"N. Thornton" wrote in message
om...
From: NickW )

Hi tech stuff is all very nice but have you checked on the price of a
suntracker lately? These types of system often don't pay you back for
maybe 20 years or so.

About £35. See redrok.com. Payback is quite practical with such a
tracker.

see:
a.. Solar PV Sun Trackers
b.. Redrok DIY LED Tracker
c.. Sohara: Directable Mirrors - A Better Way To Focus The Sun
d.. Sunflower Facetted Dishes
e.. Solar Energy Return on Investment: Solar Dish Concentrator Performance
/ TV Satellite Dish Antenna Costs
f.. Amonix Inc. - High-Concentration PV Systems
g..
h..
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"IMM" wrote in message
...

"N. Thornton" wrote in message
om...
From: NickW )

Hi tech stuff is all very nice but have you checked on the price of a
suntracker lately? These types of system often don't pay you back for
maybe 20 years or so.

About £35. See redrok.com. Payback is quite practical with such a
tracker.

see:

oops

see:
http://www.autobahn.mb.ca/~het/energ...#SolarTrackers



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(NickW) wrote in message . com...
Lets have a think. Oil heating costs about 1.4 pence / kwh.

Are you sure? I dont know, its just that gas is more than that.

Not certain but FWIW, this is my source:
http://www.chic-info.org.uk/electric.html

I took a quick look, and the prices there are a fair bit off what we
pay here. I'd check out your leccy and gas bills, and factor in
efficiency for each heating type. Roughly speaking leccy = 100%, gas =
80% efficient.


I havent done the maths here, but ave of 1/8 kW per sqm sounds much
too low.
I dont know what kind of collector youre considering, all I can say is
big trackers can pay back according to previous calcs. But it does
depend how you design them. Somewhere I've got detailed figures on
this one: want me to mail them? Might be of interest.

Yes please.

Will do.

Right. I'd be tempted to just run it slower, by using a series
impedance or transformer. Sounds pretty lousy tho if its crapping out
already.

It was making a nasty whining noise, obviously too much back pressure,
I have a 1/4 hp one on order though.

Sounds like that one was rock bottom stuff. Have you got a filter on
it btw? I just wonder if there might be something in the pump.

You may even find 1/4hp to be more than you need, in which case you
can cut energy use/noise/increase life by reducing its run speed.
Whats your temp rise with the 1hp pump, with the present plumbing
setup and fast flow rate? It should be poss to make rough calcs from
there, if youre interested in slowing it down.

I reckon if you get more than 50% through it should gain you. Youre
really losing a lot with an open collector. It wont matter that theres
light scattering.

I did another calc on the uncovered collector at the weekend. Now that
the coil is divided into 4 circuits, the flow rate is much higher but
the temp gain seems the same. Perhaps it's just better conditions now
(mid summer, high noon, no cloud at all). I got 10kw! If there is 800W
/sqm available then from my 25sqm collector, that's an efficiency of
50%. Given this, do you think the polythene will still benefit?

Yes, definitely. Youre losing loads as it is. I'm surprised to see you
getting 50% off such a collector though, I would have expected a fair
bit less. Your low water output temp will be helping a lot, but
plastic pipes and no cover would generally hit efficiency quite hard.

Well I'd be curious to see what happens if you ever space the pipes
out and put silvered mylar underneath, and polythene on top. I reckon
you'd seriously cook.

Sounds like doing the same thing for DHW has to be on the cards, thats
some heat output! If you ever do I'd efficientise it as much as poss
though, since water output temp would have to be high, so all those
extra tweaks would be much more important.

Regards, NT

Sounds like that one was rock bottom stuff. Have you got a filter on
it btw? I just wonder if there might be something in the pump.
It was OK but I was asking too much of it. I think the bearings just
got knacked from all the backpressure. If they weren't already shot,
it would be burbling away happily now that I've split the coil into 4
circuits.


You may even find 1/4hp to be more than you need, in which case you
can cut energy use/noise/increase life by reducing its run speed.
Whats your temp rise with the 1hp pump, with the present plumbing
setup and fast flow rate? It should be poss to make rough calcs from
there, if youre interested in slowing it down.

I'm not sure... maybe with the polythene on. It's just that when I
first measured it, I got 5 litres in 35 seconds with 7degrees rise.
When I split the coil into 4 circuits, I got the same temp rise but
with 5 litres in only 15 seconds. Admittedly the first measurements
were taken in less good conditions but I reckon that the black pipe
will only work efficiently up to a certain temperature - ie: not much
above ambient. So perhaps when I get my slower pump, I won't be seeing
10kw any more (although probably getting a better efficiency in terms
of electricity used / heat output).

I'll try the polythene at the weekend and post the before/after
measurements.


Well I'd be curious to see what happens if you ever space the pipes
out and put silvered mylar underneath, and polythene on top. I reckon
you'd seriously cook.
This is effectively increasing the collector size so I would imagine I
would get a large improvement.


Sounds like doing the same thing for DHW has to be on the cards, thats
some heat output! If you ever do I'd efficientise it as much as poss
though, since water output temp would have to be high, so all those
extra tweaks would be much more important.
I should imagine you'd definately need much better insulation
underneath, say polystyrene and maybe polycarbonate sheets over the
top (3m x 0.6m sheets can be had for about a tenner). I don't even
know if you'd be able to get DHW temperatures with MDPE pipe though.

I just bought 50m x 10mm copper oil pipe for about 60 quid (not for a
solar project!). You could use this on a black corrugated metal
collector surface - it could be well spaced out due to the high
conductance of metal.

Cheers

Nick.