What temps are you getting?

beertons

For those with solar, thermodynamic or something else, just curious with the good weather, how hot is your tank?

zoom_cool

My fathers tank was 80 top and 68 at bottom 300 litre tank with 40 solar tubes

Bromur

I have a 300 litre thermodynamic solar system in my house (family of 6). I installed it about four months ago with a water meter on the cold feed into the tank and a Kw hour meter on the power. To date I am using on average 240 litres a day and it is costing me 57 cent per day.

freddyuk

So if I used my standard immersion heater for the same time it would heat a full standard cylinder easily in one hour (subject to the starting temperature) as €0.57 is 3kw worth. So for 2 cylinders full I would need another €0.57 worth. Over a year I would spend €208 more in heating my water than yours (using this method) but I did not have any outlay. So the payback on capital cost of a thermodynamic system is minimum 15 years and likely to be more. Plus you have been running only in summer. In winter your efficiency will drop off with temperature and your power bill will increase.
This is just rough calculation but it makes the point. You are still subject to direct inflation cost of electricity. I can use my solar thermal to reduce my power bill by preheating the water. Capital cost is way,way lower and running costs are minimal. In summer you hardly need the immersion at all so the above calculations assume that i use the immersion 365 days for 2 hours - which of course I don't.
I am still not convinced that Thermodynamics is an answer to saving money.

MOTM

I've ~5m2 flate plate and a 250L cylinder (I'dve put in a bigger cylinder if I'd built the house). On a good summers days I've a full tank at 70 degrees by early afternoon. I'd estimate I ran the heating for <4-5 hours for close to 4 months in the summer.
Yesterday was occassionaly sunny and the full tank was about 50 degrees (although top half would've been about 40 degrees by sunrise with bottom half around 18 degrees.

dathi

30 Chinese tubes into 200ltrs cylinder 56* top and bottom yesterday

Bromur

Look, its all very easy to post the temps in your tank regardless of what heats it but it HAS to be related to the amount of hot water you draw off. Its very easy for any thermal solar system to heat a tank to 50 degrees if you use very little of it. What I am saying is that we use on average 240 litres a day and it costs 57 cent. The system meets all of our hot water needs and still has significant capacity. I have two issues with thermal solar first it is designed to provide 60% of a homes hot water, so what produes the other 40% and what does it really cost.... can it be measured? the second relates to combining the solar with the backup... how do you know the split is 60/40.... how do you know its not 80/20?
again can it be measured?
The thermodynamic system provides all of it and I can measure it to the cent.

Bromur

I just looked up the specific heat of water....its 4.1813 so my 240 litres per day if heated with a 3kw immersion the 45 degrees from 10 coming in to 55 (which is what the thermodynamic system does) would cost....
240x4.1813*45=45,158.04. divide this by the 3kw heater = 15,052.68 seconds = 4.18 hours
at a cost of 4.18*3Kw*0.161 €/Kwh (my current cost incl VAT)= €2.02 V's €0.57 by the Thermodynamic system. saving €528.86 per year.
Purchased at €4500...thats 8.5 years at current energy prices. I'd say 5 to 7 years is a realistic payback taking energy inflation into account.

MicktheMan

Bromur wrote: »

I just looked up the specific heat of water....its 4.1813 so my 240 litres per day if heated with a 3kw immersion the 45 degrees from 10 coming in to 55 (which is what the thermodynamic system does) would cost....
240x4.1813*45=45,158.04. divide this by the 3kw heater = 15,052.68 seconds = 4.18 hours
at a cost of 4.18*3Kw*0.161 €/Kwh (my current cost incl VAT)= €2.02 V's €0.57 by the Thermodynamic system. saving €528.86 per year.
Purchased at €4500...thats 8.5 years at current energy prices. I'd say 5 to 7 years is a realistic payback taking energy inflation into account.

My house is heated with ofch and I also heat my water with oil and only oil. As my hot water is generated from my ch boiler there are no extra hot water investments or servicing costs and my hot water costs me 300 euro per year (house with 3 teenage daughters, pressurised showers etc). At 57 cent per day, your cost is 208 in electricity. That is a difference of 92 euro. So you invested 4500 to save maybe 100 (>40 year payback)! Have I got this wrong?

exaisle

MicktheMan wrote: »

At 57 cent per day, your cost is 208 in electricity. That is a difference of 92 euro. So you invested 4500 to save maybe 100 (>40 year payback)! Have I got this wrong?

Yes, you have...well maybe not completely wrong, but you have to factor in the rising cost of oil against the rising cost of electricity.....which is no easy task!

Secondly, the reasons for installing a renewable source of hot water are, for some, not entirely monetary. I actually like the notion that less oil is being burned so I can have hot showers.....

MicktheMan

exaisle wrote: »

Yes, you have...well maybe not completely wrong, but you have to factor in the rising cost of oil against the rising cost of electricity.....which is no easy task!

Hmmm, and the majority of electricity is generated with ...?:)

MicktheMan

exaisle wrote: »

Secondly, the reasons for installing a renewable source of hot water are, for some, not entirely monetary. I actually like the notion that less oil is being burned so I can have hot showers.....

I was replying solely to the economic argument made....

But I often wonder if people really appreciate the extra resources required to manufacture, transport, install and maintain a complete separate system when they already have a perfectly good system installed.

As an example, suppose you have a conventional car which you need to do your long distance regular commute and you decide to buy an eco electric car to do the local shopping/school runs so you can use less petrol even though the conventional car is always available. Imo this is not a good use of resources, in fact its quite wasteful. Is it not the same with hot water?

MOTM

MicktheMan wrote: »

My house is heated with ofch and I also heat my water with oil and only oil. As my hot water is generated from my ch boiler there are no extra hot water investments or servicing costs and my hot water costs me 300 euro per year (house with 3 teenage daughters, pressurised showers etc). At 57 cent per day, your cost is 208 in electricity. That is a difference of 92 euro. So you invested 4500 to save maybe 100 (>40 year payback)! Have I got this wrong?

...or based on this, a solar thermal system in your house would bring costs down to less than the thermodynamic system (~150€ vs 208€).
Eitherway, renewable water heating should only be installed after space heating is reduced as far as is feasible. Putting solar water heating of any kind on a badly insulated house is not the way to go ... your space heating costs are likely to far outweigh water heating costs.

ccsolar

Bromur wrote: »

I just looked up the specific heat of water....its 4.1813 so my 240 litres per day if heated with a 3kw immersion the 45 degrees from 10 coming in to 55 (which is what the thermodynamic system does) would cost....
240x4.1813*45=45,158.04. divide this by the 3kw heater = 15,052.68 seconds = 4.18 hours
at a cost of 4.18*3Kw*0.161 €/Kwh (my current cost incl VAT)= €2.02 V's €0.57 by the Thermodynamic system. saving €528.86 per year.
Purchased at €4500...thats 8.5 years at current energy prices. I'd say 5 to 7 years is a realistic payback taking energy inflation into account.

Hi Bromur
Would I be correct in saying you have an invested interest in thermodynamic solar??
I'm not disputing your figures but are they independent or off a brochure?
Cc

freddyuk

MOTM wrote: »

...or based on this, a solar thermal system in your house would bring costs down to less than the thermodynamic system (~150€ vs 208€).
Eitherway, renewable water heating should only be installed after space heating is reduced as far as is feasible. Putting solar water heating of any kind on a badly insulated house is not the way to go ... your space heating costs are likely to far outweigh water heating costs.

We are talking water heating not space heating. Insulating your house will not have any effect on your hot water bills. By using the existing system that "most" people have available ie. immersion; then adding in a renewable resource is reducing the electricity and possibly oil used. The amount of reduction is really down to the effectiveness of the renewable resource installed but it will reduce your electric bill (if it is working correctly) and will not be influenced by rising electricity prices except for the pump which is minimal. Insulating the hot water store will help with the savings but only up to a point.
Using a heat source that only uses grid electricity and is subject to considerable capital outlay and electricity inflation is only going to be a good deal if the payback is reasonable but it will still be using electricity every day.
Saying you have hot water 24/7 and can easily measure the usage is not an economic argument for installing such a device. If you have one then you are going to have to support the decision and hope the electricity prices don't go skywards but as UK has an average price hike of 8% per year and new generating supplies are subject to pricing agreements that make your eyes water I would not be investing in grid power for my future heat resources however I would have a hybrid system that gives me the best of both worlds (and choice). No tax on the sun yet but I guess it must be on the agenda as the Spanish are doing it.

MOTM

freddyuk wrote: »

We are talking water heating not space heating. Insulating your house will not have any effect on your hot water bills.

:eek: Apologies, the topic had drifted into paybacks and choosing the right option so I figured other means of saving energy were fair game, particularly if they are potentially more effective. I hope nobody brings up solar space heating on this thread or they'll be in right trouble. I'll stay out of it so.

beertons

The moment kinda passed guys, i started the thread when we were having hot weather. Still be interesting to hear the temperatures people are getting through the winter.