Page 57 - Energize October 2022

VIEWS AND OPINION

The May/June graph shows two case of wind about 3% surplus is required.
extended periods of extremely low wind Looking at the two cases it would seem that increased capacity is the best solution for
centered around 22 May. On 21 May the the solar problem and storage would be best for wind.
average aggregate wind output dropped Some of the solutions suggest extensive distributed rooftop solar generation, as the
to 1% (33 MW) of the maximum output answer. This analysis has only focussed on utility solar, but the same factors apply to
for a period of 1 h, and remained below rooftop solar in times of full cloud cover. Overcast weather reduces the output of rooftop
5% (150 MW)for a period of 16 h, and solar by between 50% to 80%.
below 10% (330 MW) for a period of 24 Even worse is the occurrence of consecutive overcast days. Gauteng experiences
h. Assuming an average level of 1000 regular periods of between five and seven consecutive overcast days in summer. The
MW, the energy required to make up this cloud cover that reduced the utility solar to 30% of its output would have had the same
deficit using either storage or additional effect on rooftop PV countrywide, placing an extra load on the grid, and thus increasing
generation would be approximately any shortfall. Many of the solutions which include a large amount of distributed
21000 MWh. generation do not take this into account.
Increasing capacity is not a solution,
as plain arithmetic calculations yield that The plain man’s conclusion
double nearly zero is still nearly zero, It appears to the plain man that simply increasing the amount of wind and solar will have
and twice 1% is only 2%, twice 5% = 10% no effect whatsoever on load shedding. Solar is not available outside of sunlight hours,
and twice 10% = 20%, etc. The problem and relying on the varying wind resource would involve hour by hour or minute by minute
area here is the power requirement adjustment of demand reduction, an unacceptable situation. For this to have any effect
at the lowest wind point, and meeting requires the addition of a substantial amount of storage.
the average power level for this hour A good starting point, and something which should be a priority, would be the
would require an increase in capacity addition of sufficient storage to make the existing wind and solar dispatchable, and
of 30 times. Meeting the energy deficit any additional renewable energy systems should include storage as a prerequisite. This
however would only require an increase increases the price, but is a necessity as the conventional grid no longer has the capacity
of about 5 times in capacity. to balance renewable energy generation.
Assuming that stored solar energy Even then, adding storage to the existing fleet will only add approximately 1200 to
cannot be used to accommodate for 1500 MW of average firm power capability, although higher peak power levels may be
wind energy shortages, there would possible if stored energy is only used for peaking. This is a far cry from the 6000 MW
be a total requirement of about 43 500 required to avoid the worst load shedding case.
MWh if storage is used as a solution. In Plain thinking leads to the conclusion that the current opinion that installing more
practice, however, it would normally be wind and solar on their own will solve the power shortage crisis is unfounded, and the
possible to share storage and the figure frantic rush to expedite renewable energy projects is seen to be counterproductive,
would be somewhat lower than this. taking into account that it involves relaxation of EIA assessments, and worse, a reduction
in or total removal of local content requirements for REIPPP projects, a move that could
Storage kill the nascent renewable energy industry.
A fact that is often overlooked is A further caution comes from a recent report from within the renewable energy
that stored energy has to come from industry, which highlights problems with the conclusion of projects in the latest bid
somewhere, and the storage can windows. It seems that bid prices are now proving to be unsustainable, and successful
only be recharged if surplus energy is bidders are unable to supply at the prices bid. An industry source suggests that the
available. Under load shed conditions realistic sustainable price is up to three times the bid price. This puts the DMRE in an
there is no surplus available from awkward position as the projects can no longer proceed at the bid price. All this points
conventional generation, and energy to the possibility that renewable energy generation may not be as cheap as was thought,
to recharge the storage must come and costs need to be re-evaluated. It is also a known fact that the price of solar PV has
from the system itself. This means increased substantially over the last year, which has affected the viability of many projects
either oversizing or derating the system worldwide.
during recharge. It is not plainly obvious As I have said, this is the plain man’s approach, and many other articles, based on
which method should be used, but more sophisticated analysis, have suggested other solutions. For me, the concern still
derating for a short period to allow remains whether sufficient wind, solar and storage will be installed to cater for the type
recharge would seem the better option. of event which the plain man’s approach has highlighted, and whether a plan based on
How much will depend on the period some sophisticated analysis of statistics and probabilities will result in the continuation
between low output occurrences. In the of load shedding despite huge expense. There also remains the nagging feeling that an
solar case this is about thirty days so extra few thousand megawatts of gas generation to tide us over the crisis might not be
the output would need to be reduced a bad idea.
by about 10% (or 10% surplus supplied)
to allow recharge of the battery. In the Send your comments to rogerl@nowmedia.co.za

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