Solar Hot Water Panels
Solar hot water panels are one of the most cost-effective solutions to generate hot water for your home. Solar hot water systems can be used in any climate and since the fuel they use comes from the sun, the energy used to heat your water is absolutely free. Solar hot water panels use the sun to heat either water or a heat-transfer fluid in the collector and the heated water is then held in the storage tank ready for use.
Heating water represents the biggest energy use in your home and unlike traditional solar photovoltaic panels, solar hot water panels are less expensive, which means that you will get your return on investment much more quickly with solar water heating.
There are three types of collectors for solar hot water panels, the first is integrated collector storage which combines the solar collector and storage tank all in one, the second type and most commonly used, are flat plate collectors which are more suitable when tank roof mounting is used. The third type are evacuated tubes which are more efficient than flat plate collectors and are great for use in cold regions that are prone to frost.
Selecting the right solar collector for a solar hot water heater it very important and doing your homework in advance will ensure that your solar hot water panels will meet the needs of the particular solar heating design needed for your home.
Integrated Collector Storage
Integrated collector storage hot water heaters are created by having the collector and the storage component of the solar hot water heater integrated into one unit. These collectors are used in passive solar water heating designs. Also known as ICS or batch systems, integrated collector storage systems feature one or more tanks or tubes in an insulated, glazed box.
ICS systems work by passing cold water through the solar collector to preheat the water. The heated water then continues on to the conventional backup water heater, providing a reliable source of hot water. ICS systems should only be installed in mild-freeze climates since the outdoor pipes could freeze in severe, cold weather.
Flat Plate Solar Hot Water Panels
Flat plate collectors have been around for several decades and work by using copper pipes that run through a glass covered collector which are usually connected to a water storage tank on the roof. With flat plate solar hot water panels, the hot water can flow back and forth, in and out of the tank, which continuously heats the water. Flat plate solar hot water panels are primarily used in active solar water heating systems, solar pool water heaters, as well as space heating systems. Flat plate collectors get there name from their appearance. They are essentially made up of a flat absorber plate that is enclosed in a very light weight metallic frame which is usually made up of aluminum.
There are two types of flat plate collectors, glazed and unglazed solar collectors.
Glazed flat plate collectors are well insulated and are cased inside of a weatherproofed box that contains a dark absorber plate under one or more glass or plastic covers. Absorber coatings are placed on the absorber plate, to assist with the collection of solar radiation. The coatings used will vary from model to model. It's important to note that some coatings perform better than others. Bonded to the metallic absorber plate are risers. The risers are designed to contain the circulated fluid throughout the solar hot water heater. Depending on the systems' design, the fluid can be either water or some type of heat transfer fluid.
Inside the enclosed frame of the solar hot water panels is a layer of insulation. The frame if the panels is covered, or glazed, with a single layer of glass or special plastic. The panel glazing is very important because it must allow as much solar radiation in, while insulating as much of the heat that is gathered as possible.
Unglazed flat plate collectors are generally used for solar pool heating. They have a dark absorber plate that is made of metal or polymer, usually aluminum, and unlike glazed flat plate collectors, they are not covered or enclosed.
Evacuated Tube Solar Hot Water Panels
Evacuated tube collectors are primarily used in active solar water heating systems and space heating systems. They get there name because of they're appearance. They are made up of several absorber plates, each one is coupled with absorber coatings, and each plate and coating is covered by a glass tube. Evacuated tube collectors use parallel rows of transparent glass tubes. Each glass tube contains a copper absorber pipe which runs through the center of the tube and is attached to a fin. The coating of the fin absorbs solar energy from the sun but also inhibits radiative heat loss. Each copper pipe is connected to a common manifold which is then connected to a slow flow circulation pump that pumps water to a storage tank below. This process heats the water throughout the day and allows the hot water to be used at night or day due to the insulation of the storage tank.
The design of evacuated tubes provides each heat gathering glass tube in the panel with an insulating vacuum. The vacuums between the absorber plates and the glass tubes, reduce heat loss significantly more than the internal insulating of flat plate collectors. With the assistance of each vacuum, evacuated tube collectors generally produce higher fluid temperatures than they're flat plate counterparts.
Evacuated tube systems are also far superior to flat plate systems because they can extract the heat out of the air on a humid day and they do not need direct sunlight to heat water. Due to the vacuum inside of the glass tube, the total efficiency in all areas are higher in an evacuated tube system and they allow for better performance during times when the sun is not at an optimum angle, such as early morning or in the late afternoon. Also due to their superior insulation, evacuated tube systems can generate hot water throughout the winter in even the coldest of climates with overcast conditions.
Choosing The Right Solar Hot Water Panels
Choosing the right solar hot water panels somewhat depends on your needs and the region you live in, however for the most efficient choice, evacuated tube collectors are generally are the best choice.
Flat plate systems generally do cost slightly cheaper than evacuated tube systems because they usually have less engineering costs associated with their manufacturing. In ideal conditions, measuring peak performance, a flat plate system could compete or even beat the performance of an equivalent evacuated tube system.
Evacuated tube systems are likely to perform slightly better in lower light and colder environments. So evacuated tube system will squeeze a bit more heat out of the available sun in spring and autumn or on overcast days than a comparable flat plate system. The main benefits of choosing evacuated tube collectors is that they have a greater surface area exposed to the sun so capture more sunlight. There design allows them to transfer more heat to the water than flat plate collectors. Unlike flat plate solar hot water panels, they can be used in places with freezing temperatures. Evacuated tube collectors are more durable and broken tubes are easily replaced. They also take up less space on your roof and they do not corrode as easily as flat plate collectors.
Cost Vs. Performance
When evaluating solar hot water panels, it is always useful to think about cost vs. performance. For example, if you have a large roof space, a bigger flat plate collector could deliver equal performance or better when compared to a smaller, more expensive evacuated tube system. On the other hand, if you had only a small amount of available space, you may find you get more energy per square foot from an evacuated tube system.