Heat pump with photovoltaics vs gas and solar thermal

even if it doesn’t quite fit with your previous statement that you should always install ST

I wrote that I would always install ST again and again. In recent years, I have retrofitted ST in some of my rental properties even though this is actually counterproductive for the landlord because I cannot pass on the costs. An example: installed a system with 35 sqm in a 12-family house. Investment after subsidy 17,000€. Reduction of heating oil consumption on average 3,500 liters. Average consumption 1995-2008 was 17,000l / 2008-2013 was 13,500l. Additional costs for heating electricity about 200€. This cannot be directly applied to a single-family house with 4 people (on average about 25 people live in the property). But it does show the benefit of ST. And the effort for ST is manageable. The system delivers usable amounts of hot water from March to September. I have a Raspberry Pi with temperature sensors on the buffer and supply/return flow for logging to see what runs when.

In a 2-family house with 6 residents, the savings are about 150€/year (heating oil before 1900l, after 1600l). But there I had already prepared the buffer and risers during construction in 2001 and only retrofitted the collectors and a pump (investment about 2000€) in 2012.

That’s why my statement and why there is also ST in my current property.

And here too, EVERYONE has to decide for themselves. What works for me doesn’t have to work for others. Some drive Porsche, I drive Skoda, which doesn’t mean I have anything against Porsche….

I am a fan of masonry heaters and of ST, and if heat pumps pay off I would also install a heat pump but so far heat pumps have always been more expensive!!! In the 12-family property there was also the consideration to install a combined heat and power plant, but for that, the tenants would have had to use the electricity, and that gets difficult, otherwise that would have been an option too.

You wrote that you would always do that, but you did not include your special situation, hence the criticism of your statement! I have annual hot water costs of about €75 per year, and even if solar thermal could cover 100 percent of the hot water, it would not add up because the costs for [St] and [Puffer] are too high.

I have always written that I do it this way NEVER that everyone should do it this way.

And I always wanted to know HOW it pays off because it is always nicely said that the annual costs are so low, and when I asked where the ROI of the heat pump would be, I was told that there is no ROI for the heating but this was not justified. Well, I just wanted to know WHERE the additional investment of the heat pump pays off (ROI of the ADDITIONAL COSTS).

You wrote that your annual energy demand was 8,400 kWh. What I calculated now was simply what 8,400 kWh costs me in oil/gas. At the current oil price, that would be about €500, compared to which you put €200 electricity. For me, that means you save €300 per year.
A gas boiler with 8 kW output and a standard efficiency of 109% costs €2,000, a buffer tank €1,500, 5 sqm solar system €1,500, total €5,000 (numbers are current from the internet).
Gas earth tank €2,500, total €7,500.

Your investment was €20,200 in the heat pump + drilling. Additional cost €12,700.

With the gas condensing boiler, chimney sweep and maintenance costs of €200 are added. So the additional annual costs are €500.

Based on this calculation, I come to the conclusion that I need 25 years to recoup the additional investment. Will your heat pump last that long??
My neighbor’s ground source heat pump broke after 11 years. He bought a new one for €7,500 which, according to him, runs better/more efficiently than the old one...

I also have no problem if you say (like tabtab) that you simply book the additional investment as ‘luxury.’ Just like I did with my stove. But to say the heat pump is CHEAPER is, from my point of view, and unless I have a huge error in thinking somewhere, simply not the case.

Maybe you can tell me my thinking/calculation error.

Addendum: I have not taken into account the yield of the solar thermal system (my experience approx. 10-15%).

Now my system cost 12.5 (and that includes everything and is definitely bigger than what a normal single-family house needs), still a difference of 7,500€ and a payback period of 15 years.

It’s true that a gas condensing boiler breaks down, but it only costs a maximum of 3k to replace (including labor).

And also the statement about solar thermal (ST) is correct; with 15% savings, I have a payback period of 20 years.

However, your response seems to confirm that my calculation (except for the points you mentioned) appears to be correct.

Of course, I only see the whole thing as a snapshot as of today. Who knows where technology will move in the next few years. With a passive house, everything looks quite different again....

As a summary for me, I conclude that a heat pump with your costs/consumption pays off after 15 years. That gives me what I wanted: ROI = 15 years. If it breaks down earlier, then that’s just how it is...

And I am also confirmed in my decision. (The offer for the heat pump I had was by far more expensive than your investment.) Because only after 15 years would my gas condensing boiler/solar thermal solution be more expensive than your heat pump. If then in 15 years the heat pumps are much cheaper due to further developments and sales volume or something completely different comes onto the market, I can still switch without having wasted money!!!

Yes, that can be quite right. With a gas line, I would have also chosen a gas boiler, which is why I had requested quotes in that direction. The alternative for me was the heat pump; the tank is not an option for me.