ᐅ Operating a heat pump independently with a photovoltaic system.
Created on: 18 Dec 2015 19:51
I
Inotsara
Is there a photovoltaic expert here? Preferably an engineer specializing in this field? I am an electrician myself but have not yet had any practical experience with photovoltaic systems. So far, I only know about them theoretically and am very enthusiastic. I want to dive deeper into this topic and prepare myself for practical work. Recently, I have been looking into inverters and especially battery storage. The more I read, the bigger the gap I feel needs to be filled.
Currently, I am working on a project involving my parents' air-to-water heat pump. It’s a newly built house with two living units. The combined electricity consumption of both units is about 2200 kWh. Additionally, the pump consumes approximately 6600 kWh per year. Naively, I assumed my parents could invest around 25,000€ in a 9 kWp photovoltaic system and achieve a self-sufficient setup with very low electricity costs (about 30€ per month instead of 180€).
But that’s not the case. Firstly, a single-phase storage system is not an option because, due to the technology and grid regulations, the pump relies on the other two phases and will ALWAYS draw power from the grid. Even with a three-phase battery storage system, this problem would only be theoretically circumvented but not completely solved. Especially in winter, the pump runs at 80%-100% capacity while a photovoltaic system generates only about 30%-35% of its output in winter. In summer, the situation is almost exactly the opposite. This means we would underproduce in winter and overproduce in summer. On top of that, a three-phase battery system costs twice as much, and the number of manufacturers offering this option is very limited.
So, my question to the real experts: Should I just discard the idea of making the heat pump fully independent, or have I missed something?
I have gained a lot of knowledge in recent days through phone conversations with an engineer who is also a salesperson. However, I feel a bit uncomfortable bothering him further. He has already explained a lot to me. Also, information in written form is always better because you can look things up repeatedly and add to your knowledge. Therefore, it would be great if we could share our knowledge here together =)
Currently, I am working on a project involving my parents' air-to-water heat pump. It’s a newly built house with two living units. The combined electricity consumption of both units is about 2200 kWh. Additionally, the pump consumes approximately 6600 kWh per year. Naively, I assumed my parents could invest around 25,000€ in a 9 kWp photovoltaic system and achieve a self-sufficient setup with very low electricity costs (about 30€ per month instead of 180€).
But that’s not the case. Firstly, a single-phase storage system is not an option because, due to the technology and grid regulations, the pump relies on the other two phases and will ALWAYS draw power from the grid. Even with a three-phase battery storage system, this problem would only be theoretically circumvented but not completely solved. Especially in winter, the pump runs at 80%-100% capacity while a photovoltaic system generates only about 30%-35% of its output in winter. In summer, the situation is almost exactly the opposite. This means we would underproduce in winter and overproduce in summer. On top of that, a three-phase battery system costs twice as much, and the number of manufacturers offering this option is very limited.
So, my question to the real experts: Should I just discard the idea of making the heat pump fully independent, or have I missed something?
I have gained a lot of knowledge in recent days through phone conversations with an engineer who is also a salesperson. However, I feel a bit uncomfortable bothering him further. He has already explained a lot to me. Also, information in written form is always better because you can look things up repeatedly and add to your knowledge. Therefore, it would be great if we could share our knowledge here together =)
@ Inotsara : I have gone through the thread from the beginning, and I have a question about the Powerwall. I have had a photovoltaic system on my roof since 2013 but no storage. How much did you effectively pay for the storage and how much for your system? I did some calculations for my setup, and the storage doesn’t seem to make financial sense. It would be great if you could give some specific figures. Thanks in advance...
He calculated it as follows: He goes for KfW 40, so the plus package is also worthwhile. Under these conditions, that may be true. But KfW 40 is not economical from the start. If you recalculate from the beginning, you then stick to the Energy Saving Ordinance standard or KfW 55, and the extra cost for KfW 40 and the plus package becomes very high.
There are studies about at what storage price it becomes cost-effective... I believe around 800 € per kWh... currently, prices below 1000 € are rare.
Just try searching online.
200 cycles per year with, for example, 5 kWh → 1000 kWh * (24.8 - 12.5) cents = 123 € per year.
6000 cycles over its lifetime correspond to about 3690 € → Max. 800 € per kWh including EVERYTHING (installation, maintenance, insurance over the lifetime).
Just try searching online.
200 cycles per year with, for example, 5 kWh → 1000 kWh * (24.8 - 12.5) cents = 123 € per year.
6000 cycles over its lifetime correspond to about 3690 € → Max. 800 € per kWh including EVERYTHING (installation, maintenance, insurance over the lifetime).
@Grym: That’s exactly the problem I have. I just wanted to know how much the storage system costs and how much the photovoltaic system costs. I understand that this whole thing, and even better insulation stuff, is portrayed this way because of the intense lobbying by the insulation industry. I’m not playing that game either. I’m seeing it with a friend who is building a similar system. His construction costs are 2,700€/m² (after deducting all subsidies!!!), and no, he doesn’t have any gold-plated fixtures... with three children, I think his priorities were different. But that wasn’t really the question.
BeHaElJa schrieb:
There are studies on from which battery price it becomes cost-effective... I believe around 800 € per kWh... currently it rarely goes below 1000 €. Just google it. 200 cycles per year with, for example, 5 kWh → 1000 kWh * (24.8 - 12.5) cents = 123 € per year. 6000 cycles in its lifetime mean roughly 3690 € → max. 800 € per kWh including EVERYTHING (installation, maintenance, insurance over the lifetime).So you are assuming the battery lasts 30 years? Cool...
With my smartphones, there are already performance losses after one year.
We have a price of 0.257 EUR per kWh. Of this, 0.041 EUR is VAT, which applies anyway, so 0.216 EUR per kWh net. You feed in at 0.1231 EUR per kWh – so you lose this on self-consumption. From what I understand, you still have to declare it as a non-monetary benefit, so income tax applies regardless.
This leaves a difference compared to grid electricity of 0.216 - 0.1231 = 0.0929 EUR per kWh.
Even if the battery were free, 100 percent efficient, and everything was supplied via the battery, 4,000 kWh, which would easily cover electricity and heat pump for us, you could save 0.0929 × 4,000 kWh = 371.60 EUR per year.
Okay, Tesla Powerwall has 92% efficiency, so 8% losses. That’s another 1.1 cents lost (calculated on the 12.31 euro feed-in loss). So the difference per kWh is 0.0819 EUR.
If the Tesla Powerwall has 6.4 kWh capacity and 5,000 charge cycles, that is 32,000 kWh stored and delivered again. To break even with the grid price difference, including interest, maintenance, installation, and all administrative effort (everyone can calculate their own; for example, 4 hours per year at 25 EUR = 100 EUR per year administrative cost; well, no contractor would get up in the morning for 25 EUR to lay a heating pipe or a tile, but let's stay with this low-cost assumption for the calculation)... this means a maximum cost of 2,620.80 EUR. Strictly speaking, battery capacity decreases over time, probably from 100 percent to 80 percent? So we calculate with 90% of the costs (100 minus 80 = 90 percent average): 2,358.72 EUR.
With that, of course, no profit has been made yet. 5,000 charging cycles are about 250 cycles per year over 20 years. If I want a profit of 2,000 EUR over those 20 years, the Powerwall should cost no more than 358.72 EUR.
But even at 360 EUR, it still wouldn’t be economical, because all the administrative effort would exceed any possible profit anyway.
However, if you consider it a technical toy, you buy it for 5,000–6,000 EUR, save 2,000 EUR over 10–20 years, and write off the remaining 3,500 EUR as a hobby, and that's it. I don't want to discourage anyone. It’s a nice gadget, really.
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