re: best starting method
1 oct 2005
>your original question was asking what is the simplest and least expensive
>way to to get in to solar. since the responses seemed geared towards
>conservation of your existing power my assumption is...there must not be a
>simple and cheap method...
au contraire. you might make an air heater with an inexpensive sunspace or
polycarbonate "solar shingles" over a south house wall for space heating
with a 1-2 year payback.
or supply close to 100% of the hot water needs for a family of 4 all year
with a simple solar pond water heater like this, with a 4'x8' polyethylene-
lined tank under a greenhouse with 6'x8' of 6 mil pe or 4'x12' of 0.020"
flat polycarbonate film for the south wall and 6 mil pe for the north, with
whitewash or reflective mylar under the north. the south wall might have
a 6' slant height. the north might be roughly parabolic, like this:
. | . h
. | .
| d |
| | 3'
| | 8'
10 data 60,1020,1160,100,2410,440
15 w=4'box width (feet)
20 d=30.45001#/12'south wall to ridge distance (feet)
30 h=sqr(6^2-d^2)'ridge height above water level (feet)
40 print d,h
50 for case = 1 to 2'january and july in phoenix
60 read td,hsun,ssun'daytime temp (f), horiz and south sun (btu/ft^2-day)
70 ein=.9^3*d*hsun'direct sun from above (btu/wft^2-day)
80 ein=ein+.9^4*h*ssun'add reflected sun (btu/wft^2-day)
90 sunhours=6*case'solar collection hours
100 eout=sunhours*(140-td)*w/2'daily heat loss from top (btu/wft^2-day)
110 dhwheat=8*(ein-eout)'daily hot water production (btu)
120 db=3'depth of box (feet)
140 qb=db*w*8*62.33*(140-110)'heat stored on average day (btu)
150 rb=20'r-value of db'xw'x8' box
160 ab=2*(w+8)*db+2*w*8'box area (ft^2)
170 gb=ab/rb'box thermal conductance (btu/h-f)
180 lb=24*(125-td)*gb'box heat loss on cloudy day (btu)
190 dhwl=30000'dhw load (btu/day)
200 nd=qb/(lb+dhwl)'cloudy day storage (days)
210 print case,dhwheat,lb,nd
2.537501 5.437011 feet
daily daily numbe of
month output loss cloudy days
january 40518.5 btu 10608 btu 4.420568
july 40541.5 4080 5.267324
during the day, a $5 10 watt fountain pump would move tank water over
a 4'x8' layer of epdm rubber over a 2" horizontal polyiso board cover,
and the water would drain back at night. cold pressurized house water
would enter a $60 1"x300' coil of pe pipe under the cover and emerge to
enter the cold input of a conventional water heater inside the house,
which would do nothing most of the year. the materials cost would likely
be less than $300. see more details at http://builditsolar.com.