Solar Thermal
Solar thermal is a blanket term for any technology that harnesses solar radiant energy for practical applications. Solar thermal applications can provide domestic hot water, space conditioning, or even electricity. In the US, solar thermal technology is used mainly to generate domestic hot water, although space conditioning applications have gained ground in recent years.
Solar hot water heating has been used in the United States as early as 1920, with a resurgence of interest in the technology during the oil crisis. In warm climates solar hot water systems can provide 50-75% of hot water energy, and even in less sunny regions 15-25% of demand can be met by the solar thermal system.
Recent innovation has improved performance, life expectancy, and ease of use of solar thermal systems, and installation of solar hot water heating has become the norm in countries such as Israel and Greece, where there is an abundance of solar radiation, and Japan and Austria where there is considerably less. Spain and Israel, have mandated the installation of solar hot water systems in all new construction and an estimated 75% of all new construction is Austria incorporates solar thermal technology. In the U.S., the city of Ann Arbor has an ambitious goal of putting 5,000 solar thermal systems on its resident's roofs by 2015.
Fact Sheet
Interested in installing PV at Harvard? Our fact sheet goes through the basics of what you need to know.
Types of Solar Thermal Systems
Solar thermal systems can be broadly characterized as active or passive and as open- or closed-loop. Active systems use electricity to circulate water or the solution through the collector panels. Active systems are generally more efficient and more expensive. Passive systems use no electricity, instead relying on the convective movement of water or solution through the panels. These systems are less efficient but also less expensive and easier to maintain; as a result, they are often used in residential applications.
Open-loop systems circulate potable water through the collector panels and are not suitable for areas that regularly experience temperatures below freezing. Closed loop systems circulate a liquid solution (glycol or other heat transfer medium) through the panels. A closed-loop system is the appropriate technology for Harvard because of the cold climate.
The two types of collectors that can be used in cold climates are flat plate collectors and evacuated tube collectors. Flat plate collectors consist of an insulated panel through which antifreeze circulates. A dark backing absorbs solar radiation, which is transferred to the circulating liquid. Flat plate collectors have been used successfully for years. Evacuated tube collectors systems are a newer technology and use a partial vacuum to assist with the heat transfer. Evacuated tubes are more efficient, but they are more expensive and can break more easily. The largest off the shelf hot water tank is about 119 gallons. Systems should have a backup heater to ensure that hot water will always be provided.
Installation of solar thermal panels
(Photo courtesy of Energyworks South)
Solar Hot Water Pool Heating
Solar pool heating is one of the most cost-effective applications of solar energy. It is relatively simple to integrate a solar water heater since most pools already have a pump, filter, and plumbing. With a solar energy system, the pool's water is pumped through the filter and then through a solar energy collector(s) instead of directly back to the pool. The sun heats the water in the collector(s) before it returns to the pool. Solar pool heating can be used for residential, commercial, or community swimming pools. Over 300,000 pools use solar heating in the U.S. as did the Atlanta Olympic Games. Solar thermal is especially attractive for pool heating because paybacks are shorter. This is because solar thermal pool heating systems demand lower water temperatures than hot water or space conditioning applications and can use less expensive unglazed flat plate collectors. (Photo credit: Poppyseed Bandits)
Solar Thermal as Architectural Elements
Solar thermal panels can be used as architectural elements. They come in a variety of colors and can be used to provide protection from the elements, shade the building, or provide thermal insulation. They can be integrated into the façade of the building, not just the roof. Buildings in Austria and Norway have been successfully using these collectors since 1998. The collector manufacturer is AKS DOMA.
Ratings & Certifications
The Solar Rating and Certification Corporation (SRCC) is a non-profit that was created in 1980 to develop and implement an independent, third party, national rating standard and certification program for solar products. Certified products bear the SRCC logo and are published in their annual directory. The certification tests the maintainability and performance of the systems. Ratings are given to individual collectors and to systems and allow consumers to compare the different models’ performances under a certain set of conditions. They do not currently certify commercial hot water systems; instead, they recommend using the ASHRAE solar heating system guidelines. Annual Performance of OG-300 Certified Systems in Boston
The North American Board of Certified Energy Practitioners (NABCEP) is a voluntary certification program for solar thermal installers.
Cost Estimates
SOLID Solar estimates that a typical large scale project hot water and cooling project costs $60-$70 per square foot. To provide an exact price quote, SOLID must conduct an engineering study on the particular installation site.
Solar thermal systems range in prices depending on the size and intricacies related to installation. A typical residential system ranges in price from $5,000 (for 2-3 people) to $9,000 (5-7 people) installed (this includes design, labor, panels, piping, hot water tanks, etc). A commercial system costs about $10,000-$20,000 installed. Costs can increase up to 30% due to additional fees, such as union wages and city inspectional services. The payback ranges, but hot water systems that currently use electricity or oil have quicker paybacks than gas or steam systems.
LEED
Buildings can obtain LEED points for using renewable energy on-site. More information is available on our Renewable Energy and LEED page.
Sources/More Information
Solar Thermal Overview and Proposal for FAS
U.S. DOE: Solar Hot Water Heating
Solar Thermal Energy – New Light on a Mature and Market Ready Technology