How Does a Solar Pool Heater Work?

Basic principles of solar energy conversion for pool heating

While solar pool heaters, known as solar thermal systems, harness the sunlight to do their job, they’re not the same as solar photovoltaic (PV) systems, which you may use to power your home via solar panels or solar tubes.

Thermal systems convert sunlight into heat energy and have fewer components than PV systems. They use air or liquid for transferring heat, which makes thermal systems perfect for pool warming. These systems heat water in a cylinder, circulate it through piping to storage (where it’s held in insulated tanks) and then deliver it to knock the chill off your pool water.

PV systems convert sunlight into electricity, rather than heat energy, which homeowners can use to power appliances, lights and anything else in the home that uses electricity.

How a solar pool heater works

Here are the basics of a how a solar pool heater works:

1. Pool water flows through a filter.
2. The water is heated in the solar collector, which warms the water with solar power.
3. A pump sends the warmed water back into the pool.

A solar pool heating system becomes more advanced as you add components such as controllers, manifolds and valves. These optional features allow you to set up a system that’s as hands-on as you want it to be.

Other types of solar pool heaters

There are alternatives to these solar pool heaters, like “lily pad” (blanket) heaters, which are discs that float on the pool and heat the water using thermal energy and by providing a partial cover to the pool. Lily pad solar pool heaters prevent heat loss and add passive heat to the water.

» MORE: What is passive solar heating?

Types of solar collectors: glazed vs. unglazed

As you shop for solar pool heaters, you may notice that different solar collectors are made of different materials.

Which one is right for you can depend on the climate where you live. According to the U.S. Department of Energy, less-expensive unglazed collectors may be a good choice if you only plan on using your pool when temperatures are above freezing.

Unglazed solar collectors lack the iron-tempered glass covering that glazed collectors have. They may be plastic or heavy-duty rubber, and they’re treated with an ultraviolet light inhibitor.

While more expensive than their unglazed counterparts, glazed solar collector systems capture heat more efficiently. They’re usually made of copper tubing on an aluminum plate with a glass covering, or glazing.

Regardless of whether you go with a glazed or unglazed system, you’ll need to ensure it has freeze protection if you live somewhere with colder months.

How to choose a solar pool heater

There are several critical considerations when choosing a solar pool heater. These include the size and type of your pool, as well as local weather and energy costs.

In-ground vs. above-ground pools

Though water temperature doesn’t differ much between an in-ground pool and an above-ground pool, above-ground pools are often slightly colder than in-ground pools — and, during the hotter times of the year, they can be just a little warmer. This could affect your pool heater needs.

Sizing your system

The rule of thumb for matching a solar heater to your pool is that the solar collector must cover at least 75% of the surface area of your pool. For example, if you have an 800-square-foot pool, you need a solar heater with a collector that’s at least 600 square feet in size.

An easy way to figure out if you have the space for a large solar collector is to calculate the square footage of roof space near the pool. If you have a large yard, you can also consider how much available space you have for a ground-mounted solar pool heater.

Local weather and climate

Where you live is a big factor in how effective a solar pool heater will be. If you live in a colder region with a longer spring and early fall, for instance, your solar pool heater may struggle to keep your pool at a comfortable temperature year-round. If you live in a warmer location, however, a solar pool heater may be an efficient tool for warming your pool.

Other weather-related factors that can affect how efficiently a solar pool heater works include the presence of storms, clouds and shading. A solar pool heater needs direct sunlight to work efficiently.

Energy costs

As a general rule, a solar pool heater heats the water in your pool for a relatively low cost (beyond the initial purchase price) — usually around $200 a year. If you live in a colder region, the pool’s water temperature may drop faster and require the water pump to work harder, pushing water through the system more often. This process — providing energy for the pump — drives up the cost of heating your pool.

In colder areas, people often pair solar pool heaters with either a pool cover that works to prevent the bleed-off of heat from the exposed water or with another type of heating system.

» TIPS: How to save energy at home

How much does a solar pool heater cost?

In general, a solar pool heater costs between $2,500 and $4,000. More expensive systems often include features such as full automation. The more advanced the controller is, the more money you can expect to pay. Features such as Wi-Fi connectivity for monitoring and controlling the system drive up the cost.

As a general rule, you can expect to pay from $2,500 to $4,000 for a solar pool heater.

Installing a solar pool heater

Many solar pool heaters come in DIY kits so you can assemble all the pieces as needed. Unlike installing a solar array, there’s very little electrical work involved. The primary skill set required is installing piping.

If the system is large and requires a roof installation for the solar collector, you might consider using a professional who can safely install the collector without damaging the roof.

Larger solar collectors can be heavy, especially while the water is cycling through. A professional will be able to calculate the weight of the system against the structure of your pool.

How much money can you save with a solar pool heater?

The yearly cost of running a solar pool heater is generally under $200. Other types of pool heaters, gas or electric, cost significantly more. The total cost depends on the price of gas or electricity where you live.

A gas-powered pool heater may run upward of $2,500 per year, and an electric pool heater may cost as much as $1,000 to $2,500 annually. In many regions, a solar pool heater can be very cost-effective — most solar pool heating systems will make up for their cost in one to seven years.

Bottom line

Even if you have to supplement a solar pool heater’s ability to warm your pool with a secondary system, it may be worth it. The energy savings a well-designed solar pool heater offers mean you can spend less money each month on other types of energy to heat your pool.

You can also pair your solar pool heater with a heat-retentive pool cover so the water stays warmer for longer. However, a solar pool heater might not make sense if you live in an area without enough sunlight to get the solar collector to function efficiently.

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