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Rocket mass heater for greenhouse + generating electricity for grow lights  RSS feed

 
Rob Irish
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Location: Estonia, Zone 5/6
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I'm interested in doing a greenhouse, potentially connected to the house that could grow some herbs during the winter.

Due to the density of the forest around the house from about November to March absolutely no sunlight ever touches the house.

We are just here having a little talk about the possibility of perhaps generating electricity and storing it in a battery at the same time as the rocket mass heater running, then running LED grow lights at the same time. I'm wondering if anybody has done something like this or thought about it and would like to share some wisdom.

I'm just thinking that it could be possible to create a mini thermal generator, e.g. since the barrel gets so hot, water could be boiled and the steam spins a turbine which charges a battery bank and the water condenses and comes back so its a closed circuit. Obviously this only works as long as there is fairly intense heat in the barrel and the fire is going. But then in addition, couldn't there be a kind of tubing full of water that is in the mass, but the tubing also goes way outside into the freezing snow to cool down the water, essentially creating a kind of convection? Again spinning turbines, probably much slower than a steam generated one but still, generating charge to fill a battery?

I understand there are big dangers concerning pressure with water heating up and blowing up, but I think with all the right pressure release safety valves and proper design it could actually be quite productive.

Well, any ideas or suggestions or pointers to do this safely would be greatly appreciated!



 
Troy Rhodes
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Residential scale turbines and piston engine driven generators have been done.

If you don't invest a shit ton of energy and money into the engineering and hardware, it either won't work, or it will blow up. These are unbelievably complex systems.


Here is an example:


https://www.youtube.com/watch?v=AIFTBITYjb0



They usually use liquid or gaseous fuel to obtain better control, and the ability to computerize the system.

If it's not computerized, you have to babysit the system regularly/full time to keep it running smooth and not blowing up.


Mike Brown has some good insight into residential scaled steam power:

http://www.mikebrownsolutions.com/stmpwr.htm



None of these systems are inexpensive.


Most home grown electricity costs double or triple what the grid electricity costs. PV solar -might- be the exception today, if you live in a sunny climate and have a good sight, which apparently, you don't.




Not meant to be discouraging, but instead to alert you to the potential difficulties, and give you some resources to look at.



 
Rob Irish
Posts: 225
Location: Estonia, Zone 5/6
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Thanks for that Troy. Definitely a bit discouraging!

I don't want it to be too complex - and I think for starters I would be happy creating a non-closed steam cycle, since it is in a greenhouse, it will condense and 'rain' on the plants anyways, or create humidity which can't be a bad thing can it?

Here is a small rocket stove with a pressure cooker on it.
https://www.youtube.com/watch?v=7D1eWZ0JS5w

It says he gets about 3 hours of the generator running off 1 fill of the cooker.

a) Is it safe? Are pressure cookers able to handle the heat of a rocket stove? Would it make sense to elevate the cooker above the barrel a bit so that it runs a bit less hot?
b) What happens when the water runs out?

It seems this user in the video above gets about 30mA - 60mA from that basic turbine.

Hypothetically, if you could even say double this with a bigger pressure cooker perhaps and got in the range of 120mA - based off my newbie usage of a battery charging calculator (http://www.csgnetwork.com/batterychgcalc.html) charging say a car battery of 30Ah, it would take 300hours of running this steam turbine to charge it? So I'd have to fill up the cooker 100 times to get 1 full battery?

I'm trying to wrap my head around how long say a car battery of that size could even run a LED growing light of say 700w. 700w / 12v = 58 amps for the light? Which means one battery charge will give me .58hours (30aH / 58a )? Only 38 minutes? If I step it down to a 300w light that would be more like 1.2hours if I'm calculating correctly. I guess I have to look at much lower wattage lights. Fluoro lights I know are more in the range of 30-50w, but I am a huge non-fan of fluoro. Not sure I want to eat things that get light which I find an eye-sore, but then if I was using 30w then I could get about 12 hours off one car battery charge?

At the moment I'm giving growing micro-greens a go as a way to get some fresh food over the winter. Using the heat near the fireplace to keep them going, which I'm quite happy with. But it would be awesome to be able to even get some bigger herbs growing like some basil all year round, one of our favourites. I feel a bit dirty using fracked energy, even though in Estonia the power is really cheap, it isn't something I want to use a lot of.


 
Troy Rhodes
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If you run a boiler dry, any boiler, there is the risk to damage it, so the next time you make steam, it could explode.

That's why "real" boilers always have a means of knowing how much water is in there, and a feed pump to replenish the water in the middle of a run.

That either means constant, and I mean constant supervision, or a lot of technology and automation.

I personally would not be comfortable with an aluminum boiler, since a rocket stove can easily produce temperatures that melt aluminum.

The presence of the water is what prevents that from happening when the pressure cooker is on a conventional stove.


pressure safety valves don't work the same way on boilers that they do on water heaters. If a boiler fails, and the pressure drops suddenly, ALL the water wants to turn to steam more or less instantly. That's a steam explosion. The safety temperature/pressure valve has to be able to port the steam/water/explosion force out of the building. That's very different that the function on a water heater T&P safety valve. Mostly, it means bigger and more expensive.

Boilers are sensitive to water chemistry, water hardness and pH. If the water isn't right, it can cause corrosion and/or scale in the boiler, and then you're back to explosion city or reduced efficiency with scale.

Boilers have to be periodically tested hydrostatically to make sure they can withstand (I forget exactly) double or triple their rated capacity.


Pressure cookers and canners generally work in the 12-17 psi range. For various reasons, efficient steam power usually means 70-200+ psi. That doesn't mean you can't get electricity out of low pressure steam, it's just going to be fairly inefficient.

Again, not meant to be discouraging, but there are definite hurdles with steam power.

troy


 
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