How long does the savings from a Hills Evacuated Tube Solar Water Heater take to pay the system back?
Obviously this depends on many factors such as the actual hot water usage patterns which differ for every house,the size and efficiency of your current hot water system,the electricity tariffs in your area,how much the tariff increases will be over the next few years and so on. There are many claims made for how long it will take. Working on conservative figures we believe all of our systems will take between 3 and 5 years to pay for themselves from the savings. As important as the time taken for a system to pay itself back,is the question of how long it will last after that. A system may take 3 years to pay for itself but if it has to be replaced after 3 years,it is not an investment,you are simply recouping your money. If however it takes 5 years to pay for itself but lasts another 5 years and beyond,this is a real investment with returns comparable to an excellent financial investment. The Hills Solar solar water heaters carry a 10 year guarantee on major components,so after the savings have paid for the system,it continues to generate savings for many years. Other financial benefits are that a solar water heater will add vlaue to your house should you ever sell it. The following table illustrates the payback time and further savings on the Hills Solar water heaters over a period of 10 years. Click on the following link to see the table in PDF format.
What are the main advantages of Evacuated Tube Collectors in comparison to flat plate collectors?
There are numerous benefits that evacuated tubes offer over the traditional “flat plate” collectordesigns. Although evacuated tubes are relatively new to the South African market,they were invented in Australia almost 30 years ago and they are a well proven,superior technology,widely used around the world:
INCREASED EFFICIENCY
Flat plate collectors only provide peak energy output at midday,when the sun is perpendicular to the collector’s surface. At other times of the day,the heat collection of a flat plate is either increasing or decreasing. Due to the round shape of the evacuated tube,the sun is perpendicular to the surface of the glass for most of the day,
resulting in higher heat collection and heat output all the way from morning through to late afternoon.
The ability of the tubes to absorb heat from a wide range of angles means that the Hills Solar collector can be mounted on even east or west facing roofs with only a small decrease in performance. This versatility allows the home owner to install the Hills Solar collector where it will look best,whereas placement options with flat plate collectors are limited.
MINIMAL HEAT LOSS
Because air is removed (evacuated) from the glass tubes to form a vacuum,the insulating
properties of the tubes increases. As a result,wind and cold temperatures outside the tubes have much less effect on the efficiency of the evacuated tube collector –when compared with a traditional flat plate solar collector. The collected heat is conducted to the cold water using a specially designed heat pipe. Well over 90% of the heat captured in the tubes is held and is conducted into the cold water.
HIGH FROST PROTECTION
Hills Solar collectors can be used in sub-zero temperatures without damaging the system. By contrast,under similar conditions,flat plate systems require expensive and complicated “antifreeze”systems to be installed (remember this when comparing system costs). The glycol that is used in flat plate systems needs to be regularly replaced in order to maintain its efficiency. This is an ongoing cost,requiring replacement of the glycol every 3 years or so,with the added risk of the glycol leaking into gutters or rainwater tanks at times of glycol changeover,or if the flat plate is damaged by storms.
SUPERIOR WINTER PERFORMANCE
The high solar energy absorption of the Hills Solar evacuated tube collectors,even during overcast conditions,combined with the superior insulation properties of the tubes,provides excellent water heating all year round. While some flat plate collectors may produce similar heat output in summer conditions,they generally have reduced performance during winter –when hot water is most needed.
Important Questions To Ask When Choosing a Solar Water Heating System
In the past 2 years literally hundreds of solar water heaters have become available in South Africa with a very large range of prices and quality levels. In choosing a solar water heating system that will give you the benefits of electricity savings and efficient heating for many years,it is important that you carefully think through your decision on what system tochoose. Here are a few questions that we believe are the bare minimum that you should consider when making your decision.
1. Is the system accredited on the ESKOM Solar Water Heater Rebate Scheme?
In order to become accredited,systems have to be tested for thermal efficiency on which the rebates are based;and mechanical soundness including tests for moisture penetration,hail and freeze resistance and the ability to withstand severe exposure. The Hills “Esteem” Solar Water Heating Systems have passed the stringent mechanical tests and also rated amongst the highest for their thermal efficiency.
2. What warranty does the system come with?
A solar water heating system should pay for itself from the electricity savings over a period of about 4 to 6 years. A cheap system may pay for itself over a 4 year period but then have to be replaced. A more expensive system with quality materials and components may take an extra year or 2 for the savings to pay for it,but then give you many years beyond that of continued savings. The Hills “Esteem” Solar Water Heating System comes with a 10 year guarantee on major components and we would expect it to continue to give good service for years beyond the guarantee period. Our collector is made of quality aluminium,copper and marine grade stainless steel. The solar geyser is lined with a cross-linked polymer that enables us to guarantee it regardless of the water quality,even if used with borehole water.
3. What maintenance does the system require?
Many systems require cleaning of the collector (flat plate collectors lose efficiency if the glass plate becomes dirty),replacement of the heat transfer fluid (glycol,every 2 or 3 years) and replacement of the sacrificial anode in the solar geyser (frequency depending on the water quality). The Hills “Esteem” Solar Water Heaters require no or minimal maintenance. An accumulation of leaves on the collector would need to be removed but normally a good rainfall is sufficient to clean off the glass tubes periodically. As Hills use a direct system,there is no need for a heat transfer fluid like glycol. Our solar geysers are lined with a cross-linked polymer ensuring that the water does not come into contact with the tank. This means that there is no need for a sacrificial anode requiring periodic replacement.
4. Does the installer fit a timer to control the switching of the electrical element?
ESKOM require a timer to be fitted to control the switching of the electrical backup element in order to qualify for their rebate. We believe that any electrically backedup solar water heating system should have a timer. Without a timer,when you use hot water,the electrical element would automatically switch on and heat the water over a 2 or 3 hour period instead of allowing the solar radiation to heat the water over the course of the day. This results in significantly reduced savings from your solar water heating system. The Hills “Esteem” system makes use of a timer which ensures that the system allows solar energy to heat the water. The electrical element will only kick in at the end of the day if solar has not brought the water up to a pre-set temperature,ensuring maximum savings as well as a reliable supply of hot water.
5. Other considerations.
There are so many variations in solar water heater designs that it would be
impossible to evaluate them all in this document. We have payed great attention to
detail in the design of the Hills “Esteem” Solar Water Heaters.
1. We make use of an AC (alternating current) circulation pump where some systems use a DC (direct current) pump run off a solar PV (photo-voltaic) panel. The AC pumps are more reliable and durable and in cloudy weather,when the evacuated tube solar collectors are still generating hot water,PV panels do not generate enough current to run the AC pump,resulting in a waste of solar contribution. We can also fit a DC pump system if required.
2. Some systems continue to circulate water to the collector regardless of the temperature in the solar geyser. During very hot days when you are using little or no hot water,this can result in boiling water eventually accumulating in the geyser. This is potentially dangerous and also leads to premature failure of various components. The Hills “Esteem” system shuts the circulation pump down before the water in the geyser reaches boiling point. The controller continues to ‘manage’the temperature in the solar collector but may result in water boiling inside the collector on the roof. The resultant steam is harmlessly vented by an automatic vent on the collector.
3. We install a mixing or tempering valve standard with all our systems. This would normally be set to about 55 degrees C and automatically mixes cold water into the supply to the hot taps if the temperature in the solar geyser is above the set temperature. This is an important safety valve that we believe should be fitted to all solar water heating systems.
4. The Hills “Esteem” Solar Water Heater incorporates a flow control valve in the solar collector circuit. We have tested what the optimum rate of flow is for our various sized systems and set the valve accordingly. Systems without such a valve circulate the water at the normal speed of the pump. This results in the heat being stripped from the collector too quickly and the circulating pump being repeatedly cycled on and off. This also results in efficiency loss and reduced lifespan of the pump.
In short,the Hills “Esteem” Solar Water Heaters have been designed with meticulous attention to detail,are made of the highest quality materials and the best components from around the world,including South Africa. This ensures efficient,reliable solar water heating for many,many years as well as being a valuable asset to your home. We wish you every success in making this responsible choice for a solar water heating system to utilise this free energy source from creation.
