What are the advantages of solar water heating versus tankless water heating?

Published November 2013 by

In the last decade, the green energy industry has revolutionized the way homes heat, store and even use hot water. Rather than suffer the high utility bills of old conventional water heating systems more and more people are switching to solar water heating systems or tankless water heating systems. If you’re considering investing in a new water heating system, how do you know which is right for you? Each come with their own advantages and disadvantages so think carefully about your family’s needs.

Solar Water Heating:

There are two types of solar water heating systems: active and passive.

  • Active systems have circulating pump controls so that water that is collected in tanks is pump-circulated throughout your home.
  • Passive systems store tanks near solar panels and merely rely on convection to move water throughout the system. In essence, cold water is pulled up to the panels to heat and sent down when it reaches an optimal temperature without as much control.

How the Systems Work:

Passive System

Solar panels pull water into tubing around the outside of the panel. Energy collected from the sun is used to heat that water. When the water is warm it is transferred back into the system and cold water is pulled up again. The system will continue to circulate water so long as whatever is the storage tank is colder than the water next to the panels. If you don’t use a lot of hot water it would be in your best interest to get a temperature controller that regulates the system, otherwise your water could overheat.

Because these systems directly heat the water, the tanks need to be stored closer to the solar panels. Either next to or directly beneath the panels. In many cases, unless near a garage, they need to be stored outside, which leads to weathering of the tank faster as well as greater heat loss. These systems tend to be cheaper than active systems.

Active System

Solar panels collect water or a heating fluid in tubing next to the panels. Once whem, the system will circulate that fluid down into the tank and through a heat exchanger in the middle of the tank, which warms the water in the tank. Once the fluid that was transferred up to the panels is warmer than the fluid in the exchanger, the system will circulate again creating a constant movement of fluid for maximum efficiency.

Generally, these systems are far more sophisticated than passive ones because they offer much greater control and flexibility. For example, the tanks can be stored away from the panels in insulated areas, which reduces heat loss, and are managed by a controller. This controller often has the ability to monitor efficiency, temperature readings, differential settings, which determines how often fluid circulates through the system, and even energy saved.

Tankless Systems:

The major difference between tankless water heating and solar water heating systems is that tankless uses energy to power a fast-heating device for on-demand service. They can still be solar powered, but only if you use solar power for your electric supply. Otherwise, they are gas powered.

Solar water heating systems have their own panels and piping that are not connected to your electrical supply.

How They Work:

Essentially, a heating element of some kind, either an electric heat exchanger or piping warmed by gas burners, is connected to a containment unit. When you turn on the faucet or shower water is transferred into the unit and rapid heated. According to Energy.gov, tankless water heaters can provide hot water at a rate of 2-5 gallons per minute, gas burners operate at a slightly higher rate. Unfortunately, since there is not storage tankless water heaters are not ideal for intense simultaneous use, such as operating a dishwasher and someone taking a hot shower. Otherwise, if you are a low-use household, tankless water heaters are a great alternative to conventional heaters. They are 24-34% more efficient than conventional systems. Additionally, if you install tankless heating units at every hot water outlet you can receive energy savings of up to 27-50%.

Which To Choose:

Both systems offer advantages and disadvantages, so your choice depends on your needs.

  • Tankless systems are a great alternative for a low-use household. However, if you are a family of six who all enjoy taking hot showers every day a tankless system may not work well for you (unless you install multiple units).
  • Solar water heating, on the other hand can be a great solution to all your heating needs. Since the system is solar powered you can sleep easy knowing your are decreasing your carbon footprint and your utility bill as well. Yet, these systems require more maintenance over the long run, but solar panels last on average 25 years, which we all know is much longer than a conventional storage tank system.

Your best bet is to monitor your hot water usage and to consult with a water heating specialists who knows about both systems. They can give you feedback about each system and help you design one that is right for your home.

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