About Solar Water Heating Systems

About SWHS

SWH systems turn cold water into hot water with the help of sun rays. Around 60 to 80°C of hot water can be attained depending on the solar radiation , weather conditions and solar collection system efficiency.

They are used to heat water for a houses ,hotels, hospitals, restaurants, dairy industry, etc.

SWH systems are installed on rooftops, building terraces and and open ground where there is no shading, facing the sun set and being fed with water directly from the main supplier, using an overhead tank or through pumping.

They will generate hot water on clear sunny days [maximum], partially cloudy days [moderate], but not in rainy days or heavy overcast days [they have a back up for these periods ].

There are specific systems for soft and portable water and other specific for hard water.

Stainless steel is used for small tanks and mild steel for large tanks.

SWH tanks are insulated and keep water hot for 72 hours. 200 to 300 ltr. capacity are used in domestic settings, while large capacities are used in restaurants, guest houses, hotels, hospitals, e.t.c.

  • Tank
  • Collector
  • Frame
  • Assistant tank
  • Booster elements
  • Control systems
  • Material
SWH tank & booster element

Storage tank- A solar water heating system generally requires a well insulated storage tank to hold the solar heated water. The storage tank may sometimes be housed with the back up electric heater to boost the solar heated water to a desired temperature when the temperature of the solar heated water is lower than the desired temperature. This may happen when solar energy is not available, for example, at night or on a cloudy day.

The tank is highly insulated to keep the water hot for 72 hours. Insulation is done using high-quality polyurethane foam.

Collector

The collector is where the water is heated using radiation before it stored in the tank. There are two types of collectors:

Collectors – flat plates collectors [fpc] based solar water heaters. The solar radiation is absorbed by flat plate collectors which consist of an insulated outer metallic box covered on the top with glass sheet. Inside there are blackened metallic absorber [selectively coated] sheets with built in channels or riser tubes to carry water. The absorber absorbs the solar radiation and transfers the heat to the flowing water.

Evacuated tubes collectors – evacuated tubes collector is made up of parallel rows of transparent glass tubes, similar to florescent tubes. Each tube contains an inner glass tube and outer glass tube covered with special coating that absorbs solar energy well. As the tube is round in shape, the sun rays are always striking the tubes surfaces at right angles [that is perpendicular to the tube surface in all directions], thus maximizes the total amount of solar radiation absorbed during the day.

In addition, the tube works in the same way as a vacuum flask which air is withdrawn from the space between the inner and outer tubes forming a vacuum, which can minimize heat loss from the collector and to reduce temperature drop of the heated water or heat transfer fluid inside the tube.

The evacuated tubes employing heat transfer fluid inside the inner glass tube is known as the evacuated heat pipe collectors. Evacuated heat collectors can heat water to fairly high temperatures.

Frame

The purpose of the frame is to hold a tank and tubes together on the roof.
The assistant tank is a 7 – 9 ltr. tank that is fixed on the solar water heater tank on the inlet. It has an inlet from the water source , an outlet to feed the swh tank and a ball valve to shut the water from going into the swh tank when its full avoiding overflow.

Booster elements

This is an electric back up filled in the swh tank which boosts the water temperature to the desired temperature when the temperature of the solar heater water is less than the desired temperature. This may happen in varying very cloudy days.

Control system

A control system is a visual panel installed inside the house. The control has a display which relays the degrees of water in the swh tank. It is also used to turn the booster element on and off when the degrees of water inside swh tank reach the desired degrees.

Solar water heaters are characterised as either direct ( also called “open loop) or indirect ( also called “closed loop”) depending on whether the incoming water is heated directly in the collectors or is indirectly heated via a heat exchange.

Both types of systems, can be either active or passive. An active system uses an electric pump to circulate water or a heat transfer fluid from storage tanks through the collectors. Whereas a passive system, relies on gravity and the tendency of water to naturally circulate as it is heated, allowing water or heat transfer fluid to move through the system without the use of a circulating pump.

The main factors that will govern the choice for type of system to be installed include the climatic conditions, hot water demand, size of the system and space availability for placing extra components etc. For example low maintenance passive direct system can be used in smaller facilities with low hot water demand whereas active indirect system is usually installed in larger facilities with higher hot water demand.

Packaged type solar water heaters, with solar collectors, and insulated storage tank in one package, are also available in the market. Since the installation of this type of system is less complicated, it is suitable for smaller facilities and for household use. The packaged type solar water heaters are available at different sizes. Smaller one is sufficient for a family of 2 , and a larger can provide hot water for 8 people. These types of systems are suitable for low density housing development such as villas, low rise houses, village houses e.t.c as they tend to have more roof space for installation.

Economic benefits

Many home builders choose electric water heaters because they are easy to install and relatively inexpensive to purchase. However, research shows that an average household with an electric water heater spends about 55% of its home energy costs on heating water.
It makes economic sense to think beyond the initial purchase price and consider life time energy costs, or how much you will spend on energy to use the appliance over its lifetime. Studies show the potential savings to home owners on solar water heating systems compared with electric water heaters. Studies have found that solar water heaters offered the largest potential savings, with SWH owners saving as much as 50%-85% annually on their utility bills over the cost of electric water heating.

The analysis illustrates that the initial installed cost of the solar water heater (ksh 100.000-ksh 130,000) is higher than that of an electric water heater (ksh 50,000-ksh 90,000). The costs vary from region to region, so check for costs in your own area. Depending on the price of energy sources, the solar water heater can be economical over the lifetime of the system than heating water with electricity, fuel oil, propane, or even natural gas, because the fuel (sun shine) is free.

Paybacks vary widely but you can except simple payback of 4-8 years on a well designed and properly installed, SWH. ( Simple payback is the length of time required to recover your investment through reduced or avoided energy costs. )You can expect shorter pay-backs in areas with higher energy costs. After the payback period, you accrue the savings over the life of the system, which ranges from 15-40 years, depending on the system and how well it is maintained.

You can determine the simple pay back of a SWH by first determining the net cost of the system. Net costs include the total installed cost less any tax incentives or utility rebates. After you calculate the net cost of the system, calculate the annual energy savings and divide the net investment by this number to determine the simple payback.
An example: let us say your total utility bill averages ksh 10,000 per month and your water heating costs are average (55% of your total utility costs) at ksh 5,500 per month. If you purchase a SWH for ksh 130,000 that provides an average of 80% of your hot water each year, that system will save you ksh 4,400 per month (5,500 X 0.08= 4,400) or ksh 52,800 per year (12 X 4,400= 52,800). This system has a simple payback of less than 3 years (ksh 130,000 divide by 52,000= 2.4 ) For the remainder of the life of the SWH, 20% of your hot water will be free, saving you ksh 52,800 each year. You will need to account for some operation and maintenance costs, which are estimated at ksh 4,500 every 2 year. This is primarily to have the system checked.

 

Product differentiation

Sets Builders products apart from other new house competitors and from existing houses built much earlier without activated energy feature Installed [This is for developers, landlords].

LIFESPAN

Our solar water heaters have a lifespan of more than 15 years provided the maintenance is done on time and as provided for.

PAYBACK

Solar water heaters give you a payback period of the money spent as follows considering what you are replacing 3 – 4 years when electricity is replaced, 4 – 5 years when gas is on is replaced 5 – 6 years when firewood is replaced.

RELIABILITY AND WARRANTY

Our SWH come with a five year warranty. Our SWH have a lifespan of more than 15 years. Our SWH will ensure supply of hot water to a maximum of above 90° on a sunny day.

MAINTENANCE

Low maintenance required.

Low maintenance is required

Regular maintenance on simple systems can be as infrequent as every 3-5 years, preferably by a qualified contractor with experience and knowledge of SWH systems. Systems with electrical components usually require a replacement part or two after 10 years.

Corrosion and scaling in solar water heating systems

The 2 major factors affecting the performance of properly sited and installed SWH systems include scaling and corrosion.

Corrosion
Most well designed solar systems experience minimal corrosion. When they do, it is usually galvanic corrosion- an electrolytic process caused by two dissimilar metals coming into contact with each other. One metal has a stronger positive electrical charge and pulls electrons from the other, causing one of the metals to corrode. The heat-transfer fluid in some solar energy systems sometimes provide the bridge over which this exchange of electrons occurs.
Oxygen entering into an open loop solar system will cause rust in any iron or steel component. Such systems should have copper, bronze, brass, stainless steel, plastic, rubber components in the plumbing loop, and plastic or glass lined storage tanks.

Scaling
Domestic water that is high in mineral content (“hard water”) may cause the build up or scaling of mineral (calcium) deposits in SWHeating systems. Scale buildup reduces system performance in a number of ways. If the system uses domestic water as the heat-transfer fluid, scaling can occur in the collector, distribution piping, and heat exchanger.
In systems that use other types of heat-transfer fluids (such as glycol), scaling can occur on the surface of the heat exchanger that transfers heat from the solar collector to the domestic water. Scaling may also cause valve and pump failures on the domestic water loop.
Scaling can be avoided by using a water softener(s) or by circulating a mild acidic solution (such as vinegar) through the collector or domestic water loop every 3-5 years, or as necessary depending on water conditions.
There maybe the need to carefully clean heat exchange surfaces with medium-grain sandpaper. A “wrap-around” external heat exchanger is an alternative to a heat exchanger located inside a storage tank.

Periodic inspection list.

The following are some suggested inspection of solar system components.

  •  Collector shading- Visually check for shading of the collectors during the day (mid-morning, noon, and after-noon) on an annual basis. Shading can greatly affect the performance of solar collectors. Vegetation growth over time or new construction on the building or adjacent property may produce shading that wasn’t there when the collector(s) were installed.
  • Collector soiling- Dusty or soiled collectors will perform poorly. Periodic cleaning may be necessary in dry, dusty climates.
  • Collector glazing and seals- Look for cracks in the collector glazing, and check to see if seals are in good condition. Plastic glazing, if excessively yellowed, may need to be replaced.
  • Piping and wiring connections- Look for fluid leaks at pipe connections. All wiring connections should be tight.
  • Piping and wiring insulation- Look for damage or degradation of insulation covering pipes and wiring.
  • Roof penetrations- Flashing and sealant around roof penetrations should be in good condition.
  • Support structures- Check all nuts and bolts attaching the collectors to any support structure for tightness.
  • Pressure relief valve (on liquid solar heating collectors)- Make sure the valve is not stuck open or closed.
  • Pumps- Verify that distribution pump(s) are operating. Check to see if they come on when the sun is shinning on the collectors after mid morning. If the pump is not operating, then either the controller or pump has malfunctioned.
  • Heat transfer fluids- Anti-freeze solutions in solar heating collectors need to be replaced periodically. If water with high mineral content (i.e hard water) is circulated in the collectors, mineral buildup in the piping may need to be removed by adding a de-scaling or mild acidic solution to the water every few years.
  • Storage systems- Check storage tanks etc for cracks, leaks, dust or other signs of corrosion.

( IF YOU ARE CURRENTLY USING A BOILER, GEYSER OR INSTANT SHOWER)

RETROFITTING – converting conventional electric hot water systems to solar water heating systems

Before introduction of solar water heating systems, most house builders and owners were using electricity to heat water in homes, hotels, schools etc.

The two types of electric water heaters were the common instant shower and the expensive boilers.

Retrofitting means fitting your SWH to the existing plumbing which used to feed your boiler or your instant heater. The question remains, can this work? The answer is YES  and NO depending on whether you were using an instant heater or boiler.

Retrofitting to instant shower plumbing.

Solar water heating wont work with the plumbing initially done for instant showers. This is as a result of only having one water line, the cold water line only. This can easily be rectified, fitting an extra plumbing line for the hot water is simple and our plumbers will easily help you with that.

Retrofitting to boiler plumbing

Solar water Heating will work perfectly with the plumbing which is already done for a boiler system. This means for a house already using a boiler and you want to change to Solar water Heating, YOU NEED NO EXTRA PLUMBING DONE.

N/B In some houses you might be having hot lines but you don’t know, but you can tell by checking if your house has mixer taps, if this is the case you have both lines. You can also have one of our plumbers come and verify for you.

Retrofitting hot water plumbing when installing solar connectors has the potential  to significantly reduce both material and installation cost.

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