Advice for a solar powered heat engine.

[cyssis]

Hi!

My name's Evan, and I'm new to the boards.

I've had the idea of creating a stirling or steam turbine powered generator for a long time, and am now trying to get my project underway.

The heat source is already taken care of (a fresnel lens of about 45"x60" biased [not in focus] enough so as not to melt the 'hot' end of the engine),

as is the sun tracking system and mount for both the engine and lens.

My questions come down to two things:

1. Which should I use, a stirling or a turbine?
2. How should I use that to power an AC generator?


Some things to consider for question 1:
I have basic metal machining skills, to include lathe work and welding/ brazing.
I don't have access to a CNC machine.
The entire unit will be outside year-round, and unattended for most of that time (probably a monthly maintenance).
It must be able to start on its own, once the heat is applied. (I'm sure I could do a thermocouple activated starter motor to swing the flywheel in the case I choose a stirling engine, but I'd prefer not to).
It should have relatively low maintenance and construction costs. (I can probably get MOST of the metal donated... although not all.)
I would probably be making a reaction turbine if I went the turbine route... Less technical knowhow required, I think.


Some things to consider for question 2:
I understand I could just couple the shaft of either the turbine or stirling engine to an AC motor, and tada... suddenly it's a generator.
I guess my real question is, "How can I plug this into a power meter?"

My purpose is to build a few of these contraptions on donated money and attach them to the power grid through an electric meter. My state laws (may also be federal) require the electrical company to pay at peak hour cost per kWhr any energy you put into the grid. My electrical knowledge is lacking enough for this to be a stumbling stone, though. If I have the 110 V AC motor plugged into the power outlet, I'm pretty sure it'll run and just take my turbine along for the ride; while sucking power through the meter.

How do I put the power I make from this setup back into the power grid in that case?


Any ideas would be helpful.
I'm really excited to begin work on this project, and have several hands ready to help. I just don't want to waste their time and mine.


Thanks in advance!


Evan.


[edit]

Also, any links to sturdy & resizable stirling and steam turbine engine plans would be great!

[/edit]

 

[rake60]

Hello Evan

Welcome to HMEM

I'm sure all of your questions are being brainstormed already.

Rick

 

[cyssis]

Hey Rick,

Ha! ;D
Not sure if you meant, "...are being brainstormed already [by me]" or, "...are being brainstormed already [by others]".

In either case you're right. I've been thinking a lot about my own questions lately, and trying to figure out answers, but I'd like the model engine professionals' opinions. I got the idea mainly from a company here in my area (Albuquerque, NM) that is doing roughly the same thing with stirling engines (much larger scale), and researched the legal requirements of the electric companies myself.

I'm pretty sure I could make my own decision about which engine to use on my own-- I'd prefer some help, though. But as for the generator question... I have NO idea how to get around it... I KNOW it can be done (how else do they generate electricity in the first place?) but I just don't know what to do. And I certainly don't want to plug in a 5hp AC motor while connected to my engine and find that it starts spinning the engine rather than the engine spinning it.


Thanks for the welcome!


Evan.

 

[dparker]

Evan: We did this where I worked, using three phase induction motors. We built turbines by modifying our centrifugal pumps and running the water through them backwards, the turbine would then spin the motor somewhat faster than the synchronous speed of the motor and it would generate electricity and put it back on the grid. I would "jog" the motor and make sure it was wired to run in the correct rotation direction that the turbine would drive it. Then de-energize the motor/generator and open the valve to start the turbine, when the valve was open enough to run the motor at the synchronous speed of what ever motor we used(1200,1800 or 3600 RPM) I would energize the motor. The motor/generator would then "idle" until the valve was opened more to drive the speed up and as it did the power would be produced and go back to the grid. You want to pick a motor/generator that will be big enough to generate slightly more power than you are putting into it so you do not over load the windings. There are many electrical safety controls required for this before hooking up to the grid I am sure and these will be governed by your utility. There is much more to this than I know for a useable production system as I ran a Test Lab and everything was done for R&D purposes.
don

 

[BobWarfield]

Evan, welcome.

I have a web page with some information that may be of use: http://www.cnccookbook.com/CCStirlingGenerator.htm

One challenge you will face is that the energy you can collect with a 45" x 60" Fresnel lens is not as much as you would think. By my calculations (on the page listed), you need a couple of 6 foot dishes to develop 1,000 watts. The Fresnel would develop on the order of 300 watts if you can make it as efficient as commercial systems.

Of course my calculations could be completely in left field too!

There is a book out on building a 5HP Stirling engine that was used in India to harness power from rice chaff that is the best account I've yet seen on building a Stirling that generates useful amounts of power.

The best commercial Stirling for solar work has been Sunpower. They offer a lot of technical details on their web site. It's definitely doable to build a free piston Stirling generator, but not exactly trivial. FWIW, the free piston is using a linear AC generator that looks straightforward to construct. There are lots of interesting twists in the Sunpower Stirling to increase its efficiency, and they're currently able to run at about 2x the efficiency of solar cells, which I think winds up being 30% or so. I'm not sure I'd count on being able to build one as efficient, at least not first crack out of the box.

Cheers,

BW