Building Science: Taking another look at solar hot water

So why solar hot water in the U.S., anyway? Many homeowners have little clue about how their water is heated, its contribution to their energy bill or the alternatives available.

November 17, 2012

So why solar hot water in the U.S., anyway? Many homeowners have little clue about how their water is heated, its contribution to their energy bill or the alternatives available. Oftentimes, it is an afterthought during a home renovation project, somewhere down on the priority list after choosing the color of the bathroom tile grout. So let’s start with some basic facts.

Water heating consumes 18 percent of the energy used in American homes and is the second largest energy consumer behind space heating.That is more energy used than powering all of a home’s lights, computers, refrigerators, TVs, Xboxes and other electronic gadgets combined. Residential water heating amounts to $34 billion in annual expense and 162 million metric tons of CO2 emissions.

Solar hot water (SHW) systems trap the heat from the sun (solar radiation) and transfer it to water for use as thermal energy. SHW systems are composed of three main components: solar collectors, a water storage tank, and a circulation system to transfer the heat from the collectors to the tank. While there are many variations, essentially the solar collector gathers the heat from the sun by heating either water or a non-toxic heat transfer fluid. The heated fluid flows from the collector to a hot water tank, and used as necessary.

Solar hot water was the “original” solar technology, and saw over 125,000 units installed annually in the late 70s-early 80s during the oil crisis. The industry went into steep decline with the fall in energy prices, industry quality problems, and removal of a federal tax credit.

SHW systems of today are an effective, reliable technology that can displace up to 75 percent of the energy cost and greenhouse gas emissions associated with a home’s water heating. The industry has adopted rigorous testing and quality certification programs, including the SRCC OG300 system certification, IAPMO’s Uniform Solar Energy Code Certification for systems, and NABCEP Solar Heating Installer Certification for installers.

One of the main concerns about SHW is the value of the investment to the homeowner. While solar hot water is the most affordable renewable energy option available, the reality is that economics of solar water heating do not work for every household. Wide disparity in the cost of power, installed costs, water heating needs, and incentives mean the answer differs from state-to-state and household-to-household. This lack of consistency and transparency is one of the major challenges for the sector.

However, the economics DO work for much of, if not the majority, of the country. For those 50+ percent of homeowners heating water with electricity, heating oil or propane, the annual cost savings from a solar hot water system should offset the capitalized cost of purchasing the system. This is particularly the case for all homeowners in states with strong financial incentives for solar hot water such as Maryland, New York, California, Massachusetts, Louisiana, or Nevada.  It should go without saying the environmental benefits have long-term impact far beyond the monthly energy bill.

The opportunity is especially present during a home remodel project, as the cost and payback on a SHW system should be considered in the context of the incremental cost to go solar. If the homeowner has an old tank (10+ years) or if the project includes a boiler or water heater replacement, the additional cost of substituting in a SHW system can be quite low after incentives are factored in. Remodelers put in an estimated 3 percent of the 8 million water heaters sold annually in the U.S., representing at least a quarter of a million annual opportunities to help customers reduce their energy bills and carbon footprint. As with any renovation project, there are a number of important factors when considering a SHW system:

Costs: upfront costs for a SHW system can vary based upon the system type, collector area, and configuration of the home. The DSIRE database is an excellent, searchable clearinghouse for all federal, state and local incentives available.

Savings: annual potential savings are a function of the fuel being substituted. Electricity, heating oil, and propane are expensive ways to heat water.

Collector Siting: SHW collectors don’t necessarily have to be situated on a roof, the typical application. A roof should be in good condition with a 100 ft² area of southerly, mostly unshaded exposure.

Hot Water Demand: a typical person uses 20 gallons of hot water a day, so the potential for savings with SHW goes up with more users per household. This also impacts the sizing of the system.

Tank Replacement: regular water heaters have an average lifespan of 13 years; most homeowners only find out how old their tank is when it fails on them. If the water heater is over 10 years old and needs replacement, SHW is one way to get a new tank and lower energy bills. Solar water heaters are larger than standard tanks, and require more utility room space. The good news is the homeowner will get more hot water storage capacity than they had before. PR


Matt Carlson is CEO of Sunnovations Inc., McLean, Va. Visit

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