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)
Can you share the maths - please
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
but the capital costs will be higher - there is a diminishing return after about 50% - more sqM per Kw delivered
unless its a HP then its about 4c to 6c
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
Never disputed that just looking at a purely financial return
also look at the attached
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?
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
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!
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%
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
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)
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.
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.
FC, can we see a little more detail on the brake down of the costs here thanks
6000kWh for just heating the hot water per annum ?
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
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!
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.
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?