FAQ’s – Solar Geyser Solutions
A solar water heating system uses the natural heat from the sun to heat water for your home or building. Solar thermal technology is an increasingly popular renewable alternative to the traditional electrical geyser based water heating systems. A solar water heating system uses solar thermal collectors (solar thermal panels). These panels look a lot like solar photovoltaic (PV) panels and work in a similar way, i.e. they capture energy from the sun, but instead of converting the sun’s heat into electricity, solar thermal collectors use the sun’s energy to produce hot water.
A solar water heating system comprise of three main parts:
-Collector: The solar collector absorbs solar radiation and transfers the energy, in the form of heat, to the fluid within it. The solar collector is generally a flat plate collector or an evacuated tube collector. More basic systems may be a coil of black pipe within a box or similar.
-Transfer fluid: This is the heat transfer medium. In a direct system, the transfer medium is the potable water from the storage container. In an indirect system, the transfer fluid is generally a mix of water and glycol, which passes the energy to the storage container via an isolating heat exchanger.
– Storage tank: As with a conventional electrical geyser, the hot water storage container is thermally insulated to retain heat.
A solar thermal system is not a complete solution, you will still need a geyser to supply hot water through the night, or to supplement your hot water supply on cloudy days.
Benefits of a Solar Geyser System
-Reduce electricity costs for water heating
-Environmentally friendly
-Off set your carbon footprint
-Works during power interruptions (during the day)
-Long life
Disadvantages of a Solar Geyser System
-Upfront installation costs
-Dependent on climate
-Only heats water
-Only provides free water heating during the day
-Less efficient on cloudy days
Low pressure geyser systems consist of vacuum glass tube collectors, an insulated storage tank and an optional stand. The glass tubes collectors are filled with water and exposed to the sun, thus depending on solar rays to heat up the water in the glass tubes. These systems can be placed at ground level or on a roof.
These systems have no electrical heating element and thermostat, requires no electricity and operates on gravity-fed hot water pressure only.
Low pressure solar geysers provide an inexpensive solution to provide hot water during the day for homes and other buildings without access to electricity e.g., low cost housing, farm houses and rural schools.
Advantages
–This type of solar heater is simple, with no moving parts
–Due to its simplicity, it is usually a cheaper option (roughly 50 – 60% of high-pressure systems)
–Due to lower pressure and stress on the tank and collectors, it has a longer life span than mains pressure solar geyser systems
-This type of solar heating system is lightweight
-Provides hot water without external power
-Is highly effective in converting sunlight into heat
Disadvantages
-Has limited use with modern plumbing systems, as it can only be used where there is low water pressure
-Unless it is installed at a high level above the water outlets the water pressure will be very low
-Can cause serious scalding if not installed or used correctly
-The entire solar heater system needs to be shut down even if one glass tube breaks
-All the weight of the heater is carried by the roof which may need additional support
-The water tank does not look very attractive when installed on top of a roof
-Breaks easily
Flat plate solar collectors come in the form of insulated, weatherproofed panels that can be fitted onto roofs, is the simplest and most widely used means to convert the sun’s radiation into useful heat. The flat plate collector is an older and widely used technology because of it is simple in design, has no moving parts and requires little maintenance.
A flat plate solar collector does not provide a complete solution and needs to be combined with an electrical geyser to generate reliable hot water heating in hot to mild climates.
They can be configured for a range of domestic solar compatible geyser sizes, ranging from 50 to 300 liters.
How They Work
A flat panel collector consists of a weather tight container, flat absorbing plate, transparent front cover and insulation.
The absorber plate consists of an assembly of a copper sheet and copper tubing.
The top surface of the absorber plate is coated with either a dark coloured material or with a selective absorbent coating.
The solar radiation that strikes this coated surface is converted to thermal energy that is used to heat the fluid flowing through the tubes, and eventually into the pipes feeding the electrical geyser.
The pre-heated hot water is fed into the electrical geyser, reducing the electricity needed by the geyser to heat the water.
Advantages
-Reliable
-Proven technology having been used for over 50 years
-Long life
Disadvantages
-Prone to freezing
-Lower water temperatures
-Low performance during cloudy weather
Evacuated tube systems provide a highly efficient and modern way of heating water for homes and other buildings, during the day, using the sun’s thermal energy.
Evacuated tube collectors that combine an evacuated solar collector with an electrical geyser, are designed to offer reliable hot water heating in hot, mild, or cold climates. The evacuated tube collectors that can be integrated into an existing (retrofit), or new electrical geyser system can, be configured for a range of domestic solar compatible geyser sizes, ranging from 50 to 300 liters.
How They Work
Evacuated Tube Collectors consists of several glass tubes, each of which has concentric inner and outer walls. The inner space is evacuated and the vacuum helps keep the inner tube isolated, reducing convection and conduction heat loss to the outside. The absence of air in the tube creates excellent insulation, allowing higher temperatures to be achieved than other types of solar collectors. This design also eliminates water freezing problems during the cold winter days.
The sun’s thermal energy is trapped by the absorbing copper rods within each of the inner tubes. The heat is then conducted through these copper rods where it heats water that flows into a manifold positioned above the collector, and eventually into the pipes feeding the electrical geyser. The pre-heated hot water that is fed into the electrical geyser, significantly reduces the electricity needed by the geyser to heat the water, thereby significantly reducing the hot water heating costs.
Advantages
-Can operate in freezing temperatures
-The tubes are independent of each other and thus system can continue operating if one of them fail
-Higher absorption rate than other systems
-Significant performance during cloudy weather
Disadvantages
-More expensive than low-pressure systems
-Has the potential to overheat
-Prone to hail damage
Photovoltaic (PV) based systems combine PV panels with a micro-processor based controller that utilises solar energy during the day to heat household or commercial water. The PV panels generate the electricity used by the geyser during the day to significantly reduce the electricity costs.
Advantages
-No plumbing required
-Quick installation
-Provide remote monitoring and control via the internet
Disadvantages
-More expensive
-Does not work at night
Solar water heating systems usually cost more to purchase and install than a conventional electrical geyser. However, a solar water geyser system can save you money in the long run.
How much money you will save by installing a solar geyser system will depend on the following:
-The amount of hot water you use
-Your geysers’s performance
-Your geographic location and solar resource
-Available financing and incentives
-The cost of electricity (Municipal statement, electricity section)
-The amount of the electricity you use for your electrical geysers (Municipal statement, electricity section)
If you install a solar geyser, your electricity bill for water heating should drop significantly. Also, because the sun is free, you’re protected from electricity interruptions and price hikes.
If you’re building a new home or refinancing, the economics are even more attractive.
Determine Annual Operating Costs
Before purchasing a solar geyser system, estimate the annual operating costs and compare several systems. This will help you determine the electricity savings and payback period of investing in a more energy-efficient water heating system.
Before you can choose and compare the costs of various systems, you need to calculate the potential savings that can be achieved by installing a solar geyser system. This requires understanding the known system size required for your home, total monthly electricity charges, and an estimation of the percentage savings you can achieve versus a conventional electrical geyser system.
The following is a method that can be used to calculated the savings that can be achieved by installing a solar geyser system.
Step 1:Estimate Monthly Electricity Consumption
To estimate the annual electricity cost of a solar water heating system, you need the following:
-Monthly Electricity Consumption (kWh)
-Average Electricity Cost / kWh (Rand)
-Average Electricity Cost (Rand)
Step 2: Estimate Potential Savings
Then, use the following calculations to
-Estimated Portion of Electricity Cost Due to Geyser (Rand) (E.g., 50% of total electricity)
-Estimated Monthly Savings due to Solar Geyser (Rand) (E.g. 50% estimated portion of electricity cost due to geyser)
Step 3: Calculate Payback Period
-Take Total Cost of Solar Geyser Solution (Rand)
-Divide by the monthly savings (Rand)
-Estimated Payback (Months)
The largest electricity consuming appliance in our houses is usually the electrical geyser. It makes up typically 40-50 % of the total electricity used in many households. A solar geyser system may reduce this energy consumption figure significantly. Used carefully, with a timer device, it can also shift this demand to off-peak periods.
The following example shows a calculation to determine the payback period for a solar geyser solution
Step 1: Estimate Monthly Electricity Consumption
-Monthly Electricity Consumption (kWh) = 1000 kWh
-Average Electricity Cost / kWh (Rand) = R1,60/kWh
-Average Monthly Electricity Cost (Rand) = R1 600,00
Step 2: Estimate Potential Savings
-Estimated Portion of Electricity for Water Heating @ 50% = R 800
-Estimated Savings of Solar vs Conventional Geyser @ 70% = R 560
Step 3: Calculate Payback Period
-Estimated Cost of Solar Geyser Solution = R20 000
-Estimated Payback = 36 months (3 Years)