ᐅ Operating a heat pump independently with a photovoltaic system.

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 =)

Yes, complete energy self-sufficiency doesn’t really work or is too expensive.

BUT: I think a photovoltaic system for partial self-supply is great. You can get a 9 kWp system without batteries for about half of your budget.
We have a 7.x kWp system on the roof (south/west/east) and come close to theoretical self-sufficiency – unfortunately, we use too little energy in summer and too much in winter compared to the yield.

Batteries are just too expensive for me right now, but even without them, it’s still a good solution...

Yes, the storage system accounts for almost half of the costs, you are absolutely right. However, without storage, a system would never be an option for me. But that is just my personal view. During the day, the sun is shining and I am not at home. In the evening, we are home using most of the electricity, but there is no sunlight available. With storage, I would have the necessary energy that was generated during the day.

The question is whether the storage system, including all available subsidies, is worth it for you. You also use electricity in the summer for the refrigerator, washing machine, and dishwasher (which just needs to run at the right times).

We have a relatively high self-consumption rate and an even higher feed-in tariff (from early 2013). Despite full financing (KfW funds were/are inexpensive), the system pays off in less than 10 years. I have had the system running for just over a year, and the actual electricity generation even exceeded the planned figures.

Tip: Build a reasonably large pool in your garden and heat it with a heat pump – that way you will use enough electricity and have a happy family.

Well, I want to reduce my parents' electricity costs, not look for ways to waste the surplus energy.
In my case, a KfW 40 Plus house will be built starting October 2016. With my 5.8 kWp system, I will be busy all year long figuring out how to consume the electricity.

Inotsara schrieb:

So, my question to the (real) experts: Should I discard the idea of pump independence entirely, or am I missing something?

Firstly – no, I’m not an expert. So here you are getting only the opinion of someone who is personally interested in the topic (on a non-professional basis) and who has had a 5.36 kWp photovoltaic system on the roof for more than a year.

The topic of self-sufficiency is always interesting. But it is hardly achievable with photovoltaic alone.
You described the problem well – when production is high, demand is low; and when demand is high, the system produces the least. In my opinion, there is only one way to solve this problem. You would need to install a sufficiently (over-)sized system (e.g., 2.5 times the actual demand) hoping to cover most of the demand during periods of low production, knowing that at peak production times you will generate a significant (too much) amount that you will feed into the grid at low prices.

You might reduce this overproduction with energy storage, but you would still have to plan for overproduction. Especially when I see how little is actually produced in winter. In November/December this year, our 5.36 kWp system had about 10–15 days with less than 1.5 kWh (kilowatt-hours) produced (including several days with less than 1.0 kWp).

A few weeks ago there was a thread here presenting the "Earthship" project. The (as far as possible) self-sufficiency there is achieved through a combination of photovoltaic and wind power. I think this is a realistic approach (possibly photovoltaic and hydropower for a property with a water source).

By the way, we received good advice from the Energy Agency Rhineland-Palatinate (from the state of RLP – Kaiserslautern). We met one of the advisors at a lecture during the real estate fair in Trier and were able to ask a number of questions afterward. I have no idea if such an institution exists in Hesse. In my opinion, the most independent advice is usually obtained from non-sales-related organizations.