Solar Heating

Solar Energy HeatingImage credit: IntelFreePress, CC BY 2.0, via Flickr

The sun produces more radiant energy than Earth’s entire population could ever use. The planet absorbs more solar energy in one hour than we use in one year. Think about that for a second; think about the waste. Fortunately, solar energy is becoming increasingly viable as a renewable energy source, especially for private homeowners. This has to do with the rapid developments in solar technology, which make solar energy products more efficient, as well as with the increasing affordability of that technology, which makes solar energy more cost-effective.

Solar power can be harnessed in a variety of ways. One of the easiest ways for homeowners to tap into it is through solar water heating. Solar water heating systems provide residential homes with enough heat to take care of all their hot water needs.

 

Solar Geysers

Solar water heating systems consist of a solar collector and a geyser or hot water storage tank (or tanks, if the system is large). The collector usually consists of solar panels or evacuated-tubes and is positioned on the roof where it will get maximum exposure to the sun. For residential purpose, three types of collectors available:

1)     Flat-plate collectors.

2)     Integral collector-storage systems or batch systems.

3)     Evacuated-tube solar collectors.

A system of pipes connects the collector to the geyser, which stores water until it’s needed.

Solar water heating systems can be divided into different types: Direct and indirect systems, and passive and active systems.

 

Direct vs. Indirect Systems

Direct systems (also called open loop systems) pump household water through the collectors, where it is heated by the sun, and then into the geyser where it is stored. They are the simplest systems around and as such, are relatively cheap. On the downside, they don’t offer much protection against extremely cold or hot weather (and have a tendency to freeze when the temperature drops below zero). The components (solar panels and evacuated-tubes) also need regular maintenance and need to be replaced relatively often due to wear and tear.

Indirect systems (also called closed loop systems) pump household water through a heat exchange system. The heat exchange system basically consists of heat-transfer fluid (HTF) that circulates through the collector. It heats the water before it is stored in the geyser. In some systems, the HTF is actually fitted to a system that encloses the geyser, which allows the water in the geyser to retain heat. The HTF typically contains some anti-freeze, which makes indirect systems better suited to colder climates. They are slightly more expensive than direct systems, but they tend to be more durable and reliable in extreme weather.

 

Passive vs. Active Systems

Passive systems use convection or heat pipes to circulate water or heating fluid – they use natural heat flow without any other form of pump. This means that the tank or geyser has to be higher than the collector. They are inexpensive and low maintenance but the downside is that they aren’t as efficient as active systems and they are vulnerable to extreme weather conditions. In temperate climates, however, they tend to be quite durable. There are two types of passive systems:

1)     Integral collector-storage systems

2)     Thermosyphon systems, which rely on warm water rising and cooler water sinking, so collectors are always positioned beneath geysers or storage tanks.

Active systems use pumps to circulate water or heating fluid. They can be used with electronic controllers or other devices to optimise functionality and they can be backed up by electric or gas water heaters. Basically, they offer homeowners more control than passive systems.

It’s important to note that Eskom provides rebates for solar water heater installations, provided you use an approved supplier. Find out more about the rebate programme.

 

Solar Collectors

Solar panelsImage credit: OregonDOT, CC BY 2.0, via Flickr

The most basic definition of a solar collector is a device that collects the heat of the sun. Typically, this device is a solar panel. They range from the simple for residential home use to the complicated for industrial use and electricity generation. There are two main types of solar collectors: Flat-plate collectors and evacuated-tube collectors.

 

Flat Plate Collectors

Flat plate collectors are more common than evacuated tube collectors. They consist of four components:

1)     Dark flat-plate absorber: This is usually a sheet of high-thermal-conductivity metal or tubes or ducts. It is dark in order to maximise the amount of solar energy absorbed. It also transfers heat into the heat-transfer fluid (HTF) in a manner that keeps similar temperatures between the two (to prevent unnecessary heat loss).

2)     Transparent cover sheet(s): This allows sunlight to pass through to the absorber, while providing insulation. Some collectors don’t use any cover sheets, as is often the case for solar swimming pool water heaters. Other collectors have up to three cover sheets; they’re triple-glazed, in other words. This allows them to operate at higher temperatures, making them ideal for extreme climates. Unfortunately, it also increases the price. The covers can be made of glass, plastic and acrylic- and fibreglass-reinforced polymers.

3)     Heat-transfer fluid (HTF): This can be either liquid (water or a combination of water and antifreeze) or gas (air).

4)     Heat insulating backing: This also prevents heat loss and provides insulation in extreme climates.

The great thing about flat-plate collectors is that they expose a maximum surface area to the sun, no matter where it is in the sky and no matter whether there is full sunshine or it is overcast. Their simplicity also keeps down costs, which makes them affordable for homeowners.

 

Evacuated-Tube Collectors

Evacuated-tube collectors consist of an insulated manifold of connected glass tubes within tubes. Basically, two glass tubes are fused at the top and bottom and all the air is evacuated to create a vacuum. A copper heat pipe runs through the centre of the tube and conducts heat through the manifold and through a pump that is used to transport water in storage tank and the house’s pipes. In addition to the tubes, the manifold contains an absorber plate and heat-transfer fluid. In some cases, the tubes are made with a single layer of glass (one tube not two). This allows more light to reach the absorber plate

Evacuated-tube collectors are more efficient than flat-plate collectors and more suited to colder climates. But, they are more expensive.

 

Solar Air Heating

Solar air heating is similar to solar water heating, except instead of heating water for your home, the energy is used to heat your home’s interior. The principles are the same as for solar water heaters and the system’s components are also similar, especially when it comes to the collectors. There are two main types of solar air collectors: Unglazed collectors and glazed collectors.

 

Unglazed collectors

Unglazed collectors are essentially flat-plate collectors without any cover sheets. The absorber plate is not covered by glass, plastic, polymers or anything glazed at all. The most common type of unglazed collector is the transpired solar collector which was invented by Conserval Engineering Inc. It offers excellent solar conversion and is more affordable than many other photovoltaic systems. The difference between this system and traditional solar panels is that the collectors are typically wall-mounted, not roof-mounted.

The surface of a transpired collector is covered in micro-perforations that capture a boundary layer of heat. This is then drawn into a cavity behind the panels where negative pressure conducts it into the building’s ventilation system. In addition to capturing heat from the sun, transpired collectors’ position on the wall allow them to absorb heat from the building itself.

Some transpired systems can be roof-mounted. They can also be used in combination with traditional solar (photovoltaic) panels for increased efficiency and effectiveness. They are better suited to commercial and industrial applications, rather than private homes. In certain applications, the transpired systems are even used for night-time cooling.

 

Glazed collectors

Glazed collectors distribute heat by recirculating the air in a building through a solar collector. The exact type of collector used depends on the building’s air duct design. There are four types of collectors to suit different air-duct systems, as well as different air-conditioning needs:

1)     Through-pass collectors: Air passes from the ducts to the absorber plate through a perforated or fibrous material. It is heated and moves back into the ducts thanks to good old fashioned conductive and convective properties. They have high conductive heat transfer rates but under certain circumstances they may require the assistance of fans to get the air moving properly.

2)     Front-pass collectors. Air is directed to the front of the absorber where it enters the system and is heated.

3)     Back-pass collectors. The same as front-pass collectors except air enters the back of the system.

4)     Combination front and back pass collectors. Air enters on both sides of the absorber.

Front-, back- and combination-pass collectors are not as efficient as through-pass collectors, especially in cold climates. There can also be dust contamination issues.

Like unglazed collectors, glazed collectors can be used in combination with other solar heating systems, like photovoltaic panels to increase performance. When used with other systems they can provide comprehensive heating, ventilation and air-conditioning (HVAC) services, as you would get with modern central air-conditioning units.

Residential and commercial solar air heating systems draw air from building envelope or fresh air from the great outdoors and pass it through the collector where it is heated by conduction and ducted back into the building where air flow is stimulated passively or by fan.

 

Solar Pool Heating

Solar pool heating systems comprise four parts:

1)     Solar collector: Through which pool water is circulated.

2)     Filter: To remove debris before the water enters the collector.

3)     Pump: To circulate water between the pool and collector.

4)     Flow control valve: To control the flow of water into the collector.

Some systems also have sensory devices that will pick up on differences in temperature between the water in the pool and the collector. If the difference is big, water will be sent through the collector. If the difference is small, the collector will be bypassed.

In very hot climates, you can use solar pool heating systems to cool down your pool; all you have to do is run the water through the collector at night.

There are different types of pool collectors that are made from different materials and are suited to different climates.

Unglazed collectors (those without a cover sheet) are best if you’re going to be using your pool when temperatures are above freezing. They are typically made from rubber or plastic that has been treated with an ultraviolet light inhibitor to protect the panels. They are relatively cheap and, if you take proper care of them, can also work well in places where the weather does occasionally drop below freezing.

Glazed collectors are made from copper tubing on an aluminium plate. They are covered by glazed (tempered) glass. They are better suited to cold climates.

In addition to the prevailing climate, your choice of solar pool heater depends on the size of the pool, how hot you want your water, how big the collector is, where you’re going to put the system, whether you have an indoor or outdoor pool and whether the pool is in-ground or above-ground. It’s estimated that the surface area of the collector should equal 50 – 100 per cent of the surface area of the pool. This estimate goes up in cool climates and areas where sunshine can’t always be counted upon.

Solar pool heaters can also be used to heat indoor pools, Jacuzzis and even home spas.

 

Solar Underfloor Heating

Underfloor heating is becoming more popular, especially in new builds. Water-based underfloor heating systems that are powered by solar energy are the way to go, as they are efficient and environmentally-friendly, and they’ll save you money in the long-run. Solar underfloor heating systems generally contain five parts:

1)     Pipes: They are laid into the concrete of a new floor.

2)     Manifold: The series of valves connecting the pipes which control the temperature.

3)     Thermostat: Controls the temperature in each area. Adjusting the thermostat will open valves in the required areas, allowing hot water to flow, which heats up the room.

4)     Pump: Circulates the hot water through the pipes.

5)     Heat source: In this case the sun, but it can be electrical or gas.

Solar underfloor heating systems can be passive or active. Active systems rely on heat exchanges, which actively pump the heated water from the collectors on the roof to where it’s needed.

 

Solar Space Heating

Space heating, very simply, is heating the interior of a building. You probably already have several space heaters to ward off winter chills, including oil heaters, fan heaters, bar heaters and wall-mounted heaters. Solar space heating, provides an alternative to these electric (or gas or paraffin) options.

Solar space heating systems can be active, passive or a combination of the two. Passive systems tend to be the simpler, more affordable option, but it’s very difficult to add a passive system to an existing building, as the designs are best incorporated in the construction process. If you want to add solar space heating to your existing home, you might have to use an active system.

 

Passive solar space heating

Passive solar heating systems leverage exposure to sunlight naturally (so they include large windows) and promote the use of heat absorbent materials (like concrete).

 

Active solar space heating

These include the typical solar systems with which you are by now familiar. They consist of collectors, heat-transfer fluid (either liquid or gas) and fans or pumps to distribute the heat. Some systems also contain a storage system to store heat energy, as well as a backup or auxiliary system.

If you want to heat space, as opposed to water, you need a larger collector area and fairly sophisticated controls. Systems can be configured to provide for both space and water heating requirements. If you use a system that has been properly configured for your house, it can provide up to 70% of your heating (and hot water) requirements.

 

Homemade or DIY solar energy solutions

If you want to start incorporating solar energy into your house – to build your green credentials and to save costs – there are several DIY solutions for you to explore. For example, if you’re quite the handyman, you might want to construct a homemade solar water heating system from scratch. This requires a great deal of confidence and expertise, however, not only with regard to tools and equipment, but also with regard to where to get your supplies. There might be a great wholesale depot down the road that offers cheap materials, but how confident are you in the quality? Sometimes it’s best to pay more at a specialist supplier from the outset, so that you can avoid costly repairs just a few months down the line.

If your skills are slightly more limited, you can buy DIY solar panel kits that provide you with all the equipment, as well as easy to follow step-by-step instructions to tell you how to set up the panels, tanks, pipes and pumps. If you’re going to use a kit, do some research first to find a reliable and reputable manufacturer. This is important for several reasons. For one thing, reliable manufacturers are usually able to provide spare parts for repairs when you need them. For another, reputable companies offer guarantees on their products, and tend to offer additional support services, like helplines, so that you can call for help if you get stuck.

Regardless of whether you choose to work entirely from scratch or with a kit, it’s recommended that you consult a professional before you get started, to help you determine what type of system best suits your needs, how big the system needs to be, what type of equipment you need to build your system safely and how to ensure that your system operates effectively. A consultant will ensure that you build a solar energy system that meets your needs exactly, so that you don’t waste excess energy or come up short during winter when demand increases. A consultant will also help you find the best suppliers and help you source materials at the best prices.

If you’re at all unsure of your DIY skills, however, hire a professional contractor. Professional contractors might be more expensive than doing it on your own, but they’ll get the job done faster, safer and more reliably. They also tend to guarantee their work, so they’ll come out and do repairs or replace parts if something happens to go wrong within a certain period of time.

Many solar heating system suppliers also offer installations, either as part of the service or for a nominal fee. So if you’re going for a packaged solar heating solution, you don’t need to worry about setting it up yourself, as professional and experienced installers pop around to customers’ houses and do the job quickly and easily.

 

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