Low pressure, high volume solar engine

Here's an interesting take on using solar and/or any heat energy (even from compost piles). Using the Ideal Gas Law, you create a small pressure difference (.5psi-1psi) in a large chamber using heat, then use that pressure to run a large machine that turns an alternator. This is very similar to steam and/or stirling engines, but instead of being compact, it is huge, so losses are minimized, making for easy construction.

You need a 17 degree temperature difference to generate the .5psi. That should be easy to generate in a greenhouse, solar oven, compost pile, etc.

I think this design has some valid features, and he's using a sealed greenhouse as the collection chamber. He's got a 500 watt version running from his greenhouse. I want to build one!

You have to sort through a lot of extra info, but the concept seems valid:
http://www.mb-soft.com/public3/electzzz.html

I sent him an e-mail with a few questions. His mechanics are sound, but his design is not robust enough to actually be put into practice. Here are some questions I raised:

1. How do you determine the direction your machine will spin? The machine is theoretically symmetrical and doesn't have a specific direction for the barbell to fall.
You compare it to setting a bicycle upright which could fall in any direction. However, I see how you could balance this once its spinning by allowing its momentum to carry it past vertical. But for low RPM builds... is the designed doomed?

2. How do you keep pressure in a machine that is always spinning? If I wanted to use water as the fluid, what sort of 'piping' or apparatus would you use to pressurize each side as the machine switches positions? I think the use of water head that you suggest is MUCH more involved in your system than you make it out. Can you clarify how you imagine that system to work?

3. How do you switch the pressure differential fast enough to keep the machine spinning using solar?

4. Most importantly! Have you built a working model producing the power output you claim? If so, is there a video of it in action?

So yeah, while the energy transformation part of the machine is valid, there are no details on how you would deliver the energy to the closed vessel in terms of water pressure head, pressurized air.
He suggests using solar in a closed-scheme (I assume), but there is no details on how to provide the power to the alternating machine at a rate that would keep that machine spinning.
He also grossly oversimplifies the efficiency of the setup by ignoring the efficiencies of the energy delivery setup.

I'm interested though. Large scale, low pressure machines are usually simpler that smaller, large pressure machines.

He claims to have a 500 watt air machine running, but I haven't seen any videos.

I wrote him for more information as well, and have been discussing the design for a while. There are definitely issues to work out, but I think the concept has some merit, even if it doesn't reach the efficiency that he claims.

I like the idea and the theory sounds like it should work. I understand how a sterling engine works, but I do not understand how the air preasure would build up inside of that chamber. It did not look like he had any air lines or ducks connected near the bottom. Hot air would rise, but I do not see how it would lift 300# with out being piped to the chamber, and then I do not see how the thing would spin. I am sure I am missing something here, maybe some one can give me some insight, it sounds like something I would love to build and see how it worked.

If you read the description, he does have the air ducted to the machine. The air increases in pressure due to the 17 degree rise in temperature.

I believe this idea is flawed. While it is possible to raise a heavy weight with very low air pressure, it's possible to use heat at a low temperature to accomplish this, and it's possible to do it fairly efficiently, the problem lies in the losses encountered while cycling this kind of engine. I'm not referring merely to frictional losses, although that is a serious problem also. Consider the system: A large green house is used to heat a large volume of air. Some of this air is sent to the expander to raise the weight. So, we've just removed some mass of air from the greenhouse. Now, the "engine" cycles as the weight rotates it. However, we have to raise the weight again to get a continual output. So, the air that was placed in the expander has to be removed. You can't just send it back to the greenhouse because it's under pressure and doing so would consume all the mechanical energy we just produced. So, the only other option is to expel it from the system. So, now we start another cycle while venting the opposite side of the cylinder (to expel the previous charge as discussed). Now we have removed yet more mass of air from the greenhouse! The only way to affect a continual rise in pressure is to continue raising the temperature of the air indefinitely, and this is not possible. There has to be a means to replace the mass lost from the greenhouse, and this can't be done without expending precious mechanical energy! The only other way is to allow the air contained in the greenhouse to be cooled to lower the pressure within and allow a fresh charge of outside air at atmospheric pressure to be drawn within. However, that means we lose most of the heat energy that has been collected! The net effect is a system of pitifully low efficiency, and considering the extreme frictional losses of a very large machine, the net efficiency would almost certainly be so low as to be totally impractical.

I am certainly willing to hear an explanation as to how my reasoning here flawed. After all, it would be great if the thing works... but I know better.

A better solution is to use the density differences caused by heating air to induce a differential pressure to cause air flow. This air flow is used to power a turbine. The efficiency is low, but the system is practical because no pressure vessel is required. An interesting aspect of this system is that it continues to produce power for many hours after nightfall due to the residual heat in the system:

http://www.youtube.com/watch?v=XCGVTYtJEFk&feature=related
http://www.gizmag.com/enviromission-solar-tower-arizona-clean-energy-renewable/19287/

I believe this http://sunvention.com/sv/produkte3_e.html concept of a high volume low temp stirling engine is the end evolution of the original inventors idea. If you dig around sunventions site there are some other really interesting developments there, namely they have integrated the engine around a greenhouse for full spectrum solar energy capture. Tamera, the site where the sunventions test equipment is, also has had considerable design work done by Sepp Holzer too...

The sunpulse engine menioned in my previous reply is discussed in more detail here http://www.solarheatengines.com/2012/01/10/tamera-video-of-sunvention-sunpulse-engine/
The author of solar heat engines also has some excellent material for anyone interested in DIY stirling engines.