ᐅ Heat Pump with Photovoltaic System vs. Gas Heating and Solar Thermal Energy

The heat pump’s energy consumption is based on the first year when everything was completely dry. In the second year, consumption dropped significantly (to the value I mentioned). Our electricity is 10¢ per kWh cheaper. This makes a considerable difference in the bills. Your comparison of energy amounts is flawed because you don’t take efficiency into account. The efficiency of wood, gas, and oil heating is actually below 1 (meaning the useful heat energy you get is less than the chemical energy you "put in"). Therefore, a heat pump can very well compete significantly with other energy sources.

Aside from that, there is a suitable heat pump for every heating demand; anyone claiming otherwise has not yet researched the matter properly. There is certainly one suitable for 600 m² (6,460 sq ft).

My ground-source heat pump had an annual performance factor of 6 last year (admittedly above the average of around 5 for this technology). This means my heat cost less than 4¢ per kWh at my electricity rate, outperforming wood, gas, and oil at my local prices. And that with absolutely no effort (no fireplace) or storage space, and a minimum of maintenance (none).

The higher the heat demand, the more efficient heating pays off, making it easier to recover a higher investment.

Your photovoltaic system is great, but most people don’t have such large south-facing roof areas. Especially with photovoltaics, a heat pump works well together. It can then provide cost-neutral hot water in summer and transitional seasons, and even some heating if there is a cold night. Definitely better than solar thermal systems.

Well, I have done my research, and I didn’t say it was impossible, but rather inefficient and not profitable within 30 years.

Regarding electricity prices, since I feed electricity into the grid, I am tied to a specific supplier and cannot switch to a cheaper one.

I understand that I cannot assume an efficiency of 1, and if everything here is judged strictly, so be it. My stove has an efficiency of over 80%. The combustion chamber temperature is around 870°C (1,598°F), and the flue gas temperature at the chimney outlet before the wall is below 160°C (320°F).

I have 7m (23 feet) of ceramic flue channels. The water jacket has a rated heating output of 18 kW.

When burning 10 kg (22 lbs) of wood (weighed before burning), the buffer tank temperature increased by about 10°C (18°F) within approximately 3 hours. The stove also emits some heat directly into the room through the glass and surface. It is centrally located as a room divider between the kitchen/dining area and living room. There is nothing better than a warm masonry stove radiating heat directly.

The investment costs for a heat pump instead of a gas condensing boiler would have been astronomical (at least 3 to 4 times higher in my case).

The potential savings of a heat pump compared to a gas condensing boiler are not significant enough to justify that investment. That is why I made this statement based on MY situation.

Honestly, I don’t understand why so many people here are against solar thermal (ST). It is probably the cheapest and most proven way to generate heat (at least when the sun is shining).

Why should I invest extra money in a heat pump if I don’t see the benefit? Assuming that in 10 years, heat pumps will only cost half of what they do today, I will have already covered the cost of the gas condensing boiler twice. If it breaks down then, I can simply install a heat pump.

Of course, I can only speak for my own situation, but that is what forums like this are for: to share experiences and reasoning so each person can form their own opinion based on their circumstances.

As long as primary energy costs remain as they are now, in my opinion, a heat pump doesn’t pay off. However, the heating installation should still be designed for a heat pump (which I have done). This means keeping pipe distances as short as possible in the underfloor heating to achieve low flow temperatures.

When I read your numbers and see your investment, I also don’t believe you will see a return on investment anytime soon. I’d be interested to see what you come up with. Have you calculated it?

At 2,000 kWh per year, fuel costs for oil/gas/wood are over €200. How much cheaper would the heat pump be, especially considering the higher initial investment?

Tom1607 schrieb:

Regarding electricity prices, since I feed power into the grid, I am tied to one supplier and cannot switch to a cheaper one.

I don’t know where you live or how old your system is, but what does feeding electricity into the grid have to do with consumption?

I have a system with surplus feed-in, and I am compensated for the electricity I feed into the grid according to the Renewable Energy Act by the grid operator (not the supplier!).

The electricity supply, as usual, is provided by a supplier of my choice.

I understand that I cannot calculate with an efficiency of 1, and if everything here is judged with extreme precision, then so be it. My stove has an efficiency higher than 80%.

You started by saying that my statements were simplistic, even though yours were just as imprecise and simplistic. Now I am trying the opposite by being exact and well-founded, and you turn 180° and say it is too precise. Please decide which side you want to take! An 80% efficiency basically means something like a “performance factor” of 0.8; from your heating output of 2000 kWh from one cubic meter of wood, you then get 1600 kWh—that is already a significant difference (a simple kitchen scale is enough here, no need for a precision scale).
If 10 kg of wood heats your buffer tank by 10°C (18°F), that is an efficiency for hot water in the buffer tank of 63%. Of course, the overall efficiency is higher if you use most of the remaining heat. I pay €0.2 for this amount of heat, and I don’t have to “do anything” (no fetching wood, no storage, lighting, or cleaning, etc.). The radiant heat from a fireplace is a matter of personal preference. Personally, I find “one-sided” high radiant heat uncomfortable; I am very satisfied with the even warmth provided by underfloor heating, which is why I don’t have a fireplace and never will (financially, it would not have been an issue). So that is a very subjective argument—everyone to their own preference.

There is no return on investment (ROI) for heating; it just costs and costs... and you don’t get any money back. Otherwise, you are making a calculation error:

With 2000 kWh/year, the cost for oil/gas/wood is more than €200.

My heat pump, with last year’s efficiency, consumed 1400 kWh of electricity but produced slightly more than 8400 kWh of heat for heating and hot water. In comparison, with wood or oil (your assumed 80% efficiency), you would have had to purchase about 10,500 kWh, or with a good gas condensing boiler about 9000 kWh of gas.
My investment would not have been significantly lower with a different heating system anyway, since I don’t have a gas connection here (only a gas tank or similar), which would have required space and additional costs. Also, of course, a fireplace is not free either.

Why should I invest extra in a heat pump if I don’t benefit from it? Assuming the heat pump costs only half as much in 10 years as it does today, I will have already covered the cost of the gas condensing boiler twice over and if it breaks down then I will just install a heat pump.

This statement is somewhat illogical; I don’t know how to interpret it. How do you want to have recovered the cost of the gas condensing boiler if the running costs are higher and only the initial investment is lower?

Otherwise, I appreciate that you have shared some information. Without all this data, your statements were naturally difficult to understand or verify (e.g., your electricity price / photovoltaic capacity). This provides real added value for other users here in the forum!

Regarding solar thermal systems, I still have to strongly disagree with you, especially if you are always focused on the financial aspect:
Look at how expensive your solar thermal system was, and how little it produces! Just like with photovoltaics, you get good yields only when the sun is shining—which is exactly when you need very little hot water, particularly in a single-family home, usually just for showering (at least I only heat in winter, hardly at all in the transitional seasons). How many kWh from the thermal system do you actually use (not just as waste heat your buffer tank emits unused in summer)? I need about 1 kWh of electricity on average for hot water in summer. How long can I heat with the cost of a solar thermal system?

Unlike photovoltaics, you cannot sell surplus solar thermal energy. Imagine if your photovoltaic surplus simply vanished. Would it still be worthwhile?

If you have a heating load of 8,400 kWh, that corresponds to about 850 liters (225 gallons) of heating oil (if gas is not available, there would be liquid gas with an underground tank). At current prices, that would be around €400 (about $440) per year.

Why shouldn’t there be a return on investment (ROI)? I would have had to invest €60,000 (about $66,000) for a heat pump solution compared to €12,500 (about $14,000) for a high-efficiency gas boiler solution. That’s €47,500 (about $52,000) in additional costs — when do I get that back? => ROI??

If in 10 years I could get the heat pump solution for €30,000 (about $33,000), then I’d have the gas boiler installed...

Where is my mistake in reasoning here???

I pay €0.20 (20 cents) for this amount of heat

I don’t pay 20 cents but only 1.5 cents (€0.015). Okay, I have to store the wood and light the stove, but I would do that anyway because I like the warmth.

I don’t have a wood stove that is ‘glowing’; my stove is 2.5 m long (8 feet) and stands as a room divider between the living and kitchen/dining areas. It slowly releases the stored heat into the room. If I put wood on the fire for the last time at 6 p.m., then the next morning the surface temperature is about 30°C (86°F). When I sit on the stove bench in the morning with my coffee, I have a nicely warmed back...

For me, the utility provider is also the network operator (Bayernwerk AG, formerly E.ON). I need to check whether it is actually possible to switch providers. Although I don’t know what will happen with the 10% non-refundable yield. So far, it has been offset against my consumption... We are talking about approximately 3,000 kWh.

60,000 euros for a heat pump? Then it must be covered in gold leaf, right? :x *duck*