ᐅ Gas heating + solar thermal system

Hello. A question for the experts and experienced home builders:

We are planning to build soon and already own a building plot. A natural gas line is available on the property. Since gas is quite expensive and alternatives are often considered... Is it sensible to combine a gas heating system with solar thermal for domestic hot water preparation? Or would it be better, considering current prices, to disregard gas heating and switch completely to, for example, a pellet heating system? It will be a single-family house. The exact heating demand is not yet known.

I would appreciate some basic information to understand the options better... I will consult professionals later but want to gather information through forums first... Many thanks in advance.

Gas is not expensive if you use only a small amount. Without a specific demand, no one can help you. We are building to KfW 50 standards and expect heating costs of around 40 EUR per month. These figures are based on experience reports from people with the same catalog house. For pellets, you need a basement; we are building without one. Gas is the most affordable option for the expected consumption.

Hello Vit84,

When building a house that uses very little energy, a heat pump is the simplest system. It runs efficiently for a long time, and if you choose one of the four renewable electricity providers as your power supplier, it is even ecological.

You also save yourself from having a chimney and the annual chimney cleaning costs!

However, heating is only a very small decision when building a house, which arises during planning, because it, as Der Da already mentioned, is strongly influenced by the type of house you plan.

Best regards

K.Brodbeck

Vit84 schrieb:
...Since gas is quite expensive and people often consider alternatives...

Expensive is relative. Here about 0.07 €/kWh, heat pump electricity 0.19 €/kWh.

Vit84 schrieb:
...Is it sensible to combine a gas boiler with solar thermal for domestic hot water?

Unless it’s a passive house, the demand for domestic hot water is significantly lower compared to heating, meaning the investment in a solar thermal system has limited economic impact. Additionally, usually only a fraction of the estimated energy yield can actually be achieved, which is misleading.
If using gas, it is better to improve the building insulation (15% rule) and skip the solar thermal system.
Without knowing the actual demand (power, energy) for heating and hot water, it is not possible to find the optimal solution.

Best regards.

Hello,

Vit84 schrieb:

We plan to build soon and already own a building plot. A natural gas line is available at the property. Since gas is quite expensive, we are considering alternatives...

That depends, as €uro correctly pointed out; most such statements are based on the influence of the electricity lobby. In fact, gas will be a good alternative for the next approximately 20 years, and its supply price will remain a predictable constant. New technologies make it possible to develop natural gas sources in Germany that were previously considered unrecoverable.

Vit84 schrieb:

Is it sensible to combine a gas heating system with solar thermal for domestic hot water? Or is it better, due to current prices, to abandon gas heating and switch completely to, for example, a pellet heating system? We are building a single-family home. The heating demand cannot yet be specified. I would need some basic information...

This is one of those debated topics. Typically, homeowners cannot avoid installing a solar system for domestic hot water, as it is the simplest way to comply with energy saving regulations. Adding more insulation—as the 15% rule mentioned by €uro indicates—usually reduces usable floor area, which is counterproductive since most builders want to maximize their buildable space.

Nevertheless, it is worth considering relying more heavily on solar energy than just the standard 4.5 m² (48.4 sq ft) solar panels for domestic hot water. Sunlight is always freely available, and there are successful newly built homes that have achieved excellent—and publicly verifiable—results through solar thermal energy. In contrast, the frequently promoted “plus energy house” shows disastrous energy balance results, including electricity consumption beyond what is reasonable, with no one able to explain its source; a disappointing outcome from a policy standpoint!

There are various options to utilize solar thermal energy; starting from about 20 m² (215 sq ft) collector area with a 1000-liter (264 gallons) buffer tank, up to a genuine solar house with a 9000-liter (2377 gallons) storage tank and a pellet stove. Considering that a decent air-to-water heat pump including installation costs around 15,000 euros, it is worth thinking about investing the same amount in solar thermal energy. By the way, energy providers will sooner or later drastically reduce subsidies for air-to-water heat pumps under the heat pump tariff; it is expected that the heat pump tariff will be offered at 1-2 cents per kWh below regular household electricity rates—there is even talk of so-called “penalty tariffs.”

Best regards

Bauexperte schrieb:
... Adding more insulation – here referring to the 15% rule mentioned by €uro – usually reduces the usable floor area. This is counterproductive since most builders want to maximize their building footprint.

I see that differently ;-)

Bauexperte schrieb:
... Sunlight is always freely available, and there are already successfully completed new buildings that have achieved excellent – and publicly accessible – results using generated solar heat.[ /QUOTE] Well then, show me the results: investment cost (capital service) / actual yield. I’m curious ;-)
[quote="Bauexperte, post: 40568"]... There are different ways to use solar heat; starting with about 20 sqm (215 sq ft) of collector area and a 1000-liter (265 gallon) buffer tank, up to a true solar house with a 9000-liter (2380 gallon) storage tank and pellet stove. So – considering that a decent air-to-water heat pump including installation costs around 15,000 euros – it’s worth thinking about investing the same amount of money in solar heat.

Completely wrong. The more thermal energy you need to store, the less economical it becomes! By the way, the cost of an air-source heat pump varies significantly depending on the required capacity and is usually much lower! Gas condensing boiler plus connection costs are in a similar price range compared to, for example, an air-source heat pump ;-)

Bauexperte schrieb:
... By the way, energy suppliers will sooner or later drastically reduce subsidies for air-to-water heat pumps through the heat pump tariff; there are talks of this tariff being offered at 1-2 cents below regular household electricity rates – “penalty tariffs” are even being discussed.

Sound planners already assume standard tariffs anyway ;-)

Best regards