Alternatives...

I've been exploring alternatives to powering my home. There's obvious (and expensive) alternatives of photovoltaic, wind, and solar water heat. What I've been searching for, had no luck, and hoping maybe someone here can help. Is it possible to hook up a solar evacuated tube designed for hot water heating to some kind of turbine to generate electricity? And is it feasible to have this scaled to fit in my home.

Any other power alternative suggestions are welcome too...

Vandole's picture

Postulant

Admittedly, I am not a mechanical or electrical engineer or power generation specialist of any sort, but I believe it would be rather difficult. The two main modes of power generation involving water are steam turbines (coal, nuclear) or gravity turbines (hydro), neither of which would be great to implement with solar. (although steam is feasible, but it would depend on the weather) You're better off using solar specifically for power generation (photovoltaic cells) which would require a large module to provide a significant contribution to a household.

NorthwoodsMan's picture

Embodiment

My thought was to use the hot water comming out of the evacuated solar tube to run through the turbine. From what I've found, the evacuated tube is supposed to be more efficient at heating the water than a traditional solar heating system. The issue with that so far is finding a small enough turbine.

Capriox's picture

Embodiment

Really? You can't scavenge one out of a small motor-powered pump or something?

NorthwoodsMan's picture

Embodiment

Part of the issue is that I have been looking at steam turbines, not water. Makes a difference.

As far a the pump, I'm trying to set this up to generate electricity, not consume it. That's why I was looking at using the solar tubes to get the water moving.

Side note, this post is number 666 for me.

Capriox's picture

Embodiment

Ah, my apologies. I meant find a pump to dissemble for the turbine parts.

Robbing one piece of equipment for parts for another is a time-honored farming/DIY/backyard-inventor tradition, donchyaknow Wink

comment's picture

I have no idea how hard it would be to generate steam, but I know that you could get the water moving pretty good with the convection, and in the winter you could have a separate set that runs through your woods stove. On the moving water side of things, some pretty small generators (like from a pre-alternator car) and a just right fan from a car or truck have been used to generate power.

Kittae's picture

Postulant

There was a reality show a while back, and I didn't watch too much of it, but I think that what this fella thought up might work. It was some guy who was crazy about going all-natural, but his wife was some spoiled trophy who hated this idea because it took work. I know he ran on solar power for most stuff, but he had an exercise bike that he would work out on to provide a little boost. If someone could help me remember this show, I KNOW there are directions on the web to get a set-up like that.

MeiLin's picture

Most High

Ed Begley, Jr, the actor, was a green freak before green was green. Smile I highly recommend Make Magazine for all kinds of weird alternative power stuff, including wind power set ups made completely from junk:

http://makezine.com/

Make and its companion magazine, Craft, are INCREDIBLE.

Kittae's picture

Postulant

Ah-ha! Thanks! I didn't know Make was related to Craft--although the comparative awesomeness does seem obvious. = P

V's picture

Embodiment

The problem is that heat from a hot water heating system is not usually "quality" heat. Yes, you can make electricity off a temperature differential, but you really want a significant differential to make it very good. Steam is nice for turbines but I think it would be very very difficult to achieve from a hot water heater. Let's say you heat a pound of water from 62F to 212F. That's good, you've just added 150 BTUs of energy (212-62). However, you're less than 15% of the way there...you need another 1000 BTUs or so to turn it all to steam. Barely saturated steam, too, not superheated, and at a low pressure...it'll be tough to get much work from it before it starts condensing inside your turbine. If you were talking about something like a solar incinerator that focused light and achieved much higher temperatures for much smaller volumes, it might be more plausible, but I still think the engineering challenge would be significant. I'd be very surprised if a centrifugal pump (think propeller) worked as an effective turbine (think jet turbine with a lot of blades and stages)

This link has a nifty little equation about how effectively you can use heat to make other energy. Note that the temperatures are on the absolute scale...add 273 for C or 460 for F. So if you start at 35F in the winter and heat water all the way to 212, you're going to be at a MAX of 26% efficiency without your steam simply due to the thermodynamics. Then add the losses of whatever turbine and generator you decide to use.

I haven't dug into this too far and I hate to be a downer but my gut says "Stick with the hot water heater for hot water and use solar panels for electricity".

Nye's picture

Supplicant

looked into this last year, and the general finding was that it just doesn't scale well. He's still working on it.

Davik's picture

Embodiment

Sadly I think V has nailed this one; as someone whose degree focuses on energy production from heat transfer, small scale solar just won't cut it. To really get good returns you have to be able to heat a substantial volume of water to well above the boiling point. Thermodynamically your best bet may be to use solar as a precursor heater to your water heater to try to cut down on gas usage.
Failing that you could always try to find yourself a half dozen kilos of enriched uranium and just build a small nuclear reactor in your basement. I'm sure the NRC won't care Blum 3

Overall, if you really want electric from your solar exposure, invest in the panels and realize that it's going to be a lot of cash at the outset (also, the lifetimes on those things are pretty bad, so start budgeting for replacement in about 5 years). Wind does better in the long run, but you have to be somewhere that gets enough, and your local ordinances have to allow you to put up a 30 plus foot eyesore.

Gudy's picture

Embodiment

... for you: "sterling engine". It's the closest to what you want, probably. Note that an efficient implementation from solar power requires a parabolic mirror to focus the sun light, as well as a huge-ass heat exchanger.

Lewis's picture

I've actually been to a research seminar on this particular topic. A PhD candidate at UC Berkeley was working on developing a stirling engine that worked off of the low kind of heat differences that you see in solar thermal. He claims that you can theoretically reach manufacturining/implementation costs of less than $1/W of capacity, but honestly, I'm not sure how well the stuff will scale down to produce the kind of energy that can power an entire home. As of now, he hasn't built a 1-2 kW range engine yet. However, you can see some of the details of design in his PhD dissertation here: http://www.eecs.berkeley.edu/Pubs/TechRpts/2007/EECS-2007-172.pdf

I basically agree with V on this one...

Marri's picture

Supplicant

Yay Lewis

As far as my own knowledge (admittedly limited), my parents recently installed a solar array. We didn't want panels, because they wouldn't work with our roof, but the array seemed like a decent option cause we could stick it in the field outside. They only installed it 11/15/08, and it's already generated 4,972.8 kWh. Now, I don't know if your state makes it worth it (yay Connecticut) but they've gotten a bunch of subsidies for it. Also, because batteries to hold solar power are huge, inefficient and expensive, they simply feed power into the grid and it's credited towards their energy bill at the end of the year. It's actually becoming a problem: because you pay $.18 / kWh for electricity but they only pay *you* $.03 / kWh if you produce more than you use, it is- financially speaking- best to generate exactly as much as you use. And we're not using nearly that much Biggrin They've already switched to an electric boiler instead of a gas one because we're producing so much more than we could possibly use. If you can afford them and have the space for them, they're great. That all being said, last I checked, they're kind of insanely expensive.

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