Solar-Powered Water Heaters: Choosing the Right System for You

Solar-powered water heaters have emerged as a sustainable and energy-efficient solution to meet our hot water needs while significantly reducing our carbon footprint.

As the world grapples with the increasing demand for clean and renewable energy sources, these innovative systems harness the power of the sun to provide an eco-friendly alternative to traditional water heating methods.

In this comprehensive guide we will delve into the fascinating world of solar water heaters, exploring their various types, how they work, installation considerations, advantages, benefits, and selecting tips.

Solar-powered water heaters: Highlights

• Who should consider buying a solar water heater?
• Installation tips and how to save
• How does it work?
• Sizing tips
• Benefits
• Types
• Components
• How solar water heaters compare to other systems

Who should consider buying a solar-powered water heater?

If you live in North America (the US and Canada), you will notice that solar-powered water heaters are often more expensive than gas and electric ones.

However, the good news is that the government provides excellent tax breaks to make them more attractive and affordable. The sun offers free energy, and many enthusiasts and handymen have ideas and plans on how to build them.

Even if you have to pay the full price, keep in mind that the sun provides free and clean energy with no pollution, so why not take advantage of it?

Furthermore, many enthusiasts and handymen have already built and tested these heaters, so why not use some of these great ideas and designs that are readily available, for example, here.

In this guide, we provide you with some basic information and tips to assist you if you are planning to buy or make one. Alternatively, you can hire a professional.

A high-quality, professionally installed, and well-maintained solar-powered water heater (SPWH) can last from 20 to 30 years, almost twice as long as conventional types. The payback period can range from 5 to 10 years, but it depends on various factors.

Solar heating systems for residential applications can be found in the form of solar water heaters, solar space heaters, and solar pool heaters. We will focus on those used for potable water and pool heating.

Installation tips for the maximum performance or how to save

Most solar water heating systems are installed on the roof, with some placed on the ground. The amount of hot water generated by free solar power depends on several factors:

• The region where you live and the climate (or the site's latitude).
• The type of system you install.
• The capacity of the units.
• Sun exposure and the orientation of the collectors. It's important to note that the best results are achieved on clear days, while on overcast days, there will be approximately 60% less solar energy reaching the Earth's surface.
• The solar collector should be located near the hot water tank to maximize savings, and the tank should be situated close to the point of use.

Note: To optimize the system's performance throughout the year, it is essential to install the solar collector at the recommended angle (tilt angle), which should be equal to your home's latitude.

How does a solar water heater work?

A solar-powered water heater operates by harnessing the sun's energy through specialized solar collectors.

These collectors, typically mounted on rooftops or other sun-exposed surfaces, absorb sunlight and use it to heat a heat transfer fluid circulating within them.

This heated fluid is then directed to a heat exchanger within a water storage tank.

Inside the tank, the heat exchanger transfers the collected thermal energy to the water, gradually raising its temperature.

This process continues as long as sunlight is available, providing a continuous supply of hot water.

In cases where the solar energy absorption is insufficient, backup heaters, powered by electricity, gas, or oil, automatically take over to ensure a consistent hot water supply, ensuring reliability even on cloudy days or at night.

By combining renewable energy with backup heating solutions, solar water heaters offer an eco-friendly and cost-effective way to meet hot water needs while reducing reliance on traditional heating methods.

Sizing tips

Solar water heating systems are customarily designed to meet the specific hot water demands of a household. This tailored approach ensures an efficient and cost-effective utilization of solar energy. The size of the system hinges on the amount of hot water consumption within the household. Essentially, the more hot water you use, the larger the solar collectors and hot water storage tanks need to be.

For a family of up to four individuals, a recommended water tank capacity typically falls in the range of approximately 50 gallons. This ample storage capacity ensures that there is sufficient hot water available for daily needs.

Simultaneously, the size of the solar collector array plays a crucial role in the system's performance. A collector area ranging from 2 to 5 square meters is commonly suitable for a household of this size.

Generally, a rule of thumb is to allocate approximately one square meter of collector area per person in your home. However, if less efficient solar collectors are in use, a larger collector area might be necessary to capture an equivalent amount of solar energy.

Efficiency is a key consideration when determining the collector area required. More efficient collectors can capture a greater amount of solar energy with a smaller surface area.

Therefore, investing in high-efficiency collectors can be a prudent choice, as it not only reduces the physical space needed for installation but also optimizes the system's performance, leading to higher energy savings and a reduced environmental footprint.

The sizing of solar water heating systems is a critical aspect of their successful implementation, ensuring that households can benefit from reliable and sustainable hot water while maximizing the utilization of the sun's abundant energy.

Benefits

Solar water heaters offer a multitude of benefits, making them an attractive choice for environmentally conscious individuals and those looking to reduce their energy consumption and costs.

One of the primary advantages is their utilization of free and green energy from the sun. By harnessing the sun's abundant and renewable energy, solar heating systems significantly reduce reliance on conventional electric or gas heaters, thereby reducing energy consumption and associated utility bills. This not only leads to financial savings but also contributes to a reduction in greenhouse gas emissions, fostering a more sustainable future.

Studies have shown that a well-installed solar water heating system can meet at least 50% of a household's annual hot water needs, although the exact contribution depends on various factors such as system design, location, and climate.

During the summer months, it's often possible to heat all the required water solely using solar energy, further enhancing the system's eco-friendliness. In colder seasons, while solar energy contribution may decrease, the presence of a backup heater ensures a consistent hot water supply, ensuring comfort even during the coldest months.

Solar water heaters are very effective regardless of outside temperatures when the right type is chosen. They can provide hot water even on cloudy days or in regions with colder climates, making them a reliable choice for a wide range of environments.

One of the most significant advantages of solar water heaters is their minimal impact on the environment. Unlike traditional heating methods that rely on fossil fuels, solar water heaters do not emit harmful pollutants or greenhouse gases, contributing to cleaner air and a healthier planet.

Additionally, solar water heaters offer a sense of energy independence. By generating your hot water from the sun, you are less susceptible to energy price fluctuations and supply disruptions, enhancing your control over your energy needs.

Some solar water heating systems are designed to operate without electricity, further reducing energy consumption and increasing resilience in the event of power outages. This feature ensures hot water availability even during adverse situations.

Maintenance requirements for solar water heaters are generally low, making them a hassle-free and cost-effective option in the long run. Routine checks and occasional servicing can keep the system running smoothly for years.

Lastly, it's worth noting that some regions and governments offer incentives, tax credits, and grants to encourage the adoption of solar water heating systems, potentially offsetting installation costs and providing an extra incentive to go green.

If you would like to go into details, use the energy.gov website to find more info about estimating the cost and energy efficiency of a solar water heater.

Types of solar water heating systems

There are several solar domestic hot water systems (SDHWS) that are mostly used. Some systems are more, some are less complex, and even with different heating processes, systems can share the same components.

Passive

Passive solar-powered water heaters use gravity and natural convection so hot water can circulate through the solar collectors with no use of the external energy and moving mechanical parts.

Note: The solar collector is a flat plate collector that is designed to capture the solar heat. There are also evacuated tube collectors which are cylindrical tubes filled with the vacuum for higher efficiency.

One key advantage of these systems is their simplicity of design, making them cost-effective and less prone to problems. Great examples of passive systems include the Integral Collector Storage or short ICS (also known as the batch heater) and the thermosyphon system. You can explore DIY ideas for these systems here.

Note: The thermosyphon system utilizes natural convection, causing heated fluid to rise while colder fluid descends, facilitating fluid circulation.

Active

Active solar-powered water heaters employ a circulation pump, controllers, and valves to actively propel the heating fluid through the system, from the collectors to a point-of-use or storage tank. Their advantage over passive systems lies in improved control and installation flexibility.

Active units can operate year-round since they use a heating fluid capable of withstanding lower temperatures. The most popular types are Drainback, Draindown, and Pressurized Glycol.

In the Drainback system, protection from both freezing and overheating is achieved as the transfer fluid drains from the solar collectors and piping when the pump is turned off, thanks to the force of gravity. A drainback reservoir is used to collect the fluid from the collector.

Direct or Open-Loop

If the heating fluid is potable water, which is heated directly in the solar collector, we are referring to direct systems. In these systems, the solar storage tank also serves as an absorber. Typical examples include ICS and Draindown systems.

The advantage of direct systems is that they experience less energy loss compared to closed-loop types because water is heated directly in the solar collector. This makes these systems cost-effective and high-performing. However, one major drawback is that direct systems are susceptible to sediment buildup and freezing.

Indirect or Closed-Loop

In indirect solar-powered water heaters, potable water is heated by a heating fluid, typically an antifreeze fluid like glycol. The amount of heat transfer fluid remains constant and circulates in a closed-loop system.

A heat exchanger is a crucial component in this setup, installed in the tank to transfer heat to the water. Drainback and Pressurized Glycol systems serve as excellent examples of indirect systems.

They are particularly suitable for regions with hard water and can operate year-round, including during the winter months.

On the downside, these systems require periodic replacement of the antifreeze fluid and come with a higher price tag.

The simplest form of all solar water heaters is the batch type. It consists of a cylindrical water tank painted black, placed inside an insulated box, and covered with tempered glass. The storage tank is filled with water. They are recommended for regions with mild and warm climates.

Solar pool heating systems

As a cost-effective method of heating, solar water heating systems can also be utilized to heat swimming pools and extend the pool season. These systems operate at lower temperatures, typically around 80°F, classifying them as low-temperature systems. In colder regions, it's essential to completely drain them to prevent freezing.

Solar pool heaters are constructed using PVC pipes and rubber connectors, lacking the frame, insulation, and tempered glass cover found in other solar collectors. This makes them highly affordable, flexible, easy to transport, and simple to install on roofs. However, due to their lack of insulation, they lose heat relatively quickly.

Components

Solar collectors and storage tanks are the main components of almost every solar water heater.

Solar panels are designed to collect the solar heat, which is passed to the heat transfer fluid or potable water. The most popular ones are the flat plate panels which consist of the insulated box, cover, absorber plate, and tubes. Those models with the cover are known as glazed flat panels, while those without are unglazed flat plates.

There are also evacuated tubes and concentrators.

Unglazed collectors are operating at lower temperatures and are mainly used for pool heating. They are usually made of PP, making them very flexible. As they do not have glazing, and insulation, they have higher thermal losses making them ideal for warmer regions and not suitable for cold climates.

Glazed flat-plate collectors usually come with a box, insulation and a glazed cover, allowing more heat to be captured and less transmitted outside (reduced loss).

Evacuated tube collectors are made up of a series of glass tubes, and each tube is either single-wall or double-wall, filled with the vacuum, which works as an insulator. They are recommended for climates with colder weather, mainly due to the capability to retain heat longer than flat plate collectors.

Concentrators or concentrating collectors are mainly used in industrial applications as they deal with high temperatures.

Storage tanks are used to hold solar-heated water for future use and are usually equipped with an electric backup heating element to increase the water temperature to the desired temperature, especially during cloudy and cold days or nights. They are very well insulated to preserve the energy and can directly transfer the hot water to the tap or feed the gas or electric tank.

The heat exchanger, which can be installed inside the storage tank to transfer the heat from the collector to potable water, is wrapped around the tank or installed externally (all types belong to indirect systems).

Gas or oil boilers can provide auxiliary heat if solar heat is not sufficient for heating.

An expansion tank is used as a buffer in closed systems to reduce the effects of the excessive pressure inside the tank.

Valves such as a pressure relief valve, TPR valve, mixing valve, check valve, drain valve…

A circulation pump to move the heat transfer fluid through the system.

A controller is used to power the pump when it is required to control the use of supplementary heating systems (gas, electric, oil).

A thermometer for temperature control.

Sensors and meters.

Note: It is more expensive to install the SWHS in an existing than the new house.

Comparing solar to other water heating systems

Solar-powered water heaters offer a compelling alternative to conventional water heating systems such as electric and gas water heaters. Let's compare solar water heaters with these traditional systems in terms of key factors like energy efficiency, cost-effectiveness, and environmental impact:

Energy Efficiency

Solar Water Heaters: Solar water heaters are highly energy-efficient. They rely on sunlight, a free and renewable resource, to heat water. They can provide hot water even on cloudy days, although efficiency may vary. Over time, they significantly reduce electricity or gas consumption for water heating.

Electric Water Heaters: Electric water heaters are convenient but tend to be less energy-efficient. They directly consume electricity to heat water, which can lead to higher utility bills, especially in regions with high electricity costs.

Gas Water Heaters: Gas water heaters use natural gas or propane to heat water. While they are generally more energy-efficient than electric heaters, they still rely on fossil fuels, contributing to greenhouse gas emissions.

Cost-effectiveness

Solar Water Heaters: Solar water heaters require an initial investment in equipment and installation. However, they offer long-term cost savings by reducing energy bills. Many regions offer incentives and tax credits to offset installation costs.

Electric Water Heaters: Electric water heaters are relatively inexpensive upfront but can be costly to operate, making them less cost-effective in the long run.

Gas Water Heaters: Gas water heaters have moderate upfront costs and are typically more cost-effective than electric heaters. However, the ongoing cost depends on gas prices, which can fluctuate.

Environmental Impact

Solar Water Heaters: Solar water heaters have a minimal environmental footprint. They use clean, renewable energy from the sun, reducing greenhouse gas emissions associated with water heating.

Electric Water Heaters: Electric water heaters indirectly contribute to carbon emissions based on the source of the electricity. If the electricity comes from fossil fuels, it can have a significant environmental impact.

Gas Water Heaters: Gas water heaters produce carbon emissions due to the combustion of natural gas or propane, contributing to air pollution and climate change.

Conclusion

If you reside in a warmer, southern region, purchasing any of the aforementioned solar-powered water heaters can offer you comfort, convenience, and substantial savings. These significant savings are particularly noticeable in larger households with high hot water consumption.

Solar domestic hot water systems (SDHWS) have the capacity to provide ample hot water for an entire household, resulting in reduced overall energy usage and a decrease in pollution. Based on many years of reliable water heating, ICS, Drainback, and Pressurized Glycol systems come highly recommended by professionals.

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