Re: Solar water heating system..

Evacuated tubes with glass-to-metal seals tend to crack over time.
http://www.sunpowersolutions.com distributes Apricus systems
with no glass-to-metal seals in France...

>Where we will be, there is plenty of sun, but it also gets pretty cold

>in winter too (tho still usually sunny!)

How many kWh/m^2 of sun falls on the ground and south walls? Grenoble
(where I worked) is similar to Phila, with 620 Btu/ft^2 on the ground
and 1000 walls on an average January day with a 34 F daytime temp.

>... are the systems any good?

Yes, generally speaking.

> will it actually work to a satisfactory degree? or will the electric

> backup element always be running?

The solar hot water fraction can be close to 100% if you spend enough money.

> Considering that I can buy a large French "chauffe eau" (pressurised,

> highly insulated electric water tank) for around 200€ max,

> is it worth it?!!

That's a cheap heat storage tank and cheap backup fuel, if rarely needed.

You might buy one and build a solar preheater (since you'll be renovating)
with a $35 fountain pump (eg Tractor Supply's #3119117) and a $60 1"x300'
pressurized plastic pipe coil in a $170 3'x8'x2' tall metal stock tank (TSC
#2177285) inside an 8'x12'x7' tall A-frame structure with a $100 8'x12'
Dynaglas polycarbonate south wall at a 30 degree tilt, which might collect
0.9x12(4x620+8cos(30)1000) = 101.6K Btu of sun and lose 6h(Tg-34)8x12/R1
= 576Tg-19.6K on an average day, where Tg (F) is the A-frame air temp.
If we collect Q Btu/day of useful heat, Tg = 210.4-Q/576.

If a 4'x12' tank cover collects 90% of the sun that enters the glazing
(91.4K Btu, with the help of 2'x12' of Big Fins on the south tank wall)
in Tw F water and loses 6h(Tw-Tg)1.5x6x12 = 648(Tw-Tg), Q = 305(352-Tw).
Tw = 140 F makes Q = 64.5K Btu (19 kWh) per day, with Tg = 98 F. It might
look like this, viewed in a fixed font:

Y

^
|
7'| . <------------------------- sun
| .
| . ru . south -->
| .
| U. ru down-reflected upper ray
| . .
| . ru
| (x,y) 45 .
| . <---------- sun ru \
| . rl .8'
| L. rl ru \
| . rl down-reflected lower ray (not to scale)
|. 67.5 degrees
2'|----------------------------F .
| i | 300' pipe coil | i B
| n | | n i .
| s | | s g
| u |300 gal stock tank| u F .
| l | | l i
| | | n white 60 .
0' ------------------------------------------------------------------> X
0' 4' 8'

The north wall could be made from 4'x8' 2" double-foil polyiso boards.
... 500 W of standard PV panels under a water duct on the lid might
produce 1000 W of electrical power...

20 PI=4*ATN(1)
30 F=4'max focal distance (ft)
40 A=PI/8'kerf angle (radians)
50 X=F/(1+1/TAN(A)/TAN(2*A))'x breakpoint (ft)
60 Y=X/TAN(A)+2'y breakpoint (ft)
70 L=SQR(X^2+(Y-2)^2)'lower segment length (ft)
80 H=8*COS(PI/6)'height (ft)
90 U=SQR((F-X)^2+(H-Y)^2)'upper segment length (ft)
100 ALD=180*(PI/2-A)/PI'lower elevation angle (degrees)
110 AUD=180*(PI/2-2*A)/PI'upper elevation angle (degrees)
120 PRINT F;L,ALD,U,AUD,2+L+U

focus -- lower segment -- -- upper segment -- total segment
(ft) length (ft) elev (deg) length (ft) elev (deg) length (ft)

4 3.061468 67.5 3.522649 45 8.584117

With lots of insulation, the 300 gallon tank could provide 300x8.33(140-60)
= 200K Btu of water heating over 5 cloudy days.

Nick

Posted by Robert Gammon on June 19, 2006, 10:53 am

In the deep southeast Texas area that I live, in spite of 42 inches of
rain that we receive annually, A direct gain solar hot water heater
means that we spend very very little on hot water heating. Scald risk
is avoided because the water in the hot water tank is generally cooler
than the water coming down from the solar collector.

Lots of different designs out there for solar hot water, some good,
some no so good. Choose carefully and you CAN dramatically cut your
hot water costs. It would be best to look for products sold and
serviced in Europe. Cast your eyes a bit further than France as you
may find that both Germany and Italy offer decent solar products.

As interesting as Nick's ideas are, I don't think that you want to
build a home brew solar hot water heater.

Posted by Gary on June 19, 2006, 1:20 pm

Robert Gammon wrote:

...

> As interesting as Nick's ideas are, I don't think that you want to

> build a home brew solar hot water heater.

Why not?

--

Gary

www.BuildItSolar.com
gary@BuildItSolar.com
"Build It Yourself" Solar Projects

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Posted by Robert Gammon on June 19, 2006, 1:49 pm

Gary wrote:

> Robert Gammon wrote:

> ...

>> As interesting as Nick's ideas are, I don't think that you want to

>> build a home brew solar hot water heater.

> Why not?

Not in a house that you are in for only a couple of years, i.e. rent or
lease. Installing a commercial system, one that you can show hte owner
example sof and literature for is more likely to gain acceptance OUTSIDE
YOUR HOME COUNTRY.

So build it here on a home you own and so long as local building codes
allow, so long as homeowner deed restrictions will permit such a device
, and MANY now require details plans to be submitted in writing before
proceeding - we have to get shingle color approved, exterior pain colors
approved and the solar hot water system had to be approved by the HOA
BEFORE work began, then go ahead.

Just don't dream of doing this in a foreign country WITHOUT getting the
homeowner's approval AND consult with local real Estate professionals to
get their advice on the homebrew plan.

Could be a thing that gets you evicted over there, so be very very
careful if you intend to do homebrew in France (or Germany, or Italy, or
Spain, Or England.......)

Posted by Gary on June 19, 2006, 2:45 pm

Robert Gammon wrote:

> Gary wrote:

>> Robert Gammon wrote:

>> ...

>>> As interesting as Nick's ideas are, I don't think that you want to

>>> build a home brew solar hot water heater.

>>>

>> Why not?

> Not in a house that you are in for only a couple of years, i.e. rent or

> lease. Installing a commercial system, one that you can show hte owner

> example sof and literature for is more likely to gain acceptance OUTSIDE

> YOUR HOME COUNTRY.

> So build it here on a home you own and so long as local building codes

> allow, so long as homeowner deed restrictions will permit such a device

> , and MANY now require details plans to be submitted in writing before

> proceeding - we have to get shingle color approved, exterior pain colors

> approved and the solar hot water system had to be approved by the HOA

> BEFORE work began, then go ahead.

> Just don't dream of doing this in a foreign country WITHOUT getting the

> homeowner's approval AND consult with local real Estate professionals to

> get their advice on the homebrew plan.

> Could be a thing that gets you evicted over there, so be very very

> careful if you intend to do homebrew in France (or Germany, or Italy, or

> Spain, Or England.......)

Hi Robert,
I guess that makes sense if he is renting, or will not be there for long -- not
sure it thats the case or not?
Places vary a lot on approvals and covenants -- sounds like you live in a very
picky place. Where I am, the covenants are not very restrictive, and no permit
is required.
Anyway, was just wondering why you thought it would not be a good idea.

I think that DIY solar water heaters can be a good way to go. The cost of
commercial systems is high -- I think a lot due to low volume production. You
can save a substantial amount of money building your own. I think that the
simple payback on some systems could be as low as a couple years -- less if
energy rates keep going up. Not to mention the greenhouse gas benefits.

Gary

--

Gary

www.BuildItSolar.com
gary@BuildItSolar.com
"Build It Yourself" Solar Projects

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