SOLAR WATER HEATING BUYER'S GUIDE

At first glance the purchase of a solar water heating system might seem a little intimidating, enough so to often deter potential buyers from following through on their decision to save money and help save the environment. This buying guide takes you through some of the key factors you need to consider when purchasing a solar water heating system.

By reading this, you will come to realize that implementing solar water heat in your home or business is not as complicated and intimidating as you initially thought.

This buying Guide will cover the following topics:

• How does solar water heating work?
• Types of Solar water heating systems
• Types of solar collectors
• Determining how much water your household uses (what size system you require)

1. How does solar water heating work?

Solar water heating is an entirely different technology to solar powered electricity generation. Whereas solar power uses the suns energy to create electricity, solar water heating uses the radiating heat from the sun to physically heat water up.

A solar water heating system is made up of three primary elements:

• Solar collector: This is an energy device which has been specifically designed to absorb solar heat radiation and transport that energy into the transfer medium or liquid passing through the collector.
• Energy transfer medium: This is a medium that via the process of conduction or convection, transfers the heat that has been absorbed by the solar collector, into the water to heat it up.
• Thermally insulated hot water storage vessel or geyser: Usually consisting of an inner lining made up of copper, steel or a polymer, this is the storage vessel, or more commonly, the geyser in which your water is stored and kept warm. Different geysers with different pressure systems are used in various circumstances, depending on the overall system design.

Solar water heating geysers are usually larger than your average household geyser as they are required to store the ENTIRE water allocation for each day.

Depending on your requirements, you can either use your solar water heating system to supplement the amount of heated water required from your conventional electric geyser, or you can use it to completely replace your electric geyser and provide your total hot water allocation for each day (recommended).

As far as the positioning of your solar water heating system is concerned, it can be stored on the roof, in the ceiling or in a regular closet as with a regular electric geyser. Ideally, you want to store your water storage vessel vertically, but if this is not a possibility, it can also be mounted horizontally without too much of an effect on the performance of the geyser.

2.    Types of Solar Water Heating Systems:

There are two main types of solar water heating systems, namely:

·         Open circuit or direct systems: These types of systems circulate water directly to the geyser from the solar collector. Unfortunately, these systems aren’t anti-freeze resistant and therefore often not eligible for an Eskom solar water heating rebate if you reside in an area of the country that is susceptible to extremely cold temperatures. 

Image courtesy of sspluc.com

·         Closed circuit or indirect systems: These are systems that contain a heat transfer medium that is circulated through the pipes within the system to heat the water and then returned to the solar collector for re-heating. These systems are more resistant against colder temperatures and are therefore recommended for use in the South African inland where frosty conditions are often experienced.

Image courtesy of sspluc.com

3.    Types of Solar Collectors:

As mentioned before, Solar Collectors are the actual solar water heating panels that absorb the heat from the sun and supply the heat to be used in the remainder of the system. There are two main types of solar collectors:

Flat panel collectors: These types of collectors tend to be a little more versatile as far as their positioning and placement goes. They can be mounted on the roof, inside the roof or even separate from the roof if need be.

 Vacuum (Heat pipe) / Evacuated tubes: These tubes function similarly to the way in which a hot water (coffee) flask does; by creating a complete vacuum inside the parallel pipes that make up the collector, which results in the water staying hot once heated.

Both the above systems are equally effective as long as they are used in the correct type of system. Have a look at some of the pros and cons of each system and then decide which will best suit you and your domestic solar water heating needs.

4.    Selecting the correct size solar water heating system:

The two variables that come in to play when determining the size of the solar water heating system that you require are the size of the total collector area and the size of the geyser/storage vessel that you require.

The general rule of thumb for calculating the size of your solar hot water heating system is that on average, each person in the house requires approximately 50 litres of solar heated water per day. Obviously, this can fluctuate depending on different people’s habits, but one should aim to use on average this amount of water.

Remember though, that different household tasks and appliances also utilize hot water. Below is a table that illustrates the average daily hot water consumption for a family of four:

Sizing example for a household of four people:
Daily hot water requirement	50 litres per person (200 litres)
Hand basins	5 litres per person per day (20 litres)
Dishwashing	3 litres per meal, assume 2 meals at home daily (24 litres)
Add compensation for heat loss due to cold water mixing	244 litres x 20% (48.8 litres)
No washing machine added
Total hot water requirement	292.8 litres per day

Table courtesy of eskomdsm.co.za

You see, it’s not that complicated

As you can see, the process of selecting a solar water heating system need not be any reason to deter you from actually going through with purchasing one. Your biggest considerations are what type and size of collector to utilize, and what size storage vessel/geyser to use.

If you require any further assistance, please do not hesitate to contact us. We have professional consultants at hand to advise you on exactly what you require and what type of system will create maximum benefits for you.