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These semi-undergound greenhouses have been around for a long time in the upper midwestern states.  The most sophisticated ones employ geothermal heating to supplement the solar heat collection. 

Here' a link to a company in Nebraska that builds these greenhouses and has been in business for over 35 years. The largest greenhouse that they construct in 2550 square feet. 

https://greenhouseinthesnow.com/

If you have one you can grow citrus in the snow.

https://www.kcur.org/2016-02-11/citrus-in-the-snow-geothermal-greenhouses-grow-local-produce-in-winter

The ultimate solution to the energy situation in Europe is to build a greenhouse around your house.  This has been done in Sweden to good effect.  It's a very creative solution if you have the money to do it.  It's called a house in a greenhouse.  Why go underground if you don't have to?

https://www.designboom.com/architecture/swedish-family-envelopes-home-in-greenhouse-warm-up-weather-10-21-2021/

Bern - brilliant photo of the house in Sweden. I'd like one of those... well growing the plants would be nice.

In the UK there was a lot of enthusiasm for "conservatories", glass roofed extensions to houses. By now people are scrapping them - too cold in Winter, too hot in Summer. Rocks are not the only thing people who live in greenhouses have to worry about.

Seems lots of engineering around that Swedish glass house - probably for getting the heat out in Summer.

Fritz Kummert's book "Pflanzen fur das Alpinenhaus" (apologies for omitting umlauts; published by Ulmer) has a very good chapter on the construction of a semi-subterranean alpine house (in Austria), with detailed drawings. It's mostly a plant encyclopedia, with plenty of geophytes discussed. The design of the alpine house is intended to facilitate warming in winter and (important for alpines) cooling in summer -- all or mostly passive. It would have to be where the water table is low enough, though, or on a slope with drains provided.

In an ominous development, I have had my greenhouse heating on for two nights and weeks more of cold weather are now forecast.

Quote from: David Pilling on December 08, 2022, 05:56:01 PMIn an ominous development, I have had my greenhouse heating on for two nights and weeks more of cold weather are now forecast.

It is winter. Until the past few days it has been insanely warm Over the past two and the next few days the only thing unusual about the weather is that day temp's are not forecast to get above something like 3C over much of England. 
The forecast for around here - Leicester -is showing frosts of only 1-2C as far as the end of next week, not the 4-6C of the past two nights. Blackpool is looking 2-4C warmer than here.

The forecast is only really accurate up to something like 10 days out anyway. Beyond that they can predict broad trends only.

The winter solstice is next Wednesday, December 21st. The next few months will be telling. As you know it is the day with the shortest daylight of the year.  Fortunately, the daylight time will begin getting longer and around here it is usually noticeable a few weeks into January. I'm beginning to really like the house in a greenhouse idea. Or, the house in a cloche idea. 

The thing I like is that the earliest sunset is (here) the 17th December. After that the nights start to get lighter - although sunrise continues to get later until some days after the solstice. No argument that the shortest difference in sunrise and sunset is the 21st.

So we only have another week of darker nights.

Quote from: CG100 on December 09, 2022, 01:15:40 AMBeyond that they can predict broad trends only

Europe's fate hinges on the beating of butterfly wings.

Quote from: David Pilling on December 09, 2022, 06:46:19 PMThe thing I like is that the earliest sunset is (here) the 17th December. After that the nights start to get lighter - although sunrise continues to get later until some days after the solstice. No argument that the shortest difference in sunrise and sunset is the 21st.

That's some weird, and I understand it for about 30 minutes after I look it up each year.

That's just the friction between easy assumptions (circular rotation of Sol III around Sol, and some fuzz with the inclined axis) and  the reality. The thing what's bothering me is yes, that's the time when the radiation balance starts to get better, but it will take about another 6 weeks until the thermal inertia of the biosphere allows us to really warm up.

Actually, I'd prefer to celebrate the solstice, as it does have a meaning to me, over celebrating that birthday of someone long ago far away. Unfortunately, celebrating the solstice is popular among the extreme right. Which is where I never would want to be.

Quote from: Martin Bohnet on December 10, 2022, 01:13:41 AMI'd prefer to celebrate the solstice

Someone will live stream the events at Stonehenge on the 21st and they will be anything but right wing.

Somehow, i find it comforting that such an ancient ritual at Stonehenge is still celebrated. Perhaps in Germany  celebration of the Solstice is considered right-wing, but not here in the US to my knowledge. I may be a baptized Lutheran but I'm certainly not a Christian and like Martin, I celebrate the Solstice with friends even if undercover, especially in this little town that has too many tiny churches on every fifth street corner of whatever denomination.

It may take six weeks to really start to warm up, but believe me within 2-3 days of the Solstice I begin to be aware of the tiny increments of increasingly longer days, almost imperceptible though they may be. Such a great reason for celebration every year! I'm counting the days...

I think of Scandinavian summers as having very long days.

The issue I was warned about when my significantly smaller home greenhouse was about to be ordered was not so much keeping it warm in winter as keeping it cool in summer.

And how do they keep the glass clean . . . I have enough of a problem with windows.

In late spring, the Enid Haupt conservatory at  the New York Botanical Garden is sprayed with a white paint that degrades with  rain. By autumn they hose off the remnants. Which does require equipment with lift buckets etc.

Interesting comment about more a matter of overheating in summer... An orchid grower friend who had a 30x30 foot glass room built as an addition to the second story of their home had a different take on the issue. It had glass siding and roof and I asked about cleaning the roof... Seems she preferred not to clean it but to leave it slightly dirty to reduce the amount of direct light, thereby adding some protection.

I've taken that attitude to heart and find it works well enough, and is certainly less hassle than painting the roof with white paint. Bear in mind however we're in coastal southern Oregon... I guess my attitude is that there are always options, some more or less wonderful than others.

Regarding cleaning greenhouse roofs: I just had a window-washing company clean the polycarbonate roof of my bulb house, which gets dirty from tree pollen. I think it's important in my cloudy winter climate to get as much light as possible on my winter-flowering geophytes. Especially in more northerly latitudes, plants can fail to grow "in character" and end up stretched and floppy. Incidentally, the discussion of the winter solstice reminded me of this season when I lived in Fairbanks, Alaska, and every morning the public radio station gave out the day's length. It was a great day when it changed from "seven minutes less than yesterday" to a little increase. My plants then were under artificial light, mostly in my well-heated office and not in the freezing cabin.