in a loud car stereo system). Capacitors are becoming larger these days and might someday replace batteries, but they're not there yet. If you're looking to store thermal energy, there are heatsinks and heat exchangers.

The reason most of these are not commonly used in houses is because in the end, the energy has to come from somewhere, and we can't store energy efficiently for long.

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