Alternative technology
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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