Microgrid! the Backyard Pneumatic Grid Project





Intro: Microgrid! the Backyard Pneumatic Grid Project

The pneumatic grid project is an attempt to transmit and use energy from small unreliable intermittent renewable energy sources using low pressure air in tubing to transmit the energy instead of electricity in wires. It is now functioning but it is still a work in progress. The project has many parts, it can now work easily from a solar panel or from harnessing a little stream or brook but I want it to work from wind power too. I would love it if it could work from a Stirling engine from solar heat but I don't know how to build one.

I began the project on August 11th 2012 using a small mains electric bubble pump for an aquarium and the energy was used to run a "pallet garden". My version of a pallet garden is just a pallet of soil with a waterproof membrane under it, it drains into a bucket and it has water cycling, kind of like in hydroponics. It worked "imperfectly" but good enough that I expanded it.

In the last couple of years, I have demonstrated bubbling fountains ran by air, a system to capture heat from a solar heated wall and transfer it to grow beds, a system to filter water in a fish pond (that one still needs a lot of work) and even a bird scare ran by air!

Now I have 2 little "boat gardens" and 5 pallet gardens and my greenhouse also has water cycling. And it is now powered by 2 solar panels at opposite ends of the property attached to 2 little solar powered air pumps. It is a true "microgrid"! (Multi use end points and power generated in multiple areas).

Step 1: Why Pneumatic? Why Not an Electrical Microgrid?

The fundamental problem with electrical energy is that when you scale down production size, in a hydropower or wind power installation, you quickly reach a point where the electricity produced per year does not pay for the cost or "rental" of the machinery. It is a rule of economics that the production must cover interest on the loan for the buying of the machinery. This means that small rivers near where I lived that powered waterwheels for over a thousand years suddenly became "uneconomical" only 60 years ago! So we have a weird problem, we have disqualified huge quantities of energy from the energy economy because one modern way of using it is "uneconomical". But the Greeks and Romans were using this power 2000 years ago. Isn't it a shame to waste it? I like to challenge myself so I went to the other extreme completely! Why not use energy so tiny that it has NEVER been used before? In 1983, I wanted to water my garden in Ireland, it was right by a little stream but there was almost no "head" and very little flow in the stream. How small? 8 inches head (20 cm) and about 250 liters per minute of flow and I was only using part of that flow! I was good at science, knew there was enough energy there and just had the idea that it could be done and it should be done. But it was really tough, ram pumps looked promising but we had ducks and muddy water and my lack of mechanical skills meant they never worked properly for more than an hour.

I also had an idea for a suction pump and it took 4 to 5 years from concept to working model. But I had no plastic containers that would not collapse with the suction. A Segway to compression meant that it ended up completely different than I had expected. Eventually, I re-invented the trompe and used it to compress air. Combining mini trompe with mini airlift pump, and I had the "Pulser Pump". And it worked. And there was one beautiful thing about it. It had no moving parts. But it was very small and it only did one thing, it pumped water from the stream.

Step 2: Getting the Pulser Pump to Do More! Hint, Just Use It As a Trompe to Compress Air!

The pulser pump is pretty limited. My best one went 2.4 meters deep and pumped water to 3 to 5 meters high and it was not very efficient. Its best effort was only around 10% efficient pumping water. If you ignored water pumping and just had the trompe compress air, something like 33% efficiency was possible in the half meter head, 300 liters per minute water flow situation and compressing to about 2.4 meters of water head. That may sound puny but for a half meter head, compressed by a "machine" with no moving parts, it is not bad at all. So I turned to demonstrating that this air could do useful work. First thing was aerating animal slurry. In a farm situation un aerated animal slurry is potentially deadly. So I demonstrated that bubbling the air down in it could generate a current and could move it around and break the crust on top. I also washed silt out of sand (for building and concrete work) with it and several other things too. I washed clay off of root vegetables just by dumping them in a container and bubbling the air into the water around them. I even washed clothes!

Step 3: 1998 to 2008 Hiatus and Windowfarms

Nobody was interested in the pulser pump so I let it die. I moved to a small city in Canada and decided to put it on the internet so that other people could use it. Some people used it and demonstrated it in Europe, Asia and North America and it gradually became "popular" more as a concept than a real thing. Windowfarms came along (vertical hydroponics that was watered by airlift pumps with the air supplied by cheap aquarium bubble pumps), and I joined because I am "relatively speaking" an airlift pump expert and I made them a new airlift pump design.

My T-Joint airlift pump was very popular in the Windowfarms community and people soon used it all over the world. I also helped them by demonstrating how to use one airpump to power several vertical windowfarm units. As a learning experience this greatly helped in designing the pneumatic grid.

I never had much faith in hydroponics but liked the idea of watering soil gardens with similar methods.

Step 4: The Pallet Garden Project Begins! and a Problem With a Hole in the Ground.

I was keen to adapt the things I was learning to my type of gardening. With SOIL! I used an old air bubble pump to drive a T-joint airlift pump to run my first pallet garden. But I had a silly problem, I had to dig a hole for the T joint part. The hole was nearly a meter deep. I like digging holes but I saw it as a sticking point for most people!

Step 5: Windowfarm Friends, Decline and Rebuilding. Nano Airlift Pumps!

Windowfarms was great for a while and there was wonderful hobby collaboration. So I "worked" with people in Africa, Cambodia, CERN, France, the USA and Denmark. But the site got ruined by spam and the antispam program to fight them, it became a chore to log on and I had to give up. A lady named Eileen Jackson was instrumental in a change of course. She asked me to make a "pulser pump nano" or a "nano airlift pump". So, why not, the challenge was to make the smallest pump possible, but it had to be reliable and use the least air pressure possible! And I finally did it with "airlift in a bucket". A really small airlift pump that works well but can fit into a paint bucket.

Step 6: The Backyard Pneumatic Grid. State of Play February 2015

At this stage, the grid can be powered by the mini air pumps for aquariums, or by a solar panel running a little air pump from China or by a trompe in a little river or stream. Individual airlift pumps in the system need about half of liter of air per minute to work them. The working pressure is 11 inches of water column to 16 inches of water. (approximately 0.36 psi to 0.6 psi). A very important part of the system is at least 1 manometer to measure the air pressure in the system. (I have 2 of them, one in the greenhouse and one in the shed. My grid has over 50 meters of pipes at this stage so the manometer tells me quickly if there is problems anywhere. Mine is just a water filled u tube that is about 12 ft long with a water container at one end. I have an old 4 ft level beside it to measure water column in inches or cm. I also have food colouring in the water so it is easy to see the level. It is powered by 2 little air pumps that are designed to start when there is enough electricity and shut off again when there is too little from the solar panel. They have a little dial to control pump speed. They have been very reliable so far. They are brushless pumps and they have a pretty simple reciprocating air bladder. I bought brush motors too with fancier bladders but they were not a success. One actually ran so fast that it melted the bladder. It is a shame because they were able to pump more air than the brushless models. BUT reliability and durability is everything!

Step 7: Increasing the Scope of the Project. Things I Tried and Things to Try in the Future.

I have tried vertical, inclined and horizontal pallet gardens. Vertical was not a great success (partly because I tried to do too much experimenting in too small a space and I could not even reach some of my produce!) but the horizontal and inclined versions were successful. I did a quick demo of ebb and flow, and "ebb and float", and raft hydroponics (where the vegetable raft has "ballast tanks" and air can fill and empty them to lift the plants out of the water). This is pure demonstration, proof that it can work, I have never done hydroponics. I also used it to run solar heat extraction from a wall last year and this was very successful. I think that air and airlift pumps might be a new way to run solar thermal heat collection with rooftop collectors.

I made a strange version of the Chinese boar scares, that fills with water and then suddenly tips over and instead of making a noise, lifts up a "face" for a visual "scare".

I have also made little water wheels, and worked little bubbling fountains from the airlift pumps. New and coming soon is a concrete compost bin, with a compost tea component where the airlift will power the brewery! This is all done, I just have to connect up the air to it.

Also, I want to make an impulse pump that is air powered.

I believe that the little air bladders from the Chinese air pumps can be modified to run from wind turbines.

Another thing is vibrating lines in the wind. "Vibrating twine or singing twine" with a bladder connected to compress air with the vibrations. The bladders in the bubble pumps run at 60 hz so I am pretty sure it can be developed.

Step 8: Pneumatic Microgrid and Electrical Grid, Similarities. (could It Be a Teaching Device?)

The electrical grid has voltage and current going through the wires. The pneumatic grid has air pressure instead of voltage and instead of electrons, it has molecules of air.

I try to have as low a pressure (as low a voltage) as possible just to find the limits. The air pumps are capable of producing about 2 to 2.5 psi 27.7 inches of water column is one psi. So I am generally using half a psi while my pump can make at least 4 times as much pressure as that. If someone uses the higher pressure, I think they will get much more efficient processes. But at this stage in the game, I think we need to realize that there is lots to learn.

It would be interesting to try "alternating current" instead of the "direct current" that I am using now. "Alternating current" would simply be resonating air in a sealed tube. Actually, it might be very interesting indeed. I hope someone tries it.

Step 9: Key Components to Develop. the Bladder and Air Valves!

When I opened the little air pumps for fish tank bubbles or my best solar panel air pump, I get to some really simple components. This is the heart of the system. Essentially it is just a rubber bladder and 2 air valves. Just 2 flat thin bits of rubber are the air valves.

I believe this bladder and valve system could be replicated on different scales and work small wind and water power too. Even perhaps Stirling engines. Remember that the pressure I use is very low. So we do not need a high performance system. Maybe even a universal bladder can be made to work with wind, water or Stirling systems!



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    2 Discussions


    3 years ago

    I have been reading your ideas. I like them. I am curios about more results from some of the like the "compost" beer for slugs. That was interesting. I was curious how well it broke down the materials. I was thinking of burying a drum in my green house to compost and produce more co2. Just another crazy idea. Weed scraps, compost, co2 and not to mention tea or other uses.