Solar Water Heaters – How Do They Work?

Since we live in an era when environmental concerns often drive our decision-making, more homeowners adopt healthy attitudes and modernize their houses with contemporary eco-friendly solutions. Installing a solar water heater for home efficiently reduces the need for grid electricity while delivering sufficient volumes of hot water.

Investing in solar powered heater can substantially cut down on electricity bills. On average, the investment pays itself for about four to eight years, and the whole system serves from 15 to 40 years. That’s a significant amount of free energy and cost savings.

What Is a Solar Water Heater?

A solar water heater is a device that uses solar radiation to heat water for your home. It consists of a solar collector located on the roof of the building and a storage tank connected to it. This apparatus captures the maximum amount of solar radiation and converts it into heat.

The core processes run by every water heater are the same—a collector mounted on the roof gathers sunlight and turns it into heat. What happens with the heat next and which components take part in the process depends on the type of heater.

How Do Solar Water Heaters Work?

There are two main types of water heaters – active and passive. They use different equipment, and their circulation systems differ too. The primary distinction is that after an active water heater turns solar energy into heat, it activates circulating pumps to move it further to a storage tank, while a passive solar water heater relies on convection as the circulation system.

Active solar water heaters

An active solar water heater gathers light and turns it into heat using a roof-mounted collector. Once the collector is hotter than the storage tank, the thermal regulator initiates the transfer of the heated water to a storage tank using a circulating pump. The pump is energy-efficient and resistant to overheating because of its sporadic functioning.

If there is not enough sunshine, a backup mechanism takes over and heats the water to the appropriate temperature. Since the storage tank can be indoors to prevent water from cooling, these water heaters are effective all year round in regions with colder weather. There are two subcategories of active solar water systems:

  • Active direct system. In this case, collectors heat the water, which later runs to the plumbing system and to the house.
  • Active indirect system. The sun heats a non-freezing fluid in the collector like a water-glycol mixture. Then it runs to the heat exchanger transferring accumulated heat to the water that residents will use in the house.

Passive solar water heaters

These systems use the laws of physics to transfer water from the collector to the storage tank. The rise of temperature creates a difference in fluid density and naturally raises heated water to the tank’s surface.

Passive solar water heaters are cheaper than active ones as they do not require circulating pumps, sensors, and controllers. Though they tend to be less effective, they are most likely to serve longer. There are two main types of passive solar water heaters:

  • Integral collector-storage system. A water storage tank is mounted on the roof, and the heated water flows directly into the plumbing system. This kind of solar water system is the simplest one because the storage tank serves as a solar collector at the same time. The integral collector-storage system is usually not practical regarding its size and weight. It will only fit houses with solid constructions that can handle heavy and large systems on the roof.
  • Thermosyphon system. It is a more advanced example of a passive solar water heater, where the collector is stored beneath the tank. Cold water flows from the storage tank to the collector by natural circulation, gets heated, and returns back to the tank as hot water. Later, the next portion of cold water from the bottom of the tank flows to the collector, thus emptying space for the heated water. The process doesn’t end unless there is not enough solar energy on the collector. These systems are much smaller, and most of them allow a 40-gallon water capacity.

Storage Tanks and Solar Collectors

Typical components of any solar water heater for the home are a solar collector, a storage tank, a circulation pump, sensors, and controllers. Though many alternative assemblies are possible, two components are presented in every system: a storage tank and a solar collector.

The hot water tank can be installed individually or as a system component on the roof. You can use your standard hot water tank, which will save you money on purchasing and installing it, or you can use a specialized solar heating tank. The difference is that specialized tanks are larger, and they can store more water. Plus, the system might function better if you select a specialized tank since it has been explicitly designed to make the most of solar energy.

Solar collectors’ primary purpose is to capture solar energy and transform it into heat. Here are two types of solar collectors used for homes that function in different ways:

  • Flat-plate collector. It consists of a big, insulated plate-shaped absorber covered with glass and a couple of tubes attached underneath it. Fluid running through the pipes collects heat from the absorber and transfers it further. If the temperature outside is insufficient to heat water, water runs back to the storage tank so it doesn’t get colder, and circulating pumps shut down.

The covering material used on flat-plate collectors maximizes its efficiency. The coating of the absorber is precisely designed to absorb the maximum amount of heat and radiate the minimum back into the environment.

  • Evacuated-tube collector. This collector consists of transparent insulated glass tubes containing metal heat pipes. The metal sheets are attached to heat pipes to absorb maximum solar radiation and heat the liquid inside. The air is pumped out from the glass tubes creating a vacuum. It serves as an insulator, decreasing heat loss to the surrounding atmosphere.

Because the collector uses transparent glass cylinders, the sunlight is always perpendicular to the heat-absorbing tubes, allowing solar energy collection even when there is little sunshine.

Although flat plate collectors are often less costly, they have a lower capacity for solar absorption, and their performance is poor in colder climates. Evacuated-tube collectors are heavier and more delicate in maintenance but take up less room.

Selecting a Solar Water Heater

In the last 100 years, solar water heaters have developed significantly and come in different designs, sizes, and types. But before you start reducing your global carbon footprint and fuel consumption by installing a hot water system, you must do thorough market research to choose the suitable system for your house.

However, finding the right match for your home might be quite challenging due to the numerous available options. To help you narrow down the search, answer the following questions first:

  • How much hot water do you use? Big households that consume a lot of hot water will find solar water systems more economically viable than those with smaller needs. The savings won’t be as evident if you don’t use a lot of hot water.
  • Where is your house located? The location and design of the house are crucial factors in choosing the right system. Ideally, the house has intense year-round solar exposure without shade. But not all of us live in those conditions, so other factors should be considered.

For example, the solar collector’s position and tilt can maximize the effect, providing it is facing the right direction. Your local hot water system supplier will do the measurements to give you the most accurate numbers and provide you with information about how much sunlight your system will be able to collect.

  • What is the size of your solar water heater? Depending on the number of people living in the household, you can roughly determine the size of the storage tank and collector you need. Typically, a small storage tank of 50 to 60 gallons with a collector area of 40 square feet will be enough for a family of three. We advise you to discuss this with your solar system contractors to ensure you choose a system that matches your needs.

Answering these questions will help you understand whether a solar hot water heater is the right choice for your home or not. You also have to consider your budget and investigate your local building regulations.

Costs and Savings

Prices of solar water heaters vary significantly depending on the materials you select, the size of the system, installation and maintenance fees, and more. A typical solar water heater would cost roughly between $9,000 and $13,000. However, a smaller system might cost you as little as $1,500.

Soon after your investment, you will notice the system starts paying its value by reducing your energy bills. And the best news is that once the payback period is over, you will continue to get solar energy as free fuel. In the end, a solar hot water system may reduce your water heating costs by 50% to 80%.

Every solar water heater owner is eligible for the 30% federal solar tax credit if specific state requirements are met. Also, many states, municipalities, or local utility providers, might offer some installation incentives and discounts. Besides, with a relatively simple design, solar water heaters have rather low maintenance expenses compared to conventional water heaters.

To inquire about estimated installation and maintenance costs, get ahold of qualified contractors in your area. They will be able to determine a specific type of system you need and help you calculate what you will save on your energy bills.

Kateryna Ryzha

Kateryna Ryzha

Kateryna is an experienced writer with a focus in solar energy. She is a specialist in several topics related to energy efficiency, technical applications, renewable energy, and more as a consequence of her extensive reading.

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