5264Re: [pfaf] re: tomatoes in greenhouses
- Mar 3, 2011Hi. Thats interesting about the embodied energy used for the production of the glass and other materials.
You need to do the research for the electric solar panels. Once the embodied energy was high, and people like David Holgren were critical of it, but now its from 1% to 5% of the output over the lifetime of the panels. But, do the research to see.
Electricity is a valuable form of energy for specific uses for which no other energy form can directly be used, such as music and communications and low energy lighting.
Unfortunately it is to the electric companies advantage for us to consume lots of it, and also we tend not to be aware that we need to distinguish it as special. So we use it for things that can be perfectly well served by wood charcoal etc.
Id say one other possibility could be to open up the ground within the greenhouse, to allow the heat from within the earth to come up. I hear that the earth stays at a constant 10c a metre below the surface. But again this is more or less hearsay, so anyone interested would do well to do some research on it. Im going to. :) frank
On Thu, 03 Mar 2011 15:00 GMT Jonathan Teller-Elsberg wrote:
>Traveler in Thyme,
>Yes, you are right that the benefits of overwintering tomatoes in a heated
>greenhouse are far outweighed by the problems of unnecessary use of energy.
>But that assumes that the greenhouse exists only for the tomatoes. If a
>person has determined that they want/need a (heated) greenhouse for whatever
>reasons already, then putting some tomatoes into it doesn't much change the
>energy balance. Still, the joy of a fresh tomato shouldn't overwhelm
>someone's rational thinking and lead them to install an energy demanding
>greenhouse just for that simple pleasure.
>Having sort of defended greenhouses above, now I'll beg to differ with you
>about the efficacy of solar systems to power heated greenhouses. A passive
>solar greenhouse is great, of course, though it does entail the embodied
>energy of the materials that construct it--sometimes really significant
>amounts of energy. That goes both for greenhouses glazed in glass or in
>polycarbonate. Polycarbonate is massively energy intensive to manufacture,
>as, of course, is glass. So all greenhouses, even passive solar ones, should
>be considered carefully before being installed to determine if they really
>will be utilized intensively enough to make up for their energy "cost" (not
>to mention their financial cost).
>PV panels only up the situation. The embodied energy in PV panels is
>significant and I suspect that, on balance, I'd be better off in terms of
>global warming gas emissions eating lettuce trucked from California to
>Vermont all winter than to install PV panels for the purpose of powering a
>greenhouse for my winter veggies. (As above, if the PV panels are being used
>for other reasons already, and have the spare capacity to boost a
>greenhouse's viability, then go for it. But PV expressly for powering a
>greenhouse? I fear that's a dead weight loss for the planet when all is said
>I hope I haven't sounded too didactic. Sometimes I get on a high horse when
>I don't mean too.
>"We have changed the world, and we wonder why things won't stay the same."
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