Design compressed air energy storage for PV plant 3

[Ameen1985]

Hi All
For a PV project of 5 kW, we will use a CAES.
The preliminary design will consist of a compressor - 2 heat exchanger - Air receiver - air motor - generator - 2 water tanks as a thermal storage units to have an adiabatic systems.
For a 5 kW PV plant, an energy of 20 to 26 kWh is expected.
At this stage I don't have enough information about the components size and I want to start with the air tank size.
I want to study different sizes and different tank pressures which will accommodate a certain amount of energy.
Any help please?

 

[georgeverghese]

Storing compressed air vs compressed butane - higher flammability risk vs poorer cycle eff - engineers can find ways to manage and justify risks if they want to. There is perhaps only a few unit operations more risky than a HF alkylation unit in a crude refinery, and there are many of these around, even in places where they shouldnt be.

 

[MJCronin]

My suggestion:

If we can assume that a PV electric generation plant would only make economic sense in areas like the American Southwest, why not explore a matching 'Thermal Energy Storage" system ?. Chilled Water (or ice) can be stored for daily use in a large (nearby or remote) tank.

https://www.pge.com/includes/docs/pdfs/about/edusafety/training/pec/inforesource/thrmstor.pdf

https://www.districtenergy.org/High...tFileKey=6bd75989-da56-5cdb-e335-b53d2e97bfd1

There will probably be retired geezers living somewhere near the PV plant. Wrinklebutts have a massive need for Chilled Water to keep their Malls, hospitals, retirement homes etc cool. This is a growing need

Thermodynamically, this makes much more sense than suffering the inescapable efficiency losses of gas compression and expansion, but only detailed sizing and cost calculations will tell.

Anybody ???


MJCronin
Sr. Process Engineer

 

[georgeverghese]

Another way to generate chilled water from solar energy ( without exotic PV cells) would be with concentrated solar power acting as the heating medium in an ammonia absorption plant.
Anhydrous NH3 could also be the working medium in the Organic Rankine cycle - much less flammable too, but compression is less efficient than with C4.

 

[davefitz]

10 yrs ago there was a canadian patent for a CAES that maintains a fixed pressure during both discharge and charging by placing the PV ( bladder) below 400 ft of water.

20 yrs ago there were a few isreali designs that used storage in UG caves and variable speed compressors and turbines, but I did not retain any copies of that configuration.

25 yrs ago there was presented a method of fabricating in the field very large PV's ( 20 m dia) using ribbon wound pressure vessel fabrication methods ( china - Zhao) .

The point is, you can improve the efficiency of the cycle and the cost of fabrication if you avoid making some common assumptions.

"...when logic, and proportion, have fallen, sloppy dead..." Grace Slick

 

[Ameen1985]

Please @davefitz, if you could share some common assumptions to be avoided it will be great.

 

[davefitz]

Ameen;
In the above examples pulled from memory, the assumptions that were bypassed were (a) by using an underwater reservoir, the pressure can be maintained constant during both charging and discharging, so the varying pressure for a finite container is avoided (b) by using a VS turbine and compressor, the efficiency loss of using a constant speed machine discharging to a VP finite container is avoided, and (c) the limitations in size of the a PV ( due to shipping clearances and foundry limitations) is avoided by field fabrication, the cylinder is fabricated using (chinese) ribbon wound technology while the thick walled heads are field fabricated using russian thick weld technology. I think most technical advances are found by avoiding the unconcious assumptions built into the use of existing technology, yet obeying normal laws of physics and thermo.

"...when logic, and proportion, have fallen, sloppy dead..." Grace Slick

 

[LittleInch]

The common assumptions would be:

a) fixed volume of the receiver - if this is variable then the pressure can be maintained constant or less variable than a fioxed volume
b) can you actually either store heat and then return it or is it possible to compress and maintain the heat.
c) you need to make the Pressure vessel out of steel. There was some technology going around about use of GRE vessels for Compressed Natural Gas (CNG (not LNG) up to about 250-300 bar in large volumes so that you could ship much more easily than LNG - not seen any actually built, but CNG is a real thing in India where they pump up vessels over night at filling stations and then fuel cars and taxis with high pressure gas into tanks.

Remember - More details = better answers
Also: If you get a response it's polite to respond to it.

 

[goutam_freelance]

Another idea which is comparatively old is pumped storage although is a smaller version. Now a days micro-hydro-turbines are available which can give reasonable efficiency. You pump the water to a overhead tank from a ground level tank and when you require power you run in reverse through micro-hydro-turbine. Pumps can also be used as turbine. A rough calculation is given below for a 26 kWH storage. The economics can be worked out. This will be much safer than using high pressure vessels.

Engineers, think what we have done to the environment !

https://www.linkedin.com/in/goutam-das-59743b30/

 

[LittleInch]

A 30 m high 10m x 10 m water tower eh?

Nice and cheap....

Or rent the top floor of a high rise building.....

All for 20 kWh which I can buy for £3 / $4 a day....

Ameen - I think it is generally recognised that payback on a solar electric system to feed into the grid is about 7 to 10 years if you're getting a relatively small power tariff, but maybe a bit less if you manage to use a fair bit of the power yourself instead of buying it from the grid.

But unless you have no option, i.e. truly off grid, then energy storage the way you're trying to do it is a way to not see you money again for 20+ years.

It's your money, you can spend it like you want, but there is a reason everyone uses batteries. They work, they are very efficient, have a small footprint and don't blow up (might catch fire occasionally).

so what are your plans now?

Remember - More details = better answers
Also: If you get a response it's polite to respond to it.