German Innovation in Solar Water Heating

With the SECUSOL drainback solar hot water system, the heat exchanger coil in the tank doubles as the drainback tank. Photo: Wagner & Company. Click on image to enlarge.

I was in Boston last week for the annual Building Energy conference, sponsored by the Northeast Sustainable Energy Association. Each year this conference provides an opportunity to connect with friends and colleagues, catch up on leading-edge building design, and learn about product innovations in energy conservation and renewable energy.

I was amazed to see the large number of European companies represented in the conference trade show, with most of the leading innovation in windows, biomass heating, and solar energy seeming to come from Germany.

The product that I found most exciting this year was a unique, drainback solar water heating system, SECUSOL, from the German company Wagner & Company, which is one of Germany's oldest, though not largest, manufacturers of solar water heating systems. Wagner products are represented in the U.S. by Wagner Solar, Inc., of Cambridge, Massachusetts. Before describing what makes the Wagner SECUSOL so exciting, a few words about solar thermal systems are warranted. Over the past few years, solar electricity (photovoltaics) has garnered most of the attention in the renewable energy world. But solar thermal systems, which can include both solar water heating and solar space heating, are often significantly more cost-effective.

Most solar water heaters include flat-plate collectors through which water or a water-glycol mixture is circulated. "Closed-loop" systems have the collector filled all the time, and a pump circulates the fluid from the collectors, where solar heat is absorbed, to the tank, where a heat-exchanger coil transfers that heat to the stored water.

Other systems have an open "drainback" loop. When the sun is shining and the controller tells the pump to turn on, the water or water-glycol solution is pumped through the collectors, and when the sun goes down at night (or power is lost), the fluid in the collectors drains back to a drainback tank. This drainback configuration has the advantage of preventing the collector fluid from getting too hot if the electric pump fails or electricity is lost.

The Wagner SECUSOL system is the latter type of solar water heater, but with several significant distinctions:

Drainback design without a separate tank

Most drainback systems have a separate tank that has to be plumbed into the system. In the SECUSOL system, an oversized heat-exchanger coil in the storage tank serves as the drainback tank--so one component serves two key functions.

Elegant housingA single housing contains the well-insulated 66-gallon or 92-gallon storage tank, the controls, and the circulation pump (situated beneath the tank and accessible through a hatch). This configuration means that the single unit, which is not much bigger than a standard water heater, contains everything except the collector(s) and a back-up heating element.

Quick-mount fittingsThe plumbing lines that circulate the glycol heat-transfer fluid through the collectors and heat exchanger coils in the tank are pre-insulated flexible copper, and they connect with compression fittings. This avoids the need for soldering, speeds installation, and reduces the risk of installer errors.

Wagner's flat-plate solar collectors are among the world's most efficient, with 96% transmissivity of the glass and a selective absorber surface. Photo: Wagner & Company. Click on image to enlarge.

Pre-programmed controlsThe controls that tell the pump when to turn on and off come pre-programmed, speeding installation.

High-efficiency collectorsThe Wagner EURO C20 AR-M flat-plate copper collectors are among the highest efficiency collectors available. They feature extremely high light transmissivity (96%), a selective coating on the absorber plate, and nearly 2-1/2 inches of mineral wool insulation in the back of the collector. They can be installed flush to the roof or on a racking system, which is also made by Wagner.

Back-up heating elementA second heat exchanger in the insulated tank allows a back-up electric heating element to be installed. In this way, the single tank can provide a family's entire water-heating needs. When solar energy is adequate, the electric element isn't needed, but when there isn't enough solar, the family has hot water.

Easy, rapid installationThe various innovations with Wagner's SECUSOL solar water heating system enable it to be installed rapidly and efficiently. A skilled installer can install two complete systems per day, according to Wagner Solar, which is remarkable. This helps keep the total cost down. Tyler Plante of Wagner Solar, Inc., in Cambridge, told me that systems are typically installed for between $7,500 and $8,000.

Wagner also produces some elegant solar space heating systems with packaged components and easy integration with conventional or pellet-fuel heating equipment. More about active solar space heating in a future blog.

Wagner Solar introduced Wagner products to the U.S. market in late 2010 and has installed slightly over 100 systems to date through the East Coast, but mostly in Massachusetts, according to Plante. The company is currently expanding its dealer network. Here's a link to the Wagner Solar listing in our GreenSpec database (requires log-in). This is one of the standout products among more than two dozen packaged solar thermal entries that we include in GreenSpec.

Alex is founder of BuildingGreen, Inc. and executive editor of Environmental Building News. To keep up with his latest articles and musings, you can sign up for his Twitter feed.