Renewables & The Grid
already have these systems installed, but have yet to use them real batteries installed on the grid, and that is a whole different
for this purpose. They are generally well ahead of most of the story with its own issues.
rest of the industry in having the infrastructure to support Most of the best places to put wind turbines and solar cells
these sources. are in suburban and rural areas where the population is less
Loss of power from a system failure should cause most S-Dist dense and that means the power consumption is also lower. In
systems to automatically disconnect from the grid, since they many cases this means the size of the wires in the distribution
are seldom large enough to support the entire load in the grid are also smaller. To put larger numbers of V-Dist units into
remaining section of the grid to which they are now connected. rural areas and move the power to people who will use it may
This means that while the customer that owns the S-Dist has a involve ‘re-conductoring’ – replacing the physical wire in the
higher level of reliability, the rest of the customers do not. Most distribution grid so that it will carry more power than it does
S-Dist is very useful for shaving the peak – i.e. reducing the today. For an overhead system, where the lines are up on poles,
demand for a section of the grid when the demand for power re-conductoring can cost as little as US$100,000 a mile. For
is at its highest. This is very valuable when the grid is reaching underground systems that number can run into more than a
its limit for providing power. In the case where this is all the S- million dollars a mile. Companies like HydroOne in Canada
Dist is being used for, it might run as much as 200 hours a made the decision to re-conductor years ago and made it a
year. This is a huge capital investment for roughly 2% of the multi-decade programme to replace thousands of kilometres of
year. Most customers who would install S-Dist would do so for wire when they did maintenance.
reliability rather than to support peak-shaving. In many cases, Unlike the V-Cent, these systems are maintained by the
the price that would have to be offered to the S-Dist owner to homeowner and many of them find they do not get the power
run their generation to shave the peak would be much higher output they were promised by the salesperson, so they do not
than the cost to generate power at a central station – further make the money they expected and hence do not maintain the
reducing the number of hours that the S-Dist might run. generator. This leads to a collapse in the capability of the
Finally, these generation sources typically have a site system to make power and can make the generator even more
approval problem: Since most are diesel and gasoline engines erratic than it was when it was first installed. One of the first
running biofuels, they are noisy and smelly (imagine components to typically fail is the islanding device and the
McDonalds French fries for biodiesel). Many people do not inverter. The failure of these devices does not typically isolate
want to see them installed in their neighbourhood and even the device, but rather they fail most often when providing DC
fewer people want to hear them running at 3 a.m. power into the grid even when they should be islanded. The
failure of power electronics creates a hazard for the lineman
V-Dist who is dispatched to fix the network outage, since they have
FinallythereisV-Dist,thekindofrenewablesthatmostpeople no clue that the power is still flowing through the line and
thinkofwhenyoumentionrenewablegeneration.Human-scale many transformers will step up the voltage for this distributed
renewables that should blend into the neighbourhood. These power. The ability to monitor the health of power electronics –
solar and wind powered devices are owned by businesses and both the inverter and islanding device – is critical to the safety
homeowners. They are deployed in the low voltage network and of people working on the system, and a simple fine for failure
suffer from all the same problems as S-Dist, including issues to maintain the system is not enough to remove the human
with harmonics and phase imbalance. hazard that exists. This hazard can exist with S-Dist as well,
They have even had issues with smell and noise (for but empirical data from working with both S-Dist and V-Dist
instance, solar cells that cooked tree sap giving off strong indicates that the S-Dist sees fewer failures and more
odours and wind turbines that make noise all night long). In maintenance than V-Dist installations.
addition, these devices pose another problem for the grid
operator – they run when the environment is right and do not Summary
run when it is not. They use the grid like a large battery, Renewable generation is an important part of the future for
putting excess power into the grid and drawing power from the the electric industry: We cannot avoid it and we cannot hide
grid when they do not make enough. In similar cases, going from it. We have to work through these problems and make
from a net generator to a net consumer can take seconds. This integration of renewables easy. IEEE-1547 provided the basic
works well when the percentage of power produced from V-Dist interface for renewables to the grid, so the interconnection, the
is small, but as the percentage increases there will need to be largest stumbling block a decade ago, has been solved. Now
144 worldPower 2009
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