I was working on planning a grid-tied battery-backup system for myself. This was getting a bit complicated as there are several major components interconnected with various safety devices. These are kitted in different ways and I was trying to figure out what was the most cost-effective combination and how much of the work I wanted to do myself. It all became moot when I had to sell my PV panels to pay an insurance bill, ha ha, ain't that the oughts for ya.
Anyway I was pleased to see that the solar electric industry is getting its act together on grid-tied battery-backup. Outback has introduced a new product called SmartRE, which is the do-everything magic box, just add PV array and batteries. It won't be available until the second quarter of this year.
On the solar water heat front, I think the industry has its act together on solar for domestic hot water. You can buy a package. Not so for domestic hot water plus hydronic space heat. The solar loop part seems to be mostly figured out, drainback is the way to go. But they do not really know how to size the storage tanks. There is disagreement on system architecture - it seems there must be an anti-scald thermostatic mixing valve between the solar storage and the domestic hot water, but it's not clear whether the water for space heating should be the mixed water or the full-temperature storage water. Also, as far as I know there isn't a controller smart and flexible enough to control this kind of system. At the cottage here the system will have three pumps and three controllers to make it work. The cost of these controllers adds up. The installation requires a lot of skilled labor. I wouldn't want to do another one the way we did the HDT cottage, with one contractor doing the solar loop and another for the rest of it. It would be better to offer the whole thing as an integrated system.
Just to complete the system is costing about $14000. Throw in what it must have cost to put in the solar panels and the radiant floor tubing and I would bet you're up to $30000-40000. I think the Passive House people are right, insulation and air-sealing are a cheaper way to solve the heating problem. Unless the solar hydronic space heat industry gets its act together with slick package systems, I think in the future it will be a small, high-end niche business.