German forum about plant engineering for home: heating system, solar energy, etc ?

131 posts in this topic

5 hours ago, murphaph said:

So my very simple rule of thumb would be, the colder it gets outside, the more gas would be used. Also the time of day the heat pump runs (if air source) makes a huge difference as the available energy in the air is significantly higher in late afternoon than at the crack of dawn.

Exactly. What I am wondering is at which point (i.e. temperature) it switches to gas being more efficient / economical and how to adjust the settings for it. WE do have a air source heat pump. The service person should come in the next month or so and I will pepper him with questions. They love me :D I think I drive them nuts because I have the basic technical understanding and ask relevant questions, but lack the proper technical vocabulary so the questions sometimes come out funny.  

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There won't be a fixed temperature that you can always refer to because the price of gas and electricity vary (somewhat) independently of each other. An extreme example illustrates this: If electricity was 1c per kWh you would never switch the gas on no matter how cold it got outside, but if gas was 1c per kWh you'd never turn the heat pump on no matter how warm it got outside either. You'd need some sort of algorithm to take the current outside temperature, price of gas, price of electricity, COP of the given heat pump throughout it's operating temperature range to calculate the running costs of both systems given the current conditions and then compares the outputs and provides the currently cheaper option.

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4 hours ago, Frantic said:

Ok but probably I am dumb but I am not getting what are you suggesting. Water heating based entirely on PV ? This means a the old dear electric boiler concept that we know has an energy conversion factor not at all high...but I guess you are saying "hey, thanks to your PV you have free-electricity, why bother ?". Did I get right ?

If this is the case, how I manage the nights and the seasons with less irradiation per day ? The nights are my main issue. WIth an a battery or electricity storage ?

 

I was planning on using a MyEnergy Eddi device (https://myenergi.com/product/eddi/) as I also plan on getting an EV and using the Zappi (https://myenergi.com/product/zappi/). Additionally I am leaning towards a home battery, but it's hard to say that make economic sense just now, but in a few years, maybe. Both Eddi and Zappi monitor the spare solar output and redirect just that amount into either the water heating / electric car / home battery. So yeah, I was thinking why bother....

 

With a dumb electrical element heater that you use as a backup source for a water tank, you can size that element between 500w to 3KW, although they are typically 2KW. You can also have a number of these elements, such that the full excess load from solar goes to heating a water tank. For my solar system, it peaks at 6KW in summer, but is around 500w in winter. I consider giving energy to the grid as throwing it away, as I have to give them 6x the amount to get 1x back! Yes, wasteful I know.

 

One annoying thing, and I've yet find a solution, is a heat pump with a variable power input. They all draw a constant load. Thus you can't automatically ramp up heat production in sunny times and ramp it down when it's cloudy/at night. Thus they don't follow the solar PV production curve of the day, or at least I didn't find one that did yet.

 

If I take the 5.8Kw PV system (west roof facing only, so east roof is empty) what you can see, the idea of not caring and using an old fashioned electrical element is just pie in the sky, nonsense. At an annual 20600KWh gas consumption, that is 1766Kwh if just divided by 12, but the usage is huge in winter and low in summer. So if I apply exactly to oppose bell curve to the solar PV generation, I realize you just don't get the necessary power from my current solar PV system for the entire house and water heating. Using a heatpump (HP) with COP of three I'd need a larger solar system to actually be 100% off the grid, but at 670KW usage for such a system, it would not be worth the extra expense just for the heating.

 

So in the end I conclude if you go the PV+HP route you really need as large of a solar system as possible, but even then you'll be paying something for grid power. Doubling the number of panels to have an east/west system would have doubled the output at around a 60% cost increase as the inverter can stay the same, and all you need is the additional wiring/panels/labour.

SolarHPAnalysis.jpg

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14 minutes ago, scook17 said:

Additionally I am leaning towards a home battery, but it's hard to say that make economic sense just now, but in a few years, maybe.

Last time I did the math, based on the model I created with 2yr of daily data from my PV, for Akku to be financially neutral their price must drop by a factor of 10. I wrote this here many times already.

Oh, and let's not forget our friend MM: yes, if you have a fleet of EV, live in a 400m2 house with outdoor heated pool in a sunny region, then yes argument for Akku gets a little better.

 

On top of the financial aspect, Akku are always bad for the enviroment.

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Yeah we are still a long way away from batteries being economical. I think it's going to need an all new battery technology to make them so. Of course driving down the FIT can artificially make them more viable but we should be bloody increasing the FIT to get more renewable energy into the grid. I can't believe we won't see some radical changes to the EEG to incentivise solar on every roof.

 

I came to the same conclusion about HP + PV scook: the PV array needs to be as big as you can fit on your house for this to make sense. A few token panels won't make a blind bit of difference. I'm amazed that people still seem to be receiving bad advice about PV array sizes. A neighbour here recently covered only the east side of his roof and only about 70% of the surface area of that! He clearly stopped at the nonsense 7kWp "limit".

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@murphaphwith respect, I think you are wrong.

 

From a purely financial point of view, too big a PV is bad because on the one hand the PV cost scales (almost) linear with kWp, on the other,  over a certain kWp you no longer increase self use (very good financially) but rather increase Feed-in (not so attractive financially).

 

A good rule of thumb is one kWp per every 1000kWh of yearly consumption.

 

I have a very big PV, because when I planned it the financial aspect was only part of the whole story.

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That goes against the general consensus on the PV forum. There the motto is almost always "Dach voll machen". You are paying for the scaffolding, electrical work, inverter (the cost doesn't scale anywhere linearly with capacity so bigger is cheaper per kWp), meters, cabling, etc. The additional cost of making the roof full are not proportional to the cost of the "base installation" because of all the fixed costs. A 15 kWp installation is not 50% more expensive than a 10kWp installation.

 

But for sure you need to make lifestyle changes to maximise self consumption. If you are out working all day and only at home in the evenings that's going to be more difficult. That's a fair point.

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No.

I have been following extensively the PV forum and "make your roof full" is not the mantra there. But either way, opinions are not proof.

 

I got at the time quotation in the 4-10kWp range: cost was almost linear.

Oh, and the guys installing our PV didn't use a scaffold, they just climbed on the roof. Normal house. I guess because transporting and setting up the scaffold is much labor and therefore expensive, so for only 1day of need they prefer to do without.

 

Too big a PV, like our 10kWp, from a purely financial aspect, is very far from optimum. Our still pays off, but now that the EEG dropped much more than the cost of the panels it probably wouldn't.

 

The reason is what I wrote: bigger Anlage give you more EEG rather without extra self-use.

Self-use plateau soon, few kWp will do.

EEG pays little, it's self-use that save much.

 

Again I have own data to back this up. To have opinion, always better look at own data first. After months our installers admitted only half modules were connected, 🤣so they returned and connected the other half. Production doubled overnight, self use didn't change at all.

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7 hours ago, scook17 said:

 

So in the end I conclude if you go the PV+HP route you really need as large of a solar system as possible, but even then you'll be paying something for grid power. Doubling the number of panels to have an east/west system would have doubled the output at around a 60% cost increase as the inverter can stay the same, and all you need is the additional wiring/panels/labour.

SolarHPAnalysis.jpg

 

No way HP for reasons already mentioned:

  1. Not floor heating
  2. Radiator placed in recess of the wall...if I have to mount larger one I have to change completely their position or destroy part of the wall (if i can ). No money
  3. It would be air pump, water and geo will cost too much. I dont want noise in the garden...they make noise...ok low one but continuos. The garden end the rest of prpoerty it is not done in a way where i can hide this heat pump and don't hear it.

 

 

In the meanwhile i found this article from smartsteuer the software of Haufe group that i use for tax declaration.

 

https://www.smartsteuer.de/online/steuerwissen/photovoltaikanlage-und-steuern/

 

With the option kleinunternhemen it doesn't seem rocket science so I could go big with that and add depreciation of the PV analge across 20 years. My doubt is just about open in finanzamt a commercial activity. I remember in that case you need to pay IN ANY CASE a minimo of 5 thousands something to finanzamt, also in case of no gain. I will google better.

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There is no minimum 5k€ tax to pay.

On depreciation: this used to matter, lowering your profit and therefore your income tax. But PV income tax has been abolished, zero for all, so depreciation no longer applies. Oder?

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14 minutes ago, Gambatte said:

There is no minimum 5k€ tax to pay.

On depreciation: this used to matter, lowering your profit and therefore your income tax. But PV income tax has been abolished, zero for all, so depreciation no longer applies. Oder?

If you go greater than 10 KWhp is not abolished at all. At that point you just have the choice: KleinUnternehmer or "normal" one. With the latter the VAT comes.

 

or Am I getting you wrong ?

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@Frantic, you could well be right on PV income tax over 10kWp. But that's no longer a domestic system and the legal ct/kWk EEG is less. 

But apart from this, why would you want such a huge system anyway?😲😳🤯

Most houses don't even have enough roof space for such a huge system, especially when you discarded the N side.

10kWp is already VERY big.

 

Our, almost 10kWp,  costed 13k€, best of 7 quotes 3yr ago.

Now electricity cost is higher, PV vendors know you find PV more financially attractive than before, PV cost therefore probably more.

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12 hours ago, Gambatte said:

Last time I did the math, based on the model I created with 2yr of daily data from my PV, for Akku to be financially neutral their price must drop by a factor of 10.

https://ourworldindata.org/battery-price-decline

We will get there sometime soon, be that 5 years, 10 years, but with the huge development effort being put into EVs, the outcome is bound to be storage costs will eventually drop to a low enough level. How batteries are constructed may also change to be less environmentally damaging. 

 

There are also heat batteries (e.g. phase change material) just starting to appear in the market: 

 

 

 

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5 hours ago, Frantic said:

If you go greater than 10 KWhp is not abolished at all. At that point you just have the choice: KleinUnternehmer or "normal" one. With the latter the VAT comes.

or Am I getting you wrong ?

 

You can depreciate the solar system, by setting up a solar energy business. Actually that brings in around half the benefit of the EEG in my case. Benefit of course depends on the amount you paid, thus the actual number, and then your top tax rate, so the multiplier. However, it means you have to make a separate filing, which comes with an additional bill from the Steuerberater. The tax office considers all systems under 10KWhp, a hobby so will no longer register them. They never cover the costs because they dropped EEG to such a level as it no longer economic to have solar to sell the energy. My system was installed prior to this change.

 

If accepted as a real solar energy business, you do get the MWST back, which is 19% of the cost. Additionally as it's work on the house, you should be able to claim (I did not know at the time) 20% of the cost of the labour costs as a tax deduction, so again real value is 20% * your own tax rate where as you get actually the 19% returned to you as a business.

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6 hours ago, Gambatte said:

After months our installers admitted only half modules were connected, 🤣so they returned and connected the other half. Production doubled overnight, self use didn't change at all.

 

In a study by the Fraunhofer institute you can find here: https://www.ise.fraunhofer.de/en/publications/studies/recent-facts-about-pv-in-germany.html

The have this graph on the topic of if a battery increases self consumption.

 

With self consumption, via load shifting, started off at 29% self consumed energy when solar was first installed. Have managed to push this up to 38% last year (4th year of operation), but I come to believe the only way to get a higher percentage is some form of storage. It's just not economic as of today.

SolarBatteryUsage.jpg

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On 08/04/2022, 11:30:00, mako1 said:

Does anyone in this thread have any experience with the installation costs of Fernwärme?

 

Our old street has it fitted now. My neighbour said he'd been quoted 10 000 € to connect his house to the pipe in the street, and that running costs would be about 400 more per year than he currently pays - sorry I can't remember what fuel he currently uses. As far as he knows, no-one is going for it.

 

Also, what kind of crap are they burning at the Fernwärme, and how 'green' is it? These are questions none of us feels we have answers to. It all feels a bit slippery and 'need to know' which is unhelpful in this instance.

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24 minutes ago, kiplette said:

Our old street has it fitted now. My neighbour said he'd been quoted 10 000 € to connect his house to the pipe in the street, and that running costs would be about 400 more per year than he currently pays - sorry I can't remember what fuel he currently uses. As far as he knows, no-one is going for it.

 

Seriously 10K. Does this include all the repairs and putting back everything in its place after they dig the trench?

For comparison the gas pipe (25m) to my house cost 3K Euros and was installed with the other utilities. Internal pipework and road surface on the trench when complete is not included in that price.

 

I heard they might start forcing people to connect to such systems if they are available and you have an old oil system for example. I also hear the heating cost from this system is not cheap. The fuel is basically free if they are burning the rubbish they collect, so why it should cost a lot I don't know.

 

Found some info in German on this

https://heizung.de/heizung/wissen/typische-fernwaerme-kosten-im-ueberblick/#:~:text=Was%20kostet%20Fernw%C3%A4rme%3F,100%20bis%20250%20Euro%20j%C3%A4hrlich).

 

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@kiplette München has the best Primärenergiefaktor for Fernmärme, from the expert (wife/engineer/architekt) and we have the advantage of the terrain which makes geothermal possible (think warmpumpe on a massive scale). Of course this varies in every locale. We are just lucky in that respect.

https://www.swm.de/geschaeftskunden/fernwaerme

But it is Germany so not as transparent as it could be. We either have Fernwärme 50m from our house or we have to wait until 2028. Apparently SWM (StadtwerkMünchen) will deliver it with one price (to the building, inside is our problem) if everyone in the house uses it as the heat source but has a different price if the old codger in the first floor stays with his Kachelofen. But the wife believes you can use it with your existing radiators.

The Munich system was set up for excess heat in local power plants but München wants to be 100% klima neutral so they are using geothermal as much as possible.

 

I am wondering if what they deliver to your apartment is the Fernwärme or if some exchanger in the basement is needed to distribute. In either case, it means retrofitting pipes to deliver the heat from the basement (or exchanger in the basement) to the apartments.

As Murph pointed out, the decision is in the hands of the owners and if anyone wants to see your neighbors at their worst, I can recommend these meetings. And to make it even more difficult, some decisions require a simple majority some consensus and others something in between (a four year debate about windows was the last battle). Hint: never live in a building with lawyers.

But as the price of gas goes up, the years it requires to payback the investment (assuming the only concern is the € cost of energy and not the environmental costs) will shorten. I am hoping the younger and more aware new neighbors will see it as a good investment or at least worth a look. The kwh price is significantly less for Fernwärme when compared to the kwh price for gas (they normalize everything to the kwh for ease of comparison).

 

And regarding the Primärenergiefaktor, it is Germany so there is a DIN or norm and the local energy company probably has it hidden somewhere in their website, or in a locked cabinet that says, beware of the cheetah.

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@scook17

nice graph. But in the graph the X-axis should probably be kWp, not kWh.

Then doubling the Anlage size from 5 to 10kWp, ohne Akku, the share of on-site use drop from 29% to 17%, so the self use kWh increases actually very little. Make sense.

When I collected Akku quotes, altough I knew domestic Akku as small as 3kWh exists, the smallest I could get a quote for was 10kWh.

Not sure how much other families use, but we are 3 people, and we consume a total of 2500 kWh/yr (my wife works 100% from home, and I do 50%), 4700 kWh/yr seems excessive (yes I know the industry has financial incentives telling us we consume more than we do)

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