Buzzbarr Registered User

Hi All, this is my first post on I was hoping someone could give me some advice on the above. I have had two solar installers give me quotations on both types of technology. I must also say that i have seen both there work and these guys do top quality work in my opinion.

The first was the Thermodynamic system. A 300l tank with one solar panel fully installed and commissioned = 5200 less a grant of 800. The second is a flat plate system including 2 x 2.5m2 solar panels, a 300l tank fully installed commissioned = 4900 less grant of 800.

As you can see there is only 300 in the price difference. My question is which system should i go for. My concerns on the thermodynamic system is it is relatively new technology and there isn't any hard evidence to be found on the internet regarding running costs. My concerns on the flat plate system is between say end of September to late March i will be burning oil on a larger tank than the 130 liter copper one i have now. Can anyone tell me which one is most cost effective to run.

All advice would be gratefully received.

Do-more Registered User

If you have a look on this forum and do a general search of you will find numerous threads on "Thermodynamic solar panels" which may provide you with some additional information.

As I suspect you are already aware "Thermodynamic solar panels" (TDSP) are really heat pumps masquerading as solar panels. I'm not saying that that is a bad thing per se but it helps to know what you are dealing with when trying to make a comparison.

So in the summer time with your flat plate solar panels you will be producing your hot water for only the electrical cost of running the circulation pumps whereas with your TDSP whilst the COP should be at it's best in hot weather you will have significantly higher electrical costs as you are using a heat pump to produce the hot water rather than direct solar energy.

It's my understanding that TDSP will only ever heat your water to 45 deg C year round whereas your flat plate solar panels will heat the water to significantly higher temperatures in the summer.

As you point out there is a huge vacuum in terms of the actual running costs associated with TDSPs.

In the most recent thread here discussing TDSPs one poster claims there is a 300w heating element in the compressor which is what is providing a significant amount of the hot water in the winter.

It would be great if we could have access to data showing the actual running costs of TDSPs because without data it sure looks like snake oil to me.

You should also look at prices for good quality evacuated tube solar panels, these should provide you with better levels of hot water production in the spring and autumn particularly if you can install them to make the best of the lower sun in those months.

Perhaps you can also give us an outline of what your hot water usage is like, how many people in the house etc. adding an extra panel or two is cheapest when you are installing the system to begin with and may have a significant impact on your general satisfaction with the system in the future.

homer911 Registered User

Also to add that the coil from the Central Heating system is usually installed in the middle of the tank, along with any imersion backup, so it is only going to be heating half the tank..

Buzzbarr Registered User

There are four of us. My wife and i, on average shower once a day. My two children are only 3 and 5 years of age so they are not showering yet. But they will be showering soon enough They have a bath maybe twice a week. I have two 9.8kw showers, these will be replaced with pumped showers when i upgrade to solar. Other hotwater use is having a shave, washing the dishes and general day to day use.

My central heating system is split into two zones upstairs and downstairs. My hot water cylinder is in the recirculation loop at all times when the oil burner is running (it must be costing me a fortune). I can't isolate it. I also have an immersion heater which i use in the summer months.

I realise that tubes are more efficient, but i thought the gap between tubes and flat plate had closed a lot over the last few years.

Buzzbarr Registered User

My oil spend was 1500 last year. I have just installed a multifuel stove which heats downstairs when running. I have also just had cavity wall insulation and more attic insulation fitted too.

BryanF Moderator

ask the companies what an expected electricity bill will be for the next year. and also what it will be if we get another month of really cold weather...

i have not managed to get any data from thermodynamic 'solar' companies on this electrical usage! are you aware that they are in fact a form of heat pump..

if you go ahead with them, please buy a 50€ energy monitor and collect some actually electricity consumption figures for yourself and the rest of us.. thanks

quentingargan Registered User

Buzzbarr said:

I realise that tubes are more efficient, but i thought the gap between tubes and flat plate had closed a lot over the last few years.

The gap between tubes and flatplate has also closed, or even reversed, on price. However, in terms of efficiency, tubes were never any more efficient overall, but they work over a longer season.

There are also some misleading figures on tubes that don't take into account that they passively track the sun as it moves from east to west. So if you compare the noonday efficiency of both systems, the tubes are worse, but if you compare the efficiency at 11.00am, the tubes have sometimes a 40% or more advantage over flatplate.

Overall, it is the insulation in the vaccum tube which ensures that it goes on working for a longer season, after the air temperature has dropped and the cloud cover increased. So if your house is well insulated and the heating is off from March to October, you would be better off with tubes.

I agree with other posters that thermodynamic is a heat pump rather than a solar panel. As such, there are moving parts that will wear out, and it will use a fair amount of electricity. Heat pumps are fine with a bore hole or a ground source of some sort, but I fail to see how a small panel on the roof can be an efficienty source of energy for a heat pump that is trying to bring water to 60C.

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Buzzbarr Registered User

I have two friends at work who have installed the thermodynamic system. One was installed about four weeks ago. The other was installed about nine weeks ago. He has got his bi monthly electricity bill. He says these are rough figures, i think it was an estimated bill aswell. His average bill is usually about 150 and this bill was 176. I know we cant judge anything by this. I am trying to encourage him to buy a watt meter.

If anyone out there has installed the thermodynamic solar system and is reading this, i think we would all be very gratefull if you could pass on your knowledge and genuine running cost prices.

Do-more Registered User

On the basis of that information I can't see how one could be comfortable in taking a decision to install the thermodynamic panels.

Given that you are prepared to spend up to 5 grand on a solution which will give you lower running costs the question is what is going to give you the best return for your investment?

I think you need to sit down and try to crunch the numbers and list out all your possible alternatives.

Have you estimated how much you are currently spending on electricity to heat water? So do you know what the investment of 5K of solar panels is going to actually save you?

What's your current oil boiler like? Is it a condensing boiler? Do you have the possibility to convert to gas and go for a combi boiler?

What are your heating controls like? Maybe you could make improvements there and upgrade your hot water tank to a more efficient one and get one with a solar coil so that you have the option of adding the panels at a later date.

You appear to have been making worthwhile improvements to your house and the point I hope I am making is that you really need to sit down and calculate where you could best spent additional money. I have my doubts that solar panels are going to give you the best return at this stage.

Buzzbarr Registered User

Thanks Do-More, your thoughts are of great value to me. I think i will have to sit down and do some more number crunching. Do you have a solar DHW system, and if so how do you find it? What are your estimated running costs?

Quentin Gargan, i also think you speak a lot of sence with regards to the Thermodynamic system. Its essentially a heat pump, which potentially could give a lot of trouble with its compressor (more moving parts). And the sixty million dollar question is how much does it cost to run on electricity. With our winters getting colder. This has bound to make running cost high.

maddragon Registered User

A few houses I've assessed for grant purposes recently don't qualify as the installers are cowboys and the area of installed panels is not adequate. Personally I prefer flat plate but that's mainly for aesthetic reasons. Read the following thread for some more opinions:

solarflare Registered User

Have flat plate panels installed happy with system but you must be realistic with performance and payback time it must belooked at as part of a package to reduce your usage of oil ie. Insulation high efficiency boiler high efficiency rads thermostats on rads etc thermodynamics has no history good or bad and information is
sketchy at best

Buzzbarr Registered User

I think your right solarflare. I've done a lot of research now on TDSP, information is very sketchy. I can't seem to get straight answers to the questions i am asking. I think opting for this technology right now is a big risk. Until someone can come out with hard evidence on running costs and reliabilty i would advise to wait and see. I am not saying its not worth investing in, all i am saying is wait and see. Give it a few years and hopefully more TDSP owners will share their experiences with the system with us. It might be the best thing since the sliced pan. Who knows.

I am glad you are happy with your flat plate system. At this stage for me, its go for the flat plate system or wait a few years. I will decide soon. My house is south facing do you think 5m2 of flat plate is enough for 300l system or should i go for a larger aperature area?

solarflare Registered User

The cost between 5m and 6m maybe minimal but more panel will help or go for 200l tank depends on youre daily usage most tanks in houses are only 120litre so u can judge for yourself if it is enough for a days usage plus some thermal storeage when weather is at its best for water heating

Do-more Registered User

Not sure how you guys compare different solar panels. I'm in Sweden and here the national test institute SP test all solar panels. I'm not sure how the test is made but they publish standardised data giving the expected yearly output of each panel and per m2 with climate data for Stockholm and the panel mounted due south on a 45 degree pitch.

It's a great help to be able to compare panels from different suppliers in this way as the outputs vary widely between panels.

Here's a link to the SP test results, I'm not sure how useful it is for you in Ireland due to the different availability of panels but it might be useful to some, the Kingspan panels are on the list for example.

Is there anything similar available in Ireland?

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