POWER April 2011 - 47

FUTURE POWER
proved incrementally at the local level, offering
services specifically tailored to the
needs of customers. "
What's more, Berst continued, " Utility
engineers have historically opposed the concept
of microgrid 'islanding' on the basis of
safety. " Their fears may be less justified with
a smarter grid and new inverter technologies
that enable faster and safer disconnection/
connection to the larger grid, and Berst cites
evidence that " a few utilities are beginning
to embrace microgrids rather than viewing
them as a threat. " In fact, those that are willing
to consider something other than business
as usual are recognizing the potential value
of microgrids to provide grid stabilization-
provided smart grid control technologies are
part of the system.
Virtual Power Plants
In contrast with microgrids, " virtual power
plants " are a newer concept. Essentially, a
virtual power plant consists of aggregated
DG resources that are treated as a single
entity. Typically, the individual resources
would be small, but when pooled together,
they would be of a size to provide reactive
power or support peak power demand. Given
their multiple locations (and, possibly, different
generation technologies), it's easy to see
how controlling a group of small, dispersed
generation sources would be facilitated by
information- and communication-technology-assisted
grid control.
Here's how Siemens describes a virtual
power plant: " The virtual power plant concept
complements the big utility companies
with their large, central power plants by creating
new suppliers with small, distributed
power systems linked to form virtual pools
that can be operated from a central control
station. Such a pool can unite wind power,
cogeneration, photovoltaic, small hydroelectric,
and biogas systems as well as large
power consumers such as aluminum smelters
and large process water pumps to function as
a single supplier. "
Movable Generation: EVs and
More
Movable, or portable, DG has been used
for some time in niche applications, such as
powering irrigation or electrifying portable
fences. Such sources typically are not gridtied.
However, with a smarter grid, they need
not be excluded. With the addition of a microchip
and communications technology to
determine who owns and gets credit for the
movable power generation, the owners of a
portable solar-powered fence, for example,
could earn revenue from it on days when it's
not being used to corral weed-eating goats
(Figure 1). Conceptually, all they would need
to do is set the module in the sun and plug
it into virtually any power outlet. Theoretically,
any portable solar-powered device with
a plug could become a movable generation
source.
Until the necessary electronics are incorporated
into all renewable-power devices,
the most common type of portable power is
likely to be electric vehicles (EVs). Although
EVs can only store, not generate, power,
when they discharge to the grid, their electrons
contribute to supply in the same way
as a pumped hydro system or a coal-fired
power plant. And those EVs-which will be
showing up in more-noticeable numbers this
year (mainly in China, the U.S., Europe, and
Australia)-are the most distributed, and redistributable,
power source currently imaginable
(Figure 2).
The long-term net benefit of EVs to a distribution
grid are as-yet unknown, but even
an EV advocacy group, the California Plugin
Electric Vehicle (PEV) Collaborative,
1. Portable power. A small PV module powers a portable fence that corrals weed-eating
goats. When the module isn't needed to power the fence, it could be used to feed power to the
grid if it were equipped with the appropriate communication module and plugged into a smarter
grid. Source: POWER
notes in its strategic plan that, given the existing
grid, " Over the next decade, electricity
demand from PEV charging is unlikely
to require new power plant or transmission
line capacity. But even in small numbers,
PEVs could stress local electricity distribution
networks. Under certain circumstances,
a cluster of PEVs in a particular neighborhood
could overload or shorten the life of
a local transformer and require equipment
upgrades. "
However, with a smarter grid, both PEVs
and the grid could benefit. According to the
PEV Collaborative, " If appropriate technology
and communication protocols develop,
intelligent charging stations may allow PEVs
to adjust their charging rate to provide additional
services that contribute to increasingly
efficient operation of the electricity grid. "
Summaries of two Electric Power Research
Institute (EPRI) research programs
nicely illustrate the potential pros and cons
of EVs as well as the hopes and fears of utility
distribution system operators.
One EPRI report looking at the impact of
PEVs included evaluation of " the impact of
the smart grid on load shifting and economic
benefits in terms of deferred capacity investment. "
It found that there is a net benefit for
the grid and utilities.
Another one noted that " Both vehicle owners
and utility companies would benefit if
PEVs could draw power during off peak periods,
but implementing a demand response
program will require grid-to-PEV bidirectional
communications to allow the utility
system to influence the timing and amount of
energy the PEV draws from the grid. " (Emphasis
added to the part that many customers,
especially in the U.S., fear. Note to utilities:
Customers are going to demand the ability to
override utility charging curtailment, aka demand
response, programs. This is America,
where automobiles were invented, and after
paying a premium for PEVs, drivers are going
to expect that they can drive, and charge,
when they want to.)
Pole-Mounted PV: Literally
Grid-Integrated Solar
Petra Solar describes itself as " a clean energy
technology company that provides solar
and smart grid solutions for utility, commercial
and residential applications. " Though it
makes systems for rooftop installation, its
notable twist is " an integrated utility grade
solar, smart grid, and power management
solution primarily designed for deployment
on utility distribution and streetlight poles. "
That's right, small PV modules feed juice directly
to the grid, from the grid.
The company says its SunWave UP Series
systems " consist of a high efficiency
April 2011 | POWER
www.powermag.com
47

http://www.powermag.com

POWER April 2011

Table of Contents for the Digital Edition of POWER April 2011