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Solar Hot Water Basics: Introduction to Solar Thermal

Understanding How Solar Powered Hot Water Heaters Work

Solar Hot Water Basics: Introduction to Solar Thermal

Solar water heaters, also known as solar domestic hot water systems, use the sun’s energy to provide cost-effective, low-carbon hot water for the home. They can be used in any climate, and the fuel they use—sunshine—is free.

Both passive systems and active systems effectively generate hot water for domestic use. When using an active system, one may also choose between flat-plate collectors and evacuated-tube collectors to gather and convert the solar energy.

Types of Solar Hot Water Systems

The overall goal of any solar hot water system is to utilize the sun’s energy to create hot water for domestic, residential use. This can be done using one of two types of systems.

Passive systems operate in the same manner as a bucket of water or garden hose left in the sun. They do not use mechanical or electrical parts to create and deliver hot water. The sun directly heats water stored in a large tank on the home’s roof using a solar panel often referred to as a collector. That water then flows from the tap. A thermostat is pre-programmed to the desired water temperature and, if necessary, a conventional hot water heater heats the water to the desired temperature.

solar hotwater tank setup

Figure 1: Example of Passive System

Due to their simplicity, passive systems are less expensive to install, tend to last longer and tend to require less repair. However, they are also less reliable, less functional in cloudy or cool climates and dependent on the sun’s intensity to provide hot water. When there is no sun, there is little or no hot water.

Active systems use pumps to circulate water between the solar energy collector (PV panel) and the large storage tank. Water is stored in a large tank in the home and pumped through collectors (PV panels) on the home’s roof, using a heat-transfer fluid if necessary, that keeps water from freezing in cold climates. This warm water is then returned to the tap. A controller is used to ensure that the pump only runs when heat-transfer fluid is present and to ensure that water is always at the desired temperature. Storing water inside of the house and utilizing a heat-transfer fluid ensures that hot water is provided in cold climates or during non-daylight hours.

example of active solar water system

Figure 2: Example of Active System


When using an active system, it is necessary to choose between three types of collectors, flat plate collectors, storage collectors and tube collectors to gather and utilize solar energy. The benefits of each type vary with the climate.

While active systems are more expensive, they are more reliable and make solar hot water a reality in cloudy or freezing climates (a “heat-transfer fluid,” typically propylene glycol, is used to keep the stored water from freezing in cold climates). They also allow the water tank to be situated above or below the tap. In a passive system the tank must be located on the roof. This allows situation of the tank for minimum radiant heat loss and thus maximum efficiency.

What’s It Going To Cost Me?

Many state, federal and third party incentive and rebate programs are available to subsidize the cost of installing solar hot water. Since the water heater is typically the second-largest consumer of electricity in the home (after the AC unit), supplying the electricity needed to power it through solar hot water saves homeowners money on their utility bills that will help pay for the up-front installation costs over time.

Typically the federal tax credits allow a 30% credit of the total cost on the installation and are capped at $2000. It is necessary to save all documentation related to the system and have the system certified by Solar Rating Certification Corporation.  

State incentives vary by state but include offerings like state-level tax incentives, rebates, property tax credits, sales tax exemptions and more. The Database of State Incentives for Renewable Energy will help you determine which incentives your project is eligible for.

Local utilities, local non-profits and other foundations or third-party organizations also offer incentives and rebates which can be determined by contacting your local building department or chamber of commerce.

The Bottom Line

Solar hot water offers a cost-effective, environmentally-conscious way of providing solar hot water for the home. Since the hot water heater consumes the second-largest amount of energy in the home, installing solar hot water lowers energy bills. While solar hot water installations vary based on the climate in question, it is possible to install solar hot water in any climate. Incentives and rebates make this an even more feasible possibility. Get started today!

To learn more about this subject, get started with an Everblue solar training course or call us today at (800) 460-2575!

About Lesley Cowie

Lesley has been passionately advocating for and working with green building and renewable energy since 2009. She has experience with LEED certification, home energy auditing, blower door testing, solar energy, and more. She holds many certifications, including LEED Green Associate and NABCEP Certification. Her work has won numerous awards over the past decade.

One reply on “Solar Hot Water Basics: Introduction to Solar Thermal”

  1. Energy Performance Certificate

    Is there some kind of built Solar Energy Heater? or You need to Do it your self?

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