[fclauson]

Originally Posted by daheff

if you were 50% out it'd be 1800...not 2400. 2400 is twice 1200 (100%+ 100%)

So you are spending €1800 per year in year one for your hot water - you need to look at that - a well controlled h/w system for a family of 6 should be costs a lot less than that (and remember we are only talking about hot water and only the saving in heating hot water in the summer)

Originally Posted by MicktheMan

I just did rough sums and it looks like the 1200 saving is in year 15 alone!
I make the total saving over the 15 years at roughly 9400!

(This assumes that the fuel inflation of 12% is annual and not total inflation over the 15 years)

Can you share the maths - please

Originally Posted by saibhne

Just a few questions on this:
Why would you take 15 years as the period to determine your ROI? Solar systems can operate for 30 years or so..

please don't kid your self - after 15 years tubes, pumps, and anti freeze fluid will all need replacing/repairing - not a total replacement but a majour refurb - and by then the hyrdogen fuel cell will be available and the refurb will not be necessary

Also if a house is well insulated like swanners is then why not invest your money in something that has a good return?

And a few comments.

I think a 60% solar fraction is entirely possible - depends on whether the system you install is designed to give you that.

but the capital costs will be higher - there is a diminishing return after about 50% - more sqM per Kw delivered

It's worth noting that 12c per kWh is assuming the water is being heated with gas/oil really. If the water is heated with electricty your cost per kWh is more like 15c per kWh inc VAT and rising.

unless its a HP then its about 4c to 6c
but
I agree - it does depend - and may be if you are just using an immersion for your h/w then spending 4K may help with this might make sense (although you should look at other heat sources if you are refurbing your h/w & heating system

The value of having a clean and Irish source of fuel in our energy mix is also not quantified here. In terms of energy security this is advantageous as it is in terms of climate change mitigation. As a country we buy 90% of our energy needs from other countries - we are very exposed in this regard and we need to change this to be more competitive as an economy. Solar thermal can be a small contribution to this and is an easy one to make happen.

Never disputed that just looking at a purely financial return

[fclauson]

also look at the attached

[BryanF]

Originally Posted by fclauson

please don't kid your self - after 15 years tubes, pumps, and anti freeze fluid will all need replacing/repairing - not a total replacement but a majour refurb

Francis how will the lifespan of your preferred HP compare with the SP?
what sort of guarantees and assurances have you gotten?
what's the efficiency and potential maintenance comparison over their lifespans?
Is it relevant that your SP/fossil v HP comparison is based on a passive house standard distribution?

[goat2]

i hope to get the tubes, but what is really off putting is the price, too much, i will look to go down the diy route, putting a tank in attic which will be warmed up by the panels, and feeding my hotpress tank off this, that way i will have less to buy, just ordinary inderect tank and change connections around a bit

[MicktheMan]

Originally Posted by fclauson

Can you share the maths - please

kWh price increasing at 12% per annum, 60% of annual dhw from solar

Year ----kWh ----Price/kWh ----Annual dhw cost ----60% saving
1 -------3500 ----0.12 ---------420 ----------------252
2 -------3500 ----0.13 ---------470 ----------------282
3 -------3500 ----0.15 ---------527 ----------------316
4 -------3500 ----0.17 ---------590 ----------------354
5 -------3500 ----0.19 ---------661 ----------------397
. . . . .
. . . . .
. . . . .
14 ------3500 ----0.52 ---------1833 ---------------1100
15 ------3500 ----0.59 ---------2053 ---------------1232
--------
Total saving over 15 years 9394

Note that general inflation has not being taken into account!

[fclauson]

Mick - you are right - I made a BIG mistake in my maths

but (tries to recover)

fuel prices today assuming oil we should use about 0.085 at say 90%
http://www.seai.ie/Publications/Stat...y_2012_pdf.pdf
which changes things a bit = €7437 costs after 15 year

If your system cost €4.5K then thats €2937 saved

All I was trying to point out is that there are not the BIG immediate savings with solar to be made which people thing
with a pay back of 11,12,13,14 years depending - its a long term investment

[fclauson]

Originally Posted by BryanF

Francis how will the lifespan of your preferred HP compare with the SP?
what sort of guarantees and assurances have you gotten?
what's the efficiency and potential maintenance comparison over their lifespans?
Is it relevant that your SP/fossil v HP comparison is based on a passive house standard distribution?

Brian - basically I don't know - my parents fridge is 20 years old - I had one which failed after 5 - (both use the basic same compressor technology that a HP does)

[MicktheMan]

Originally Posted by fclauson

All I was trying to point out is that there are not the BIG immediate savings with solar to be made which people thing
with a pay back of 11,12,13,14 years depending - its a long term investment

I agree ... most people don't have the first clue what it costs them to heat their water or even what is the most efficient method.

[recedite]

Originally Posted by fclauson

Lets say its 3500 Kwh (thats for a family of 6) ....

Also, 5000 - 6000 Kwh (units of electricity) is more realistic for a family of 5 people.
So, 5500*€0.12*0.6*15 years = €5940 even with no fuel inflation.

Better to pump a few grand into our own green economy, than to be permanently importing dirty fossil fuels from abroad. And if you can save money while you're at it, everyones a winner.

[BryanF]

Originally Posted by fclauson

Brian - basically I don't know - my parents fridge is 20 years old - I had one which failed after 5 - (both use the basic same compressor technology that a HP does)

Originally Posted by fclauson

also look at the attached

FC, can we see a little more detail on the brake down of the costs here thanks

[fclauson]

Originally Posted by recedite

Also, 5000 - 6000 Kwh (units of electricity) is more realistic for a family of 5 people.
So, 5500*€0.12*0.6*15 years = €5940 even with no fuel inflation.

Better to pump a few grand into our own green economy, than to be permanently importing dirty fossil fuels from abroad. And if you can save money while you're at it, everyones a winner.

6000kWh for just heating the hot water per annum ?

[fclauson]

Originally Posted by BryanF

FC, can we see a little more detail on the brake down of the costs here thanks

Sure

the usage numbers are taken from a combination of DEAP and PHPP - both have their own view on how much energy demand my build will have.

Using those as a base number I then calculated the costs for each system over 15 years (which was selected for no good reason other than than oil & gas boilers have a life of about that)
Assumes equal capital outlay (which is a bit skewed because at the low energy demand end of the scale a HP is cheaper to install than SP + Thermal store + Oil or Gas)
Also remember that as part of this I have to hit part L renewables - because obviosuly the very cheapest from a capital costs perspective would be a cheap and chearful oil boiler on its own.

given these energy demands then I calculated running costs

Attached is the spread sheet - just change the YELLOW boxes to enter you own deamand figures

Please do me a favour and publish your results here - so we can do a bit of a public compare

[Do-more]

Originally Posted by recedite

Also, 5000 - 6000 Kwh (units of electricity) is more realistic for a family of 5 people.

I made an attempt to quantify energy usage for our DHW a few months ago.

All our DHW is heated by electric immersion. I should have fitted an energy monitor on it last year to get an accurate figure but could only do a guesstimate from our electricity bill.

Working backwards so that any errors or inaccuracies add to the DHW portion of the bill I figured that for our family of 4 worst case is currently 3000kWhr per year for DHW.

I was surprised at that myself expecting it to be higher, granted the kids are only 5 & 8 so are not teenagers standing in the shower for 30mins a time!

[MicktheMan]

Originally Posted by recedite

Also, 5000 - 6000 Kwh (units of electricity) is more realistic for a family of 5 people.

Our dhw is only heated by our non-condensing ch oil boiler (have never used the immersion) and we use between 300 and 320 liters of oil per year to heat the dhw.
This would tally pretty well with FC's figure for dhw use. There are 5 in our household including 3 teenage girls!
So the 5-6000 kwh figure is deffo on the high side.

[Merch]

Originally Posted by fclauson

Sure

the usage numbers are taken from a combination of DEAP and PHPP - both have their own view on how much energy demand my build will have.

Using those as a base number I then calculated the costs for each system over 15 years (which was selected for no good reason other than than oil & gas boilers have a life of about that)
Assumes equal capital outlay (which is a bit skewed because at the low energy demand end of the scale a HP is cheaper to install than SP + Thermal store + Oil or Gas)
Also remember that as part of this I have to hit part L renewables - because obviosuly the very cheapest from a capital costs perspective would be a cheap and chearful oil boiler on its own.

given these energy demands then I calculated running costs

Attached is the spread sheet - just change the YELLOW boxes to enter you own deamand figures

Please do me a favour and publish your results here - so we can do a bit of a public compare

Equal capital outlay for HP to Sp based on a new instal maybe?? I cant imagine the capital outlay for a HP, space heating system to be cheaper than any other existing system given the kind of work needed to be done.
Is the efficiency for the HP given an average across a year as it surely will go up and down through the year? and be different for space and dhw? what is the COP for dhw using HP, thought HP was better for space heating than dhw and better performance on the basis it was run quite continuously at low temp and not on and off, thereby offsetting the gains? unless it is in a 24hour occupied building.
HP still uses electricity, only, whereas SP offsets the amount of gas/oil used to heat water reducing the consumption. HP only maintains the advantage if the COP can be guaranteed to be between certain values all the time surely?
Out of curiosity, in the event of a power/pump failure, what fail safe prevents damage to solar thermal (tubes) if the pump doesnt run for the above reasons?