Solar Water Heater Basics
Solar power is a pretty magical thing. By adding a solar water heater to you your home, you can cut utility costs, save money, and reduce your carbon footprint—what’s there not to love? While most of these systems will add a bit more complexity to your home, they do so in favor of cutting out fossil fuels and, instead, harnessing power directly from the sun. It’s better for the environment and better for your wallet—and that’s something to feel good about.
How Solar Water Heaters Work
A solar water heater works much the same way a greenhouse does. Sunlight travels into the solar collector through a glass-plated front panel, where an absorber layer of dark material soaks up the sunlight and generates heat.
The collector is insulated to hold that heat in, and a heat exchanger or simple copper pipes transfer that heat to the water that moves through the collector. The process repeats over and over again, continually warming water while the sun is out. All the sunlight-heated water collects in an insulated storage tank, keeping it heated for future use.
The Installation Process
Unless you’re an expert, installing a solar water heater system will be pretty tricky. First, solar collectors are mounted on a south-facing roof to collect sunlight and transform it into heat. Next, a heat exchanger and additional water storage tanks are installed, if necessary. Finally, all the plumbing and pumps are put into place for water to move around the system. The installation process is as simple as that, but it can only be completed correctly with a lot of planning and preparation.
The Different Solar Water Heater Collectors
There are three different solar collectors that are used regularly to heat water in solar hot water systems. They are batch collectors, flat-plate collectors, and evacuated tube collectors. Each works well for specific-use cases, which is why it’s important to understand them thoroughly before choosing one.
Batch solar collectors are designed to heat up batches of several gallons of water at a time. They can generate very high temperatures and work well for most heating applications. The collectors are designed for use in warm climates because they do present a risk for freezing during below-zero temperatures.
Their basic design is a black tank holding water within an insulated box. Water travels into the tank and back out again. Most of the time, the water movement is completely passive and occurs as the water heats up and cools down.
Flat Plate Collectors
Flat plate collectors look similar to solar panels and provide heat effectively when the sun is strong. Although rarely more than six inches thick, they do take up a large amount of roof space. A flat plate system has a single inlet and outlet point, and it routes water through a series of small copper pipes to effectively exchange heat to the water moving through them.
In terms of both cost and efficiency, flat plate collectors are between the batch collectors and the evacuated tube models, which make them the middle-of-the-road choice. However, they’re less effective in windy conditions than evacuated tube collectors, and they lose heat faster in very cold climates.
Evacuated Tube Collectors
Evacuated tube collectors are known for being the most efficient of the bunch. They work by heating water in a tank through the vacuum tubes mounted beneath. A benefit to using evacuated tube collectors is that they’re successful at generating heat even in cloudy conditions, and they don’t suffer heat loss from wind like other systems do. They also lose heat very slowly in cool conditions, allowing them to create heat in below-freezing climates effectively. They are the most expensive option, but they are the best option in many circumstances.
Types of Circulation Systems
There are two different types of circulation systems used to channel the water through a solar water heater—passive and active. The simple difference between the two is that passive uses no water pump to move the water, while active does. However, there are also some bigger differences in how the systems can be set up, which is important to know for anyone who’s considering having one installed.
Active Circulation Systems
Active circulation systems pump water between your home, the solar collectors, and the storage tanks. An electric pump moves the water between locations and it’s turned off when water does not have to be moved. The system is simple and straightforward, and it allows the collectors and storage tanks to be set up in any configuration that you like, without worrying so much about positioning.
Passive Circulation Systems
Passive circulation systems are a bit more complex to set up in terms of how they are built. This is because the water storage tank for the system has to be positioned above the collectors that heat the water. The system relies on the generated heat to rise to the tank water, creating a circulation that pulls in new cool water.
Indirect Versus Direct Circulation Systems
While there are only two different circulation systems, each of them can be designed to act directly or indirectly. An indirect system heats up an anti-freeze solution in a closed loop and then uses a heat exchanger to transfer heat from that closed loop right to your water.
A direct system pumps your water through the system and heats it directly. While it’s more efficient, it can’t be used in every situation. For instance, a direct system will freeze if it’s below freezing outdoors for too long.
Both systems have their benefits, and it’s important to explore both options before installation, but if you live in a northern climate, you’ll likely have no choice but to go the indirect route—or to only use your system during the warm months.