Alan Campbell is a mechanical engineer and an avid reader of newspapers. Every so often, he faxes me news- paper cuttings of interest.
Recently, he sent me a cutting titled ‘New solar energy powers German school’. Many thanks, Alan. In the article, we are advised that a R190 000 solar energy plant has been installed at the German school, in Cape Town, and will provide six classrooms with solar power for computers, projectors, sound systems, and so on.
The system consists of photovoltaic panels, a dc-to-ac inverter and a battery bank. The estimated power production of the system is about 2 000 kWh/y. The system was donated by SolarWorld, a big international supplier of solar energy products.
So, should we stand back and cheer? Yes, I think, since it shows students that solar power is possible and that it can work. Should we cheer loudly? Well, perhaps not too loudly. At R190 000 and 2 000 kWh/y, the payback of the installation is about 100 years, even if one allows for escalating power costs. But a learner, Joseph Urban, gave a speech in which he said that the savings in carbon dioxide (CO2) generation were the equivalent of the CO2 generated when driving a car from Cape Town to Berlin – which is more or less correct.
But it all got me thinking. Firstly, the stuff from SolarWorld was not made in South Africa, but in Germany. Let’s assume it all arrived in a 6-m container, by ship. (We dare not think it was flown here.) A container ship produces about 10 g of CO2/t for every kilometre travelled, so, if we say that a 6-m shipping container with all the batteries and stuff weighs about 3 000 kg, then shipping the equipment to Cape Town gene- rated 320 kg of CO2. Flying people out to put it all together generates about 3 kg/t for every kilometre, so a person weighing 85 kg would generate 5 100 kg of CO2, which would be the same as the CO2 generated if a car was driven from Berlin to Cape Town and back. Thus, for the first two years of operation, the carbon saving would be negative.
We must also remember trees. A forest that is 600 m × 600 m absorbs the CO2 generated by a car driving to Berlin from Cape Town. Thus, if the people in Cape Nature just stopped cutting down the yellowwood and pine trees in Newlands and Cecilia forest – wow, we wouldn’t even need to install a solar system at the German school! Well, except for the educational aspect of it.
Is it a good idea from an engineering point of view? Well, yes, it shows that sunlight can charge a battery, which can supply an inverter that can create electricity, which can be used in the classroom. But it would be far more economical not to have the battery at all – one could just feed the inverter from the solar panels and have the inverter feed into the power system of the school – far more efficient, since the battery charge and discharge is only 50% efficient.
But the system at the German school does lead the way. If you want to see a working solar installation, well, it’s right there and I am sure they wouldn’t mind if you phoned ahead and then went to look at it.
I, too, have a solar installation planned for my local church. The church is lit with eighteen 150-W PAR lamps. I’m installing eighteen 22-W light-emitting-diode lamps. Then we’ll be installing our own solar power system, panels, inverter and batteries. So, if you want to feel really good, you can send your kids to the German school and come to my church on Sundays.
But remember a good lesson – before doing anything that claims to reduce CO2 emissions, consider whether the CO2 cost of the installation outweighs the benefits, and make an informed decision.
But, in all seriousness, well done to the German school, and I hope the system expands and expands.
But, in all seriousness, well done to the German school, and I hope the system expands and expands.
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