On Tue, 07 Mar 2006 12:03:12 +0000 Ajh wrote :
Just installing the thermal store is over
GBP400 and I already possess a number of secondhand panels, it's not
worth my while installing them yet.

So where do I find typical figures for solar insolation for London UK
in the "heating" season October to May.

If you really want to wade through some numbers (UK average, not London
specific) check out SAP-2005 appendix H

http://projects.bre.co.uk/sap2005/

--
Tony Bryer SDA UK 'Software to build on' http://www.sda.co.uk
Free SEDBUK boiler database browser http://www.sda.co.uk/qsedbuk.htm
[Latest version QSEDBUK 1.12 released 8 Dec 2005]

"Peter Parry" wrote in message
...


Solar water heating may be marginal but solar pv is a wonderful way
of wasting money.

People 'waste' their money in all sorts of ways.

How would you spend what others spend on pv?

We were somewhere around Barstow, on the edge of the desert, when the
drugs began to take hold. I remember Peter Parry
saying something like:

I don't see how. Sure, if you buy factory-made panels and all the
necessary pro stuff and pay for the installation.

I'm not sure DIY construction of solar photovoltaic panels is really
going to catch on :-).

True. Otoh, as time goes by older generation PV panels become surplus
fairly cheaply - being in the right place at the right time helps a lot,
though. Best place seems to be the US for much cheap surplus.

This is a DIY group. Building panels from base materials and feeding a
pre-heat cylinder works out at less than a couple of hundred quid if you
DIY the whole thing from salvaged materials.

I've helped build such a system for warming a swimming pool and it
works quite adequately - it's also very large and pretty hideous.
Where we built it it was possible to hide it behind a large hedge but
not many people have a farm to play with.

True also. I'm fortunate in having a large building with a South-facing
gable wall which can accomodate several panels at ground level.
--

Dave

wrote:
This thread is from uk.diy, and is kinda relevant for a.e.h too.


Ed Sirett wrote:


Putting the question the other way around, could you say what the total
installed price for a marginally justified system would be - with a 20
year payback say.

If you'd payed a lot (£2,000 say) for the system then I have no doubt
you'd not recover the cost. What might be the threshhold?



Good question. I'll have a go.

Lets say it saves £20 a year heating dhw only.
Lets say we want it to break even after 10 years, interest is 5% and we
optimistically ignore the risk of system failure, underperformance or
repair for the moment.

A system that does this in 10 years is worth paying £157 for now.

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

If one got a bit desperate and justified a 20 year payback, system
value would rise to £251. But I dont think thats justifiable in truth,
nor is the extra spend allowance very significant. Either will make a
cheap system and nothing more.


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. This preheats the header tank,
which of course must be hot water safe in this design. That rules out
use of plastic header tanks where already fitted. Metal headers are ok,
a plastic one would need replacement.


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
4x8 sheet 7mm WBP ply £? rough guess £5
stainless roof fixings £? guess £5
black paint £1

CH pump £30

loft piping insulation: cardboard and/or rags £0, sellotape to hold in
place temporarily £0.50, string to fix it permanently £0.50.
header tank insulation: as above, no more spend needed
connecting 2 pipe ends to header tank: £2
1mm cable from lighting jbox to pump £1-2
FCU & pattress £2
panel thermostat, bimetal, £5

HW header tank if metal one not already present: £ not sure, and will
vary according to source

Now, if you had to buy all the above new, total cost is:
£73 + maybe a new header tank

The numbers look quite a bit better if you've got various bits lying
around already, or can use chuckouts to build it from. Then it might
actually be worth the 2 days work.

But given the low value overall of such systems, I dont think this is
the way to go. More sensible to go for a system that delivers much
more, such as flat panel solar space heating, which is cheaper, easier,
requires no roof access, and delivers more payback.

Solar flat panel space heating is little more than a frame, polythene,
black mesh cloth and holes in the wall. I'll let someone to play with
the numbers if they wish.


NT

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

Doctor Drivel wrote:
wrote in message
oups.com...
Mark wrote:
Ed Sirett wrote in message

If you'd payed a lot (£2,000 say) for the system then I have no doubt
you'd not recover the cost. What might be the threshhold?

That's still a moving target, how much
will energy prices have to increase
before we can't afford NOT to fit some
type of solar heating.

another good question, and another
bastion of solar DHW support. So,
lets find out:

At todays prices a £2000 commercial system saves in the region of £20
per annum on hot water bills. This is in the region of a tenth the
amount that woud be needed for the unit to eventually pay its install
cost.

To pay back £2000 @ 5% over x years would require a yearly payback of
- calculator time -

over 10 years: £254.52 per annum
over 15 years: £189.84 per annum
over 20 years: £158.40 per annum
over 25 years: £140.28 per annum
over 50 years: £117.6 per annum
over 100 years: £100.68 per annum
infinity years: £100 per annum.


Look at the 10 years figure. That doers not take into account that energy
may be twice as much in 10 years and has risen steadily along the way. The
payback calcs are more complex than this simplistic view.

youve not understood the figures.


That is having one installed commercially. DIYing the installation will
payback rather quicker. Also saving £20 per year in DHW bills is rather on
the conservative side. I know of a few solar systems that produce 2/3 to 3/4
of all DHW needs, and these must save far more than £20 per right now. If a
solar system is DIYed, is large covering most of the roof, or all of it, and
this energy gained is used to supplement heating too, then the matter maybe
more beneficial again. Solar heating is more feasible in cold northerly
Scotland, as they have a heating season 9 months of the year, so any free
energy gained is a bonus at any time. And as free energy is being collected
for 9 months, more of it is being captured over the year. It all adds up.

If theres one thing I agree with you on, its that solar heating _can_
be made to pay. But most solar heat systems are designed with
inadequate skill and will never pay back their cost.


NT

samc wrote:
wrote:
This thread is from uk.diy, and is kinda relevant for a.e.h too.


Ed Sirett wrote:


Putting the question the other way around, could you say what the total
installed price for a marginally justified system would be - with a 20
year payback say.

If you'd payed a lot (£2,000 say) for the system then I have no doubt
you'd not recover the cost. What might be the threshhold?



Good question. I'll have a go.

Lets say it saves £20 a year heating dhw only.
Lets say we want it to break even after 10 years, interest is 5% and we
optimistically ignore the risk of system failure, underperformance or
repair for the moment.

A system that does this in 10 years is worth paying £157 for now.

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

If one got a bit desperate and justified a 20 year payback, system
value would rise to £251. But I dont think thats justifiable in truth,
nor is the extra spend allowance very significant. Either will make a
cheap system and nothing more.


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. This preheats the header tank,
which of course must be hot water safe in this design. That rules out
use of plastic header tanks where already fitted. Metal headers are ok,
a plastic one would need replacement.


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
4x8 sheet 7mm WBP ply £? rough guess £5
stainless roof fixings £? guess £5
black paint £1

CH pump £30

loft piping insulation: cardboard and/or rags £0, sellotape to hold in
place temporarily £0.50, string to fix it permanently £0.50.
header tank insulation: as above, no more spend needed
connecting 2 pipe ends to header tank: £2
1mm cable from lighting jbox to pump £1-2
FCU & pattress £2
panel thermostat, bimetal, £5

HW header tank if metal one not already present: £ not sure, and will
vary according to source

Now, if you had to buy all the above new, total cost is:
£73 + maybe a new header tank

The numbers look quite a bit better if you've got various bits lying
around already, or can use chuckouts to build it from. Then it might
actually be worth the 2 days work.

But given the low value overall of such systems, I dont think this is
the way to go. More sensible to go for a system that delivers much
more, such as flat panel solar space heating, which is cheaper, easier,
requires no roof access, and delivers more payback.

Solar flat panel space heating is little more than a frame, polythene,
black mesh cloth and holes in the wall. I'll let someone to play with
the numbers if they wish.


NT



people are looking at this the wrong way

cost is a first approximation of energy. I use it here because the
traditional approach of looking at the energy embodied in the physical
parts of the product is far too inaccurate, since it takes no account
of the real energy costs of real world businesses. The whole point of
these figures is to demolish 2 false claims:
1. that solar dhw will pay back its money investment
2. that solar dhw will pay back its energy investment


givern the above would any one
ever buy a car,computer,tv e.t.c .

Cars are usually a good investment. Computers are usually a good
investment. Both have financial payback, and both improve quality of
life. A £2000 solar dhw system does neither.

TVs are a waste of upto a quarter of people's lifetime. All those hopes
and dreasm people have, if only they had the time.. they do, they just
choose to waste it away on junk tv.


NT

"samc" wrote in message
...

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

I've posed that question lots of times. Nobody has ever given an answer.

Mary

On 6 Mar 2006 15:53:46 -0800 someone who may be
wrote this:-

Solar flat panel space heating is little more than a frame, polythene,
black mesh cloth and holes in the wall.

Only if the building being heated is a single room.

If the building has several rooms then one needs to get the hot air
into these rooms.


--
David Hansen, Edinburgh
I will *always* explain revoked encryption keys, unless RIP prevents me
http://www.opsi.gov.uk/acts/acts2000/00023--e.htm#54

On 7 Mar 2006 06:58:47 -0800 someone who may be
wrote this:-

The whole point of
these figures is to demolish 2 false claims:
1. that solar dhw will pay back its money investment
2. that solar dhw will pay back its energy investment

The only problem is that your "figures" did not demolish anything.
For a start you assumed a very low level of savings on the cost of
heating domestic hot water.


--
David Hansen, Edinburgh
I will *always* explain revoked encryption keys, unless RIP prevents me
http://www.opsi.gov.uk/acts/acts2000/00023--e.htm#54

a écrit :
This thread is from uk.diy, and is kinda relevant for a.e.h too.


Ed Sirett wrote:

Putting the question the other way around, could you say what the total
installed price for a marginally justified system would be - with a 20
year payback say.

If you'd payed a lot (£2,000 say) for the system then I have no doubt
you'd not recover the cost. What might be the threshhold?


Good question. I'll have a go.

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






I'm curious to how you figure £20 a year in savings... (not having all
the information, the inital posts are no longer....)

If I look at dshw system here in France, I have;


min cover : 50% (lets be conservative) = 1000kWh electric avoided
average cover : 65% (for the most proactive region) = 1500kWh electric
avoided
electricity costs : 0.11€/kWh

so yearly savings = 110€ to 165€






(the rest of the equation here is, for flat plate hot water collectors
cost (installed, all taxes included) : 5500€
subsidies : tax credit 50% materiel costs (say 50% of 4000€)
local subsidies - bring total subsidy up to the 80% EC limit in many
regions)
current loan rates : approx 4% insurance included
current savings account interest rates : approx 4% (best case) approx
1.5% (average case))






Lets say we want it to break even after 10 years, interest is 5% and we
optimistically ignore the risk of system failure, underperformance or
repair for the moment.

A system that does this in 10 years is worth paying £157 for now.

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

If one got a bit desperate and justified a 20 year payback, system
value would rise to £251. But I dont think thats justifiable in truth,
nor is the extra spend allowance very significant. Either will make a
cheap system and nothing more.


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. This preheats the header tank,
which of course must be hot water safe in this design. That rules out
use of plastic header tanks where already fitted. Metal headers are ok,
a plastic one would need replacement.


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
4x8 sheet 7mm WBP ply £? rough guess £5
stainless roof fixings £? guess £5
black paint £1

CH pump £30

loft piping insulation: cardboard and/or rags £0, sellotape to hold in
place temporarily £0.50, string to fix it permanently £0.50.
header tank insulation: as above, no more spend needed
connecting 2 pipe ends to header tank: £2
1mm cable from lighting jbox to pump £1-2
FCU & pattress £2
panel thermostat, bimetal, £5

HW header tank if metal one not already present: £ not sure, and will
vary according to source

Now, if you had to buy all the above new, total cost is:
£73 + maybe a new header tank

The numbers look quite a bit better if you've got various bits lying
around already, or can use chuckouts to build it from. Then it might
actually be worth the 2 days work.

But given the low value overall of such systems, I dont think this is
the way to go. More sensible to go for a system that delivers much
more, such as flat panel solar space heating, which is cheaper, easier,
requires no roof access, and delivers more payback.

Solar flat panel space heating is little more than a frame, polythene,
black mesh cloth and holes in the wall. I'll let someone to play with
the numbers if they wish.


NT

I'

"David Hansen" wrote in message
...
On 7 Mar 2006 06:58:47 -0800 someone who may be
wrote this:-

The whole point of
these figures is to demolish 2 false claims:
1. that solar dhw will pay back its money investment
2. that solar dhw will pay back its energy investment

The only problem is that your "figures" did not demolish anything.
For a start you assumed a very low level of savings on the cost of
heating domestic hot water.

Indeed!

Mary

wrote in message
oups.com...
Mark wrote:
Ed Sirett wrote in message

If you'd payed a lot (£2,000 say) for the system then I have no doubt
you'd not recover the cost. What might be the threshhold?

That's still a moving target, how much will energy prices have to increase
before we can't afford NOT to fit some type of solar heating.

another good question, and another bastion of solar DHW support. So,
lets find out:


At todays prices a £2000 commercial system saves in the region of £20
per annum on hot water bills.

Hmm
How much is the average family's hot water expenditure over the two summer
quarters, a suggested saving of £20 seems awfully low even for a DIY jobie.

Im interested to know because my own consumption is not typical as we have
three B+B rooms that are normally occupied throughout this period.
When I fitted it 20 years ago it made a useful reduction in the amount of
oil used during the summer.
But in honesty I cant now remember by how much.



-

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

wrote:

Mark wrote:
Ed Sirett wrote in message

If you'd payed a lot (£2,000 say) for the system then I have no doubt
you'd not recover the cost. What might be the threshhold?

That's still a moving target, how much will energy prices have to
increase before we can't afford NOT to fit some type of solar heating.

another good question, and another bastion of solar DHW support. So,
lets find out:


At todays prices a £2000 commercial system saves in the region of £20
per annum on hot water bills.

I don't know how you get your figures, but the average North American uses
some 40 THOUSAND US gallons of hot water yearly. The water heater usually
runs in excess of 120F, from a coldwater supply well below 70F. Raising
40,000gal * 50F = 320,000lb * 50F = 16,000,000 BTU, which if I am not
mistaken is going to cost around $25/million BTU to heat. So that comes
out to $400/year. A tad more than £20, and well worth replacing even with
a system that only generates half your hot water.

Ack! I'm beginning to sound like Nick. GOTO 100.
--
derek

wrote:

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

You can risk it. I'm investing in the glycol flat-panel system.

--
derek

wrote:

It's more rational to say

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

Nick

Make an error on usenet? That usually provides plenty of free hot
water.

"Derek Broughton" wrote in message
...

I don't know how you get your figures, but the average North American uses
some 40 THOUSAND US gallons of hot water yearly.

My neighbour used to tell me that only mucky people have baths...

Mary

Derek Broughton wrote:

I don't know how you get your figures, but the average North American uses
some 40 THOUSAND US gallons of hot water yearly. The water heater usually
runs in excess of 120F, from a coldwater supply well below 70F. Raising
40,000gal * 50F = 320,000lb * 50F = 16,000,000 BTU, which if I am not
mistaken is going to cost around $25/million BTU to heat. So that comes
out to $400/year. A tad more than £20, and well worth replacing even with
a system that only generates half your hot water.

Where did you get your figures?
About 25 years ago, I was living in a drought-stricken area of the US.
Limits were put on water use - 50 US gallons per person per day. That was
for ALL water, not just the heated stuff. The only thing that suffered was
the garden - which wouldn't have been using heated water, anyway.

We were somewhere around Barstow, on the edge of the desert, when the
drugs began to take hold. I remember "Mary Fisher"
saying something like:


"Derek Broughton" wrote in message
...

I don't know how you get your figures, but the average North American uses
some 40 THOUSAND US gallons of hot water yearly.

My neighbour used to tell me that only mucky people have baths...

He probably couldn't be bothered taking the coal out of it.
--

Dave

I think you are off on your figures. According to
http://www.fsec.ucf.edu/solar/apps/sdhw/dhwsave.htm the typical home uses 20
gallons of hot water per day for the first two persons and 15 gallons of hot
water for each additional person. That would be 25,550 gallons of hot water
per year for a family of four.

"Derek Broughton" wrote in message
...
wrote:

Mark wrote:
Ed Sirett wrote in message

If you'd payed a lot (£2,000 say) for the system then I have no doubt
you'd not recover the cost. What might be the threshhold?

That's still a moving target, how much will energy prices have to
increase before we can't afford NOT to fit some type of solar heating.

another good question, and another bastion of solar DHW support. So,
lets find out:


At todays prices a £2000 commercial system saves in the region of £20
per annum on hot water bills.

I don't know how you get your figures, but the average North American uses
some 40 THOUSAND US gallons of hot water yearly. The water heater usually
runs in excess of 120F, from a coldwater supply well below 70F. Raising
40,000gal * 50F = 320,000lb * 50F = 16,000,000 BTU, which if I am not
mistaken is going to cost around $25/million BTU to heat. So that comes
out to $400/year. A tad more than £20, and well worth replacing even with
a system that only generates half your hot water.

Ack! I'm beginning to sound like Nick. GOTO 100.
--
derek

"Grimly Curmudgeon" wrote in message
...
We were somewhere around Barstow, on the edge of the desert, when the
drugs began to take hold. I remember "Mary Fisher"
saying something like:


"Derek Broughton" wrote in message
...

I don't know how you get your figures, but the average North American
uses
some 40 THOUSAND US gallons of hot water yearly.

My neighbour used to tell me that only mucky people have baths...

He probably couldn't be bothered taking the coal out of it.

You're making asumptions. Plural.
--

Dave

In message .com,
writes

TVs are a waste of upto a quarter of people's lifetime. All those hopes
and dreasm people have, if only they had the time.. they do, they just
choose to waste it away on junk tv.

.... And newsgroups

( you can check out any time you like
but you can never leave)

--
geoff

David Hansen wrote:
On 7 Mar 2006 06:58:47 -0800 someone who may be
wrote this:-

The whole point of
these figures is to demolish 2 false claims:
1. that solar dhw will pay back its money investment
2. that solar dhw will pay back its energy investment

The only problem is that your "figures" did not demolish anything.
For a start you assumed a very low level of savings on the cost of
heating domestic hot water.

The figures in this thread have stated the savings amount required to
make it worthwhile. If you think you can save well over £100 a year
with a £2000 water heater, go for it. I dont.


NT

wrote:
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.

Welcome to uk.diy Nick. Maybe you can give them a pointer or 2 on how
to make a constructive DHW system that pays its way, too much talk of
junk designs here.

Yes, its 20 uk pounds. I'm not sure how you use all that hot water


NT


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

Derek Broughton wrote:
wrote:
Mark wrote:
Ed Sirett wrote in message

If you'd payed a lot (£2,000 say) for the system then I have no doubt
you'd not recover the cost. What might be the threshhold?

That's still a moving target, how much will energy prices have to
increase before we can't afford NOT to fit some type of solar heating.

another good question, and another bastion of solar DHW support. So,
lets find out:


At todays prices a £2000 commercial system saves in the region of £20
per annum on hot water bills.

I don't know how you get your figures, but the average North American uses
some 40 THOUSAND US gallons of hot water yearly. The water heater usually
runs in excess of 120F, from a coldwater supply well below 70F. Raising
40,000gal * 50F = 320,000lb * 50F = 16,000,000 BTU, which if I am not
mistaken is going to cost around $25/million BTU to heat. So that comes
out to $400/year.

We dont spend that much here.


A tad more than £20, and well worth replacing even with
a system that only generates half your hot water.

Half your how water would be $200 a year, roughly £100 per annum. It
would take - as said before - the remaining life of the universe to pay
this off, if there were zero risk of it ever needing repair etc.

We arent average north americans.


NT

In message , Harry Chickpea
writes
wrote:

It's more rational to say

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

Nick

Make an error on usenet? That usually provides plenty of free hot
water.


Hot air system, you mean


--
geoff

The message . com
from contains these words:

Yes, its 20 uk pounds. I'm not sure how you use all that hot water

Well, they have to bath the car once a week. (insert pseudo-smiley)

--
Skipweasel
Pay no attention to the man behind the curtain.

Mary Fisher wrote:


"Derek Broughton" wrote in message
...

I don't know how you get your figures, but the average North American
uses some 40 THOUSAND US gallons of hot water yearly.

My neighbour used to tell me that only mucky people have baths...

LOL. I accept that North Americans are much more wasteful of water - heated
or not - than Europeans, but a difference of $400+ to £20 for the cost of
heating that water just doesn't make sense.
--
derek

wrote:

Derek Broughton wrote:
wrote:

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

You can risk it. I'm investing in the glycol flat-panel system.

Nick's point was that a draindown system without antifreeze can be
designed to be safe in winter.

I know what his point was. He might even be right. I, however, have no
intention of risking it. I can, and will, profitably install a glycol loop
system with heat exchanger.
--
derek

wrote:

David Hansen wrote:
On 7 Mar 2006 06:58:47 -0800 someone who may be
wrote this:-

The whole point of
these figures is to demolish 2 false claims:
1. that solar dhw will pay back its money investment
2. that solar dhw will pay back its energy investment

The only problem is that your "figures" did not demolish anything.
For a start you assumed a very low level of savings on the cost of
heating domestic hot water.

The figures in this thread have stated the savings amount required to
make it worthwhile. If you think you can save well over £100 a year
with a £2000 water heater, go for it. I dont.

The "figures" are a ridiculously low number for cost of hot water that you
made up. I can _easily_ save £100 a year with a system that will cost me
about that much. Check back next year for real use figures...
--
derek

Ron Purvis wrote:

I think you are off on your figures. According to
http://www.fsec.ucf.edu/solar/apps/sdhw/dhwsave.htm the typical home uses
20 gallons of hot water per day for the first two persons and 15 gallons
of hot water for each additional person. That would be 25,550 gallons of
hot water per year for a family of four.

OK, I'll accept those numbers. Anyone got a better figure on the average
cost of heating water? My numbers for heat required are, if anything, on
the low side, but at $25/million BTU, and only 25,000 gallons per year,
you're talking $250/year (somebody else said $20/month, so same ballpark).
Still plenty to make a commercial solar water heater pay off.

--
derek

S Viemeister wrote:

Derek Broughton wrote:

I don't know how you get your figures, but the average North American
uses
some 40 THOUSAND US gallons of hot water yearly. The water heater
usually
runs in excess of 120F, from a coldwater supply well below 70F. Raising
40,000gal * 50F = 320,000lb * 50F = 16,000,000 BTU, which if I am not
mistaken is going to cost around $25/million BTU to heat. So that comes
out to $400/year. A tad more than £20, and well worth replacing even
with a system that only generates half your hot water.

Where did you get your figures?
About 25 years ago, I was living in a drought-stricken area of the US.
Limits were put on water use - 50 US gallons per person per day. That was
for ALL water, not just the heated stuff. The only thing that suffered
was the garden - which wouldn't have been using heated water, anyway.

See Ron's cite - I'll grant you that you don't _need_ to use 50 gallons of
hot water, but the average family does, anyway. You're right, that's not
40,000 per year, but still an order of magnitude above Meow's figure.
--
derek

wrote:

Lets say it saves =A320 a year heating dhw only.

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

Welcome to uk.diy Nick. Maybe you can give them a pointer or 2 on how
to make a constructive DHW system that pays its way...

It isn't worth doing much to save 20 pounds per year, but it might make
more sense to collect both hot water and space heat from a polytunnel,
which might have a linear parabolic reflective north wall over a 2'x6'x8'
shoebox tank with an EPDM or polyethylene film liner and a $60 1"x300' piece
of pressurized polyethylene pipe for a heat exchanger and a horizontal
draindown EPDM cover with a small pump to move water up 2" over the cover
when the sun is shining, and a greywater heat exchanger, eg 2 55 gallon
drums with PE pipe in series.

Gary Reysa and I have been working on this sort of DIY stuff. See

http://BuildItSolar.com.

Nick

On Tue, 07 Mar 2006 20:33:24 -0400 Derek Broughton wrote :
OK, I'll accept those numbers. Anyone got a better figure on
the average cost of heating water?

The latest SAP 2005 algorithms for a 100m2 house, 110 litre factory
insulated cylinder give a required raw energy input for DHW of
3172kWh. Divide this by the boiler efficiency to get the actual
energy required.

--
Tony Bryer SDA UK 'Software to build on' http://www.sda.co.uk
Free SEDBUK boiler database browser http://www.sda.co.uk/qsedbuk.htm
[Latest version QSEDBUK 1.12 released 8 Dec 2005]

On Tue, 07 Mar 2006 22:34:03 +0000 Ajh wrote :
Thanks for the link but the figures are too coarse as they show
annual heat falling on the surface of the panel. To make a judgment
I need to know how much of that heat arrives during the space
heating season and how much in the water heating season.

The figures used in the SAP calculations where applicable are 50%
during the heating season (taken as 34 weeks) and 50% during the rest
of the year.

--
Tony Bryer SDA UK 'Software to build on' http://www.sda.co.uk
Free SEDBUK boiler database browser http://www.sda.co.uk/qsedbuk.htm
[Latest version QSEDBUK 1.12 released 8 Dec 2005]

wrote in message
ups.com...
David Hansen wrote:
On 7 Mar 2006 06:58:47 -0800 someone who may be
wrote this:-

The whole point of
these figures is to demolish 2 false claims:
1. that solar dhw will pay back its money investment
2. that solar dhw will pay back its energy investment

The only problem is that your "figures" did not demolish anything.
For a start you assumed a very low level of savings on the cost of
heating domestic hot water.

The figures in this thread have stated the savings amount required to
make it worthwhile. If you think you can save well over £100 a year
with a £2000 water heater, go for it. I dont.


I do.

Mary


NT

"Guy King" wrote in message
...
The message . com
from contains these words:

Yes, its 20 uk pounds. I'm not sure how you use all that hot water

Well, they have to bath the car once a week. (insert pseudo-smiley)

We don't. When he does wash it he uses cold roof water from the butt.

"Grimly Curmudgeon" wrote in message
...
We were somewhere around Barstow, on the edge of the desert, when the
drugs began to take hold. I remember "Mary Fisher"
saying something like:

My neighbour used to tell me that only mucky people have baths...

He probably couldn't be bothered taking the coal out of it.

You're making asumptions. Plural.

That he had a bath at all and that he could afford coal?

That it was a he and that coal was used in the house.
--

Dave

wrote in message
ups.com...

Half your how water would be $200 a year, roughly £100 per annum. It
would take - as said before - the remaining life of the universe to pay
this off,


Don't be daft.

"Derek Broughton" wrote in message
...


Why half? I can get 80% at least. You only do laundry when the sun's out
(which is true anyway because I'm off grid), you take showers in the
afternoon, and do dishes in the evening.

It has changed the way we use hot water.

And it's turned us into thermoholics - watching the thermometer every time
we pass!

Mary