Solarthermie

[Gambatte 897]

Thinking of installing solarthermie on our roof. We already have Photovoltaik.

Anyone here has own experience with solarthermie?

[mtbiking 1,878]

8 hours ago, Gambatte said:

Thinking of installing solarthermie on our roof. We already have Photovoltaik.

Anyone here has own experience with solarthermie?

we have one and I’m extremely happy with it right now. We turn the gas heating completely off sometime between March and April and heat the water only with the sun until October. During the cold months it helps but it’s not enough to heat the water completely, specially after we turn the floor heating on, obviously. Although I’ll see this year: unlike in the last years I’ll be controlling the gas consumption closely and use the Kachelofen for warm instead of gas as much as possible. My expectation is that we won’t need much gas at all.

 

Ours was installed in 2017. I’ll check the contact for the dimensions, etc and come back to you.

[Gambatte 897]

Great, thanks 

 

Our roof is East and West. And because PV, and windows, it has only very little space left.

Otherwise we have a South facing wall, with much space available. I wonder which is better, the East West  roof with 40grad neigung, or the South wall...

 

Ironically, we already have water hoses between the roof and the utility. The company that built our house was instructed NOT to add these pipes, but they screwed up things and installed them nevertheless, also causing damages in the process 🤣. Well, maybe they come handy now😏...

[optimista 5,839]

My BIL has solar roof heaters... one year the water was boiling in the pipes... he was running off water to stop it. Dunno if or how he fixed it. Guess it was exceptional but can happen.

[Gambatte 897]

5 minutes ago, optimista said:

My BIL has solar roof heaters... one year the water was boiling in the pipes... he was running off water to stop it. Dunno if or how he fixed it. Guess it was exceptional but can happen.

Not an expert but this sounds like the installation, design, dimensioning, whatever, was not what should have been in the first place...🤔

[sluzup 248]

We visited family in the UK and rather than have the solar water panels, they had a PV immersion controller.  The info says that If your home has a hot water cylinder (tank) this is likely to include an immersion heater, even if gas is the primary energy source.   This seems a much simpler way of using solar to get hot water.  Anyone use something like this here?  We don't have PV yet but hope to get it at some point in the near future.

[Frantic 72]

On 27/8/2022, 09:49:30, mtbiking said:

we have one and I’m extremely happy with it right now. We turn the gas heating completely off sometime between March and April and heat the water only with the sun until October. During the cold months it helps but it’s not enough to heat the water completely, specially after we turn the floor heating on, obviously. Although I’ll see this year: unlike in the last years I’ll be controlling the gas consumption closely and use the Kachelofen for warm instead of gas as much as possible. My expectation is that we won’t need much gas at all.

 

Ours was installed in 2017. I’ll check the contact for the dimensions, etc and come back to you.

How many square meter of panel and which orientation of the roof (and inclination in degree)? 

[Gambatte 897]

4 hours ago, sluzup said:

PV immersion controller.

At least until the recent gas price spike (and possibly still now) this would result in a financial loss.

The PV electricity we don't use directly is sold to the grid at 10 ct/kWh. If we use it to warm water, we would save 6ct/kWh of gas, while foregoing 10ct/kWh of feed-in.

 

With gas now much dearer than 6ct/kWh the balance maybe shifted.

[Gambatte 897]

Just spoke to an installer. Solarthermie needs an extra 300l (if only Warmwasser), or 700l (if also Heizung Unterstützung) in the Heizungsraum.

Maybe we can squeeze in a 300l tank, probably not a 700l one.

[Frantic 72]

It depends also from the square meter of panel you are installing but it is important that you have a water buffer enough big to manage the huge amount of heat you will get in summer. If the liquid that transport the heat from the panel to your water buffer doesn't properly "cool down" by releasing the heat in a buffer at a lesser temperature then at certain point it will reach a so high temperature that it will evaporate and your solarthermie implant will stuck (stagnation).

On the other hand choosing a too  much big buffer is not the best decision. Although the warm water will stay always on top and the gas heater will provide heat just to this top part (if needed) , anyway you will have a certain degree of dispersion from top to bottom, across the layers of water at different temperatures.

 

From what I read online and from the offer I got, for 4-5 people and 10m2 panel surface the volume of this Pufferspeicher range from 750 to 1000. But I guess this is the case where you want to use the solarthermie also for "supporting" the heating like the HB told you.

 

[dstanners 1,529]

We are getting the Buderus Solarpacket Logaplex s109, which needs a 300l tank. There are better panels (the s110) but they would need a 400l tank.

All in all, the cost for us is just over 10k, but there are Foerderungen available, at about 30% (including the costs of installation).  

BAFA - Förderprogramm im Überblick

I have spoken to the BAFA folk, and they have said that in principle what I am doing is fine. I just have to complete the form (which is very simply), but in order to do so I am waiting for a quote from a scaffolding firm, as that isn't included in the above cost, but would also be subsidised.

Once you have filled in the form, you will get a response from BAFA that they have received the application. Then you can get your order in for the work.

 

[Gambatte 897]

Thanks x the BAFA link, will look into it.

Meanwhile just spoke with an installer (he hasn't been at our house yet, but he saw the photos of our Heizungsraum).

It seems we do have enough place for the "smaller" tank, so we can have Warmwasser, but not Heizungsunterstützung.

 

Cost probably in the 10-15k range.

Bloody expensive. I will do some math, more for the fun of it😊, with simple assumptions for gas price inflation and stock market return.

Of course I have no way to know how much this will lower our gas consumption, in kWh/yr, not happy about it but I don't know what else I could do...😐

[Dembo 493]

I'm surprised people still do this as it seems like what you did when PVs were still expensive. Surely in comparison to PVs it's complicated to install (even before you mention the huge Pufferspeicher) and you have the problem of it producing more than you can use in the summer; at least with PVs you could sell the surplus. Or am I missing something?

 

 

[Gambatte 897]

https://www.verbraucherzentrale.de/wissen/energie/erneuerbare-energien/solarthermie-solarenergie-fuer-heizung-und-warmwasser-nutzen-5568#:~:text=Beispiel%3A%20Eine%2010%20m%C2%B2%20gro%C3%9Fe,etwa%20325%20Euro%20im%20Jahr.

 

Beispiel: Eine 10 m² große Anlage spart unter günstigen Umständen jährlich etwa 2.500 kWh Erdgas ein. Bei einem Gaspreis von beispielsweise 13 Cent je Kilowattstunde (kWh) sind das etwa 325 Euro im Jahr. Bei niedrigen Betriebskosten von rund 150 Euro im Jahr beträgt die Einsparung innerhalb von 20 Jahren circa 3.500 Euro.

 

3500eur savings for an investement of 10-15 keur...

[mako1 864]

I was perusing the documentation for one of the Bruderus systems mentioned above and noticed if you dig around, you can find the efficiency ~77%,

 

This corresponds with the information on a publicaiton I found: https://journals.sagepub.com/doi/full/10.1177/0144598718815240

 

If you have the efficiency and do the math, you can calculate what you will be producing (for a Xm^2 collector) and be able to check your installer's math/calculation.

 

PV panels (another topic) have much different physics and their efficiency is  based on what  energy you can extract from the Standard Test Condition solar irradiance value of 1000 W/m².

https://en.wikipedia.org/wiki/Solar_cell_efficiency

But any solar panel/technology should also list the efficiency (usually less than collector efficiencies).

 

If you can save 3500 a year for 15K investment, your payback is <5 years, nicht schlecht, herr specht!

Knowing you don't have to worry about price variations, priceless.

Someday down the line the Germans will rethink altbau (denkmal-, ensembleshutz, usw...) retrofitting and allow apartment dwellers to benefit from this.

 

[jeba 4,345]

23 hours ago, Frantic said:

It depends also from the square meter of panel you are installing but it is important that you have a water buffer enough big to manage the huge amount of heat you will get in summer

I´d recommend to use vacuum tube panels. They will probably more expensive per sqm than flatbed panels, but because of higher efficiency they will be useful even in winter. If I had to do it again, I´d only use half the number of panels but vacuum tubes rather than flatbeds.

[Gambatte 897]

1 hour ago, mako1 said:

If you can save 3500 a year for 15K investment, your payback is <5 years, nicht schlecht, herr specht!

Kidding?

The link I posted says Einsparung innerhalb von 20 Jahren circa 3.500 Euro.

Difficult to save yearly 3500 eur of gas when our yearly consumption is 9700 kWh (or 700 eur, pre-Ukraine at least).

 

[Gambatte 897]

1 hour ago, mako1 said:

If you have the efficiency and do the math, you can calculate what you will be producing (for a Xm^2 collector) and be able to check your installer's math/calculation.

 

But this ignores the fact that much of the energy a Solarthermie brings inside your house, in the form of warmed water, is in the summer, when your gas boiler would possibly not need to operate anyway, so much of this free energy is unwanted and unused.

[jeba 4,345]

1 hour ago, Gambatte said:

so much of this free energy is unwanted and unused.

Indeed. In summer, our 1000 l storage tank heated our bathroom to more than 30 degrees.