samc wrote:

wrote:

Lets say it saves £20 a year heating dhw only.

Would that be 20 UK pounds per year? Sounds like a very poor water heater.
It seems to me that American families pay about $20 per month for hot water.

Lets say we want it to break even after 10 years, interest is 5%...
A system that does this in 10 years is worth paying £157 for now.

Would you believe 154.43 pounds?

From this emerges one clear conclusion: we need either a lot more
saving or a lot less cost than commercial solar dhw systems deliver.

Or both. Solar water heaters are typically undersized and overpriced.

If one got a bit desperate and justified a 20 year payback, system
value would rise to £251.

Would you believe 249.24 pounds?

Now, since almost all solar dhw setups fail miserably to pay their way,
lets see how low cost we can get. Start with a dirt cheap direct
drain-down system for summer use only.

There's no reason a draindown system can't work in wintertime.

Collector and loft piping:
100' garden hosepipe: £20
sheet of green house polythene: £? Lets say we use a £1 poundland
plastic patio table cover set...

How about a solar-pond type water heater instead?

people are looking at this the wrong way givern the above would any one
ever buy a car,computer,tv e.t.c .

It's more rational to say

I need hot water. What's the most economical system?

Nick