How to Choose the Right Active Solar Heating System?
Advantages & Drawbacks

Solar energy is becoming increasingly popular as a source of power for homes and businesses, and active solar heating systems are a key component of this trend.

Active solar heating systems use mechanical components to circulate water or air and control the heating process, making them more efficient and flexible than passive solar heating systems.

If you are considering installing a solar-powered water heater, it's important to compare different types to determine which one will be the most cost-effective for your needs.

In this article, we will also explore their advantages and disadvantages, to help you make an informed decision.

We will also compare active systems with passive solar heating units to determine whether the extra investment is worth it when it comes to heating domestic water.

Active solar heating systems: Benefits and considerations

• Benefits
• Types
• Things to consider (how to select)
• Advantages
• Disadvantages
• Active vs. passive solar heating: Key differences

Benefits of active solar heating systems

Active solar heating systems are a highly sought-after and eco-friendly solution for warming homes and water. These systems are commonly used for domestic hot water heating in colder regions, where solar collectors gather the sun's heat energy and transmit it through a heat exchanger to heat the water that is stored in the storage tank.

Active solar water heaters incorporate a pump, sensors, and controllers, which work in harmony to offer superior efficiency and performance compared to passive systems. In colder climates, antifreeze must be used as the thermal fluid to prevent freezing. Since the solar heating system typically fails to meet the required heat or temperature, backup heating is required, which may involve electrical heating elements.

The performance and efficiency of these systems are dependent on various factors, including the system design, material quality, installation, and maintenance quality, as well as the duration of solar exposure.

The system may utilize controllers with sensors to manage the pump or photovoltaic solar collector, ensuring that the pump operates only when solar heat energy is available.

Ultimately, active solar heating systems offer an environmentally-friendly, cost-effective, and energy-efficient means of heating homes and water. With proper design, installation, and maintenance, they can be a reliable and sustainable source of heat energy for residential and commercial buildings.

Types

There are several types of active solar heating systems, each with its own set of advantages and disadvantages. From glycol pressurized systems to drainback systems, homeowners have a variety of options to choose from to ensure their homes and water are heated efficiently and effectively.

Active solar heating systems are design to use liquid-to-water and air-to-water heat transfer to heat the water. Two types are the most popular:

• Active solar heating that is using antifreeze or pressurized glycol
• Drainback system

The above examples of active solar water heating systems can use photovoltaic panels to run the pump and operate as:

• Direct or in the open-loop systems
• Indirect or in the closed-loop systems

Direct or open-loop system

Direct active solar energy systems utilize solar collectors where the household water is heated directly, which is the reason for being more efficient than indirect systems.

On the other side, the main disadvantage is that they require more maintenance due to the mineral buildup problem. In the case of solar panels, which are built from small size tubes, scaling might clog the pipe, reduce the water flow and decrease the collector efficiency.

Indirect active system

Indirect active solar water heater systems are closed-loop systems where the solar fluid remains within the single circuit. Solar thermal fluid, glycol, for example, after it is heated in the collector by the sun, is moved by the pump to the heat exchanger and where it transfers the heat to the domestic water.

Indirect systems mainly use popular solar panels or flat plate collectors and also evacuated tubes and concentrated collectors.

A good example of the closed-loop glycol design is the Rheem Solpak active solar system.

Active solar heating - Open-loop system

The simplest active solar water heating system is an open-loop system, often seen in warmer regions, where freezing never occurs. The main components are the solar collector, pump, controllers, sensors (i.e., temperature limit), and valves (i.e., tempering valve, isolation valves, and air vent).

In the open-loop systems, the solar collector is attached to the storage tank with the pipes. Once the water is heated inside the collectors, the pump circulates the heated water, and when it stops, the circulation stops as well.

The most popular and used collectors for this active system are solar panels or flat-plate collectors and vacuum tubes.

Pressurized glycol system or Antifreeze systems

An antifreeze pressurized system is an example of a closed-loop active solar heating system, where the water inside the storage tank is heated by the fluid that absorbs the sun's heat inside the solar collectors and runs through the heat exchanger.

The heating fluid is usually a 50/50 propylene glycol and water solution that works as the antifreeze. A double-walled heat exchanger must be used if the heat transfer fluid is considered toxic and single-walled if the fluid is non-toxic.

Due to its ability to work in a lower temperature environment, closed-loop, with the antifreeze active solar heating, is the only reliable solution in colder regions.

Pressurized glycol systems are the most versatile systems of all solar water heating systems. They can be installed in any direction and far from the heat exchanger. Fill and drain valves must be installed as the system is pressurized - to add or change the fluid.

Drainback systems

A drainback system is another example of a closed-loop system where the circulating fluid is distilled water. The main advantage of the drainback system is its ability to empty the solar collector when the pump is turned off. Drainback active solar water heating systems can be installed in both colder and warmer areas.

The main components of the drainback system are the collector, pump, large storage tank (size depends on the demand, i.e., 80 gallons), small drainback tank (for example, 10-gallon), sensors, controllers, and valves.

In warmer areas, when the storage tank gets hot (but not above the maximum as the temperature limit sensor controls it), the solar fluid drains out of the collectors preventing the system failure.

In colder areas, drainback active systems are subjected to freeze-ups unless you put the antifreeze solution and remove all the water from the collectors and piping, and when the system is not collecting the sun's heat. Provide sufficient continuous slope of the solar panel, keeping the pipes and collector protected from freezing.

Distilled water is used to transfer the heat from the solar collector to domestic water, and it is stored in the drainback reservoir. Distilled water is used, due to its capability, to increase heat transfer and prevent mineral buildup.

To allow complete drainage, a slight tilt of the collectors is required. This is why the collector has to be installed higher than the storage tank. Flat-plate panels are the most popular choice, but they can also use evacuated tubes.

Drainback active heating systems are reliable and long-lasting. If this system is designed correctly(i.e., collector and the pump size), there won't be any problem, and it will work perfectly for a long time and in any climate. Drainback kits are also available for DIY projects.

Note: Adding the antifreeze to the drainback system can decrease the efficiency of the solar collectors. When the system is drained, the thin film of the antifreeze stays on the tube walls, dries, and leaves small deposits, which can build up over time, affecting the water flow and heat transfer. If only distilled water is used, the fluid rarely needs to be changed.

Photovoltaic systems

Photovoltaic (PV) operated active solar heating is using the pump only when the sun is shining. The pump is DC (direct current) and is performed by the PV panel that converts the sunlight into direct current electricity. The PV power can be used for both direct and indirect systems. PV systems are reliable and efficient, providing hot water when power outages shut down other systems.

Things to consider

When selecting an active solar heating system, it's essential to consider several factors that will affect its efficiency, effectiveness, and longevity.

The first and perhaps most critical factor to consider is the climate and location of your home. The amount of sunlight and the intensity of the rays will affect the efficiency of your solar heating system.

Therefore, it's important to choose a system that is appropriate for your geographical location and climate. For example, a glycol pressurized system may be more suitable for colder climates with low sunlight, while a drainback system may be more appropriate for warmer regions with high sunlight.

The orientation of your solar collectors is another important factor. Ideally, they should face south in the northern hemisphere and north in the southern hemisphere to maximize sun exposure.

Another important factor to consider is the cost of the system. Active solar heating systems can be more expensive than other heating systems, and you'll need to consider the upfront costs as well as the long-term savings. It's important to determine your energy needs and budget to select a system that provides the best value for your investment.

Selecting the right collector type can also make the difference. There are different types of collectors, including flat-plate and evacuated-tube collectors. Each type has its advantages and disadvantages, so you'll need to choose one that fits your needs.

You also want to consider a backup system for cloudy days, energy storage system, and the installer's experience and qualifications to ensure quality installation and reliable operation.

Advantages of active solar energy heating

• Reduced environmental impact: Using active solar energy heating reduces the use of fossil fuels, which contributes to greenhouse gas emissions and global warming. By using renewable energy sources, such as solar energy, we can reduce our carbon footprint and help protect the environment.
• Free renewable energy: Solar energy provides free energy to produce heat and power.
• Efficient: Active systems are very efficient on sunny days, and they can still be used efficiently in rainy and cloudy weather. They typically have higher efficiency compared to passive solar heating systems. This is because active systems use pumps or fans to circulate the heat, which results in better heat transfer and distribution.
• Installation flexibility: These systems can be used at almost any location and building type, as they don't have to be exposed to direct sunlight. They can be integrated into the design of a new building or retrofitted into an existing one.
  
• Year-round use: They can be used year-round, even in colder climates, as long as there is enough sunlight to heat the collectors. This makes them more versatile than passive solar heating systems, which may not be effective during colder months.
• Reliability: Active solar heating systems are generally reliable and can operate efficiently for long periods of time with minimal maintenance.
• Financial incentives: Many governments offer financial incentives for the installation of active solar heating systems, such as tax credits or rebates. These incentives can help offset the upfront costs of installation and make the system more affordable for homeowners and businesses.

Disadvantages

• Active solar heating systems can be complex, making them very expensive. They require pumps, controls, and valves, which can be more challenging to install and maintain.
• Electricity is required to power circulation pumps, sensors, and controllers.
• Some maintenance is required.
• They require a significant amount of space for the collectors and the storage tank.

Active vs. passive solar heating: Key differences

Active and passive solar heating are two different approaches to using solar energy to heat buildings or water. The key differences between them are as follows:

• Technology: Active solar heating systems use pumps, controllers, and other mechanical components to circulate water or air and control the heating process, while passive solar heating systems rely on natural convection and radiant heat transfer to move air or water and heat a space.
• Efficiency: Active solar heating systems tend to be more efficient than passive solar heating systems because they can be designed to collect and store more solar energy, and they can be controlled to optimize heating efficiency. While active systems can work in places with rainy and cloudy weather, passive systems rely on weather conditions.
• Cost: Active solar heating systems are generally more expensive to install than passive solar heating systems, due to the need for mechanical components and professional installation. However, they can offer greater cost savings in the long run due to increased energy efficiency and lower operating costs.
• Maintenance: Active heating systems require more maintenance than passive solar heating systems due to their mechanical components. Pumps, controllers, and other components must be checked regularly to ensure they are working properly.
• Flexibility: Active systems are more flexible than passive solar heating systems in terms of the type of buildings and applications they can be used for. They can be used for both space heating and water heating, and can be designed to work in a wide range of climates and building types. Passive solar heating systems are generally best suited for space heating in areas with a lot of sunshine and mild temperatures.

Are they worth the investment?

Whether or not an active solar water heater is worth the investment depends on several factors, such as the cost of electricity or gas in your area, the size of your household and hot water needs, and the cost of installing the system.

In general, these systems can offer significant cost savings in the long run compared to traditional water heaters, as they rely on a free and renewable source of energy (the sun) rather than non-renewable fossil fuels. Additionally, many local and state governments offer incentives and rebates for installing solar energy systems, which can help offset the initial cost.

That being said, the upfront cost of installing an active solar water heater can be higher than a traditional water heater, and the savings may not be immediately apparent. It's important to carefully consider your individual circumstances and do the math to determine whether an active solar water heater is a worthwhile investment for your home or business.