Artificial lake to store energy - just a crazy plan?

[CaptainPanic]

Ok, here's a lot of numbers. I'm sure you can all find comments. I am very interested to hear them.

 

My idea is to make an artificial lake with a water level that goes up and down to store energy. We need to smooth out the differences between electricity production and consumption when we want to use. I've always heard that it's economically not interesting, or perhaps not even technologically feasible.

 

I've done a simple back-of-the-envelope calculation to start some discussion. Please comment

 

The artificial lake

Area: 1 km2

10 meter deep (average), Total height = 10 meters

 

Total volume: 1000x1000x10 = 107 m3, or 1010 kg.

 

Height of the water = 10 meters max., but on average only 5.

 

Energy storage = m*g*h = 1010 * 9.81 * 5 = 500 GJ

 

Costs

 

100 kW electric engine = €10000,--

90 kW pump (connected to 90 kW electric engine) = €7200,-- to 10600,--

So: 100 kW pump+engine costs 10000 + 10600, let's keep it at € 20,000 .--

(So: a 1 MW pump costs 200,000.--

(source: DACE price list of equipment, not online, sorry)

 

1 ha of land in the Netherlands costs about € 37300,-- and prices are lower in the north. (it’s assumed that buying a piece of a lake and building a large dam around it is about the same price as the land).

 

(http://www.lei.dlo.nl/nl/content/agri-monitor/pdf/dec2002prijslandbouwgrond.pdf)

 

 

Dimensioning

 

Assuming that the storage should be for 2 hours, we can determine how much energy can be stored (and if this is reasonable).

 

500 GJ/ 2hr = 69 MW during 2 hours.

 

 

Total costs

1 km2 of land is 100*37300 = 3.73 million euro.

69 MW of pump capacity = 13.8 million euro

Total: 17.5 million euro.

 

Margin on electricity stored is:

3 cent / kWh = 8.33 euro / GJ - (this can be one of those major discussion points that never has a conclusion)

 

So for 500 GJ, this is € 4,150.-- per time.

 

 

Pay back time

Payback time of 20 years:

 

So, during these 20 years, the lake should be filled / emptied 4216 times to recover the investment of 17.5 million euro (interest and tax not included).

 

I have no idea about interest and tax, but let’s just double the costs: 35 million euro.

 

We need to fill the lake 8400 times. This is 1.15 times per day. If this would be used to smooth out for example solar energy (which has a peak and a no-production time about once a day, assuming that the sun keeps doing what it’s been doing for the last 5 billion years)… this seems to have potential.

 

Can anyone tell me if this is unrealistic? If the filling/emptying of the lake can take more time then less power can be stored, but those sources that can store are being served for a longer time. This reduces the need for pump capacity, making it all cheaper. Pumps are the big investment. Even in a densely populated country like the Netherlands, it seems like the land is not the main cost.

[insane_alien]

it already happens. and has been done for some decades.

 

http://en.wikipedia.org/wiki/Hydroelectric_energy_storage <some more on it.

 

earliest i can find so far is1929. only 79 years too late.

[CaptainPanic]

I know it is normal technology in areas with natural differences in height: hills and mountains. It doesn't happen in a completely flat country like mine (yet). I am trying to prove that you don't need a hill to store energy with this technology.

[insane_alien]

i'm not sure how you plan to make money of the lake itself. you's still need some form of energy production.

[CaptainPanic]

That's the 3 cent margin I want on each kWh.

 

kWh prices are between 11 and 20 cents in Europe. I am thinking that 3 cents would perhaps be acceptable for producers if they have to choose to shut down or sell at a price 3 cents lower than the market value.

 

I see many windturbines that are not working, and I can imagine that the owner wouldn't mind to let the turbine work even though there is no demand... temporary energy storage could buy this energy at a lower price and sell it during peak hours (for example between 18:00 and 20:00 in the evening).

 

Right now, the gas turbines can be switched on and off quite fast, and there is not a lot of wind and solar energy, so there is actually no problem at all, and no demand at all for any storage. But I hope that wind and solar will be increasing a lot in the (near) future.

[Mr Skeptic]

You may need twice the land if you intend to recycle the water. Actually building the height difference may be complicated for flat land, perhaps two lakes of different height?

 

Did you include the price of the dam in the price of the land?

 

Did you account for energy losses while pumping?

 

Also, the lake should be used for things like fish farming if possible to make extra money.

 

In any case, its definitely doable if someone is willing to pay enough for energy storage. However, it might not compare too well with a higher height difference but lower volume method.

[swansont]

Also, the lake should be used for things like fish farming if possible to make extra money.

 

In any case, its definitely doable if someone is willing to pay enough for energy storage. However, it might not compare too well with a higher height difference but lower volume method.

 

Fish are probably not going to fly, as it were, if you come close to draining the lake. They also don't react well with turbines.

 

Energy differential can be quite high in the right locations. Pump at night, drain during the day.

 

As to the OP, I'm not sure that 10m is sufficient; there will be pressure requirements to turn the turbine, and there will be flow energy at the end, so you won't extract all of potential energy from the water. As Mr Skeptic points out here, a larger h gives more energy, so if the losses are a fixed value, you become more efficient as h goes up.

[Sayonara]

Fish are probably not going to fly, as it were, if you come close to draining the lake. They also don't react well with turbines.

To be fair though, these problems are easily overcome.

[insane_alien]

yes, a filter on the back of the turbine and a truck waiting to go to a birdseye fish finger plant would make everything shiny again.

[gcol]

As to the OP, I'm not sure that 10m is sufficient; there will be pressure requirements to turn the turbine, and there will be flow energy at the end, so you won't extract all of potential energy from the water.

 

So why not back to simple technology? An old-fashioned waterwheel will efficiently work with low heads, relies on volume/weight, not velocity difference, and although would be larger, would surely be long lasting and reliable.

[swansont]

So why not back to simple technology? An old-fashioned waterwheel will efficiently work with low heads, relies on volume/weight, not velocity difference, and although would be larger, would surely be long lasting and reliable.

 

Sure. It depends on what geometry is available to you.

[CaptainPanic]

About the price of the land: I think the best way would be to make 1 part where the water level goes up, and one where it goes down. Then you do have a max. 20 meter water level difference in the middle, but the length of the dam (which is more costly) can be minimized.

 

I was assuming to use existing lakes, and to build a dam around them. To be honest, I simply assumed that the price of the land is roughly equal to the price of a lake with newly built dams. The reason I assumed this is that a large portion of the land in the Netherlands is actually reclaimed land, and it was a lake before. Therefore, a piece of lake with dams imho should not be more expensive.

 

Regarding fish, sorry, haven't thought of them. Perhaps with some filters (fine nets) you can save them, and make some extra money from growing fish? This might turn into "growing seagulls" pretty soon though.

 

Regarding pumps/turbines. You're right, I should take an efficiency into the equation. I would assume 80 or 90% efficiency. So, between 64 and 81% efficiency in total (water goes through twice). I don't see any problems with the low head requirements.

 

Thanks for all replies.

[alan2here]

In england it is disappointingly flat. However we store water at height in water towers.

http://www.fingalcoco.ie/media/Media,8367,en.jpg

 

Most of them look different from each other however they are usually bizarre looking.