Asking for advice from off-gridders about the recent blog “Solar thermal is really really dead”.
A recent blog by Martin Holliday has me rethinking our approach to our Super insulated off grid retirement home. I’m not going to rehash the blog but I’m wondering how people who specifically live off grid view the opinions in it. I’ve spent enough time living in off-grid situations to know that the math about our mechanical systems is different when there is no energy “bank” to go back to when you’re short.
Our project is a super insulated off-grid three story house (walk out basement) 2200sf, south facing with windows calculated for passive heating, two stories of concrete floors. We’re shooting for R60 walls and R100 roof. It’s located north of Montreal, so its completely unrealistic not to have a backup heat. The original plan was to have two Solar thermal panels that would heat two water tank “batteries”. Those tanks would preheat water for a propane instant water heater for the radiant floor, with a twin unit for DHW. The whole idea was keep the house just warm enough to keep from freezing when unoccupied, about 12C, and to heat with wood when we were there. The house would be unoccupied about half the year. As with everything about this project its DIY, I’m my own contractor.
That was then, the shell is now up, sealed and finished, with the inside completely bare, only three weeks behind schedule, my fault, I was late in ordering the windows. The blog by Martin has me rethinking the wisdom of my solar thermal approach. I always understood that a radiant floor wouldn’t be warm in this application but I figured if I was going put in the floors, I might as well throw some pex down and take advantage. I must admit I also liked the idea of no ducting. Has anyone had experience with radiant floors off-grid? On the flip side I’m much more comfortable with installing PV (a kissing cousin to my day job) and I like the idea of simply expanding a system that I’m already going to install. I just find it hard to believe that I can get the same BTU per square foot with PV as from solar thermal. This is a concern because the south facing wall real-estate is at a premium. I’d love to hear some input from the practical experiences of the members here.
I’ve include a photo of the house below. The space between the two bottom floors is ear marked for PV panels which will provide shading in the summer.