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Kat: No need to have "<b><i>rules of thumb</i></b>" or Reuben's "<b><i>instinct</i></b>" ; simply total your energy usage from your fuel & electric utility bills and convert to kWh/yr less fuel wasted. Since a PV system is nearly 100% efficient for electric space & water heating, you can estimate the PV array size. If your roof is too small, install a ground array in your backyard. <div> We live in an all-electric house and use about 20 MWh/yr. Our average monthly bill is $237 -- which is a lot less than my neighbor's oil + electric bill. </div><div> Unfortunately, our local utility will not offer rebates for a ground-mounted 20 MWy PV array and our roof is too small to fit 20 MHw worth of PV panels. </div><div>Carmine <br><br><div><div id="SkyDrivePlaceholder"></div><hr id="stopSpelling">Date: Thu, 15 Mar 2012 15:57:55 -0400<br>From: molasses@q.com<br>To: greenbuilding@lists.bioenergylists.org<br>Subject: Re: [Greenbuilding] is it ever sensible to use PV to heat water?<br><br>
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</style><div style="font-family:Times New Roman;font-size:12pt;color:#000000">I think that my house would be a good candidate for PV instead of solar water heating, and someday when I have the money it's what I plan to do. Here is the situation with my house:<br><br>Portland, Oregon<br>700 SF one-level home w/ 200 SF unfinished, uninsulated basement open to vented crawlspace<br>Urban area with one plane of gable roof south-facing; deciduous trees in neighbor's yard partially shade roof during the summer<br>Poorest zip code in Portland - 100K of upgrades to this house would not make financial sense<br>Nowhere near enough roof area (or money) to put a solar array on the roof that would take care of entire (modest) annual electrical load of occupants, though we'd come a lot closer to covering summer loads with a PV array than higher winter loads<br>Heavy cloud cover for weeks just when we want the most hot water (winter)<br>Gas water heater currently in basement<br>Get rid of natural gas (personal preference)<br>No room for large storage tank (unless it's in the basement) (solar systems require rather large tanks, yes? The ones I remember seeing have 2 tanks, both 60 gal or so)<br>Don't want a tankless electric because they're not very efficient (? if I'm remembering right - perhaps this will change by the time I have the money)<br>Put 20 gal electric tank on wall above washer/dryer (storage space is at a premium!) on switch/timer, set temp high and use mixing valves to prevent scalding. Leave off most of the time, turn on 45 min before showering. Timer keeps WH on for 75 min (?).<br><br>I'll be able to afford the change in water heaters LONG before I would ever (perhaps never) be able to afford a PV array or a solar water heating system. Given my situation, I think PV would make more sense than solar water heating.<br><br>From that I can maybe derive a few rules of thumb:<br>1) solar access<br>2) storage space<br>3) money (I can do this plan in stages - electric water heater now, PV array later)<br>4) occupant usage patterns<br>5) ???<br><br>-Kat<br><br><hr id="ecxzwchr"><b>From: </b>"Reuben Deumling" <9watts@gmail.com><br><b>To: </b>"Greenbuilding" <greenbuilding@lists.bioenergylists.org><br><b>Sent: </b>Thursday, March 15, 2012 11:55:15 AM<br><b>Subject: </b>[Greenbuilding] is it ever sensible to use PV to heat water?<br><br>My instinct says 'rarely.' but in the following case I wonder:<br><br>two person household; very frugal with hot water usage; already flip breaker on electric tank water heater off most of the time<br><br>planning on adding a PV system that will produce more than they use in the summer (minimum system size requirements for grid connected subsidies.... you know). <br>
<br>Neither solar PV or solar thermal contribute much of anything in the winter here (cloudy PNW)<br><br>Are there rules of thumb?<br><br>Thanks.<br>
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