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SILICON
CHIP
www.siliconchip.com.au
Publisher & Editor-in-Chief
Leo Simpson, B.Bus., FAICD
Production Manager
Greg Swain, B.Sc. (Hons.)
Technical Editor
John Clarke, B.E.(Elec.)
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Jim Rowe, B.A., B.Sc
Nicholas Vinen
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glyn<at>siliconchip.com.au
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David Maddison B.App.Sc. (Hons 1),
PhD, Grad.Dip.Entr.Innov.
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2 Silicon Chip
Publisher’s Letter
The economics of hybrid
solar systems
Our report on a hybrid solar system in the October 2015
issue has created a great deal of interest among our readers.
People are particularly interested for a number of reasons
and two of those reasons are the escalating cost of electricity and the daily service charges levied by the energy
retailers. These daily service charges are usually regarded
by consumers as unjustifiably high, especially since they
have been increasing at a much higher rate than the actual
energy tariffs. So much so that many readers have entertained thoughts of going
off-grid altogether.
And that brings us to the hybrid solar system described in October. Compared
to any normal domestic grid-tied solar system, this is a large system indeed, with
a particularly large installation of deep-cycle lead-acid batteries. Such a large battery bank is absolutely necessary if the system is to be able to cope with a period of
rainy days when the output from the solar panels is likely to be severely curtailed
and of course, to cope with normal power demands at night.
No matter which way you look at it, the system is a credit to the owner, Geoff
Woodman, who has really been a pioneer – there are not too many other domestic
installations of this size in Australia and of those that have been installed, most
have been by owners who are very well-heeled and not really concerned with the
all-up cost.
However, those who are not so well-heeled need to look very carefully at the
economics of such an installation before going ahead. This is particularly the case
where the proposition is to go completely off-grid because that requires an even
larger and more costly battery bank.
Two correspondents in this month’s Mailbag pages have been quite forensic in
their analysis of the economics of Geoff Woodman’s system and if you read their letters carefully, the only logical conclusion is that the economics simply don’t add up.
You can certainly question some of the assumptions in the two letters. For example, I think their assumptions about solar panel life and decline in output are
overly pessimistic. However, there is no doubt that solar panel outputs do decline
and more so if they are never cleaned. Nor can you expect that a bank of solar panels
will never need any maintenance or repairs. Just think about how individual solar
panels or their bypass diodes may fail. What’s more, the connections will almost
certainly be subject to corrosion and the isolating switches or solenoids may fail or
go high in contact resistance.
From stories in our Serviceman’s Log pages, we already know that the grid-tied
inverter is the weakest link in a typical domestic system and that is not likely to be
any better in a larger hybrid system which will employ several inverters. Finally,
there are the storage batteries and these definitely do have a finite service life. Lithium batteries are likely to be a lot better but they are not a mature technology yet
and no-one really knows how reliable they will be in the long term.
Some readers may quibble about the likely return on investment and opportunity
cost. Some may not fully understand how the calculations on such an investment
are made – they are similar to the calculations for principal and interest payments
on a home loan but in this case you would start with a principal amount which is
invested, say $50,000 at 5% after-tax, so you earn $2500 per annum. Then you deduct
the cost of energy for the year, say $3000, to end up with $49,500 and then the cycle
repeats each year so that your principal is gradually reduced. But that ends up being
a more economic proposition than spending that money on a solar hybrid system.
Ultimately, no matter how optimistic and environmentally conscious you may
be, and how you may twist the assumptions about return on investment, there is
no avoiding the conclusion that hybrid solar systems are simply not an economic
proposition at the present time. Furthermore, those costs will need to be substantially reduced before such installations become economically attractive.
Leo Simpson
siliconchip.com.au
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