Here is one for you that you never see.
I well known double pane window seller had some information about the effectiveness of them.
What they said was people in the north got a lot more out of them in the winter than the people in the hot southwest.
It wasn't Anderson I cant remember who it was.
Basically the savings in energy cost for the hot south west wasn't worth the cost of the expensive windows.
Then there is the fact they are sealed and gas filled.
If this leaks out and you get air inside they fog up.
So here is my solution and common sense when you want it warm inside draw back the curtains.
When you want it to stay cool close the curtains.
The other one is called window awnings.
They have been around for years but no one uses them any more.
Now here is a wild idea of mine.
If you can get hold of a water cooled engine driven generator not only could you use it to power heaters but you could circulate the engine cooling water through the soil to warm it up.
You could also capture the heat coming from the exhaust to run it into the structure.
This is how the Volkswagen beetle warmed the inside of the car.
It was air cooled and they had an engine shroud and the cooling fan running air across the engine and into the cab to heat it.
The windshield wipers ran off the pressure from the spare tire.
It functioned just like a steam engine.
A big Stirling engine would be even better.
Back in the 70's when the oil crises was going on ford motor company was designing one for cars.
Then the cheap Arab oil started flowing in at low prices and killed the project.
https://www.google.com/url?sa=t&rct=...kM38_KG5TD-bzw
As for any of the engines the best thing to do is to run off diesel or natural gas.
The problem with the diesel is it isn't going to get as hot and they are expensive.
The natural gas engine will last almost forever.
Put your thinking caps on and do some research.
The big boys have been sticking it to us for years to keep the oil and power companies rich.
Why would they spend money and do research to cut their own throats.
Worth