Excess Solar Energy Storage As Compressed Air

Dear All,
Please suggest me some tips for Excess Solar Energy Storage:
I have installed Solar Power system at my home which has the following details:
PV Modules Installed capacity= 2.160KW (08modules with 270Watt/panel)
Off/On grid Inverter (Has multiple functions including Net-metering option) = 3.5KW
Deep Cycle Batteries= 04 (120Amp each)
Average Energy consumption (Load) = 15KWH (60% of this is used at night-from Grid)
Net-metering option is not available in our area. What I am asking here, Can I store excess Solar Energy as compressed air during the day time and use it at night?
What will be the compressor specifications/type for providing 9KWH during night hours?
How it can be coupled with an A.C. generator?
Is there any system already in market that meets my set-up demand?
Batteries cost is higher if we take into consideration the replacement within 20 years(approximately 05-06 times)

Hi Sohaib;  Welcome to Permies.

I see that you are using 8, 270 watt panels ,That is  a very respectable sized solar aray.  But you are only using 4 120 amp hr battery's. This seems like a very small battery bank for the masive solar charge you are produsing. Are you dumping excess power when the sun is shining ? If you are, then you need larger battery's.
The battery's are the heart of a solar system. Bigger batterys mean more solar power stored to use at night.

On to your question.  Compressing air to spin an alternator/ generator would work (I think) But I believe the storage capacity of compressed air to run more than a short time would require  Huge tanks next to your home. I think that cost wise and logistically this would be hard to implement.

In my opinion , by incresing your battery capacity  2 or 3 times your current size. You would store enough power during the day to hardly need grid power in the night.

A good friend and innovative creator put an air compressor on top of of a 60 foot tower attached through an old VW Micro-bus  trans-axle he's got a five blade wind turbine. For storage he's buried several large propane tanks nearby. He has an extensive workshop which runs off compressed air. This is probably the best use of compressed air as storage I have seen.  Those propane tanks can usually be bought cheap from Propane companies as they lose the tanks  accreditation.
Brian  

Hi Brian;  Your friends set up sounds really cool!  Any chance you could get some photos and detailed info and share it in a post here at Permies???
I suspect your friend has some very large tanks buried to run his shop.

If you have a bit of slope on your property then two water tanks, a solar pump going up, and a micro hydro set up on the down hill will allow you to store excess solar energy as potential energy in the form of water. I don't know anything about air compression but it seems like moving and storing water would be cheaper and easier than compressed air. Although Brian's friend's set up sounds really cool, especially if you have a use for lots of compressed air.

Sohaib Naqvi wrote:Dear All,
Please suggest me some tips for Excess Solar Energy Storage:
I have installed Solar Power system at my home which has the following details:
PV Modules Installed capacity= 2.160KW (08modules with 270Watt/panel)
Off/On grid Inverter (Has multiple functions including Net-metering option) = 3.5KW
Deep Cycle Batteries= 04 (120Amp each)
Average Energy consumption (Load) = 15KWH (60% of this is used at night-from Grid)
Net-metering option is not available in our area. What I am asking here, Can I store excess Solar Energy as compressed air during the day time and use it at night?
What will be the compressor specifications/type for providing 9KWH during night hours?
How it can be coupled with an A.C. generator?
Is there any system already in market that meets my set-up demand?
Batteries cost is higher if we take into consideration the replacement within 20 years(approximately 05-06 times)

You could heat water and reduce the energy requirement from other sources.

You could tie a heat pump to it.

You could drive a deep freezer to sub zero when there is excess and allow the normal operation when using the grid or battery.

Food deyhdrator or freeze dryer, rock tumblers, etc.

Automation with square d remote breakers is straight forward from the relay in your controller or a voltage triggered relay control.

Most of these except heating water would likely be a larger outlay in cash than adding to your battery.
Even then, the battery would find itself full and have power to spare at times.

Heating and or cooling space, domestic water or other process heat (food dehydrator, etc.) Is a great sink for excess solar production.

As I understand it and from what I recall larger scale projects can get decent efficiency because they are able to harness the heat losses of compressing the air. Smaller scale projects have the problem that there isn't enough heat to be really useful to gather, but enough energy lost to make inefficient compared to other storage methods. It's kind of a toss up all around on troubleshooting and maintenance as they all have their gotchas chemical, electronics, lubrication or outright replacement.

With that said, when I looked into this before, I convinced myself that an air compressor (scroll or piston)wind turbine for an input and a Tesla turbine for output to permanent magnet alternator would be the way to go. Unfortunately this is quite a ways down on my have time to try list.

If I had an excess of PV power I'd likely pursue storage of hot water if for some reason more battery storage was not possible.

Does anyone have a handy dandy table that would compare storage efficiency methods?

Sohaib,

Arrrgh!! So what to do with excess electricity.  Since you are asking the question I assume you also imply that you are trying to save that electricity as effectively as possible, meaning that you want to recover as much of that saved energy as possible.

The short answer is yes, you could store that power as compressed air.  I don’t know much of that energy could be recovered but it could be done.  Other alternatives include pumped hydro or even a spinning flywheel.

My personal best guess for best energy storage would be into batteries.  As a rule, the fewer steps the energy has to go through the better.  You will lose energy at each conversation.  For instance, if you go the compressed air route, your will lose energy converting to 120v ac power, mechanically running the compressor and oddly enough, you will lose some that is converted to heat.  On the return side, you will lose energy in piping and fittings, on the mechanical side again, and electrically converting to the correct voltage, etc.

I don’t want to be a real downer, because this could be an option, but my guess is that you will lose a lot of that energy to inefficiencies.  My personal best guess is that storage directly to battery offers the best efficiency for homeowner sized options.

All of this is just my personal thinking, so take it with a grain of salt.  I do wish you the best of luck on your endeavor and please keep us updated on your future progress.

Eric

Lots of good ideas. What about looking at the entire house or dwelling as storage. The entire house as a integrated system. For a look at what one electrical engineer would do if he wanted to rethink solar and integrate it into many facets of home design check out www.electrodacus.com. If I was to start all over with solar and home design I would consider these options.
Solar panels are at a subsidized low cost presently. I’m curious to see what will happen in the next few years. And batteries of course. These factors all play into the design.
I have NO affiliation with Electrodacus. The schematics and codes are all open source. Actually I’ve noticed some similarities to Paul’s use of crowdfunding and a educational aspect.
 

Eric
I highly appreciate your response and concerns regarding energy losses...but still figuring how to utilize this energy...a storage cum electricity generation system with an efficiency of 30% will also be feasible since part of the energy that will be stored is in excess amount...if i dont' store it, it is a waste...

Thanks again for your valuable comments and suggestions...

Frank li,

Thanks for you suggestion but unfortunately i live in an area which has moderate climate throughout the year...i am from pakistan...where it is a great potential for solar...however in my area warm water is not a necessity...we need it only in two month...i.e. Dec & Jan...

Thanks Jeremy

Stephen Iowe,

I have considered this option and have worked with detail...but all goes in vain when i found that large tanks will be needed to run this system work...I live in a house 25ft x 45ft with a maximum height of 45ft...Space is an issue and you cannot cross the boundaries in this well managed housing society...

Brian Rodgers,

Please share pics and detail of your good friend...it might give me some clues...Thanks in anticipation...

Sohaib,

Actually I kinda like your line of thinking—save whatever you possibly can, even recognizing that some losses will be inevitable.  So while yes, you could store excess energy as compressed air, I would want to compare that to other storage methods first.

Out of curiosity, why your interest in compressed air?  It certainly can be done and in fact is done with some renewables when they generate an excess.  My personal understanding (and I don’t know this for fact, so if someone has numbers to back themselves up, I defer) is that this can work for really large scale better than small scale.  The reason for this is that as the compression chamber empties, the velocity/pressure of the escaping air drops, not unlike an older battery getting near the end of its life.  Would your plan be to store the air in a compressor and then release the air through some turbine connected to an alternator?  This would be quite the setup and I would love to see it in action.


As an alternative,I personally would consider pumped hydro where you pump water up a hill and then recover by a turbine connected to a alternator.

How every, as I stated earlier, the more changes the energy goes through, the worse the efficiency.  With that in mind, why not just store the excess energy in a decent battery?  If you are wanting to be inventive and do it yourself I completely understand.

By all means though, please keep us updated and informed.  This sounds like a really interesting project and I would love to see where it goes from here.

Eric

The Amish have been doing this for years, they use them to run fans.     I heard of one buying a railroad car tank.   They used this with compressed air.


The more I think about it, an engine that ran off of wood gas with one of these compressors could store a tremendous amount of energy.


I have been looking into high pressure tanks like 1000 psi.     With these you could store lots of energy in a portable space.     Carbon fiber tanks are great for storing this energy, I know in Europe they run cars with this method.

Here are two excellent articles online from LowTechMagazine:


Ditch the Batteries: Off-Grid Compressed Air Energy Storage
https://www.lowtechmagazine.com/2018/05/ditch-the-batteries-off-the-grid-compressed-air-energy-storage.html



History and Future of the Compressed Air Economy
https://www.lowtechmagazine.com/2018/05/ditch-the-batteries-off-the-grid-compressed-air-energy-storage.html

It sounds possible that your season of needing to cool your house will coincide with the sub-continent's hot dry summer of May and June, which are also the times of year when the sun is at it's highest, strongest, and longest daylight. So using excess to cool your house might be suitable. The more thermal mass you have in your house, the more stable the temperature will remain, for example, if you cool the house more in the daytime when there is excess solar power, and then turn off the electric cooling system at night.