Is Solar worth it, Financially Speaking?

Tester46

Given the costs of solar panels and systems and given the limited SEI grants, is it worth getting solar in to heat DHW. I mean that from a purely financial point of view, not from an environmental point of view.

How long does solar take to earn back its costs (installation and maintenance)?

Lashed

I was doing a couple of quick calcs yesterday and discovered that at today's prices solar panels will take around 30 years to pay for themselves. That's providing nothing goes wrong with them in the meantime.
You would be much better off putting your money into insulation, windows and heating controls.
A good mixed fuel boiler and small high efficiency stove is a much better option for DWH and even with an immersion heater for the summer than solar panels on the market today.

sinnerboy

Lets look it this another way ( rhetorical question )

Why do you think the 2008 B Regs REQUIRE a min provision of renewables ?

sydthebeat

Tester46 wrote: »

Given the costs of solar panels and systems and given the limited SEI grants, is it worth getting solar in to heat DHW. I mean that from a purely financial point of view, not from an environmental point of view.

How long does solar take to earn back its costs (installation and maintenance)?

if you spend €20 on a bag of coal..... and burn it in an open fire which is 30% efficient....

do you go back to the coal supplier and ask him for €14 back as you didt get the benefit it???????

same with oil or gas burning in a 75% boiler......

The whole pont about solar being a 'renewable' source is that it DOES have a pay back period.... oil and gas and solid fuel doesnt....

Your electricity coming in from your ESB line is 36% efficient... imagine getting an ESB bill and only paying 36% of it on grounds that you dont get the full 100% value for your money...

sinnerboy

100 % agree Syd . But many won't invest unless they see a quick payback

( Damn - answered my own rhetorical question ) :pac::pac::pac:

kevymoss

In my opinion it really depends on your usage. If you family uses say 150 Ltr - 200 Ltrs per day It will pay itslef off quite quickly 5-8 years depedning on oil prices

Lashed

sydthebeat wrote: »

if you spend €20 on a bag of coal..... and burn it in an open fire which is 30% efficient....

do you go back to the coal supplier and ask him for €14 back as you didt get the benefit it???????

same with oil or gas burning in a 75% boiler......

The whole pont about solar being a 'renewable' source is that it DOES have a pay back period.... oil and gas and solid fuel doesnt....

Your electricity coming in from your ESB line is 36% efficient... imagine getting an ESB bill and only paying 36% of it on grounds that you dont get the full 100% value for your money...

Electricity is the only fuel that has 100% efficiency. Just because most of it produced is lost before it gets to the grid doesn't mean you don't get full benefit.

All boilers below 90% efficiency are now off the market.

I'm not saying throw a bag of coal into an open fire. Throw 1/8 of a bag into a solid fuel stove/boiler which has 70% efficiency and it'll last all day.

You can also call a stove or solid fuel boiler a renewable source if you choose to burn logs.

Average cost of solar panels with all bells and whistles would be 5000 which would buy you an awful lot of timber.

sydthebeat

Lashed wrote: »

Electricity is the only fuel that has 100% efficiency. Just because most of it produced is lost before it gets to the grid doesn't mean you don't get full benefit.

ive never seen a post at contradicts itself in such a short space....

you pay for what it cost ESB to produce it,....

Im afraid you are completely incorrect in your opinion on this.

Lashed wrote: »

All boilers below 90% efficiency are now off the market.

do we ignore the 1.7 million existing housing stock in Ireland!!!?????

Lashed wrote: »

I'm not saying throw a bag of coal into an open fire. Throw 1/8 of a bag into a solid fuel stove/boiler which has 70% efficiency and it'll last all day.
.

throw nothing at your solar panels and it will produce a lot your domestic hot water needs for most of the year.

Lashed wrote: »

You can also call a stove or solid fuel boiler a renewable source if you choose to burn logs.
.

yes you can, and your point is.....?
it is 'renewable' because there is a common assumption that we currently can grow timber at the same rate at which we consume it...

Lashed wrote: »

Average cost of solar panels with all bells and whistles would be 5000 which would buy you an awful lot of timber.

not if you factor in an average cost of 10,000 to build a shed to store the timber...

quentingargan

Lashed wrote: »

Average cost of solar panels with all bells and whistles would be 5000 which would buy you an awful lot of timber.

First, a declaration of interest - I own a substantial chunk of a company that sells solar water heaters, and at Cork Institute of Technology I teach plumbers how to install them.

There is a lot of baloney talked about payback times, a bit like the good old days of double glazing salesmen. Many companies suggest that their EUR6,000 systems have a payback time of five years. Anyone out there spending 1,200 a year on hot water?

Hardware costs have come down as the market has grown, and the total hardware cost for retrofitting, after the grant, is roughly between €2,000 and €3,000 including all bells and whistles (and a heat dump which I consider essential for the longevity of the system, but which seldom gets included in the bells and whistles department).

This includes replacing the cylinder, something which isn't an "additional" cost when putting systems into a new house. I had always opposed grant aiding installation into a new house, because I don't think it is needed. The government clearly moved from the carrot to the stick when they withdrew the grant for new houses, but made it mandatory instead!

I reckon in most cases solar water heating will save you EUR350 a year. This will rise as energy prices rise (which they will) so payback time will reduce during the life of the system.

But there is a degree of satisfaction from knowing that your hot water came from the light and not the dark....:cool:

Q

sydthebeat

quentingargan wrote: »

But there is a degree of satisfaction from knowing that your hot water came from the light and not the dark....:cool:

Q

i like that one...

i may use it again...

holdfast

No its not worth it, they payback is too long for most people to consider.

But meets building regs and you can feel good about yourself (PS I have one and bought it for 3500 euro and with my demand and alternative heating options the payback will be in the region 12 years. )

Lashed

sydthebeat wrote: »

ive never seen a post at contradicts itself in such a short space....

you pay for what it cost ESB to produce it,....

Im afraid you are completely incorrect in your opinion on this.

You asked ''Is solar worth it financially speaking?''
You didn't ask Is it worth it from a carbon footprint point of view?

You can't do anything about what it costs for the ESB to produce electricity. The same as you can't do anything about them paying an average wage of 76,000.

If you turn on your Immersion, it is a 100% efficient way of heating the water. There is no heat waste. This is a known fact. A 3.5kW immersion will use 3.5kW. 100% efficiency. No waste.

Now if the ESB want to waste 74% of the energy it took to get the electricity to you, you will pay for that in your bill but you have not wasted any energy.

Now don't get me wrong, it is an expensive way of heating your water and should only be done in summer when it is not worth firing up your boiler or stove.

do we ignore the 1.7 million existing housing stock in Ireland!!!?????

The 1.7 million housing stock would be much better off getting a high efficient boiler than solar panels.


throw nothing at your solar panels and it will produce a lot your domestic hot water needs for most of the year.

You are not throwing nothing at your solar panels if you take into account that you may have spent 5000 on the cost of them.



yes you can, and your point is.....?
it is 'renewable' because there is a common assumption that we currently can grow timber at the same rate at which we consume it...

Again not carbon footprint not but ''financially speaking''. Timber if you have access to it is free not 5,000

not if you factor in an average cost of 10,000 to build a shed to store the timber...

The shed will not need repair or replacement after a few years whereas panels most likely will. I have been talking to a plumber recently who only after just over a year has been out replacing cracked panels and fogged up tubes.

We all know the cost of a plumber call out and that's before he has to do anything or use any materials.

sinnerboy

Yeah . I've just had to replace my tyres . Never buying a car again .

quentingargan

Lashed wrote: »

The shed will not need repair or replacement after a few years whereas panels most likely will. I have been talking to a plumber recently who only after just over a year has been out replacing cracked panels and fogged up tubes.

We all know the cost of a plumber call out and that's before he has to do anything or use any materials.

Flatplate panels, properly installed, should last 45 years with no maintenance. The only possible reason for your plumber to be calling out is either bad panels, or bad workmanship. The same applies to tubes, though the tube itself needs to be changed after about 20 years (they cost about 5 euros each).

A common cause of failure is that plumbers are unwilling to spend €200 on a motorised valve and radiator to dump surplus heat when the house is unoccupied, or the water is not being used. In that situation, the panel goes to 220 degrees (tubes) or 160 degrees (flatplate), and the system boils. That is OK occasionally during a power cut, but regularly bringing panels to those temperatures damages the panel, pipe insulation and antifreeze.

Sadly, SEI doesn't insist on standards in this area.

sinnerboy

quentingargan wrote: »

Sadly, SEI doesn't insist on standards in this area.

Nope . They fill up their Grant Approved installer list by simply taking money off those who pay them , giving Joe Public the impression that some of of QA is in operation

..... now in what OTHER sphere of SEI activity has something like this also occurred ...... nope - can't think of any

quentingargan

sinnerboy wrote: »

Nope . They fill up their Grant Approved installer list by simply taking money off those who pay them

Eh, thankfully they don't charge to go onto that list, but you do have to pay a fee - usually 600 quid - to attend a FETAC approved course. Its the courses that are a mixed bag.

But initially when the grant was launched, and up until March last year, the only qualification required was a tax clearance certificates. Taoiseagh need not apply ..... (is that the plural of taoiseach??).

BER assessors is a different matter - €1,000 to register with SEI, €500 a year thereafter and a few more €s with every assessment you send in. Pity the property boom ended - here was another nice little earner...

sinnerboy

quentingargan wrote: »

Eh, thankfully they don't charge to go onto that list, but you do have to pay a fee - usually 600 quid - to attend a FETAC approved course. Its the courses that are a mixed bag.

My bad .

Ah.... the Fetac courses yes . My BER Assessor Fetac training provider contacted me to do that course - covering installation of Solar , Heat Pumps and WP Boilers .

Now , assembling a flat pack , changing a fuse in a plug or plunger-cleaning a blocked sink is about the extent of my hands on construction skills ............. they would have taken my money all the same


Again ...... what other SEI type activity does this sound like ........ no .... thought i had it .... it's gone

.

metalscrubber

Sinnerboy,

You a bold person!

Aptly named then!

BMurr

I was going to install my own system, I'm handy with the spanners etc and can't see it being too difficult if I can get all the parts as a package. I did contact a company based in Dublin who were willinmg to put me through their course for 50 euro which would have shown me how to do the job. Trickiest bit seems to be getting the panels on the roof, scaffold needed etc. Where would one go to get the 'kit' for a vacuum tube system?
In a moment of madness I did get a guy in to give me a quote to install a system, he went to trouble of measuring and was going to send me the quote. No quote arrived so I figure if he couldn't get that part of the process right what was going to happen when he actually got the commission? Better to take control of it myself I reckon.

quentingargan

BMurr wrote: »

Where would one go to get the 'kit' for a vacuum tube system?

I'll respond with address of panel suppliers off the privately. I also do but based in Bantry, W. Cork. It is possible to self-install, and you may well do a better job than some "professionals":eek:.

Q

rosullivan

quentingargan wrote: »

I'll respond with address of panel suppliers off the privately. I also do but based in Bantry, W. Cork. It is possible to self-install, and you may well do a better job than some "professionals":eek:.

Q

Hi, Have PM'd you re that list. How much roughly is a standard pack with bells and whistles (incl heat dump)?

Thanks

quentingargan

rosullivan wrote: »

Hi, Have PM'd you re that list. How much roughly is a standard pack with bells and whistles (incl heat dump)?

Thanks

Hi, I will PM you that info. A heat dump is just a high temperature motorised 3 port valve and a radiator or two (depending on the panel size). The controller usually has an output for the motorised valve. That's why I am disappointed that heat dumps are very seldom included in the installation .
Q

Traditional

Ther is new stuff coming on the market this year call tec panels wireless, pipeless, at a price that everybody can afford ,and they can be placed on a wall , in the garden etc , it will heat everything , hot water, central heating even you pets house or kennel
solar panels are goin to be a thing of the past , dont even think of buying them , its old tecnology now .

Traditional

nice little earner all right on the net you can buy them for 50e great , that will knock the stuffing out of that earner !!

Matt Simis

Traditional wrote: »

Ther is new stuff coming on the market this year call tec panels wireless, pipeless, at a price that everybody can afford ,and they can be placed on a wall , in the garden etc , it will heat everything , hot water, central heating even you pets house or kennel
solar panels are goin to be a thing of the past , dont even think of buying them , its old tecnology now .

TEC as in thermoelectric cooler? Every TEC Ive used requires insane amounts of power (electrical) to run. Or maybe something different.. got any links?

congo_90

This thread is more off topic than an AH thread could ever be. Op asked if it's finiancially worthwhile to have solar heating.
So why are we talking about FETAC courses etc? TBH I know fcuk all about heating but was interested in this thread. this should be locked

MickLimk

Traditional wrote: »

Ther is new stuff coming on the market this year call tec panels wireless, pipeless, at a price that everybody can afford ,and they can be placed on a wall , in the garden etc , it will heat everything , hot water, central heating even you pets house or kennel
solar panels are goin to be a thing of the past , dont even think of buying them , its old tecnology now .

Traditional wrote: »

nice little earner all right on the net you can buy them for 50e great , that will knock the stuffing out of that earner !!

Have to be the most bizarre posts on this topic I've ever seen!

I'd love to see details of this tec panel system that will somehow heat everything without wires and pipes. I'd also like to know where you can get solar panels for €50...

Traditional

well you wont get them in heat merchants or any other store in Ireland , look if you want to source things well you can now this minute , you have the world at your fingers , the big wide net !the greeks have invented it , and they are a mean race , they wont spend , every house in greece have solar , do you think they would pay the prices of a solar system we do in Ireland ?

BMurr

MickLimk wrote: »

Have to be the most bizarre posts on this topic I've ever seen!

I'd love to see details of this tec panel system that will somehow heat everything without wires and pipes. I'd also like to know where you can get solar panels for €50...

Could that be something to do with that wireless transfer of electrical energy invention that Microsoft announced last year??

shcoff

quentingargan wrote: »

The same applies to tubes, though the tube itself needs to be changed after about 20 years (they cost about 5 euros each).

quentin a typo surely?

quentingargan

shcoff wrote: »

quentin a typo surely?

Nope. There are tubes where the heat pipe is welded to the glass - they are expensive to replace. The flask type where the glass flask is separate to the heat pipe are mass produced in China and are cheap as chips. If you were buying 40 or 60 of them to replace a whole set, that would be the price - maybe a bit less. Q

mspark.guinane@

sydthebeat wrote: »

if you spend €20 on a bag of coal..... and burn it in an open fire which is 30% efficient....

do you go back to the coal supplier and ask him for €14 back as you didt get the benefit it???????

same with oil or gas burning in a 75% boiler......

The whole pont about solar being a 'renewable' source is that it DOES have a pay back period.... oil and gas and solid fuel doesnt....

Your electricity coming in from your ESB line is 36% efficient... imagine getting an ESB bill and only paying 36% of it on grounds that you dont get the full 100% value for your money...

I agree, it's not all-about-the-money.......:rolleyes:
a new approach to both "money" & awareness of the environment is thr crucial point of action.
+ the "Gods of the Grid" give you nothing........!:mad:

quentingargan

mspark.guinane@ wrote: »

I agree, it's not all-about-the-money.......:rolleyes:

And even if it was "all about the money", according to the Stern report, preventing climate change is going to be a lot more affordable than living with it....

Tester46

Did anyone hear recently about some company in Galway that claims to have a "new" type of solar panel that they claim is something like 75%(?) more efficient than current solar panels at the same cost? Is that right? Is that possible?

(I have no connection to them, but someone told me about this this week and I'm trying to find out more)

homer911

http://www.boards.ie/vbulletin/showthread.php?t=2055483414

Tester46

homer911 wrote: »

http://www.boards.ie/vbulletin/showthread.php?t=2055483414

Thanks - Posted this there - maybe someone here has some ideas?

My plumber is currently quoting me €6,000 +VAT for what he described as a "3-panel in roof flat face integrated velux solar system". What should I be asking him?

I have the list of parts from that company's website [NOTE: quentingargan PM'd me a website] - should I also be asking about:
- the controller
- size of expansion tank (what size - 25l?)
- flat panel or tubes
- heat dump (e.g. a rad)
- integration into my non-pressurised central heating system
- whether 3-coil cylinder (which is extra) is copper or stainless steeland level of insulation (looking for 100mm as it's in a seperate boiler house)
- whether all piping is insulated

- What else?

Thanks.

GoneShootin

Traditional wrote: »

Ther is new stuff coming on the market this year call tec panels

link?

Evergreen

Has anybody tired to calculate the payback of solar panels for an average domestic installation? Here is an example based on electrical usage.

Hot Water Heating Costs:
Immersion on 3 hours per day
3.5kW immersion heater
ESB costs 20 cent per kW incl VAT, Rental, PS levey, etc
3hrs x 3.5 kws x 365 days = 3832 kWhrs per year
3832 x 20 cent = EUR 766 per year hot water heating costs

Solar Installation Costs:
EUR 5500 7.2 sq m solar panels, 300L dual coil tank, installation, VAT, etc
EUR 1500 grant where available
EUR 4000 with grant

Savings
EUR 766 x 70% (solar contribution) = EUR 536 per year

Payback With Grant
EUR 4000 / EUR 536 = 7.46 years

Payback without grant
EUR 5500 / EUR 536 = 10.26 years

gizmo555

Evergreen wrote: »

Has anybody tired to calculate the payback of solar panels for an average domestic installation? Here is an example based on electrical usage.

Hot Water Heating Costs:
Immersion on 3 hours per day
3.5kW immersion heater
ESB costs 20 cent per kW incl VAT, Rental, PS levey, etc
3hrs x 3.5 kws x 365 days = 3832 kWhrs per year
3832 x 20 cent = EUR 766 per year hot water heating costs

Solar Installation Costs:
EUR 5500 7.2 sq m solar panels, 300L dual coil tank, installation, VAT, etc
EUR 1500 grant where available
EUR 4000 with grant

Savings
EUR 766 x 70% (solar contribution) = EUR 536 per year

Payback With Grant
EUR 4000 / EUR 536 = 7.46 years

Payback without grant
EUR 5500 / EUR 536 = 10.26 years

Hmmm . . . there's a number of flaws in that calculation.

(1) You're including the ESB standing charges in the cost of water heating by electricity. However, no matter how much you reduce electricity usage by, the standing charge remains the same, unless you disconnect your supply entirely. The valid comparison is with the marginal cost per kWh, currently 18.6c including VAT.

(2) The price of electricity is due to fall by 10% in May, reducing the cost to 16.4c/Kwh.

(3) You can now get a guaranteed 12% discount off the ESB's prices from Bord Gais & Airtricity, reducing the price further to 14.7c/kwh.

(4) The "average" household does not heat all of its water with electricity. Most make substantial use of some form of central heating boiler. Anyone who is in fact using 100% electricity would be very well advised to switch to night rate electricity. This will cost from Bord Gais or Airtiricity after the May price cut 7.8c/kWh.

This reduces your savings to 3,832 kWh x 7.8c x 70% = €209.23. Payback with grant 19.11 years. Without grant, 26.29 years.

Your assumption that a solar system will contribute 70% of domestic HW needs is also about the highest I've ever seen - are you really saying this is the "average" one could expect?

Evergreen

I agree 100% that this calculation is flawed and I have included charges becuase that is what you pay. The more electricity you use the lower these contributions are but at the end of the day they are still there. Also, you cannot exculde VAT from the 18C charge.

I am not saying that this is the exact payback period, it is just an example of how to calculate payback on such a system. If you are using oil, gas or wood pelelts then the payback period is different again, just using a straight ESB charge, which is what most urban dwellers use, is the easiest way of demonstrating a payback calculation.

Evergreen

Also, forgot to address your mention of 70% contribution. Most solar sellers will quote 70% contribution for solar plate panels and higher for evacuated tube collectors.

I have flat plate panels on my roof and that is all that is being used to heat my water since the second week in February - it will remain that way unitl the end of October. During the winter (Dec-Jan) my solar panels bring the water temperature up from 10°C to 25° on most days, higher on sunny days lower on cloudy days

gizmo555

Evergreen wrote: »

I have included charges becuase that is what you pay. The more electricity you use the lower these contributions are but at the end of the day they are still there.

Yes, but the point is you cannot reduce these charges by installing a solar system. You cannot therefore validly include them in your payback calculations.

Evergreen wrote: »

Also, you cannot exculde VAT from the 18C charge.

Sorry if my previous post was unclear, but all the prices per kWh I quoted are VAT inclusive.

Evergreen wrote: »

I am not saying that this is the exact payback period, it is just an example of how to calculate payback on such a system.

It certainly isn't exact and with all due respect it is a very poor example.

Evergreen wrote: »

just using a straight ESB charge, which is what most urban dwellers use, is the easiest way of demonstrating a payback calculation.

It is the easiest way of coming up with an unrealistically short payback period. In my experience most urban dwellers don't use 100% electricity, and even if they did the most cost effective course would be to get onto a night rate tariff, not install a €5.5k solar HW system.

Evergreen wrote:

Also, forgot to address your mention of 70% contribution. Most solar sellers will quote 70% contribution for solar plate panels and higher for evacuated tube collectors.

Well you may be right, but all I can say is it's obviously in the solar sellers interest to quote a high figure. Most others would give a lower figure, e.g., Quentin Gargan, who lectures on the topic and is a keen advocate of solar (you'll have guessed I'm not!) quotes an average of 60% in other posts on this forum.

quentingargan

I think the renewable energy industry has to get away from codding people about payback times. Energy prices have just crashed, which may be bad news for the climate if payback is the only consideration in considering energy sources.

However, if you believe that global oil production will peak (or has already peaked) then energy prices will rise again. Thus the cost of energy displaced by solar panels etc. will rise.

People buy houses even though the mortgage payments are 50% higher than rent, but they do this because they know that rent will go up and up, whereas their mortgage is a fixed sum which will eventually end - in some cases after 30 or 40 years.

If you apply the same sort of logic to solar water heating and other renewables, then you will find it is very feasible. If you believe energy prices will continue to fall, I'd stick to the oil burner, maybe replace it with a condensing one, and R-E-L-A-X....

Personally I think oil prices have only fallen because of a fall in demand, and when (if) the recession bottoms out, we'll find oil at $200 or more a barrell. But there is no proof of that, only a hunch. It depends who you believe.

Evergreen

gizmo555 wrote: »

Well you may be right, but all I can say is it's obviously in the solar sellers interest to quote a high figure. Most others would give a lower figure, e.g., Quentin Gargan, who lectures on the topic and is a keen advocate of solar (you'll have guessed I'm not!) quotes an average of 60% in other posts on this forum.

I can't answer for every solar system out there and what kind of contribution they make towards heating water and under what circumstances they are installed. But, it all comes back to quality of equipment - if you install a low quality panel with a poor absorber then you are going to get low contribution levels and vis versa. If you deal with an installer who wants to place solar panels on a westerly facing roof or on a roof that is in the shade then you are going to have a lower contribution as well.

You may be right in saying that my calculation is simplistic, but it was never intended to be anything else. I don't see anybody else offering an example of calculating a payback period for panels. Speaking of payback periods, nobody ever speaks of them when considering installing fossil fuelled heating systems when it is totally obvious that there is no payback period.

quentingargan

Evergreen wrote: »

I can't answer for every solar system out there and what kind of contribution they make towards heating water and under what circumstances they are installed. But, it all comes back to quality of equipment - if you install a low quality panel with a poor absorber then you are going to get low contribution levels and vis versa. If you deal with an installer who wants to place solar panels on a westerly facing roof or on a roof that is in the shade then you are going to have a lower contribution as well.

You may be right in saying that my calculation is simplistic, but it was never intended to be anything else. I don't see anybody else offering an example of calculating a payback period for panels. Speaking of payback periods, nobody ever speaks of them when considering installing fossil fuelled heating systems when it is totally obvious that there is no payback period.

The whole point of solar is that it works well in the summer time, and that during this time it is displacing the most expensive hot water, either produced using the ESB, or using a boiler very inefficiently because it is not required to heat the house. But to claim both a 70% solar fraction, and to set this all against day-time electricity is definitely over-egging it.

By the way, I don't know of any installers who would do this except when there is no suitable south facing roof. I usually quote a solar fraction of 60% because that is an industry standard, but it all depends on the size of panel, size of storage, and amount of water used. If you put a 6Sqm system with 300L into a house with 2 people, you will achieve 70% OK, but their water use would be a lot less than 3 hours a day of an immersion running.

The Gods honest truth is that you cannot come up with a simple formula for payback time. You can use software models from Tsol or Retscreen to calculate this, based on geographical location, amount of water used, size of panel, storage capacity and storage losses etc. You will get a different result for every single household.

Using daytime electricity as the reference point in this calculation invites ridicule from the nay-sayers.

The truth is that there are hidden costs to using fossil fuels - climate change being the main one - albeit that this is disputed by David Bellamy and others.

thaddeus

Evergreen wrote: »

You may be right in saying that my calculation is simplistic, but it was never intended to be anything else. I don't see anybody else offering an example of calculating a payback period for panels. Speaking of payback periods, nobody ever speaks of them when considering installing fossil fuelled heating systems when it is totally obvious that there is no payback period.

How about this:

Using the following formula to determine the amount of energy it takes to raise the temperature of a liquid (Q=cmΔT). This scenario assumes the householder uses an electric immersion to heat water outside of Winter and that an oil boiler heats the water in winter. This assumes the oil heating system (pipework pumps and boiler etc..) is 60% efficient - I'm basing this on memory so I'm not sure if this is an accurate figure so if anyone has any other more solid info fire away..

I've also chosen 200L as a water requirement based on a 4 person household taking a 5 minute shower each @ 7L per minute = 140 Litres
plus some hand washing/cleaning @ 5L per person = 20 litres
and a bit left over for the extra few minutes this family may stay in the shower or the odd time they have a bath.
see: www.ilsu.ie/documents/SemRE/SHSolar.pdf for some other calcs on water usage which are similar.

Q = energy required
c = specific Heat capacity of water 4186 joules 0.001162778 KWh
m= mass of liquid (litres) assumes 1 litre = 1 kg 200 litres
ΔT= temperature differential 50 (60 degrees -10 degrees assumed ambient temp of water)


Q=cmΔT = 11.62778 kWh to heat 200L of water from 10 degrees to 60 degrees. Assumes this is the daily requirement of energy.

Annual requirement : 11.627787 x 365 days = 4244.14 KWh
cost of electricty 14.27c per kWh
cost of oil 6.1 c per kWh


4 months of oil used in Winter with Central heating on (assumes 60% efficiency in oil heating system)
= 11.627787 x 120 days x Euro 0.061 x 1.4 (system efficiency adjustment)
= Euros 362.45

8 months heating using elctricity outside of winter
= 11.627787 x 245 days x Euro 0.1427
= Euros 406.52

Total Cost of heating using Oil and Electricty:
406.52 + 362.45 = Euros 768.97

If Solar can provide 60% of this requirement it would replace:
768.97 x 60% = 461.38
If 5000 euro was spent on a system then payback at today's prices would be:
5000/461.38 = 11 years or so.

This is only one scenario really so if you used purely oil to heat your water the figures would change of course but it is indicative. There is a notable absence here though in the fact that we cannot apply the external costs of using fossil fuels to these calculations. According to this study: http://ec.europa.eu/research/infocentre/article_en.cfm?id=/comm/research/infocentre/export/02-10-env02_134.html&item=Energy&artid=134 the price of petroleum could double if the true cost of the externalities (mostly health related) were applied. It's not a big leap to assume external costs would apply to oil/gas/coal as well.

Evergreen

Well done, that's an excellent example

gizmo555

Evergreen wrote: »

Well done, that's an excellent example

No, it's cobblers.

thaddeus wrote:

4 months of oil used in Winter with Central heating on (assumes 60% efficiency in oil heating system)
= 11.627787 x 120 days x Euro 0.061 x 1.4 (system efficiency adjustment)
= Euros 362.45

Do the calculation - 11.627787 x 120 x 0.061 x 1.4 = €119.16 - not €362.45.

Even that is overstated - the current price of a litre of kerosene from my local supplier is 42c, giving a price per kWh of 4.126c, not 6.1c. This brings the real total cost of hot water from oil down from €362.45 to €80.60.

I could go on for quite some time picking holes in these figures, such as the assumption that central heating is only used from Nov to Feb, or that the boiler efficiency really is as low as 60% in wintertime, but as ever it boils down to the same thing - the only way to make an economic case for solar HW is to assume most of the energy displaced is standard rate electricity. If this really is the case, one should just switch to night rate electricity - you can get this from Airtricity now, which is 79% renewable sourced.

thaddeus

gizmo555 wrote: »

No, it's cobblers.

Do the calculation - 11.627787 x 120 x 0.061 x 1.4 = €119.16 - not €362.45.

Even that is overstated - the current price of a litre of kerosene from my local supplier is 42c, giving a price per kWh of 4.126c, not 6.1c. This brings the real total cost of hot water from oil down from €362.45 to €80.60.

Fair cop - I copied the wrong figure from my excel sheet and the price of oil was based on calculations done a few months ago so prices have gone down since. No need to be rude about it though Gizmo - only trying to get to the bottom of this, that's why I showed the calculations so they could be checked. You criticised Quentin Gargan above about doing what you are doing right now.

At these new figures the total is 406.52 + 80.60 = 487.12 x 60% = Euro292.72 - payback time on a 5000 Euro system is 17 years - still a good investment as it will then be able to produce approximately 3000 Euro worth of energy in the following 10 years. These are all based on today's prices - what will be the price of electricity in 20 years time?

gizmo555 wrote: »

I could go on for quite some time picking holes in these figures, such as the assumption that central heating is only used from Nov to Feb, .

That's what happens in my household and is from my experience quite common in Ireland - a valid assumption I thought. Also as our building standards rise and houses become better insulated and as temperatures rise due to Climate Change there will be less need for central heating so the Nov to Feb analogy is apt here too. Check out http://www.c4i.ie/docs/IrelandinaWarmerWorld.pdf to see Ireland will see a 10% decrease in degree days in the coming decades which will decrease the requirement for central heating.

gizmo555 wrote: »

or that the boiler efficiency really is as low as 60% in wintertime,.

As I said in my post that was from memory, I can't find a definitive figure so was being conservative but realistic in my calculation, also to clarify it's not the boiler it's the system efficiency, this includes the mechanism of getting the heat from the boiler to the water in the cylinder - I think you'll need to be a bit more definitive here and back up your statement if you are going to pick holes.

gizmo555 wrote: »

but as ever it boils down to the same thing - the only way to make an economic case for solar HW is to assume most of the energy displaced is standard rate electricity. If this really is the case, one should just switch to night rate electricity - you can get this from Airtricity now, which is 79% renewable sourced.

Fair enough, wind is renewable but is there wind power capacity available to heat all the water required by 4 million Irish people overnight? As from the calculations above there is roughly 5 kWh of energy required to heat 100L of water to 60 degrees.

If you take the www.ilsu.ie/documents/SemRE/SHSolar.pdf figures of 50L moderate requirement per person per day this gives

4000,000 x 50 = 200000000L per night
@ 5 kWh per 100L = 10000000 Kwh or 10 GWh of energy.

Airtricity have about 1000MW generating capacity in Ireland http://www.airtricity.ie/ireland/wind_farms/republic_of_ireland/operating/index.xml nowhere remotely near enough electrical capacity to generate our hot water demand by wind power/renewables overnight. Suggesting people simply go on to night rate electricity is not a sustainable solution, there is not enough energy available to do the job.

gizmo555

thaddeus wrote: »

Fair cop - I copied the wrong figure from my excel sheet and the price of oil was based on calculations done a few months ago so prices have gone down since. No need to be rude about it though Gizmo - only trying to get to the bottom of this, that's why I showed the calculations so they could be checked. You criticised Quentin Gargan above about doing what you are doing right now.

At these new figures the total is 406.52 + 80.60 = 487.12 x 60% = Euro292.72 - payback time on a 5000 Euro system is 17 years - still a good investment as it will then be able to produce approximately 3000 Euro worth of energy in the following 10 years. These are all based on today's prices - what will be the price of electricity in 20 years time?

OK, I withdraw the term "cobblers" - lets just say your figures contained obvious and gross errors, and still do - you're assuming that showering and washing is done in water at a temperature of 60C. This would in fact cause scald burns in seconds:

http://customer.honeywell.com/WaterControl/Cultures/en-US/Prevention/Burn+Chart/Default.htm

The normal and safe temperature for washing and showering as per the above link is around 40C - this would reduce the energy needed in your example by 40% and the savings along with them. This would bring your estimated annual savings down to €175 and extend your payback period to over 28 years. You also have to assume that in the course of that 28 years you incur no maintenance costs on your system and there is no reduction in your domestic hot water needs.

Rather than continuing with complicated calculations of what a solar HW system could, should or would do, why not look at pg 41 of the slideshow you linked to? This gives figures for real world measurements of the actual contribution a 6m2 flat panel system made to domestic HW needs in 2004. It came to around 1,350 kWh for the year, allowing for the several months when solar energy produced exceeded demand. Even if all the energy displaced was electricity, the savings would still be less than €200 at current prices.

Now I fully accept that energy prices will rise, probably very substantially, over the coming years. But it stands to reason that energy efficiency measures which have the shortest payback periods now will continue to do so as prices rise, and that savings made are generally speaking in proportion to the fossil fuel use displaced. On this basis it seems clear to me that solar hot water systems come very low down the order of priorities. It is amazing, for example, that the "Warmer Homes Scheme" intended to pay for energy saving measures in low income households is only available on pilot basis in certain parts of the country at the same time that solar HW systems are being grant aided by up to €1,800 nationwide.

Evergreen

I'd just like to point out that the presentation you are both referencing here is way out of date in terms of solar panel output

• He quotes 350-400kWh/m2/yr output for flat plate which is way off, a good Austrian made panel should achieve min 540 kWh/m2/yr with 1000 kWh/m2/yr (1000 kWh/m2/yr covers most of the country with the South East getting slightly higher). He also rates tube collectors at 400-500 kWh/m2/yr, you wouldn’t want to be touching tubes that delivered anything under 600 kWh/m2/yr and even that is well below average.

Solar Area Recommendation is out-dated

• He recommends 4 square meters of flat plate, currently the average area is closer to 6.5 square meters and rising. If Ireland follows the growth curve in Austria the average installation will be closer to 10 square meters per hose hold in 5 years time.

Solar heating contribution is too low

• He uses the figure of 50-60% contribution, this is a very low figure and probably low becuase he is using under powered panels combined with low surface area. I have 6.3 sq meters of solar panels on my roof and they have been providing 90% of my hot water since the 2nd week in February.

So if people are going to start referring to expert studies to either support, or knock, an argument it would be worthwile getting one that is up-to-date.