Mechanical Technology July 2016

Mechanical Technology — July 2016

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Special report

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driving the implementation of microgrids,

according to Duarte, “is to reduce the

carbon footprint of electricity generation

as a whole”. “The management software

allows us to make decisions on a mil-

lisecond basis as to how to generate the

electricity needed in the cleanest way

possible,” he says.

Talking about advancing renewable

penetration, he says that in spite of the

rise in installed renewable capacity in

South Africa as a result of the REIPPPP,

the penetration of renewables in terms

of supporting load demand remains

low. “Current generation capacity is at

around 43 GW and we now have some

3 000 MW of installed renewables. This

translates to an installed penetration

of around 6.0%,” he says, comparing

this to Germany, where up to 78% of

daily electricity demand could come from

renewables.

“But high renewable penetration in-

troduces power supply volatility, which

creates difficulties for system operators,

who need to balance the grid via deflec-

tions and stabilisation strategies.

“While all renewables are associated

with volatility, the battery storage and

flywheels embedded in microgrids are an

ideal way of managing this. Distributed

microgrids, at suburb level for example,

can significantly increase overall renew-

able penetration, while making the whole

system more stable and reliable. Even

if hundreds of microgrids are intercon-

nected, each one balances itself, so the

grid itself is not destabilised in any way

by the variations in renewable energy

generation,” he assures.

Modelling local load profiles

Another distinguishing feature of the

microgrid is that emphasis is placed on

modelling the generation needs based on

the load profile of the facility or area to

be supplied. “There is a concerted and

upfront effort to balance the generation/

supply equation. It is not just a matter of

putting up a PV system, connecting it to

the distribution boards and hoping it will

generate as much power as possible,”

Duarte argues.

ABB offers upfront power consulting,

which results in investment cost savings

by ensuring a reliable consumer-oriented

system and power quality. Operational

cost savings are also achieved: by

optimising network configurations and

the intelligent use of modern automa-

tion equipment; and maintenance cost

reductions through the implementation

of reliability centred maintenance.

At the starting point of this offering is

a grid study to determine the prevailing

load and connecting standards. “If the

load turns out to be lower than the gen-

eration capacity of the chosen solution,

then the initial capex investment will

never be used to its potential. Conversely,

if the renewable component of a chosen

system is too small, then the likely return

on investment will also be low, as will

emissions reductions.

“As part of our grid study, we also

determine how to comply with local

regulations. Whether in rural Africa or

here in Longmeadow, systems must all

comply with power quality requirements

and safety regulations,” he says.

Adding to this offering is a steady state

analysis – how much power is needed

under normal operating condition, which

governs the overall capacity (kVA) of

the microgrid – and a dynamic analysis

model is also needed: “The effects of

step loads being introduced, the need for

critical loads to retain their supply and

the impact of partial supply outages all

need to be taken into account,” Duarte

explains. “This helps to size the battery

store or flywheel capacities, for example.

It also helps to identify ways of expanding

the system, when the need arises.”

Depending on the size of the system

and the variety and number of genera-

tion sources, the complexity of microgrid

increases. To cater for this, visualisation

and automatic control functionality has to

be introduced – “and this is where ABB

really excels,” believes Duarte.

From the analyses performed during

the consulting phase of a project, ABB is

able to make specific recommendations

about the generation components re-

quired, the load curves and the response

envelopes. The microgrid analysis report

includes a business case, which makes

for a bankable solution that can be taken

directly to a funder. “We strive to find the

sweet spot with respect to capex and

opex, which, ideally, combines genera-

tion options for lowest LCOE, highest reli-

ability and resilience and least possible

environmental impact,” he adds.

From a reliability perspective: “ABB

has over 25 years of experience in this

field and its research and development

department is turning 100 this year.

We have a service and remote monitor-

ing capability that enables web-based

monitoring to be implemented on any

plant anywhere in the world,” he says

pointing towards the prevailing genera-

tion and load profile of the Longmeadow

demonstration plant.”

The online monitoring system shows

PV generation at 364 kVA, with the grid

draw being reduced to 650 kVA on a

1.14 MW load. “In the event of a grid

outage, it will first bring in the PowerStore

from batteries, and if the outage lasts

longer than 15 or 20 minutes, the diesel

generators will automatically kick in to

meet demand load,” he explains.

In the municipal context, there are

numerous ways that Microgrids can play

a major part, not only in the southern

African region, but especially in South

Africa too.

Across Africa, Duarte sees modular

and containerised microgrid solutions as

ideal for augmenting weak grids.

“For new factories being mooted in

places with power limitations, and mu-

nicipalities striving to supply the stable

power needed for emerging economies

to thrive, microgrids are an increasingly

viable option,” he concludes.

The 380 kWh Li-ion battery bank and PowerStore controller are all housed in three ‘plug-and-

play’ containers.