Different Types of Solar Water Heaters Explained

If you’re in the market for a new water heater, you’ll probably come across different types of solar water heaters while comparing options. Basically, solar water heater systems use rooftop collectors to convert sunlight into hot water, so you end up relying far less on electricity and saving more over time. These systems have been steadily gaining popularity because they are dependable, need very little maintenance, and fit well with today’s push toward greener, more eco-friendly homes. And, as solar tech becomes better every year, the benefits of water heating quickly add up. So if you’re weighing your options, here’s a quick guide to all the different types of solar water heaters currently on the market.

Different types of solar water heaters explained

All solar water heaters work on the same basic idea. Sunlight is captured by a collector, and that heat is then carried into water or a heat-transfer fluid that moves through the system. The difference comes in how each system captures that heat and sends it where it needs to go. This is where the two main categories come in: Active systems and Passive systems.

1. Active solar water heating systems

Active solar water heating systems use pumps and electronic controls to circulate water or heat-transfer fluid. The movement is powered rather than natural, which gives more consistent heating throughout the day. There are two kinds of active solar water heating systems, namely, open-loop, or direct, systems and closed-loop, or indirect, systems.

In open-loop systems, the water you use every day flows straight into the collectors, gets heated by the sun, and returns to the tank ready for use. There’s no separate fluid or heat exchanger, which keeps the setup simple and lets the water heat quickly. 

On the other hand, closed-loop, or indirect, systems use a special heat-transfer fluid instead of regular water inside the collector. The fluid absorbs heat from the sun, carries it to a heat exchanger, and warms the household water without ever mixing with it. Because this fluid resists freezing and scale buildup, the setup works well in colder regions and in homes with hard water.

Both closed-loop and open-loop systems can use flat plate collectors or evacuated tubes. Closed-loop systems particularly benefit from evacuated tubes in colder regions because the tubes hold heat better.

2. Passive solar water heating systems

Passive systems don’t use pumps or electronics. They run entirely on natural convection, which means hot water rises and cold water sinks. This creates a steady flow without requiring any powered components. They cost less, last longer, and need less maintenance. Just like active solar water heating systems, passive systems also come in two main types, namely, Thermosyphon systems and Integrated Collector-Storage (ICS) Systems.

In Thermosyphon systems, a collector is placed below the tank. As the water warms inside the collector, it rises into the tank above. The process keeps repeating until the entire tank reaches a stable temperature. Integral collector-storage units combine the tank and collector inside one insulated box.

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Water sits inside the built-in storage tank, which is exposed to sunlight through a glazed cover. The inner surfaces are lined with reflective materials that direct more heat toward the water, helping it warm up through the day, while insulation reduces heat loss at night. Thermosyphon systems commonly use flat plate collectors, while ICS units use a built-in storage tank that acts as both collector and heater.

And that about does it for our different types of solar water heaters guide.