sparks
ELECTRICAL NEWS
august
2013
6
contractors’ corner
Working knowledge by Terry McKenzie-Hoy
Generating power into the grid
AS the fact dawns on the common person that
electricity can be generated as well as consumed, a
‘eurekamoment’occurs when the person reasons
thus:“Ah… If I have a wind turbine or a solar
panel… I can sit around and become rich by gener-
ating power into themain supply and Eskomor the
municipality will payme lots and lots of cash…”
It sounds a great idea.Well, if it was then every-
body would be doing it, wouldn’t they?
The fact of thematter is that, yes, you can gener-
ate electricity with either wind or solar power and
feed it into the grid…but it would cost a lot of
money.
The wind power people – who are about to
visually desecrate the Cape with 150mhigh wind
turbines (think: taller than any building in Cape
Town, Durban and Pretoria and only the Ponte
building and the Carlton Centre in Johannesburg
being taller) – fall under a special agreement
whereby Eskom is forced to buy power from
themat an elevated price. But, unless you are
going to put a 150m tower in your back garden,
forget about that.
Solar panels do generate power. They are also
like the beach in Spain: Costa Plenty! Solar power
costs about $1.50 per watt installed. An average
house uses about 13kWh per day, so if you want
to only generate enough power for your own
needs, you will have to generate 13kWh.
Since you can’t do this at night when the sun
has gone to bed, you will have to do it during the
eight or so hours of daylight – so your solar panel
will have to be at least 1,8kW.
Unfortunately, batteries are only about 60% effi-
cient so the power has to go up to 2,7kW. But then
you would have to supply the loadwhile charging
the battery so... You need 3kWof solar cells and
batteries and stuff. Allowing for the wiring and all
the other bits and pieces, you would have to pay
out about R70 000 to take amedium-sized home
off the grid. Your income will be R2 per kWh
or about R780 per month, so the payback will
take about nine years. Or not…as the price of
electricity escalates, you could achieve payback
within four years but every year after that, until
the whole installation wears out, you will be
getting about R1 000 per month, escalating by
about 7%per year. It’s not quite wonderful…
yet. But it’s a great deal more wonderful than it
was in past years when the payback periodwas
about 12 years andmore.
Now, neither Eskomnor themunicipalities are
going to let you put energy back into the grid, or
at least not yet. The best you can do is to put in
an installation that generates all the power that
you consume and does it in parallel with the
grid so that you have a source of supply should
you have a sudden demand.
I doubt that many reading this column would
know how to run a battery and inverter in paral-
lel with the grid (not because you’re stupid but
rather because it’s quite uncommon). However
it’s really quite simple andmany grid tied invert-
ers are available on themarket.
There are things to watch out for: most impor-
tantly, the supply to the inverters from themains
should be well protected. Call me old fashioned
but I think that high rupturing capacity (HRC)
fuses are the best for this. They are cheap, easy
to replace and keep the fault currents low so
that, in the event of amisconnection, there is
a quiet‘plink’rather than a huge‘bang’ac-
companied by that burning smell. I am sure
we are standing on‘the crest of a wave’and, at
some point in the future, when the cost of grid
electricity is high and the recovery cost from
solar generation is so good, that there could be
a big upsurge in the installation of solar genera-
tion systems for homes and offices. I believe all
electrical contractors should get up to speed on
these systems because, as withmost markets,
the first people there will have a head start.
And, importantly, don’t forget that a Certifi-
cate of Compliance is still required for grid-con-
nected solar generation systems.
Go for it.
MannyMoutinho, CEOand founder of Johannesburg-based
Mantech Electronics has, with immediate effect, been appoint-
ed as an executive director to the board of theMobiconGroup
of Companies, listed on the Hong Kong stock exchange. In ad-
dition to his new responsibilities toMobicon’s board and share-
holders, Moutinho remains as CEO for the group’s operation in
Africa, namelyMantech and Suntronika. Moutinho, besides his
formal training in electronics and businessmanagement, also
brings to the group, in excess of 25 years of experience in the
electronics and components distribution industry.
Enquiries: (011) 493-9307
Directorship for
Moutinho
