Can one house supply two other houses?

Good day to all readers!

The trend in Europe is clearly moving towards climate protection and CO2 reduction. Currently, my house and my parents' house are still heated with oil. I moved into my house in the year 2000, and my parents' house is almost 100 years old; the heating system was replaced ten years ago. My house is quite well insulated; I use about nine liters per square meter per year for heating and hot water. My parents' consumption is only slightly higher because the house was built with a double shell almost 100 years ago. Further insulation measures are hardly realistic because the roof structure would probably have to be renewed for that.

There is a theoretical possibility of building a third house on the property in the coming years. I would preferably like to find a solution where no oil or gas is burned at all, for example operating a ground source heat pump using photovoltaic power. Since the roof shape of the two existing houses is not suitable for photovoltaics and solar thermal systems, I am currently wondering whether it is possible to plan and build the third house in such a way that it can also supply the two old houses.

In the end, I would like a future-proof solution because I want to live in the third house someday and live off the rental income of the two front houses. In ten years, it will hardly be justifiable to have to have a tanker truck come once a year...

Is this realistic or completely hopeless?

Matthias

You can install a geothermal heat pump in the 3rd house that also supplies the other two houses. Photovoltaics are a bit more complicated. Why are the roofs not suitable? Photovoltaics work more in a way that the feed-in tariff in the summer pays for the electricity for the pump in the winter. Using photovoltaic electricity to heat the houses in winter does not work with that consumption.

With only one heat pump, all three houses should require similar supply temperatures; otherwise, at least one operates with a lower coefficient of performance than necessary.

For rental, I would rely on separate and simple heating systems, due to ensuring the hygiene of domestic hot water heating and the poorly predictable heating habits in rental properties.

So a large heating system vs. three small systems? How far apart are the houses? I can't say whether it is worthwhile, but I can only support boxandroof's objection regarding renting, and I would rather recommend keeping everything separate. Who pays for what if something breaks? What happens if, for example, the parents' house is sold or rented out at some point?

So I don't think it will ever come to selling individual houses because they all lie on a shared driveway. From house center to house center, the two existing houses are about 20 meters apart, and the center of the new third house to be built would be about 50 meters away from the center of the two front houses.

By the way, the two existing houses do not have underfloor heating, but regular radiators. I'm not entirely sure about the flow temperatures; I still have to check that. For the new house, I would probably work with wall heating on the exterior walls.

What alternatives would there even be if you wanted to improve the existing houses? The roof surfaces are quite fragmented due to dormers, so there is hardly any area for photovoltaics and solar thermal systems. That would of course not be a problem with the new house.

And I'm also not entirely sure if the principle "produce electricity in summer and buy in winter" works, because if everyone does that, we will have a surplus in summer and scarcity in winter.

Matthias

What alternatives are there at all if you want to improve the existing houses? The roof surfaces are quite jagged due to dormers, so there is hardly any space for photovoltaics and solar thermal systems. With the new house, of course, that would not be a problem.

I would avoid solar thermal systems; they are uneconomical and add complexity. Photovoltaics usually work more than you think, even on dormers.

By the way, the two existing houses do not have underfloor heating but normal radiators.

That speaks against a heat pump and even more against a shared heat pump since the old houses would “drag down” the efficiency of the heat pump like the new one.

You would have to bring the old houses up to par in terms of insulation and heating surfaces to get close to the new house. I don’t think that is sensible. Is a gas connection possible? Otherwise, continue with oil or separate heat pumps which can run with different efficiencies/flow temperatures.

Whether the principle “producing electricity in summer and buying it in winter” works, because if everyone does that, we have an oversupply in summer and scarcity in winter.

That was probably meant purely financially, not ecologically or practically. Financially, that is the case because the subsidy does not currently differentiate between buying and selling electricity in winter/summer.

I would simply consider photovoltaics independently of the heating system, even if a heat pump can benefit a little from photovoltaics.