For definitions I'd look to the Galvin Electricity Initiative; the
defintion is at http://galvinpower.org/microgrids .|
Phil has a lot of excellent points. From the perspective of EMIX, I
think that a microgrid reflects a market with electrical switching.
Storage may be benefitical, as might alternate generation, but the
DR/Curtailment within and consumption from outside are all part of my
model of microgrids.
The interesting question is in Phil's first line "to whom is the
definition important?" My discussions on the topic assume that there is
a community of interest boundary, but that the boundaries are mutable.
And the ability to buy/sell/transfer/consumer energy inside the
microgrid with its own controls seems pretty central.
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Phil Davis wrote:
One question worth answering is to whom is
the definition important and how will it be used? For example, a micro
economy can be your household, neighborhood, or town, and it cannot
print money (legal tender, that is). A Macro economy includes a
regulatory authority, and it can print money. Therefore, the rules of
operation are different for each but with similarities.
With respect to microgrids, and with the
possible exception of the LBNL wording, the example definitions seem to
imply asset requirements imposed on the smaller group by a larger
group. This is appropriate if a micro grid has legal standing and is
subject to market rules or regulatory authority. If that indeed is the
case, then said authorities also will define what a micro grid is, much
the same as DR Capacity is similar to but not exactly the same between
NYISO and PJM. the result will be a patchwork of definitions. The U.S.
is known for that.
Microgrids are a big topic in the buildings
industry. There are some building owner/management companies (The
Irvine Company, and CBRE come to mind) who use the term referring to
plans to link buildings into portfolios, then use internal "balancing"
capability to negotiate more favorable contracts with energy retailers
and DR aggregators, and on and on...So we need to accommodate both
large scale authorities and the informal groupings that are coming
together in markets in response to increased awareness of potential.
For me, the most useful definition of a
micro grid is some grouping of entities such that they are under (or
have the capability to be under) a central control point and that the
central control has the ability to measure, model and therefore
accurately describe and predict the state of that group together with
its capability to act in a specific way. The consumer of that
information might be an LSE, ISO, CSP, etc.
The actual resources contained within that
micro grid are less important than the predictability of how that micro
grid can behave together with its communications reliability. Perhaps
"micro grid" also should have some legal component that gives a central
point the ability to contract with external entities. In that way, a
potential usage such as "micro grid certified" could mean that the
expensive and time consuming work of audits, analysis, retrofits, and
commissioning has been done and and asset grouping is ready to
communicate and act in a meaningful way.
Such a definition could be useful to LEED
certification, market participants, market value, etc, while still
offering the flexibility that diverse capabilities (gen, non gen;
storage, non storage) could interact with interested third parties that
specialized in each area.
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microgrid should have some storage
The 'interesting additions' came from a paper/presentation at the same
site (second link from end of original email -- DOE Electric
Distribution Transformation Program site) summarizing the results of a
survey of technical experts. The table on page 10 summarizes their
findings showing the position of each of 11 of those experts on various
questions aspects of a microgrid. The question of whether a microgrid
*must* have storage was only answered in the positive by 2 of the 11
experts (DTE Energy and CERTS microgrid). 3 others answered that
storage was "preferred but optional" (Northern Power, Scandia, and
GE). The other 6 had no comment on the question. Northern Power's
definition of a microgrid is "2 or more distributed generation or
storage assets ... assets may be combinations of power generation and
energy storage devices depending on the requirements of a specific
So the idea seems to be definitely generation, and optionally storage.
They recommend storage, so, yes, 'should', but don't seem to think it
would be required. There was mention in a couple of the papers that
backup would be handled by the grid. I suppose that's where 'seamless'
becomes most important ...
Regarding 'driven by DER', here is the full sentence: "Many microgrid
concepts appear to be driven by DER technology rather than by energy
service requirements." I saw similar statements in at least one other,
maybe two, of the sites mentioned below. I'm not entirely sure what
constitutes 'energy service requirements'. I'll try to find the other
Holmberg, David wrote:
don’t think I agree with any of the “interesting additions”, except
that every microgrid should have some storage to allow meeting typical
demand requirements. I’m not sure what “driven by DER” means. Certainly
there has to be some DER. The definition and value of high reliability
is in the eyes of the beholder.
Yes, the primary recurring attributes seem to
- can operate independently from grid or in parallel
- can seamlessly move from one mode to the other
- independently controlled at the local level, no need for central
- driven by DER, co-locates generation and load
- highly reliable
Interesting additional notes from the survey presentation at the same
site are the 'points of varying agreement'
- generation capacity must be < 1 KW
- must contain > 1 generation source
- must connect to the grid at a single point
- must contain storage (batteries, etc)
- must be able to meet full load requirement
Holmberg, David wrote:
all agree as far as I can tell. I like the http://www.electricdistribution.ctc.com/microgrids.htm,
along with the EI idea of hierarchy put together.
We've been using the term microgrid (among others) frequently and today
it came up again but with the thought it might also be applicable to
subsystems within the 'macrogrid'. At the same time, in the Dutch
'microgrid' paper, they use the term Virtual Power Plant (not so much a
microgrid, but more of a role a microgrid may assume). 'Microgrid' is
used and defined differently by different entities and the definition
is evolving, as are most in this space, and new terms are devleoping.
Perhaps it would be helpful to start a glossary for terms like these we
may use in the spec so everyone understands the definition as they are
used by EMIX? The defining process may have the added value of
generating more clearly articulated scope and price communication
For instance, below are several different defs/characteristics for
microgrid I've run across recently. Each specs a different set of
characteristics from which we could generate an amalgam of those (and
any from other sources) characteristics most relevant to EMIX and
perhaps then define some use cases using these characteristics to drive
Just throwing this out, as an example, to start gathering glossary
"Small, local versions of the bulk power grid that optimize the local
distribution system and may include local generation and storage. A
microgrid may contain smaller microgrids and may be part of a larger
microgrid; communication interface at the edge of each microgrid is the
Subsystem of generation and associated loads that can separate from the
distribution system to isolate from disturbances without harming the
transmission grid's integrity and providing higher local reliability by
islanding generation and load together. Allows for local control of
distributed generation, eliminating the need for central dispatch.
From NAESB report to NIST
A microgrid, a local energy network, offers integration of DER with
local electric loads, which can operate in parallel with the grid or in
an intentional island mode to provide a customized level of high
reliability and resilience to grid disturbances. This advanced,
integrated distribution system addresses the need for application in
locations with electric supply and/or delivery constraints, in remote
sites, and for protection of critical loads and economically sensitive
development. By operating microgrid in the islanding mode, critical
loads can continue to operate, impervious to grid disturbance events.
A key feature of a microgrid, is its ability, during a utility grid
disturbance, to separate and isolate itself from the utility seamlessly
with little or no disruption to the loads within the microgrid (e.g.,
in the CERTS Microgrid concept, no impacts on power quality). Then,
when the utility grid returns to normal, the microgrid automatically
resynchronizes and reconnects itself to the grid, in an equally
seamless fashion. A critical feature of the CERTS Microgrid is its
presentation to the surrounding distribution grid as a single
self-controlled entity. A CERTS Microgrid appears to the grid as
indistinguishable from other customer sites that do not include DER.
This presentation means that the microgrid avoids many of the current
concerns associated with integrating DER, such as how many DER the
system can tolerate before their collective electrical impact begins to
create problems like excessive current flows into faults and voltage
fluctuations. The peer-to-peer concept insures that no single
component, such as a master controller or a central storage unit, is
required for operation of the microgrid. Therefore, by its very design,
the CERTS Microgrid can continue operating with loss of an individual
component or generator.
: (slide 4, also more detail at slides 9-11)
No clear definition, but characteristics include ability to operate
'islanded' or 'grid parallel', and to switch seamlessly between these
two modes, and to include significant DER capacity; driven by DER
technology rather than by energy service requirements.
Smaller-scale electrical systems spanning college campuses,
municipalities and business parks, where energy is generated, stored
and very closely managed on an intensely local level. Without being
hooked into one of the larger national grids, there are less likely to
be disruptions due to peak demand or excessive power loads. Easier to
do DR. Can store enough energy to keep power flowing during blackouts
or other disruptions. This makes them ideal for emergency services,
hospitals, and of course, the military.
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