DIY Doctor

How to build a potential energy battery ?

Postby yonatan » Thu Feb 21, 2019 9:04 pm

Hello,
I want to build a green energy storage system. Where an engine lifts a big mass with the electric energy that is available at the moment, i.e solar/wind/grid. Then release the mass from about 30m - 50m to create an electric energy. Was thinking to use gear transmission to control the speed of the system energy discharge and electric voltage.

will appreciate an advice on the following:
1. How to I calculate the potential electric energy using the height and mass.
2. I also want to be able to calculate the time of discharge VS gear transmission VS mass VS height.
2. any recommendation of a design and parts type to purchase (turbine, dynamo, engines, gear transmission set etc.) will be appreciated.

thanks!
yonatan
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Postby ericmark » Thu Feb 28, 2019 12:03 pm

I was surprised how little power was needed for a garden pond pump, and so how little would be generated by running water through a small turbine, and that is likely the easiest way to use potential energy.

The problem is be it lifting a weight or pumping water you need a minimum amount of energy to start with, so when we have an excess of x kW the pumps in electric mountain can pump the water back up, but the power was coming from two nuclear power stations which at that time could not alter power quickly.

Using the power reasonably easy, but putting the power into the unit is a problem, likely best option would be two pumps of different sizes giving three levels of power use, or a lead acid battery which stores the energy first then uses it to lift the weight, which raises the question why not just use a lead acid battery?

In the main we use heat to store energy, you can get sterling engines which will turn heat into motion, but only seen it done with central heating boilers and fans on solid fuel fires.

A Newton is near enough a 0.1 kilogram, so lifting a kilogram one meter is a 10 Joules so if you have some thing stored at top of house and drop it to bottom we will work on 5 meters so one kilogram = 50 Joules of energy, so let us consider 100 litres of water which weighs 100 kg and is size of standard cistern. So that's 5000 Joules so if that is drained through a hydraulic motor driving a generator with no losses to power lights in the house, say 100 watt of lighting, 5000/100 = 50 seconds so it would power the lights for 50 seconds.

Once you work this out you realise why it's not normally used as a energy store, electric mountain is I think still classed as worlds biggest battery, but the tesla battery is now getting close as a power bank to equalling it.

Other than an electric secondary cell the next best is likely latent heat of fusion of some selected salts, can't remember which salt is used (salt = killed acid) but with a melting temperature of around 60 degs C it can be used to store heat in a small area so it can be well insulated and store heat for a much longer time than water, it was used in the 60's and 70's but did not catch on.

Idea at the time was to store off peak electric to heat the house in a way where if not required it could be kept for weeks, unlike the bricks in a box which would not store the heat for over a day.

We do now use hot water instead of bricks, as this can be stored for a week in a well insulated tank, and can work both central heating and domestic hot water, however the problem is the space required and weight.

Again 70's there were some special council houses built in North Wales with a central room holding the bricks for off peak electric heating and fans to circulate heat only when required, I was told this system could store the energy for a week, however at that time we did not have double glazing so blowing air around the house resulted in blowing the air past the cold windows so a greater heat lost than with non blown air.

Once double glazing was fitted, the house was too hot, so never really worked.

There have been many attempts, including turning electric into hydrogen gas to be burnt latter, however we saw what happened to air ships using hydrogen gas.

And even today we have to assess the risk, when Richard Hammond crashed the electric sports car and it took 5 days to put out the fire, one has to ask if we had a pile up with electric cars on a motorway how would we deal with it? Those batteries are far too dangerous at the moment, be it high pressure steam and Richard Trevithick's bus, or Howard Hughes car, we realised steam on the road was not really safe and it was in the main only used on railways.

Through the ages we have seen the errors of rushing in with new ideas, Ronan Point flats with gas, and Grenfell Tower flats with insulation has shown the problems of rushing in, in both cases it was not just the loss of life with the accident, but also the problems in making many more blocks of flats safe.

And if a team of engineers missed the problems, what chance is there that you and me with see the dangers?
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