Alternative technology
25
Commercial large-scale installations
The difference between small systems and large-scale solar water heater installations are just that : scale . In exactly the same way as large-scale utility solar PV farms , the solar PV collectors are placed in a series similar to when being placed onto a roof in the home . Solar water heater collectors are no different .
By
James Green
Unlike solar PV where no economically viable storage system ( batteries ) exists , solar water heating installations can look at a number of options for water storage .
Large existing tanks of , say , 10 000 litres can be retrofitted with solar collectors running in series or in parallel . On new installations , it may be a question of cost . Realistically , because domestic electric geysers are produced in such large quantities ( approximately 450 000 per annum ), the cost of putting 10 tanks in series and / or in parallel of 200 litres to create 2 000 litres , will be less than 50 % of the cost of a large tank of 2 000 litres .
One issue that does arise is the amount of space available . Solar water heating collectors take up space , as do solar PV panels . So depending on the commercial application , it may be sensible to incorporate additional heating technologies such as heat pumps , gas boilers , heating oil boilers or even electrical resistance elements .
As is always the case , an estimate or actual energy audit needs to be undertaken .
Determining the amount of hot water being used , refer to Heating Water and a Bit of Science on Electricity Consumption and use the specific heat of water formulas . Usually , because the tanks are being used more than one full cycle in a 24-hour period , additional tanks and solar collectors will be required in almost exactly the same way as in a home with a 150l geyser and four residents .
Again , the problem of space comes into play , and there may be even greater need to integrate with other heating technologies . For projects such as a hospital for example , where large reserves of hot water are needed and the threat of legionella exists , heat pumps may struggle to get the entire tank ’ s volume up to 62 ° C for a period of one hour every 24 hours . Almost certainly gas or oil boilers will be a better option .
In hotels , in contrast , a large-scale heat pump , where solar is used as pre-feed , may prove to be the most economical option from the perspective of capital investment and return on investment .
The major attraction of solar water heaters in comparison to other technologies is the return on investment combined with the speed of payback , as well as ongoing minimal running costs . Life expectancy is also likely to be longer than that of heat pumps . All of the heating technologies have a role to play . It is just a question of the specifics of each individual project . PA
James Green is the CEO of Ubersolar and Pay As You Go Solar .
“ Life expectancy is also likely to be longer than that of heat pumps .” www . plumbingafrica . co . za February 2017 Volume 22 I Number 12