On 2008-01-27 16:02:49 +0000, David Hansen
said:

On Sun, 27 Jan 2008 13:16:18 +0000 someone who may be The Natural
Philosopher wrote this:-

No solar collector needs direct sunlight to proiduce useable heat. In
pathetically small quantities.

As opposed to merely *rather* pathetically small quantities.

Yawn.

Meanwhile those with an open mind heat nearly all their hot water in
summer with the panels you appear to despise so much, produce a
significant proportion of it in spring and summer and produce some
of it in winter. No doubt you would claim that they are all
imagining this hot water.

Nobody is disputing that there is *some* heat produced.

The equation is a simple one.

How much heat is produced in the course of (for example) a year from
such a panel?

How much would the gas to produce the same amount of heat cost?
Project that cost forward assuming an increase in gas prices.

The write down the cost of the boiler over its lifetime and the cost of
the solar panel over its lifetime.

That provides the data for the cost of a system using only gas and one
using the panel as well and one should be able to calculate the total
cost of ownership and use of each.
Clearly, there will be some operational cost saving between using gas
plus solar vs. gas only.
That's the cost argument. One could even do it on an operational cost
basis only, ignoring the capital cost.

The other arguments on appearance, feel good and interest in tehnology
are valid in themselves.

However, let's have some honesty here and a clear justification of the
economic arguments if there are any.