Stephen  and Rebekah Hren , authors of The Carbon-Free Home: 36 Remodeling Projects to Help Kick the Fossil-Fuel Habit, just installed a small solar hot water heater on their North Carolina townhouse. Their house, as you might have guessed, is already carbon-free, so this is just icing on the cake.
If you’re not yet in a carbon-free home, installing a solar hot water heater will save you money and fuel all year round…yes…even in the winter. Here’s a project from The Carbon-Free Home that explains the steps.
Batch Solar Water Heater
Project Time: 3 to 4 days.
Energy Saved: High.
Ease of Use: Variable; depends on climate.
Maintenance Level: Low.
Skill Levels: Carpentry: Intermediate. Plumbing: Advanced. Electrical: Basic.
Materials: Variable, depending on complexity of system; include ball valves, check valves, boiler valves, 75 psi pressure-relief valve, tempering valve, roofer’s caulk, glycol, stainless-steel lag screws and washers, roof collars, panel mounting hardware, flexible and rigid ¾-inch copper piping, pipe hangers, pipe insulation, various copper fittings, hose.
Tools: Soldering kit (including flux, torch, solder, and so on), pipe cutter, measuring tape, drill and drill bits, holesaw kit, razor knife, pencil, screwdriver, hammer, fire extinguisher, rope, ladders.
Sophisticated batch-collection systems are plumbed into household water lines, so the usual household pressure moves the water through the collector, as opposed to a pump moving antifreeze or distilled water through a heat-exchanging system.
Quite a variety of ways exist to plumb batch collectors. The batch collector can be the only source of hot water, or it can feed a backup tank adjacent to the normal tank, or it can feed straight into the regular household electric or gas heater. It is possible to plumb batch collectors with backup gas or electric tanks. This ensures the collector can be bypassed in cold weather or, vice versa, the backup tanks(s) can be bypassed and turned off when it is sunny enough to rely solely on the batch collector. It is also possible to place a batch collector (or any other solar thermal system) in-line with an instantaneous hot-water heater, but it must be a model with incoming water temperature sensing.
Off the shelf, high-end batch collectors are installed in a very similar fashion to the closed-loop pressurized system detailed above. The main differences lie in plumbing—adding the extra backup tank if there is one—and in the fact that batch collectors don’t need a pump or controller because household water pressure pushes water through the collector. High-end batch collectors should come with a plumbing diagram to follow. Three-way (bypass) valves on the supply and return lines allow various configurations, including bypassing a backup tank or bypassing the batch collector. Many plans can be found at the DIY Web site www.builditsolar.com .
- Build It Solar . Great compendium of DIY solar hot water and other solar projects.
- Consumer’s Guide to Solar Water Heaters. 
- Interstate Renewable Energy Council . A nonprofit organization that supports market-oriented services targeted at education, coordination, procurement, the adoption and implementation of uniform guidelines and standards, workforce development, and consumer protection.
- North American Board of Certified Energy Practitioners  (NAPCEP). Develops and implements credentialing and certification programs for solar thermal installers.
- Solar Energy International . A nonprofit offering renewable energy education including on solar thermal.