The main advantage of using DC power to run a solar thermal installation is that you can draw that power from a PV panel and, at the same time, eliminate the need for a controller.
Since PV-based power will only switch on when the sun shines, the solar thermal installation's pump will only run when there is heat to be gathered. When the sun disappears, both the PV power and the pump will switch off.
Before you start any serious plumbing work, make sure you have the right tools. Your system schematic (you did create one, didn't you?) will tell you how much piping you need, as well as all the fittings and other consumables required.
You will also need:
Like any expensive equipment containing lots of metal and liquid, a solar thermal collector array needs to be grounded. Collectors can act like huge static electricity absorbers, gathering charge from nearby lightning strikes and passing it along all the copper pipes to the controller (in an AC system). One big power surge and your controller goes pop!
There is a definite art to plumbing with copper pipes. Thankfully it's fairly quick to learn, though your first few cuts and joins are likely to produce amateur results. If you've never installed copper pipes before, buy some extra parts and practice!
Like most questions in the solar thermal arena, the choice of an AC or DC system is subjective, depending on your needs and your system type. Let's start with the unavoidable limitations:
If you're new to plumbing, you will want to practice soldering pipes before you try your skills on an actual solar thermal installation. It's not difficult but it's extremely important to do the job well or you'll get leaks and other problems. Practice makes perfect!
Radiant floor installations rarely need more than seasonal adjustment. Typically, they are set up at the time of installation and just need to be switched on or off depending on the time of year.
At installation, the ball valve on the heat exchanger bypass stays about 1/3 closed at all times, forcing some of the hot solar fluid through the heat exchanger, but allowing most of it to go to the radiant floor heating (or shunt loop in the off-season).
Although the collectors are installed, the tank in place, the heat exchanger piped in and the plumbing done, there is no guarantee that your solar thermal system has no leaks. You need to test it before you fill the solar loop or allow water into the storage tank. You can check the system for leaks using air or liquids.
All types of solar thermal system need maintenance, though a well-planned installation using high-quality equipment needs very little compared to most active mechanical systems.
Solar collectors are big, heavy pieces of equipment which are both very tough and very fragile at the same time. They weigh 85-140 pounds per collector (38-64 kilos) and are usually shipped on a pallet carried by a big rig truck.
So how are you going to get them safely onto the roof of your house? Carefully, that's how!
