# Solar heating....very basic questions



## Squonk (28 Oct 2009)

I'm toying with the idea of getting solar heating installed and I have some very basic questions that I can't find answers for on AAM or elsewhere on the 'net.

1) I got a new copper cylinder last year. It is connected to my oil central heating as well as to a back boiler. I never light a fire so I don't use the latter option. Would I need to get a new cylinder if I went ahead with solar heating, or could I use my current one though the backboiler connections?

2) Does the solar heating also heat up the house through the central heating system? Or is only water for showers etc that gets heated up?

3) My house faces due south. I would put the panels on the south-facing roof obviously, but is there any real benefit to having panels on the east facing slope as well?

4) I've read lots of debate on flat plates versus tubes. To me the tubes look terrible and Mrs. Squonk would kill me if I put them on the roof. Is the efficiency improvement of the tubes worth it though?

Thanks


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## villa 1 (28 Oct 2009)

1. You'll probably have to replace your cylinder as it's current size may not be enough to satisfy the panels/tubes if you fit them.
(4m2 = 2 flat panels = 4 occupants = 200 litres hot water storage

2. Solar panels/tubes are great for hot water heating alone. Using them for space heating is a waste of time and money. Huge capital expense. Update your oil boiler to a condensing model and this will satisfy your space heating needs adequately.

3. The panels are best fitted between these parameters, 30 degrees east of south and south west but due south is the best. The panels should also be fitted at tilt angles (roof) of between 20 and 45 degrees.

4. Tubes are approximately 10% more efficient than flat panels but flat panels win hands down on the looks dept.

Hope this helps. Don't be conned by sales pitches!!


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## lightswitch (28 Oct 2009)

" Don't be conned by sales pitches!! "

Do not indeed.  I was told by one of the major manufacturers that the cost of ownership would not be re-couped, in this country, for at least 10 years.  You only need to look at our sky most days to figure this out though I guess


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## Squonk (28 Oct 2009)

Thanks very much villa_1 for your great response. I had read somewhere that the return-on-investment for panels was 2-3 years?


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## villa 1 (28 Oct 2009)

Depending on your hot water use, 5-10 years payback. Remember though they are not sun panels!! They are solar and will be even effective on cloudy days. If I was building a house or buying a second-hand one I would definitly fit flat panels or tubes.


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## lightswitch (28 Oct 2009)

villa 1 said:


> Depending on your hot water use, 5-10 years payback. Remember though they are not sun panels!! They are solar and will be even effective on cloudy days. If I was building a house or buying a second-hand one I would definitly fit flat panels or tubes.


 
The 10 years roi came from someone very high up in a large solar company that I was having a social chat with.  Prior to that I had been interested in them myself.  How long do they actually last?  Does anyone know.


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## DavyJones (28 Oct 2009)

villa 1 said:


> Depending on your hot water use, 5-10 years payback. Remember though they are not sun panels!! They are solar and will be even effective on cloudy days. If I was building a house or buying a second-hand one I would definitly fit flat panels or tubes.




Have you figures to show a 5-10 year payback? I would be interested in seeing them if you have. 

I estimated, to fit panels in my own house, would have a 7 year payback, inc grant. This is me, getting panels at cost price, fitting/commisioning and certify them over a weekend.


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## villa 1 (28 Oct 2009)

My own figures, given the price of the installation versus the savings on hot water use and the cost of heating this water with carbon fuels per annum. This of course will be totally dependant on hot water usage, building occupancy and fuel prices.


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## DavyJones (28 Oct 2009)

villa 1 said:


> My own figures, given the price of the installation versus the savings on hot water use and the cost of heating this water with carbon fuels per annum. This of course will be totally dependant on hot water usage, building occupancy and fuel prices.




I would be interested to hear your opinions on the subject.

 I am not overly convinced on the merits of solar, solely from a financial point of view. If someone wants to do it from a green prospective, then it is all good.

I don't have an invested interests in any products but would advice a client to upgrade boiler and heating controls before fitting solar panels. Although we provide all these services I never feel the need to push any of them unless they are,in my opinion, in the interest of my client.

How much would it cost to fit panels and a 300L cylinder in an exisitng house in your part of the world?


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## DGOBS (28 Oct 2009)

One serious calculation that didn't factor in the grant came in at a 20 year payback
assuming nothing ever went wrong (ie pumps etc)


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## quentingargan (29 Oct 2009)

I wonder what would be so bad about a return on investment of ten years? That would be equivalent to getting 10% on money on deposit, provided of course that the system is durable.

There are two sources of saving - one is that a well insulated cylinder which is usually a significant part of the cost of a solar water heating retrofit wil also make the central heating perform a lot better. 

The second is that your solar panel provides your hot water during the summer time when, hopefully in any half-decent house, the central heating is out of commission. During this time, hot water is particularly expensive because you either use an immersion or you run the central heating, warming up boiler, flue and heaps of pipework just to get a small cylinder of hot water. 

So a ten year payback is realistic in many cases, but not all. Of course, the savings will increase as energy prices rise, bringing downt he payback time. That all depends on whether you think oil will ever be scarse again.

It is possible to retrofit a new coil into an existing cylinder, but only if Squonk's cylinder is a really good one, well insulated etc., and large enough for daily needs. For example , or the Willis Sola Syphon. The problem with the syphon system is that it only works when the panel gets very hot. 

The difference between tubes and plates is not that tubes are more efficient across the board, but that they are more efficient in spring and autumn when the colder conditions has more impact on flatplates (which have poor insulation). If your house is well insulated and the heating is off for six months or more of the year, then a vacuum system will produce much better savings. 

Flatplates should last 40 to 45 years with no problems. Vacuum tube and flask systems will last about 20 years after which the tubes will need changing. With flasks, the replacement tubes are cheap enough (about €5 per flask). With tubes where a small flatplate is incorporated into a single glass tube, the replacement is much more expensive. 

Lastly, don't go near anyone who promises a return in 2 to 3 years. You can get that sort of return from loft insulation if you have none, but that's the only energy saving item that I know of with that sort of payback time (though many will claim otherwise) Q


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## RVR (29 Oct 2009)

One important thing to note is that payback is based on several factors, so you can't say "Solar pays back in x years full stop"?

1. Cost of system - cheapest is not always best (see item 3) but this does affect payback

2. Hot water Usage - the more hot water usage in the house, the quicker the payback.  I.e. a house with 5 people in it will use much more hot water than a house with 1!!!

3. Collector efficiency - collectors on the greener homes scheme list can vary by up to 50% in efficiency, for the same size panels.  The more efficient the panels are (as long as the price is reasonable of course), the better.

There is specialist solar software out there that can give you an proper indication of energy produced per year for a given set of parameters (water usage, insolation (energy from the sun) at a particular location, collector size, tank size, etc).  However results usually vary from system to system.

So i don't think I've really answered any questions... but as quentingargan says, any supplier who says "2-3 years" without blinking an eyelid might be worth querying on!!!!


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## villa 1 (29 Oct 2009)

As an ex-contractor now involved in training I would be guessing as to to the price of a solar installation but from talking to contractors they have informed me that 5000 euros would be a sufficient figure to allow for retro fitting a solar installation. That is of course dependant on the quality of the materials used, ie, panel/tubes, Cylinder, pump station etc. Some contractors are drilling tiles/slates to provide entry for pipework into roofs. I do not like this idea. I would prefer the use of lead fashing/slate. Take into account the size and weight of the hot water cylinder when fitting into an existing dwelling. New solar cylinders have to be very well insulated.
I would agree my fellow southerner Quintan. Solar systems are by far the most cost effective way of providing sustainable energies in building construction. Solar water heating will provide substantial savings on energy costs especially in summer months.
Well insulated houses will no longer need ultra expensive heating systems, especially the renewable types, re, pellet boilers, heat pumps or the famous multiple solar panel/monster buffer tank/underfloor heating systems. What a waste of money! And not to think if the carbon footprint in manufacturing these goods.
Insulate and more, install solar panels/tubes for your hot water alone and heat your house with an condensing oil/gas boiler controlling same with proper/simple to operate heating controls. 
There are to many vested interests conning people into shelving out vast quantities of money into products/systems that will never work properly and will definetly never pay them back. This is just not my own opinion but the opinion of many contractors/trainees that I meet on a daily basis.


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## galwaytt (29 Oct 2009)

villa 1 said:


> 2. Solar panels/tubes are great for hot water heating alone. Using them for space heating is a waste of time and money. Huge capital expense. Update your oil boiler to a condensing model and this will satisfy your space heating needs adequately.


  Huge capital expense ?  In my house, the only difference is the size of the buffer tank.  The basic heat delivery - gas, UFH, solar panels, is the same, so it's down to tank pricing, basically.



lightswitch said:


> .....I was told by one of the major manufacturers that the cost of ownership would not be re-couped, in this country, for at least 10 years. You only need to look at our sky most days to figure this out though I guess


...they're not SUN panels, they're SOLAR panels.  Even on a mild day, they make a contribution.   Are you not expecting to live in your house, or your house to last, 10 years ??


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## villa 1 (29 Oct 2009)

What I meant is trying to heat your home with a vast array of solar panels and a whopper of a big costly calorifier/buffer that will then have to satisfy your ufh system. The capital cost in these systems just does not make economic sense. Factor in the cost of heating up these whopper buffers with Gas/oil after when the solar diminishes, like now at the moment


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## DavyJones (29 Oct 2009)

Ok, lets talk figures.

Let us take for example, a four person household, two adults, two children.

50L per person per day, in my opinion is grossly over-estimated. Considering the average house hold cylinder in Ireland is about 130L, Lets work on that.

How much does it cost this famliy to heat their water every year using a HE A rated appliance? 

Lets consider, 130L cylinder is fitted with cylinder stat and is interlocked with boiler as per current building regs.

Lets also assume this famliy has an electric shower, that they use daily for 20 mins. 
Once solar is installed, it will be removed, now lets also factor in the cost of installation of new shower.

If we estimate, that a solar panel installation will cost €5000, minus grant, so about €3600.

What is a real realistic pay back?

, taking into account, maintance over  life time of system. for example, pressure loss = call out charge for repressurising, (assuming it doesn't happen in year 1), pump failure, (the pump won't last the life time of the system) 1 pump change plus labour would have to be considered.

If a person had €3K to spend, what is the best option?

Upgrade boiler and heating controls to SEI and building regs level

or 

fit solar panels?


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## quentingargan (30 Oct 2009)

A house gets by with a 120L cylinder because while I am luxuriating in the bath, the heating is getting the next bath ready. The reality is that most households nowadays are using about 40L or more of hot water per person per day. 

In general the trend over the last few years has been that hot water useage has risen, while improving insulation has caused a decrease in demand for space heating. 

But there is a pecking order in potential savings. I have seen solar panels put on houses that had no decent loft insulation. If you have a really old inefficient boiler, of course you should change it. But that doesn't mean that solar doesn't stack - it just means that you also have a very wasteful boiler...

But solar may not stack for a modest household with very low hot water use. 

In relation to solar space heating, it is worth noting that a lot of the systems sold originated in Austria which has similar summer solar radiation to Ireland, but more than double our radiation in December and January. Cold, bright winter days. It just doesn't stack here, unless you already have a large buffer tank for a log gassifying stove.


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## plynch (8 Nov 2009)

I must say this is great banter and very informative, so on the subject of money, I really don't have running costs tallied and am also trying to prevent myself from getting into analysis paralysis, in that state I tend do nothing. So I'm making the following assumptions and since I feel like I'm in the midst of some people who know the industry quite well, someone is probably going to tell me to lay off the crack pipe but here it goes...

Occupants - 2 adults, 4 children (3 girls) - some are young so we are currently at ~28 showers per week and rising, also have a showermate pump.
System Install - 4.5k less 1.5k grant = 3k (I plan on helping the plumber too so may even be less)

If I can reduce one oil fill per year ~EUR 500 - I'm looking at a 6 year payback. That may be optimistic but I agree with quentingargan, you run the central heating, warming up boiler, flue and heaps of pipework just to get a small cylinder of hot water and I have a zoned system so I have the ability to heat just the hot tank.

I believe oil will rise again, (in fact it seems like it can't wait) it is currently trading at ~$70 PB and with each positive report on the US economy it rises. 

Also how many times have the kids said, the water is gone, you override the time clock thinking you'll come back in an hour only to come back several hours later to undo the override....


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## quentingargan (8 Nov 2009)

I think 6 years is optimistic - I would expect a system like this to save you about €300 to €350 at todays energy prices. That's still a 10% return on investment, and rising as oil rises. 

If you are a competent DIY / plumber, there's nothing to stop you changing over your cylinder yourself for example. If you are comfortable with heights, sorting out the scaffolding might be welcomed by some installers, though quite a few have quick roof access platforms. There are ways of getting the costs down if you are willing to roll up your sleeves, so it would seem the pipe isn't doing you any harm. Must get the name of your dealer


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## DavyJones (9 Nov 2009)

€500 seems a bit high, remember you will only get useable hot water for half the year, doing well, this in effect doubles your payback time.

Most if not all installers won't want your help. they will have a fixed way of doing something and will want to get on with it.


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## sandrakmy (9 Sep 2010)

Hi I WAS JUST READING THE THRED ON SOLAR PANEL AS I AM CONSIDERING GETTING THEM , AND I AM AMAZED TO SEE THAT THE ROI IS ABOUT 20 YEARS I WOULD HAVE THOUGH IT WOULD BE ALOT LESS THEN THAT THE COST OF HEATING WATER IN MY HOUSE HAS WORKED OUT @ €70 PER MONTH IN THE SUMMER ONLY SAY 6 MONTHS SO THEREFORE SOLAR WOULD SAVE € 420 PER YEAR, NOT EVEN TAKEN INTO CONSIDERATION THAT THEY DO CONTRIBUTE ABOUT 25% TO 40% OF THE WATER HEATING COSTS IN WINTER ,SO WOULD BASED ON THE SUMMER SAVINGS ALONE WOULD IT NOT TAKE 7 YEARS, 
THE FIGURES WE HAVE MUST BE COMPLETELY WRONG IF 20 YEARS IS THE ESTIMATED ROI


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## quentingargan (9 Sep 2010)

Crikey! €70 per month for hot water? You must be all be squeaky clean. I assume you are using an oil boiler set to hot water only? It may be a very (very very very) inefficient boiler and with a lousy uninsulated cylinder, yes, that's possible. 

In calculating payback, people often forget that almost half the cost of an install is changing the cylinder, which usually also offers savings for the whole year. 

You can put in a 40 tube 200L system for just under €3,500 after the grant. The payback on that should be well less than 20 years on that... Q


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## bartbridge (24 Sep 2010)

Can I ask if there is any benefit in having geothermal and solar panels installed in a new build or is it pointless? The geothermal will be heating the house and water, I just wondered if solar panels would be more economical in the summer months for heating the water?


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## quentingargan (25 Sep 2010)

bartbridge said:


> Can I ask if there is any benefit in having geothermal and solar panels installed in a new build or is it pointless? The geothermal will be heating the house and water, I just wondered if solar panels would be more economical in the summer months for heating the water?


 
Geothermal isn't great at getting water right up to the temperature required for domestic hot water, so there is usually a more expensive top-up measure. Also, you probably won't want to use the geothermal at all for most of the summer time, and that is when solar works best. 

Installing solar on a new house isn't expensive, and will help your BER assessment and help you meet your Part L compliance etc. as well.


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## huskerdu (25 Sep 2010)

DavyJones said:


> €500 seems a bit high, remember you will only get useable hot water for half the year, doing well, this in effect doubles your payback time.
> 
> Most if not all installers won't want your help. they will have a fixed way of doing something and will want to get on with it.



You are assuming that the panels do nothing all winter.
The water coming into your tank from the cold water supply is approx 12 degrees. Our solar panels heated our water to at least 22 degrees all last winter, which significantly reduced the cost of water heating all winter. 
One day last winter there was snow on the ground, and the panels were working and the water was 30 degrees. 

I do agree with the estimates of payback time of 6 to 10 years, at current oil prices but I dont see the price of oil going down. 

I dont get why people think that the tubes are ugly and the flat panels are alright. I think both are slightly ugly, but unless you are standing on the pavement across the road looking up, you dont notice it anyway.


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