Solar water heaters, also known as solar hot water systems, are used all around the world to generate hot water, mainly for household needs. They are environment-friendly as the fuel they use, i.e., sunlight is a renewable source of energy.
Solar water heating systems work by transferring the heat from the sun-warmed collector into either air or liquid, which is then circulated through your home’s existing water heater.
According to the Environmental and Energy Study Institute, more than 1.5 million homes and businesses use solar water heating systems in the United States. But how do solar water heating systems draw energy from the sun?
In this blog, we will shed light on how solar heaters work and explore the different types of solar water heaters are used commonly worldwide.
Let’s get started.
How Do Solar Water Heaters Work?
A solar water heater is a water heating appliance that collects light from the sun and uses it to heat water.
Unlike traditional water heaters, a solar water heating system does not use electrical energy or gas to heat water. Instead, the high-efficiency appliance draws power, known as solar radiation, from the sun and converts it into heat. This heat is then absorbed by a heat transfer fluid or used directly to heat tap water from the main supply.
Each type of solar water heater works differently. However, each solar heater has a collector array that collects radiation, an energy transfer system, and a storage tank for the tap water. Solar water heaters can work in any climate and weather as long as there is a presence of fuel, i.e., sunlight.
6 Types of Solar Water Heaters
6 types of solar hot water heaters are most commonly used in the United States. They differ based on the processes they use to heat up the water. In this section, we will look at each type in detail.
Active Solar Water Heater Systems
Active solar water heating systems are different from other systems because they have circulating pumps and controls.
In an active system, the circulating pumps transport water or a heat-exchange fluid from the water storage area into your domestic plumbing structure. You will have to place the water storage inside your home. These need a power source to provide energy to the water heater pump.
There are 2 types of active solar water heater systems:
1. Active Direct-Circulation Heater Systems
In an active direct system, circulating pumps pump water from the storage tank to the collector array during day time and transport it back into the plumbing system. Hot water is re-circulated from the storage tank to flush the collectors for freeze protection.
People use this system in regions where freezing temperatures are rare or infrequent since recirculation requires more energy and flushing decreases operation time.
2. Active Indirect Water-Heating Systems
An active indirect system is common in areas that experience freezing climates.
In this system, the circulation pumps circulate a heat transfer, non-freezing liquid through the collector array. The most frequently-used liquids for freeze protection are water-propylene glycol and water-ethylene glycol solutions. The heat exchanger transfers the heat to the tap water.
This process is highly efficient. According to the US Department of Energy, this system provides 61% to 63% water-heating energy each year.
Passive Solar Water Heater Systems
In a passive solar water heater system, there are no pumps to circulate water. Passive systems are the simplest types of solar water heaters. No electrical or energy equipment or extra solar panels are needed to operate these systems.
Passive systems are cheaper than active systems but are also less efficient. Conversely, they last longer and are more reliable than active heating systems.
There are 2 types of passive solar water heating systems:
3. Thermosiphon Hot WaterPassive Systems
A thermosiphon heater heats water or an anti-freeze fluid such as glycol. The liquid then rises, by natural convention, from the collector array to the storage tank placed at a higher level than the array. No pumps are required to move the fluid.
This heat transfer increases temperatures and heats the water in the storage tank. Since these systems work by natural convention, they are most efficient in areas with high solar radiation.
4. Integral Collector-Storage (ICS) Passive Systems
Integral Collector-Storage (ICS) systems are cheaper than thermosiphon heating systems. They work best in regions where the temperature rarely falls below freezing point, preventing pipes from freezing.
If your household needs significant water during the daytime and evening, you should get a passive ICS heating system.
The ICS passive system comprises a big, black storage tank or tube system, which is built into an isolated glazed box with a top that allows sunlight to pass through. The sunlight heats the water in the black tank, and the water flows back into your plumbing system for use.
Other Types of Solar Water Heaters
5. Drain-Down Solar Water System
A drain-down solar water system is a solar heating system in which treated or untreated water is circulated through a closed loop. The heat exchanger then transfers the heat to the tap water.
In the absence of solar heat, at night, the fluid in the collector array is flushed with the help of gravity to avoid freezing or natural convention that causes cool water in the collector to reduce the temperature of the hot water in the storage tank.
6. Air Solar Water System
The air solar water system has an additional component— the fan. In this system, the collector array collects the air moved by the fan through an air-to-water heat exchanger. You can then use the heated water for domestic purposes.
A downside to this system is that it is inefficient (it is only efficient when it’s windy/airy).
Solar Heater Tanks and Collectors
3 kinds of solar water collectors and water storage tanks are attached to different types of solar water heaters:
- Flat-Plate Collectors: Most households use these. They consist of insulated weatherproof boxes with dark absorber plates. The insulation prevents heat loss in the system, and the absorber captures maximum solar radiation.
- Evacuated Tube Collectors: An evacuated tube collector array consists of rows of transparent glass tubes positioned parallel to one another. Each tube in the array has a fin coated with solar radiation-absorbing material and an outer absorber metal coating.
- Integral Collector-Storage (ICS) Tanks: An ICS solar water heating system has a glazed box that contains tubes or tanks. The solar collector receives cold water, preheats it, and transfers it to water heating units.
Advantages and Disadvantages of Using Solar Water Heaters
Solar water heaters have the following advantages:
- Work throughout the year; hot water is available all year round.
- Have a one-time cost; they have no monthly charges since they do not require a power supply or fuel
- Are green and environment-friendly; guarantee no pollution and help in the reduction of carbon dioxide emissions
- Use a renewable source of energy efficiently; they turn about 80 percent of the sun’s radiation into heat energy needed to obtain hot water
- Can run up to 20 years
- Are less space-intensive
And the following disadvantages:
- Have a high initial cost when it comes to equipment and installation
- Require direct sunlight to function
- Do not function efficiently on cloudy, rainy or foggy days
- Can corrode
- Require frequent maintenance
- Can overheat if the size of the storage tank isn’t suitable for the collector
Choosing a Solar Water Heater
It is difficult to choose a solar hot water system when so many different options are available in the market. When choosing amongst the various types of solar water heaters for domestic use, keep the following tips in mind:
- If you do not experience temperatures below freezing point, go for an active direct solar heating system.
- Active indirect water heaters can resist severe weather conditions and damage, so get one if you live in a colder area.
- If you use more hot water during the day than at night, opt for a passive system, such as ICS, that produces hot water in batches.
- If you have a swimming pool and need a system to heat it, an active indirect circulation system with a heating fluid is the best option for you.
- Only get a thermosiphon system if you have plenty of roof space since you will have to install it on the roof.
- Lastly, select a solar water heater for your house depending on the intensity of sunlight in your region, the requirement for hot water in your home, and your budget.
Conclusion: Types of Solar Hot Water Heaters
This brings us to the conclusion of our discussion on types of solar water heaters.
Solar water heaters are an excellent way to gradually reduce on your household’s gas and electric bills.
There is a variety of solar water heaters on the market today, and it can make your head spin as to which one is right for you. The more information you have, the better-informed decision you will be able to make with confidence.
We hope we were able to shed light on all the important factors that you need to know and consider before you go ahead and make your purchase.
Don’t forget to share your thoughts and experiences with us in the comment section below.