compressed air to run 2000w petrol generator

[almac]

instead of batteries to store solar power how about running an air compressor during the day then discharging this compressed air through the air intake of a 4 stroke petrol generator to drive the engine . would this be better than battery storage? not worrying about the heat loss during the compression, too technical

[emartin00]

It would be far less efficient than batteries, that's for sure. A generator isn't designed to run on air, and probably wouldn't run that well.
Utilities do use compressed air storage in some areas, where there a large underground caverns to store air. But it's not very efficient even with specifically designed equipment.

[Robert1234]

I suspect that would be one pretty big air tank for a home system.

[SunEagle]

Compressed air is one way to store energy but it is certainly not anywhere being efficient or most practical due to the space needed and maintenance required to keep the system working.

[J.P.M.]

I suspect that would be one pretty big air tank for a home system.

+1. Think of something about the same size as the home.

[peakbagger]

That approach has been proposed for gas turbines. About 1/3rd of the power going into a gas turbine goes to compressor section to compress the incoming air. Compressed air would be stored in underground salt domes during off peak and then injected downstream of the compressor section near the combustor so that the turbine puts out a lot more power compared to conventional version. There is additional benefit in that the air stored underground is lot cooler and therefore denser.

Compressed air has lousy power density, a compressor is not very efficient in converting power to compressed air or used as an expander so the overall wire to wire efficiency is poor. The only way it works is to scale it up to point where salt domes can be used to store huge volumes of air.

[Sunking]

Nothing new about the idea and already been done long ago. There was even a car made to run on compressed air. Navy torpedo use to run on compressed air, and just about every jet engine is started on compressed air.

Just like converting water to hydrogen to store energy has all failed. Sure it physically works, but once you look at the efficiency fails miserably. Been a long time since I looked at the conversion numbers, but you are looking at 10's for efficiency. Means you burn 10 gallons of fuel to get 1 gallon of energy. Piss Poor conversion and the reason why there are no commercial units out.

[ButchDeal]

WWII Submarine engines (diesel electric boats) start their big engines on compressed air.
Some old planes used to use shot gun shells to start radial engines (with no shot of course).

[SunEagle]

Ah the kinetic kick start option. I remember seeing that.

[almac]

so the heat loss during the compression is most of the energy? , so to make this efficient there needs to be heat capture during the compression stage, and heat returned during the decompression stage.

[ButchDeal]

so the heat loss during the compression is most of the energy? , so to make this efficient there needs to be heat capture during the compression stage, and heat returned during the decompression stage.

yeah thats trivial.
and then there is the low storage power of the compressed air. according to this page https://en.wikipedia.org/wiki/Compressed_air_car , about 50Wh per liter of compressed air at 4,500psi (which is a lot of pressure).

Would be a lot simpler, more efficient and practical to just split water to hydrogen and oxygen, then run your generator on that at night.

[J.P.M.]

so the heat loss during the compression is most of the energy? , so to make this efficient there needs to be heat capture during the compression stage, and heat returned during the decompression stage.

The heat of compression is removed and usually rejected by intercoolers for multistage compressors and aftercoolers for all compressors. The gas is then stored at something closer to ambient temp. the compressed gas is then cooled, usually when expanded either in a thermodynamic cycle (and work extracted), or a throttling process (unrestrained expansion). Otherwise, the storage tanks and to a lesser extent the piping in compressed air systems would need to be larger and also more robust. Additionally, inter/aftercooling removes moisture that would otherwise accumulate in the system and/or cause problems.

[SunEagle]

yeah thats trivial.
and then there is the low storage power of the compressed air. according to this page https://en.wikipedia.org/wiki/Compressed_air_car , about 50Wh per liter of compressed air at 4,500psi (which is a lot of pressure).

Would be a lot simpler, more efficient and practical to just split water to hydrogen and oxygen, then run your generator on that at night.

The surprising thing, is that even with the low efficiency of using compressed air I read somewhere that they are going to build a 1200MW CAES up in Delta Utah next to an existing coal powered generating plant that will soon be retired. The plan is to use wind power out of Wyoming and the HV distribution lines that are already in place.

[Bala]

You cant just put air into the intake of an engine, so you would need to replace the petrol engine with an air motor that has a governor that will run at 3000rpm. You will also need a 5hp motor to run a high pressure air compressor. So work out the logic of how much solar you need to run a 5hp electric motor long enough to compress enough air to run a 5hp air motor for any given length of time.

[Sunking]

You cant just put air into the intake of an engine, so you would need to replace the petrol engine with an air motor that has a governor that will run at 3000rpm. You will also need a 5hp motor to run a high pressure air compressor. So work out the logic of how much solar you need to run a 5hp electric motor long enough to compress enough air to run a 5hp air motor for any given length of time.

Thus is why is an exercise in futility. That is why Air Powered cars went bankrupt before they went on sale. Pretty stupid if you know one gallon of gasoline in an ICE gets you down the road 30 miles, or that same gallon of gas used to compress air only gets you 3 miles down the road. Once you understand that then you are no longer call yourself Dan.

[J.P.M.]

Compressed air systems are among the least efficient methods to provide motive power to anything. That was OK when energy was cheap, with the energy used to compress the air being removed during interstage or aftercooling cooling and either recovered for use as heat (not often), or simply rejected.

Most of the energy used to compress the air is already relatively low entropy shaft mechanical energy (work) input at the compressor, with that energy already coming from probably some fossil, nuclear or renewable (hydro ?) source. The idea of compressing air is usually done in industrial applications where the medium (compressed air) has the advantageous property of being able to transport the energy of compression in the gas over relatively short distances through pipelines, say in an industrial plant, and then having that available energy that was added at compression extracted at some other location by expansion in, say a tool of some sort - maybe even a device that will extract shaft work - i.e. a compressor in reverse (but not in a reversible cycle of course).

Compressing air (or other gasses) is a way of transporting power (or storing energy) that increases entropy more than a lot of other, and most common ways to get the job done. There is a relatively large segment of American industry that grew up and thrived on making equipment that compressed air for such uses in the days of cheap energy and when there was less concern for the environment. That segment is now trying to readjust itself to the new realities of not so cheap energy and more environmental awareness, regardless of the validity of those realities.

[Sunking]

JPM compressed air machines are stil in use today and will be tomorrow. How many mechanics are going to give up Air Powered Tools, Artist give up Air Brushes, Euro Adults and US Kids giving up Air Riffles, Navy giving up on catapults (OK that is steam) or Aerospace giving up jet engine starters. You know what I am saying; air powered machines have their place and will be around forever. Good lesson in Potential Energy efficiency.