On Mon, 28 Nov 2005 13:39:33 +0000, David Hansen
wrote:
On Thu, 24 Nov 2005 22:00:05 +0000 someone who may be Peter Parry
wrote this:-
How do you collect something which isn't there in adequate amounts to
begin with?
You are asserting that there is not an adequate amount.
Yes.
This is
based on one twenty year old system that you have experience of (and
perhaps you are disappointed with).
Please read this slowly as I've now said it three times and you seem
to have difficulty comprehending it.
The measured results I obtained were consistent with the measured
results obtained by the DTI when they tested "more modern" systems
(including your pet Solartwin). There was no appreciable
performance difference between the system I installed then and
systems being installed now. Moreover the control system was
considerably more capable than most of the rather noddy ones which
seem to come with commercial systems these days.
I wasn't "disappointed" in it - it behaved exactly as predicted and
was an interesting experiment. However, it ultimately saved nothing.
Despite the very low installation cost (because of the source of the
materials) over its whole life it never recouped even that low cost.
"More modern" in this field is in many respects no different from
"more modern" of 20+ years ago. The collector tubes I had then were
producing the same performance as identical "modern" ones.
On the other hand one can see what people with more modern systems
have to say.
I'm really not interested in perceptions, only reality. The
measurements I took over ten years were in line with those obtained
by the DTI - the performance was measured - why do you find it so
difficult to understand this simple fact?
You asserted that the two comments on the Solartwin web
site could not be relied on (but your assertions could be relied
on).
I said the two comments you quoted were possible made up, that if
they were true were selectively quoted and in any case were
subjective. My statements are based upon objective, reproducible
measurements. Why do you have this aversion to measurement?
Well, the comment below has not been put on the Solartwin web site
and neither is there a link from Solartwin to the pages concerned.
They are http://www.drstephentaylor.plus.com/page4.html and
http://www.drstephentaylor.plus.com/page14.html from which the
following comment is taken, "On a sunny day in mid June when the
system was first running it heated a full tank to 70oC".
On a sunny day in mid June my system could do likewise, it couldn't
(nor can his) in mid December.
So, even if your particular system does not collect adequate amounts
of energy that does not mean that all solar water heating systems
don't collect adequate amounts of energy.
There wasn't an adequate amount of energy to collect all the year
around. The technology had nothing to do with it. Again you show
this distaste for figures.
The maximum amount of energy in ideal situations in the UK varies
from about 0.5kWh/m2 in the winter to 5kWh/m2 a day in the summer. A
solar hot water system has a total collection efficiency of around 30
to 70%. Let's assume the higher figure. That equates to 350W/hr of
energy per sq/m per day. For a typical 2sqm panel installation
that's 700W/hr a day.
Assume a daily household requirement of about 100L of water at 60degC
and an input temperature of 10degC in the winter. The specific heat
of water is 4.2Joules per gram per deg C so the energy required (in
kJ) is 4.2 x volume in litres x temperature rise in deg C. In our
example 4.2 x 100 x (60-10) = 21MJ or 5,800W/hr a day. In the winter
therefore the solar heater can provide no more than 12% of the
required energy. This is for an absolutely perfect site. If the
panel isn't aligned due south it can drop by 50%. If the panel isn't
cleaned frequently it can drop by another 5-10%.
In the summer the same collector can manage 7,000W/hr a day, more
than is needed and of course the excess cannot be stored. Each day
you throw away the equivalent of nearly two days worth of winter
energy gain.
Heating water in the summer is simple - I've achieved higher
temperatures than 70degC with plastic bag. Heating adequate amounts
of water to acceptable temperatures all the year around is completely
beyond the capability of a modern commercial domestic solar heater.
Compare Tony's figure of GBP15 energy saving per year with other
yearly energy savings you could make :-
Double Glazing - GBP82
Energy Efficient dishwasher - GBP13
Energy efficient Fridge Freezer - GBP35
Energy efficient Fridge - GBP15
Upgrading ;loft insulation - GBP58
Replacement condensing boiler - GBP 256
(Figures from the Energy Saving Trust)
Overall Solar water heating saves trivial amounts of energy and
money. In energy terms the cost of manufacture, shipping the major
components around the world and installation probably comfortably
exceed the useful energy they collect in their lifetimes. The only
thing they do is help the crazy political game - if you move
manufacturing to China you "save" CO2 from the UK's "balance sheet".
You actually contribute far more CO2 to the world supply of course
but if it's CO2 made in China it doesn't matter and it doesn't count
in the fairyland of Kyoto - absolute insanity.
--
Peter Parry.
http://www.wpp.ltd.uk/