Underground Greenhouse (walipini) or Climate Battery - which makes more sense?

I'm in zone 7b (Northern AL) and am debating between a partially underground greenhouse (walipini) or installing a climate battery. My goal is to grow subtropical plants/trees and not need supplemental heat. Thinking out loud here, it seems like the major differences between the two are as follows:

underground: requires retaining walls $$$$, drainage/water management $$.

climate battery: requires mechanicals - fan $, air purification $$, pipe & fittings are super expensive right now $$$, the specs/science still seems shaky because of a lack of  testing and consensus among designers.

I'm leaning toward the walipini because of the minimal use of technology and it seems much more straightforward - dig a hole, support the walls and add drainage.

What am I missing in my analysis?

Thanks!

What temperature difference do you need to maintain on your coldest night?

Might a passive solar greenhouse do good enough in AL?  Mine is fairly well built and delivers a 40 degree improvement over cold snap night temps.  IE if it's -30 outside it's around 10 inside...

Mike Haasl wrote:What temperature difference do you need to maintain on your coldest night?

Might a passive solar greenhouse do good enough in AL?  Mine is fairly well built and delivers a 40 degree improvement over cold snap night temps.  IE if it's -30 outside it's around 10 inside...

30 degree difference. That's asking an awful lot from a passive gh and I don't think its worth the risk. But I should probably check it out since I donated to the kickstarter.  Any idea where I can view the movie?

Thanks!

Mine is unrelated to the movie.  I'm not sure if the movie is out yet or where to view it.  My greenhouse is here but it was a challenge to build.

Do you have a south facing slope you can work with?  Or could you dig down 3-4' and mound the dirt on the north side to earth shelter it?

I think if you get a bit of earth protection it should help buffer AL summer temps and help in the winter.  But if you go full walipini, be sure to check your winter sun angles to see how much shade the south wall will cast.

You might want to see if Mike Oehler's greenhouse book is at your local library.  That's another blended option of earth and above ground.

Paul Ladendorf wrote:My goal is to grow subtropical plants/trees and not need supplemental heat.

I mean this with humor, no intention to offend... but maybe you should move to the subtropics? I always try to be a realist. You can grow citrus in Montana... but it takes a lot of time and money. I think it is good to ask yourself why. Why do you want to grow subtropical plants/trees in Alabama? Just because it's cool? To start a business? Is there a better option to grow?

Sometimes you ask yourself honestly, and you come up with a good enough reason to do it anyway. I have to contend with cold more than heat, but in general I think I would lean towards the climate battery. Finding the balance between something big enough to handle what you want, but not so big that you are wasting space and heat can be hard. But if you get that built with insulation and a climate battery to adjust the heat, I think you could do it.

Matt McSpadden wrote:

Paul Ladendorf wrote:My goal is to grow subtropical plants/trees and not need supplemental heat.

Why do you want to grow subtropical plants/trees in Alabama? Just because it's cool? To start a business? Is there a better option to grow?

I strictly want to grow subtropicals because its cool. :D