Solar Batch Water Heater

In October I'm going to try to start building a solar batch water heater and put it in our south yard and see how it fares throughout the winter. I'm patterning it somewhat off the one shown on this page with 1-2 8-10" pipes. You might think that these don't work when it gets down to -10F, -20F, -30F, -40F. You would be wrong. Someone puts a demo model of a solar batch water heater in a store parking lot called "Khaluun Us" (Hot water in Mongolian). I used to bike past it thinking nothing of it. One day it was about -20F in the afternoon and I was biking home and noticed hot vapor coming off the top. 

The one I'm building will have 1-2 big pipes in a box designed to be placed on the top face of an earthship similar to a global model probably with much of the pipe on the inside of the house, probably above the bathroom area on the front face, possibly resting on one of the bottle walls for the bathroom. The good point about solar batch water heaters is they're simple and inexpensive. The bad point is if you don't make them properly, they'll freeze and break open. There is a good discussion on solar water heaters in either vol. 2 or 3 with the pro's and con's of various approaches. Basically though Mongolia is quite cold with moments below -40F/-40C in winter, they get so much sunshine (233 full days of sunshine on average) that people typically have deep tan though they're at 48 degrees north. This means we can fully take advantage of any and every solar application and reduce the load on the solar electricity system.

I saw in one global model where they made a very expensive solar water heater with glycol (anti-freeze), where only glycol is heated through the solar water panel. The hot glycol is circulated through a water tank, heating the water. The good part is that the glycol will never freeze. The bad part is that it is inefficient and water will take longer to heat up, and it is possibly the most expensive set up.

So my plan is to get materials and build a solar batch water heater from October. This means getting: insulated glazing the right size, thick insulation (R-40?), as well as insulation around the feeder pipes. They say this is how they usually fail: the feeder pipes freeze. So the key is to over insulate and make sure the thing can be mounted on a future earthship. If it fails this winter, then I'll find out why and fix it. I need to figure out the water volume since the one on the above page seems way to much.