Energy Storage - The Key to Renewable Energy?

Now, I'm not that familiar with the units of 'specific heat' and so forth and would like to see the calculations you guys and girls can come up with.

http://cr4.globalspec.com/thread/26331#comment277006

Regards JD.

Sounds workable to me. Over here in the US, we already use geothermal heat pumps. An aquifer maintains a year-round temperature of perhaps 10 degrees C. In summer when the temperature is 25 degrees C, the aquifer makes a much more efficient heat sink than the 25 C air and saves on air conditioning costs. In winter when it is -25 C, a heat pump can still extract heat from the 10 degree water.

With your idea, a storage system with high enough temperatures to run an ORC generator might not be practical on a single house scale. Figure the surface area of the tank, the R value of the insulation, and the temperature differential, and you can calculate the losses over time. The volume of a storage vessel increases geometrically while the surface area increases linearly- that's why whales are as big as they are- thermal efficiency. So the bigger the tank, the lower the losses per liter. As far as insulation goes, a foot or two of plain old compressed fiberglass would be fine- the more insulation, the better the efficiency, so figure that into the long term capital cost.

A landfill would be a perfect site for one of these systems. Bury the tank in the landfill, and the thermophillic reactions (same reason a compost pile gets hot) will reduce the temperature gradient. Burn the flare gas in a boiler and heat the water in the tank. On top of the landfill is a good spot for low-tech solar collectors, too- surprising how much heat you can get out of a black plastic pipe suspended 1 cm above a sheet of white plastic and covered with clear plastic.

Using refrigerant instead of water as a thermal fluid will allow the hot water in the tank to yield electrical or mechanical energy as well as thermal- this system is already being used for low-temp geothermal power. It can be operated in reverse to take the lower temperatures of the solar collectors and heat the tank to 100 C. On peak demand, cut the gas flare heat over to the ORC generators temporarily, then go back to heating water when demand drops. A million litres of water can store a lot of energy- that's 4180 joules per degree c per liter, plus at 100 c you can store 2,260,000 joules per liter before it boils.

Good luck with your idea.

I had tackled this when I still had disposable income and a house I could theoretically experiment on

But while there are efficiencies to be gained "going bigger", what you actually need for sizing this thing is the general period that evacuated solar water heating tubes are not effective. So the number of days you cannot collect solar. You'll be surprised how few.

So in New Mexico (yes it not only gets cold - it snows) our average "coast period" was less than three days. So awful and overcast we couldn't collect solar.

Now, part of this mandates evacuated solar tubes, which aren't cheap, but are stunningly efficient.

Some of this is available from whomever signs your local building permits / zoning authority / or even heating professionals.

You need to know "insolation? days" which are mapped world-wide and available from solar resources on the web.

You need to know what in the US they refer to as the "Design Temperature" which is very localized (so off to the zoning office), and indicates the temperature equivalent of the 100 year flood for temperature. It is that 90th percentile cold temp reflected in your area.

And then as part of the mechanical design you will need some reflection of the snow loading - so grab this at zoning, too.

Then once you have heated your house, how to get energy out of the excess you have stored? Gotta tell you I hadn't cracked this one. I wanted a Sterling engine, but the only commercially produced ones are going to the desert for years to come, and they haven't even projected a consumer price.

So I'll go back to lurking and see what the community can come up with.

Hi Edignan

Thanks for your comprehensive reply! As for the recovery of energy out of my storage tank, I thought of using an Organic Rankine Cycle system - essentially a heat pump - which does require power input to run, but is capable of shovelling the heat out of the storage fluid with ease.

Meanwhile I came across an article about a franchise supermarket store owner, who uses hot water pumped into deep well drilling holes to store energy.

The heat is the excess temperature produced by his aircon and refrigeration units. the heat stored in the underground water ( it's not even in a tank!) serves to heat the store for the whole winter. Seeing that the shop is in Germany, we are looking at least at 4 months of heating requirement. I could not find out, how much hot water they pump down into the well, and how the water is kept there.

An ORC system doesn't necessarily require external power. If your heat source is hot enough to boil the thermal fluid (refrigerant, in the case of low-temp heat extraction) in the evaporator, it can drive a turbine to provide output power and run its own compressor. Like a Stirling engine, you do need a heat sink to dump the heat from the condenser (such as the atmosphere.) The greater the temperature differential between the heat source and the heat sink, the more power available. Chena Hot Springs Resort in Alaska converted from diesel generators to low-temp geothermal power.

The biggest problem in changing the typical home heating installation is the level of knowledge of the installers.

They don't want these complex systems. Just put a gas/oil burner and traditional central heating system and you're done.

In theory an underfloor heating system already safes approximately 10%, just by reducing the water temperature. But typically an installer doesn't understand this and will put the temp higher and adds a reducer/mixing valve (you need hot water from the tap, so you need the high water temp level)

What you need is controllers and decent programming, ask this from Joe the Plumber.

In theory a normal home could be heat supplied with 60.000 liter of water and a delta between 70 and 30°C.

You will need a heat pump to generate the hot potable water.

But if you play it a bit more intelligent you can replenish the vault as soon as wind is blowing or the sun shines.

Again this is a mixture of techniques which can only be managed by engineers.

Another technique which can be used is latent energy storage: a paraffin which melts at 64°C stores the heat of the solar panels and gives it back at the constant solidification temperature. Different types of paraffin can be used to maintain different levels of heat.

There even exist systems to keep the mobile phone stations cool: store the heat in melting paraffin and re-use this during the night to keep the panel at the wanted temperature. as soon as the day starts the excess heat is than rapidly exchanged with the still cool surrounding air.

But these systems are more expensive than traditional air conditioners (at least to buy it initially) so you seldom see it installed.

So it is simple: money keeps the whole world from using intelligent systems.

But it is not so far away in history that Joe the Plumber was convinced that insulation was thrown away money.

Give me the basis to experiment a bit and I will build you a system which can turn each home into a passive House, without the special architectural jokes. (but adequately insulated)

First off, water is a very good choice look at the table of specific heat capacities further down this Wiki article: water has the highest specific heat capacity per unit volume of any known substance.

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

And in response to the pump the water to a higher reservoir camp, do the sums: you have to lift (pump) 420 litres of water 50 metres to store the same amount of energy as heating 1 litre of water by 50 degrees C.

But why stick at a hot water reservoir, if you use a Vertical Axis Wind Turbine (VAWT) to directly drive a compressor you can simultaneously heat and cool two tanks of water. Most energy used in a modern home is used in either heating or cooling: you can use the hot water and cold water almost directly via heat exchangers to do this.

There is one thing better than the specific heat capacity of water, and, that's the specific latent heat of fusion of various substances. You can considerably reduce the size of the required tanks by using some of these. On the cold side use a tank filled with salt water but mostly filled with flexible containers (polypins/wine containers) full of water/ice. On the hot side fill the tank with ordinary water, but, take up most of the volume with flexible containers full of paraffin liquid/wax.

The one problem here is that you will have to get your ORC (for the electrical requirements) to work on a temperature differential of 0°C to between about 60 and 80°C (depending on the paraffin you choose).

I totally understand the perspective, and not to 'protect' the auto industry, but we are comparing apples and oranges.

In the 40 years, our vechicles weigh less, (my full size station wagon that I could put a full size sheet of plywood down flat in, totally inside, and it fit BEHIND the drivers area) weighed considerbly more than my current 2001 Ford Ranger. My ford ranger cannot carry a sheet of plywood flat in its bed, and the box is the long box and is about 2' short to be able to put it in the box. The station wagon had a 318cu in inch V8, and got about 20 to 25 MPG. The Ford Ranger gets about 30MPG (measured). The wagon could cruse all day above 100MPH, and the Ranger can't hit but 70 going down hill with a tail wind. It also has a small, Hitachai, engine.

I am sure the 1963 Dodge 440 model station wagon was MUCH worse on polution than the Ranger is. It could also carry 6 people with ease and a lot of camping gear. My Ranger carries 2. The Dodge wagon had a PVC valve but that was it, no catilytic converters or anything.

Your Subaru is 'full time 4 wheel drive', with the latest polution controls, and may or may not have a larger engine than the Fiat your Dad had. His had NO polution controls. Your Subaru propbably has fuel injection, and your Dads was carburated. He NEEDED to change oil every 3K miles, and you can go 7K (by most mfgrs specs), but I would not do it if I wanted to keep the vehicle running).

After working around the 'oil patch' I know the fuels are different. No lead now days, the fuel is 'cracked finer' and more of the 'light aeromatic hydrocarbons' are removed (because they can be sold as other products for more $$, and you will not know or ususally care). Your new vechicle has thinner metal and more light weight construction and plastic than the Fiat.

Safety issues have also changed the construction (and cost) of vehicles.

...

And then are we comparing needs or wants. Do we NEED as much transportation as we use? Do we make decisions to use it whether we need it or not?k

I can't figure it all out. ... I used to like getting a full tank, and heading out to 'explore the back roads with my honey or family. We don't do that anymore.

...

Our society has changed, and our vehicles have too.

IF someone figures out a really better way, I am all for it. We can then look back on ICU as specialty engines like we see steam today.

I want batteries that last the life of my vehicle, make it weigh the same or less, need recharging only every 300 miles, the car has charging cells built into the structure to reduce (not necessarially eliminate) the need for external charging. Have public 'charge stations' that charge by the columb of charge with micro-payments, and the stations can be ubiquitous. (have parking spots with inductive coils in given 'charging spots', and card/coin operated payments). ... I want the car to be crashworthy when run up against other vehicles AND trucks. ... I wouldn't mind a battery car with a 'single wheel trailer' that carries a propane tank and small ICU that runs a generator to charge the batteries on the cars command for long distance runs.

I want a better system than we have using trucks for long distance travel. Containers are much cheaper to move, even if trucks do the 'last miles'. How about having non-long distanct trucks convert to propane or cng (compressed natural gas). Even doing that with cars would save lots of wear on the ICUs today.

... And then even if these products exist, 'will the buyers come'? I like the philippines answer. If your car is over X years old, pay a tax annyally or turn it in to be crushed. After Y years the tax rate goes up by an order of magnitude, until all that is left is 'show cars' and 'antiques', which could be un-taxed if they are driven under 100 miles a year (or pick a number).

... enough of solving the worlds problems. ... back to surfing the net' :)

Well....

I recently (this decade) went digging in to figure out the mysteries of manifold fuel injection.

I see why manufacturers liked it.

Rather than drill two holes in the combustion chamber and actually meter fuel to the cylinder - they came up with the fuel rail and manifold injection. All made of plastic and firing an entire bank on a single pulse.

So a left / right firing (squirting?) sequence for my V6, and use the intake as a bucket where the fuel will wait until the valve opens.

Cheap, simple, hard to screw up - yet they DO get better mileage. Than the previous carbureted model.

I had an '84 Honda Accord which got 40 miles/gallon. The new accords get in the mid 20's. So much for advancement...

Hello,

I think you will find the following article informative. I have been very interested in this same concept for a number of years. There are a number of articles on the Internet regarding these installations in Germany.

http://www.solites.de/download/06-Eurosun.pdf

John