Solar Thermal

Solar power is a form of renewable energy whereby light and heat energy from the sun are collected and converted into a useable form of energy (i.e. electricity) for human consumption.
Credit: Dept. of Energy

The two most popular technologies that harness solar power are photovoltaics (convert solar power to electricity) and solar thermal (convert solar power to heat).

Solar thermal systems capture the sun’s energy by heating liquid (i.e. water), which can then be used in various applications. In residences, these systems are typically used to heat domestic hot water, to heat pool water or for space heating (i.e. radiant floor heating). However, solar thermal collectors can also be used by utilities and power producers to generate electricity. Depending on your current energy sources and the type of application, you could replace some of your natural gas, oil, or electricity needs with solar thermal.

Types of Solar Collectors

The Energy Information Administration divides solar thermal collectors into low-temperature, medium-temperature, and high-temperature:

Low-temperature solar thermal: These collectors use absorbers to collect the solar thermal energy. They provide heat of less than 110 degrees Fahrenheit. ex) Swimming pool solar heater

Medium-temperature solar thermal: Flat-plate or glazed collectors are used to harness the solar thermal energy, which is transferred through a liquid or air medium. Medium-temperature solar thermal systems provide heat that is typically between 140-180 degrees Fahrenheit. ex) Domestic hot water heating (includes evacuated tubes)

High-temperature solar thermal: Parabolic dishes or troughs are used to collect thermal energy at or above 180 degrees Fahrenheit, which is then converted to electricity by power producers or utilities.

Domestic solar hot water heaters are a common green building technology used to produce hot water for a residential property. They are composed of a solar collector and a storage tank. On average, it will reduce water heating bills by 50-80%.

How Much Does It Cost?

If you compare the estimated cost of installation (with tax incentives) with your annual utility cost savings, you can determine the payback period for the solar thermal system. The shorter the payback period, the more likely you will see the returns on your investment. Payback periods are variable and depend on your energy usage, your current utility costs, the cost of the system and how well suited your home is for solar (which will affect the system’s efficiency and output).

A typical solar thermal system for domestic hot water heating costs an average of $4000 to $6000 in the United States, including labor. However, federal, state, local and utility incentives for renewable energy installments can reduce this cost.

For example, the federal government offers a Residential Renewable Energy Tax Credit that is applicable to solar PV, solar thermal, small wind and geothermal heat pump systems. The tax credit is for 30% of the cost of the system, including labor. According to DSIRE, “Solar water heating property must be certified by SRCC or a comparable entity endorsed by the state where the system is installed. At least half the energy used to heat the dwelling's water must be from solar.”

There is also a federal Business Energy Investment Tax Credit (ITC) for 30% of the cost of a solar thermal system (including hot water, solar thermal electric, and solar thermal process heat. This is applicable to the commercial, industrial, utility and agricultural sectors (not residential).

To find incentives by state or local utility, check out the Database of State Incentives for Renewables and Efficiency (DSIRE).

You can also estimate how much a solar PV or solar thermal system will cost based on your location and current energy usage using this calculator. For a more accurate quote, contact your local solar contractor. Most will give you a detailed estimate for free.

Solar Thermal vs. Solar PV

Solar thermal is used to convert solar energy into thermal heat, while solar photovoltaics (PV) turn solar energy into electricity. Solar thermal systems are known to be more efficient than solar PV, with over 50% efficiency. Solar PV systems often convert less than 15% of the energy into electricity.

This means that to produce the same energy output, a solar thermal system would be smaller than the PV system. Plus, solar thermal system materials are typically cheaper than solar photovoltaic components.

However, solar PV does have some advantages over solar thermal. PV systems are eligible for net metering, which is selling excess electricity that your building produced back to the grid. This can increase the system’s ROI. Solar thermal systems that produce thermal energy cannot partake in net metering.

Also, solar PV can be used year-round, while solar thermal systems can remain idle during the summer if they are used to replace space heating (not to mention that when you do need space heating, it’s the winter – when you get the least amount of sunlight).

While each system has their advantages, the best one to start with really depends on the type of energy you want to replace first in your building. Your current utility bills and available tax incentives are key for choosing whether solar thermal or solar PV will be more advantageous for you.

Installing Solar Thermal Systems

It is recommended that you hire a solar contractor to install a solar thermal system in your residence. When looking for a solar contractor, find one with a license, previous installation experience, and positive customer references.

Many solar contractors will provide a free assessment of your home before doing work. They will be able to tell you how much the system will cost based on your home’s orientation, your current energy use, shading, available tax incentives, etc.

Some installers may have credentials that ensure their experience and knowledge of solar thermal. For example, the North American Board of Certified Energy Practioners (NABCEP) has a Solar Heating Installer Certification.

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