How To Install a Solar-Powered Water Heater

Solar-powered water heaters are an eco-friendly and cost-effective solution for homeowners looking to reduce their energy bills and carbon footprint. These systems harness the sun’s energy to heat water, providing a renewable alternative to traditional water heaters. In this article, we walk through how to install a solar-powered water heater, its benefits, and important considerations for homeowners. This Old House plumbing and heating expert Richard Trethewey demonstrates installation in the video above.

Understanding Solar-Powered Water Heaters

Solar-powered water heaters use solar collectors to absorb sunlight and convert it into heat. This heat is then transferred to a fluid, typically an antifreeze solution, which circulates through the system to warm the water in a storage tank.

As solar energy expert Lou Boyd explained on This Old House, “A solar collector changes light energy into heat energy that we can use for useful domestic purposes. The sunlight will go through a cover glass, hit a black absorber plate, that’s usually made out of copper, and turn into heat. Then we have a liquid that’s being piped up through the bottom of the collector, up through these riser tubes.”

Types of Solar Water Heaters

There are two main types of solar water heating systems:

• Active systems: These use pumps to circulate water or antifreeze through the collectors.
• Passive systems: These rely on natural convection to move water through the system.

Active systems are further divided into direct circulation systems, which pump household water through the collectors, and indirect circulation systems, which use an antifreeze solution to transfer heat to the water.

Components of a Solar Water Heating System

A typical solar water heating system consists of the following parts:

• Solar collectors: Usually mounted on the roof to capture sunlight
• Storage tank: Holds the heated water for use
• Heat transfer fluid: Often an antifreeze solution that circulates through the system
• Pumps: Circulate the fluid through the collectors (in active systems)
• Controller: Monitors temperatures and activates the pump when necessary
• Backup heating system: Provides hot water during cloudy days or high-demand periods

Collector Types: Collectors come in two main types. The most popular are flat-plate collectors: insulated glass boxes with copper pipes attached to heat-trapping absorber sheets. Under ideal conditions, they can produce 150-degree water, well above the 125-degree water in a typical water heater. More efficient tube-type collectors encapsulate the absorber sheets and pipes in glass vacuum tubes for maximum insulating effect, and they can heat water up to 200 degrees.

Pro Tip: Richard Trethewey, This Old House plumbing and heating expert, explains how the closed-loop system works: “None of this water that’s heated on the roof ever comes out a tap. It stays in this loop all the time.” A separate pump runs tap water through a heat exchanger, where it gains heat from the closed loop before being sent to the household supply.

Benefits of Solar-Powered Water Heaters

Installing a solar-powered water heater offers several advantages for homeowners:

• Reduced energy costs: Solar water heaters can significantly lower your monthly energy bills.
• Environmental impact: These systems reduce reliance on fossil fuels, decreasing your carbon footprint.
• Long-term savings: While the initial investment may be higher, solar water heaters typically pay for themselves over time.
• Increased home value: Solar installations can boost your property’s resale value.
• Energy independence: Rely less on external power sources.

Installation Process for Solar-Powered Water Heaters

While homeowners who have experience may be able to manage installation on their own, we recommend enlisting a professional. Here’s an overview of how the installation process should go.

Preparation

Before installation begins, the following preparation should be completed:

• Site assessment: Determine the best location for solar collectors, typically on a south-facing roof.
• System sizing: Calculate the appropriate system size based on household hot water needs.
• Permitting: Obtain necessary permits and approvals from local authorities.
• Equipment selection: Choose the appropriate solar collectors, storage tank, and other components.

The video shows an in-depth demonstration of how to find the ideal spot for the solar collectors and make necessary measurements and calculations.

Roof Installation

The first major step in the installation process is mounting the solar collectors on the roof. Here’s how it’s done:

1. Remove roof shingles in the installation area.
2. Install flashing to ensure a watertight seal.
3. Mount the solar collectors securely to the roof structure.
4. Install a temperature sensor on the collector to monitor heat levels.

Plumbing Connections

After the collectors are in place, the plumbing connections are made.

1. Run insulated supply and return lines from the roof to the mechanical room.
2. Connect the lines to a pumping station in the basement.
3. Install a new water heater with a built-in heat exchanger for the solar system.
4. Connect the water supply pipes to the new water heater.

System Controls and Safety Features

To ensure safe and efficient operation, several control and safety features are installed.

1. Install a controller to monitor temperatures and activate the pump when necessary.
2. Add a tempering valve to prevent scalding by mixing hot water with cold water.
3. Connect a gas backup line to provide hot water during periods of low solar radiation.
4. Implement pressure relief valves to ensure system safety.

Important Considerations for Solar-Powered Water Heaters

Think through the following factors during installation. 

Climate and Sun Exposure

Your solar water heater’s efficiency depends on the amount of sunlight it receives. Keep in mind your local climate and the orientation of your roof when planning the installation.

For areas with less sun exposure or frequent cloudy days, a larger or more efficient system might be necessary. Roof orientation and tilt can affect the system’s performance. Ideally, solar collectors should face south and be inclined at an angle equal to your latitude for maximum efficiency.

Maintenance Requirements

While solar water heaters are generally low-maintenance, regular inspections and occasional servicing are necessary to ensure optimal performance. Regularly perform the following:

• Check for leaks in the system.
• Clean solar collectors.
• Inspect antifreeze levels and quality.
• Test pressure relief valves and other safety components.

Routine maintenance involves checking the system for any signs of wear or damage and ensuring that all components are functioning correctly. Filters and pumps may require replacement over time, and solar collectors should be free of debris to ensure maximum efficiency.

Integration With Existing Systems

When installing a solar water heater, consider how it will integrate with your existing plumbing and heating systems. In many cases, the solar system will work in conjunction with a backup water heater to ensure a constant supply of hot water.

Proper integration ensures that the system can meet your household’s hot water needs even during periods of low solar output. Professional installers will assess your current system and determine how best to incorporate the new solar water heater without disrupting your daily routines.

Professional Installation for Solar-Powered Water Heaters

While some homeowners may consider installing a solar-powered water heater themselves, we highly recommend professional installation. Experienced installers have the expertise to ensure that the system is configured correctly and operates efficiently. They’re familiar with local building codes and regulations, ensuring compliance and safety throughout the installation process.

Hiring professionals also provides peace of mind that the installation will be done right the first time. This reduces the risk of potential issues and ensures that the system will perform optimally over its lifespan. Professional installers often offer warranties and maintenance services, adding an extra layer of security for homeowners.

Pro Tip: When hiring a solar installer, get at least three bids—five is better for a full picture of the options and prices—from companies referred by friends, neighbors, or tradespeople you trust. The bids should include the federal tax credit and any available local incentives, which you can verify at dsireusa.org.