Avery 80-Gallon Residential Solar Hot Water System
Project: Eighty-gallon flat-panel solar hot water system
Goal: To reduce use of electricity
The Challenge
When Nicole and Mark Avery moved into their circa 1800 school house in Spencer, NY, one of the first things they noticed was how much electricity they were using. "We didn't have a huge freezer," says Nicole, "we weren't running a million lights, we weren't gamers, so where was all this electricity going?" One summer, she and her husband started methodically unplugging things for a few days at a time until they found the culprit: their electric water heater. They tried keeping it unplugged while they weren't using it, which meant having to plan for showers, but they quickly found that by doing so they could cut their electric bill roughly in half. They considered upgrading to a more efficient model, but decided to try to cut out heating their water with electricity as much as possible, without going to fossil fuels. They would harness the sun instead.
The Solution
The Averys had seen a couple of solar hot water systems, including one near their home. They spoke with those homeowners, who also had a full photovoltaic (solar electric) array and became convinced they wanted a similar system. They considered putting PV on the roof of their schoolhouse but the orientation would not have worked, and they didn't have the space to have a free-standing system on their property. Fortunately, their garage roof faced south, so even though it didn't provide enough area for a PV system, it was perfect for solar hot water.
People have been heating water with sunlight for thousands of years and modern solar hot water systems are built on the same principles as the earliest systems, with a few significant improvements. Today, there are principally two types of solar hot water (also known as "solar thermal") systems: evacuated tubes or flat panels. Both systems are based on the fact that black objects absorb the sun's radiation. Beyond that, the issues are keeping those black objects hot (reducing conduction, convection, and radiation to the ambient air); circulating water, or antifreeze, through them; and keeping the water or antifreeze hot.
Evacuated tubes use the principle that convection, a significant source of heat loss, does not occur across a vacuum. By piping water or antifreeze through a copper tube inside two concentric tubes with a vacuum between them, the fluid in the copper tube heats up with minimal heat loss back to the environment. Flat plate collectors look much like photovoltaic panels from a distance (indeed, it's possible to have both electricity and hot water in one system, but the efficiency is somewhat less than a single-type system), but instead of silicon collectors, they have absorber fins and pipes running vertically through them from a main inlet pipe at the bottom to a main outlet pipe at the top. Water or antifreeze flows from the inlet pipe up through the heat fins and out the top pipe to the house. In both systems, heat exchangers are often included to increase the fluid temperature as needed, and/or they are put in line with a conventional electric or liquid fuel-fired water heater.
Choosing one system or another is often a matter of preference. Flat plate collectors are typically more efficient than tube collectors in full sunlight but they lose their efficiency more quickly when skies are overcast. They are also less prone to damage from things like small tree limbs and hail and tend to last longer than tube collectors, which can lose their vacuum over time.
The Averys chose a flat panel system that could be supplemented by their existing electric water heater. Their 4' x 8' Alternate Energy Technologies panels were installed by Bob Nape in the summer of 2007. They chose to run glycol through the system, along with a small, 20W PV panel to run the pump, and feeding into an insulated 80 gallon steel tank, which keeps the water hot for three to four days.
To pay for the system, Nicole borrowed against her retirement and coupled that with a federal tax credit of $1500 and state incentives through the NY State Energy Research and Development Authority (NYSERDA) totaling $2000 or 30 percent of the system cost.
Results and Future Plans
Overall, the Averys are very happy with their system. One winter, during a period of heavy snowfall, their PV panel was covered with snow, which meant the pump wasn't getting any power and water wasn't circulating but the solar hot water panels were still heating up. The pressure relief valve saved the system from damage but now the Averys have a 30-foot roof rake to make sure the PV panel stays clear.
The system requires minimal maintenance. Their water has a high mineral content (aka, hard water), which means they have to bleed the system periodically and rinse it with vinegar to dissolve the deposits (which is something they had to do with their electric water heater, too), but otherwise, it doesn't require anything.
In the summer, the Averys have been able to cut their overall electric costs roughly in half, with less dramatic but still noticeable savings the rest of the year. They expect their payoff to be roughly 8 years. Nicole, a Town Board member in Spencer, is hoping the system inspires others to tap the sun's energy for heating water.
More Information
- Solar is Hot is Bob Nape's company
- The Department of Energy has an Energy Savers web site, with a page devoted to solar hot water systems
Contact:
Nicole and Mark Avery
nso1@cornell.edu
607-589-6433
