Now, let's talk about the types of solar hot water systems. On the basis of component types and functioning, the system can be divided into two categories. The system that contains circulating pumps and control are known as Active solar water heating system and which doesn’t contain these are called the Passive Solar Water Heating System.

A. The Active Solar Water Heating System:
On the basis of the type of circulation system and the heating fluid, the Active Solar Water Heating Systems are of two types:

1. Direct Circulation Systems:

In the direct circulation system, there is a closed loop of pipes through which water flows between the solar collectors and the tank. Water from the tank goes to the solar collector tubes and return backs to the tank from where it is diverted to the end-use application. This type of system is more suitable for working at the location where the temperature never goes below the freezing point throughout the year.

Advantages of Direct Circulation System:
• Simple and Reliable: The direct circulation system is simple and more reliable. The concept is simple, less maintenance, no additional fluid, and lesser energy loss make them more reliable.

• Affordable: It requires lesser plumbing components, moving parts, and labor which makes it less expensive than the indirect one.

Disadvantages of Direct Circulation System

• Not efficient in very cold weather: In conditions of severe cold, when the temperature goes in the negative, plain water gets freeze and can even burst the plumbing components. Thus, this type of system is not applicable at all locations, at all temperatures.

• Not efficient for multiple heating needs: If you are looking for heating your two pools of water from the same system, it is not efficient. Multiple purposes mean multiple heaters.

2. Indirect Circulation Systems:

As the name suggests, in the indirect circulation system, a nonfreezing fluid like glycol, methanol, etc. are pumped into the collector tubes and heated. This fluid heats the water by means of heat exchange. It is most suitable for the places where the temperature goes below the freezing point of the water.

In simple words, the sun heats the circulating fluid and that fluid heats the water.

Advantage of Indirect Circulation Systems:

• More efficient in a cold climate: As in this type of system either circulating fluid is used as a solar collector or it is mixed with water which further lowers the freezing point makes this system more efficient for such weather conditions.

• Suitable for multiple purposes: Hear can be exchanged to multiple arrays of water make this system suitable for multiple purposes.

Disadvantages of Indirect Circulation Systems:

Less Efficient: Because of the involvement of the heat exchange phenomenon, a great amount of heat is lost, make this system less efficient than another type.

Expensive: More plumbing components, additional fluid, and the setup take along additional cost which makes the entire system expensive.

3. Comparison of Direct Circulation System & Indirect Circulation System
Both the system have their unique features and their applications. If you are residing in India at a location where the temperature regularly falls below the freezing point like in Himalayan states – Himachal Pradesh, Uttarakhand, Jammu & Kashmir, Sikkim, etc. and have multiple heating demands, opt for the indirect system. Else, if you are residing in Indian states where the temperature rarely goes below the freezing point like Rajasthan, Uttar Pradesh, Bihar, Gujrat, Karnataka, and other majority Indian states and have heating demand for a single purpose, opt for the direct circulating system.

B. The Passive Solar water Heater system:

Passive systems are less expensive, also less efficient. But this type of system is more affordable and has a longer effective operational life. Further, it can be divided into two categories:

1. Integral collector-storage passive systems

Popularly known as “Batch” or “bread box” solar water heater, Integral collector-storage systems consist of solar collector and water storage tank in a single unit. It is the most simple solar water heater both in installation and operation. Consist of the large diameter of copper or other heat-conducting tubes and black painted storage box, water flows into the pre-heated tubes and get heated. Being a passive system, this system doesn’t require pumps. Water flows at normal pressure in the tubes. Heat is transferred by the simple phenomena of convection.

Advantages of Integral collector-storage passive system:

• Simple mechanism, easy installation, and operation: Being a passive system, this type of solar heater doesn’t require additional pumps or electronic control. Lesser components make the overall cost cheaper. Moreover, less maintenance is required.
• Cheaper alternative: It is the cheapest among the other types of solar water heater and most preferable for any DIY projects where homeowners can install their own built solar water heater with minimum cost.

Disadvantages of Integral collector-storage passive system:

• Low performance and efficiency: performance and efficiency are very low. You can’t simply rely on such kinds of heaters. Additional backup is required.
• More weight: Due to the presence of a heavy collector tube, the weight of this type of heater is the cumulative sum of water, collector tube, storage tank and some add Ons. So, mostly they are mounted on the ground. For roof mounting, the additional supporting structure is required.
• Not workable at the freezing point: This type of heaters doesn’t work satisfactorily at freezing point or on a cloudy day. However, recent design innovations have made it possible in new versions of ICS systems.
• More Heat loss: The collector also acts as a water storage unit in this type of system. For avoiding more heat loss, double or triple glazing layers have been provided on the tubes which further add ons to the weight of the system. Still, there is considerable energy loss in this system.

If you are looking for cost-effective solutions in an area where the temperature rarely goes below the freezing point, also your hot water demand is more significant in daytime or evening, you can opt for this as it is the most cost-effective alternative.

2. Thermosyphon systems

It is the most widely used solar water heater due to more efficiency, satisfactory performance, and cost-effectiveness. In this system, solar collectors are placed below the storage tank. When the sun shines, the collector fluid gets heated and rises to reach the storage tank and from there, it reaches to the end utility points. It’s the basic working principle of the thermosyphon system.
Vertical tanks are more effective as the main operation of the thermosiphon directly depends on the stratification of the water in the storage tank. Also, this system requires the utmost attention to the roof design while installing because of the heavyweight of the system.
Advantages of Thermosyphon systems
• Highly reliable: these types of systems are most widely used because of its reliability, good performance, and efficiency.
• Cost-effective: Being a passive system, it requires lesser component than the active one. Thus, it is more cost-effective than active systems.
• Less Maintenance: It involves lesser maintenance and operational cost. Thus, a faster cost breakdown can be achieved.

Disadvantages of Thermosyphon systems
• Freezing point operation: The thermosyphon system doesn’t work properly at the freezing point which makes is unapplicable for cold prone regions. For such locations, additional fluid is required to use either to mix with water or as a collector fluid.
• Multipurpose uses: For multipurpose use, separate heaters are required which makes it a costlier alternative for multipurpose applications.
For the household purpose, the thermosyphon system is more advisable considering the non-requirement of additional pump, plumbing components, and electronic control. But for larger applications at a commercial level, you must prefer the active system.
The solar water heater system always requires a backup system for a cloudy day or increased demand. Also, an additional backup of conventional heating systems can be added in case of nonfunctioning of the solar heating as an option.

Author's Bio: 

About the author: Green 4 Life Energy is an Indian venture of Green 4 Life Oz - an Australian company with an experience of more than 15 years in Rooftop solar. With headquarter at Jhansi, in Uttar Pradesh, Green 4 Life Energy Pvt. Ltd. has pioneered the concept of harnessing valuable sunlight for energy production by its innovative, affordable and international standardized solar solutions, specializing in high efficiency PV module and comprehensive EPC solutions. We are at fore-front of developing and deploying technological tools to organize and aggregate the roof-top solar industry. Our partnerships with globally renowned and leading solar equipment manufacturers ensure peerless high-quality products and services. With our international presence and firm customer base, we are active contributor in framing the solar revolution in the largest democracy of the world, India.