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Solar Hot Water: A "Systems" Engineering Approach to Improving Efficiency Equipment

Solar hot water systems are an unsung hero of the efficiency industry. Sun-powered equipment that provides hot water for showering, household uses and, in some instances, space heating, routinely achieves efficiencies three-times greater than leading Photovoltaic (PV) equipment.

Despite impressive performance, outside of Federal Tax Credits, few incentives have been available to encourage installations of the technology. As more states and efficiency programs introduce incentives that could address the costs associated with solar hot water, it is a great time to review a number of unresolved engineering considerations limiting performance and hampering adoption among consumers.

Fail-Safe Pumping Options, Cost-Effective Emergency “Heat Dump” Equipment & System Monitoring/Optimization

In full sun conditions, solar thermal systems make large quantities of hot water—very quickly. Ironically, this capability is one of the greatest challenges of the systems. With few exceptions, existing designs and equipment do not allow the collectors to be shut off.

To understand why this can be a problem, think of a scenario where a wind storm interrupts power to a home on a summer day, cutting electricity to the circulating pump. The roof mounted collector panels continue to capture sun and energy. Before long, the water temperature exceeds safe levels.

There’s also what is known within the industry as a “Solar Surprise.” A homeowner or system user goes on vacation for a week during the summer, and without anyone around to consume hot water— “surprise!” The system overheats, discharging hot water to the floor of the mechanical room.

As far as system failure calamities go, there are worse things than some hot water on your basement floor. Still, these design flaws fly in the face of the first rule of energy conservation technology: Especially when more expensive technology is involved, new systems must be at least as reliable and trouble-free as what they are replacing.

DC Current (DC) Pumps, Heat Dump Radiators & System Monitoring

The answer to keeping solar hot water systems functioning properly during power outages can be Direct Current (DC) pumps. Powered by mini photovoltaic panels mounted on the hot water collectors, DC pumps circulate water through the solar collectors to the storage tank without the need for grid electrical power. When the sun is out and hot water is being generated, the DC pumps are running—it’s as easy as that.

Unfortunately, the typical DC pump, PV panel and DC pump controllers must be individually sourced and none of the components are designed from the “ground-up” to work together. Even more problematic is the fact that the budget for these three minor components is normally in the $400 to $500-dollar range. That’s comparable to a standard residential gas hot water heater.

Similarly, “Heat Dump Radiators” are an essential means of discharging excess heat from solar thermal systems during the summer. However, existing, readily available “Heat Dumps” have been adapted from other applications and are insufficiently engineered for solar applications. They are also far too expensive for widespread adoption.

Integrating monitoring controls also adds a lot of value to solar hot water systems. They make troubleshooting considerably easier, and minor changes to the flow of liquids and operating temperatures within these systems can have considerable impact on their efficiency. A number of states are offering expanded incentives for installations that include monitoring capability.

Don’t Just “Make it Work” When it Can be Manufactured Better

While each of these components are integral to more resilient solar hot water systems, when field assembled they are just another example of “Make it Work Engineering.” The end result is devices that are marginally suited for the applications in which they are used, time consuming to assemble and expensive.

Identifying problems, optimizing operation and troubleshooting is notably easier with enhanced systems. However, what is really needed is a new approach where the better components are engineered from the design stage. Looking towards the future, monitoring and components like DC pumps and heat dump radiators need to be engineered into systems in production to make solar hot water more cost effective and better performing.

Redesigning systems “from the ground up,” would greatly improve the performance and serviceability of solar hot water systems and allow the technology to meet potential. All told, a “systems” approach to solar hot water engineering would ensure that future systems perform better and are cheaper to install. In my experience, those factors are what drive the rate of consumer adoption up exponentially, leading to greater sum total energy savings from a promising technology that’s yet to have its day in the sun.

The Institute for Sustainable Communities recently released Resilient Solar: Powering and Empowering Communities, a report that shares the stories of trailblazing resilient solar projects in New York City, Baltimore, Duluth, and San Francisco, and connects readers to tools, resources, and lessons learned that they can put to use in their own communities.

Matt Conway's picture

Thank Matt for the Post!

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