Re: Solar heated hot water

["mark_harrison_uk2" <mph@xxxxxxx>]

Bruno,

Thank you for an excellent, informed, and clearly heart-felt post.
It's been about 3 years since I was last involved in the Solar PV
industry, so I've done a bit of checking on the web before I've
posted :-) (I was working with the BP Solar guys on the rollout of
solar panels into all new BP Petrol Stations.)

--- In ukha_d@xxxxxxx, Bruno Prior <bruno@r...> wrote:
I can't say I'm much of
> an expert on it, but I have heard it said that the environmental
> cost of the energy and rare materials required to produce the
> panels is barely compensated by the environmental benefit of
> using them. But this is only hearsay - a PV expert may be able to
refute this.

The payback period IN ENERGY TERMS, not in financial terms is
currently regarded as up to 5 years for multicrystalline-silicon
modules, and 1-2 years for Thin-film PV. (Most of BP Solar's products
are multicrystalline.)

This, however, ONLY applies if you discount the energy cost of
producing storage, so only really applies to grid-connected systems.
Your points about energy storage capacity/flexibility in the grid are
well make, and something I need to go think about.

[...]

> The practical problem is simple - the pattern of output from solar
> panels does not remotely match your pattern of consumption. They
> generate least in winter - you use most in winter. They
> produce their maximum output in the middle of the day
> [big jump to two different pieces of the post]
> Having said all that, everything has its place. The high cost
> of PV may be a small price to pay in places like much of Africa
> where the absence of any grid connection means you have no
> other source of power to keep  your medicine cool or run the
> lights.

Keep the medicine cool, yes. Run the lights, no. The "energy
proportional to sun" characteristic, which is such a problem for
developed nations, is exactly the set of characteristics you need to
deal with the "keeping medicine cool" problem - namely it heats
up
more when the sun's beating down, but that's exactly when you
generate most power... and it's using heat-pumping technology to do
the cooling anyway, so typically about 300% efficient.

Regards,

Mark