Until recently, solar thermal (hot water) systems and heat pumps have been the main technologies available for reducing hot water costs.  These systems can save between 50% and 70% on hot water costs, depending on the time of the year.  Winter performance does drop off significantly due to less solar thermal power available.  While these systems do save on your geyser heating costs, it is not always as efficient as believed as there are service and maintenance costs to consider.

Solar Thermal systems use solar thermal (heat) energy to heat water.  It is commonly believed that these systems produce about 70% of the energy required to heat the water. This assumes that the geyser is big enough to store enough hot water for evening and morning use.  This is often not the case as most homes in South Africa only have a 150L or 200L geyser.  This means you are using your standard element every night to “top-up” the solar geyser for morning use, reducing the proportion heated by the sun.

The element also uses much more energy in winter as the sun is lower in the sky and does not hit the panels at the optimal angle, meaning your solar production is reduced.  In addition, daylight hours are shorter so there is less time for your solar to harvest sunlight.

Our team have installed thousands of solar hot water heat pumps systems in South Africa, as well as hybrids of the two and, while these systems offer a solution that will save you money on your electricity bill, not many people consider the high costs for their maintenance and service that extends you payback period.

Here is a breakdown for your reference:

• Pumped solar systems use pumps to circulate solar heated water. These pumps can fail and need replacing as they are an integral part of the solar thermal system – Approx Cost: R1650-R1950*

• Non return valves prevent reverse thermosiphoning, where hot water rises from the geyser up into the panels on the roof and cools down. Reverse thermosiphoning is disastrous for your savings as you lose all your stored heat overnight.  Non return valves also block up and need replacing to prevent any unnecessary losses – Approx Cost:  R650 – R750*

• TP valves and PRV valves control expansion when the geyser heats up and do drip or release water to reduce pressure and prevent the geyser from overheating. During summer these valves are working overtime and can fail.  It is also important to replace these as soon as possible when this happens to prevent any damage to the geyser – Approx Cost:  R850 – R1250*

Another alternative are Heat Pumps, that use ambient air temperature to heat the geyser and claim around 67% efficiency, but this is based on an ambient temperature of 21^oC.  When the temperature drops below this, the energy efficiency of the heat pump also drops. The actual saving will depend on the specific environment and condition of the heat pump.

Heat Pumps also require annual servicing and, since they are made of many moving electrical parts, these may need replacing over the life of the heat pump.

Here is a breakdown of the potential costs:

• Annual service – Approx Cost: R650 – R950*
• PC boards can get damaged with power surges and sometimes need replacing – Approx Cost:  R2250 – R2850*

• Compressors are vital but they can fail over time and need replacing – Approx Cost::  R4500 – R6500*

• Heat Pumps use a refrigerant gas, like air-conditioners which requires refilling from time to time – Approx Cost:  R2350 – R3500*

XTEND elements are energy efficient, long lasting ceramic elements for geysers that offer a cost-effective alternative to solar thermal systems and heat pumps. By installing Xtend elements you reduce water heating costs by around 25% over the life of the element.  If you do experience significant scaling and are normally changing elements every 3-6 months, you may need to remove and clean the element by wiping the stainless-steel tube to remove any excessive scale build up.  This is still a better and less expensive option than replacing an element every 3-6 months.

XTEND service – Approx Cost:  R550 – R850*

Element replacement – Approx Cost:  R850 – R950*

When combined with solar PV, XTEND elements turn your geyser into a thermal battery, storing power generated in the day for use when needed.  By turning on the geyser during the day you “soak” up any spare power which is normally wasted.  Solar systems produce more in the middle of the day, when demand is usually at its lowest, which results in the system throttling down (reducing production to meet demand).  If you use XTEND and turn the geyser on at this time, it will take the power from the solar first and heat the geyser for minimal cost.  The geyser then keeps warm until the evening usage  

*All prices above are indicative and include labour and VAT.

Below is a summary of the comparative savings for a 150L geyser using 150L per day @ R2.72/kWh (City of Cape Town 2021/22 incl VAT). The numbers are illustrative.