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204Re: [hreg] Workshops and threads

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  • Kim & Garth Travis
    May 11, 2000
      This has been a detailed reply and you sound very knowledgeable. I have a few
      further questions.

      > There are two types of PV solar electric systems, stand-alone and
      > utility-intertie.

      Why can we not have a hybrid of the two systems? I know you say:

      > If the utility power goes down, you don't have any power. This is
      > done as a safety measure, because if the grid is down, you don't want to
      > backfeed power into it and maybe fry a lineman who expects no voltage to be
      > present.

      But; many people run a generator hooked into their power system with a relay that
      controls a main breaker switch and prevents power from going out on the line when
      the grid is down. If one could use the grid as their batteries so to speak and
      only keep a minimum of batteries for power outs, then the cost of a back up system
      comes out of the budget and can be applied to the cost of PV. Here in the rural
      part of Texas, when the power goes out we loose our water and septic system.
      Having some sort of backup system is a necessity. The size of the system depends
      on how rich you are and what you have to have. The problem with generators is
      that if you run out of fuel, and there is a power outage, you can not buy fuel.
      Gasoline does not store well, so you must use a diesel generator.

      > It's expensive to produce power with PV panels. Refrigeration uses about 20%
      > of the power in a typical home. We have a large side-by-side refrigerator that
      > uses 913 kwh/year. If you plug this into my solar sizer tool, it comes up with
      > these figures on a system to run the refrigerator.
      > Location -Houston TX, 24V system / 5 day backup
      > Refrigerator 250whr * 7hr/day = 2.5 kwh/day @ .08 per kwh (HL&P) = $73/yr.
      > Needed: 8 - 6V, 350 ahr lead-acid batteries @ $169 ea., 8 - 100W PC panels @
      > $479 ea., 1 1500W inverter @ $739 ea,
      > 1 60A charge controller @ $269 ea.
      > System production: 2.66 kwh/day System load: 2.48 kwh/day
      > Total system cost $6700
      > Total paypack time @ .08 per kwh = 94.63 years

      The obvious response to this is that you need the fridge that NASA has developed
      that does not need battery back up to make it through the night. I am designing
      my place to use far less electricity than a "normal" home. One of the tactics
      that we are looking at is using pumps that run on DC current for the hydronics and
      other parts and hooking them to small PV installs. This avoids the cost, both
      environmental and financial of a large set of batteries that must all be replaced
      at once.

      > Here's a quote from an article in Home Power magazine
      > #64 written by James Udall and one from William Lord's website that sums up my
      > feelings pretty well on the payback issue:
      > "If PV systems get to $2 watt, everyone will do it and won't ask why. Today,
      > though, we've got to wrestle with the economics. "What's the payback?"
      > probably got its start after the first oil crunch, when some builder was
      > trying to figure out whether it made sense to add fiberglass insulation to his
      > next 2 by 4 shell. Duh. Twenty years later, "what's the payback?" has become a
      > mindless chant. In no other realm does this mentality prevail. Your wife's
      > pregnant!? Jeez, I'm sorry, kids aren't cost effective. Honey, let's buy a new
      > sofa. Have you done a cost-benefit analysis? We've been brainwashed, infected
      > with bean counter disease."

      While this is an interesting comment on financial planning, when there is a finite
      amount of money available, the decision of what to buy has to be based on

      > Solar Capital of the World!: Yes, Maine has been the cat's meow during the
      > month of June, 1999 as the American Solar Energy Society held its annual
      > convention in Portland...and I got to speak about "Living Well with Solar in
      > Maine." It was an impressive gathering. Most notable was Steven Strong's
      > answer (my architect) to the question about pv payback? "Engineers in
      > Switzerland have meticulously attempted to measure the electrical output of
      > asphalt shingles and other conventional roofing material, " he noted. "Because
      > there is no current flowing, there appears to be no payback on most roofs
      > throughout the world...unlike a solar roof," he concluded with a sly grin.

      The pay back on the roof is lack of damage. Ask me I know. I have been living
      with a leaky roof since a tornado hit my place last June. The real pay back is
      being able to sleep through the night, not listening for a storm. There is
      nothing wrong with trying to save money and the environment at the same time. By
      going to an alternative building method, our finished home will have cost about
      1/4 of a normal stick frame shell.

      > > I am still interested in solar cooking but find that the wind is a major
      > > problem. I would like to correspond with anyone who is doing solar
      > > cooking, but at present I cannot join another group in Houston.
      > I have the same problem. My cooker can't handle moisture or wind. I decided
      > that I wasn't going to solar-cook on a regular basis until I could build a
      > unit that could stay outside all the time because that's the only way it would
      > be useful.

      > James Ferrill

      Does anyone have any design ideas to make a solar cooker convenient? I do most
      of my cooking outside in the summer months, [May through Oct.] and have placed my
      auxiliary kitchen on the NE side of my building for comforts sake. The real,
      indoor kitchen is therefore on the same side of the building to make life
      convenient. A solar cooker needs the south or SW exposure. This leads us to the
      problem of carrying food either through the building or around the building.
      Carrying hot food through doorways, [auxiliary kitchen is screened] leads to

      I have heard of, but not seen heat wells designed for heating water. Does anyone
      know if such a concept would work for cooking? This could possibly solve the wind
      problem as well.

      > Kim Travis
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