Internet DRAFT - draft-nordman-nanogrids
draft-nordman-nanogrids
Network Working Group B. Nordman
Internet-Draft Lawrence Berkeley National
Intended status: Informational Laboratory
Expires: January 10, 2013 K. Christensen
University of South Florida
July 9, 2012
Nanogrids
draft-nordman-nanogrids-00
Abstract
A nanogrid is a very small electricity domain that is distinct from
any other grid it is connected to in voltage, reliability, quality,
or price. Nanogrids could form the basis of a future electricity
system built on a bottom-up, decentralized, and distributed network
model rather than the top-down centralized grid we have today in most
parts of the world. This document introduces the idea of a nanogrid
to the IETF community for two purposes -- to inform the work on
energy management presently underway in the EMAN working group, and
to describe how future communications within and between grids could
be accomplished with protocols that are the product of the IETF.
There appears to be no fundamental conflict between the nanogrid
concept and the current drafts in the EMAN working group.
Status of this Memo
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Copyright Notice
Copyright (c) 2012 IETF Trust and the persons identified as the
document authors. All rights reserved.
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1. Overview
A nanogrid is a very small electricity domain that is distinct from
any other grid it is connected to in voltage, reliability, quality,
or price [CIGRE] (also [NG-2009]). Nanogrids could form the basis of
a future electricity system built on a bottom-up, decentralized, and
distributed network model rather than the top-down centralized grid
we have today in most parts of the world. Central to nanogrids is
the ability to communicate electricity price and availability to
enable matching demand with varying supply of electricity. For the
remainder of this document, we use "nanogrid" to refer to those which
use price to manage supply and demand. Nanogrids bring an Internet
approach and architecture to our electricity system.
2. How Nanogrids Work
A nanogrid must have at least one load or sink of power (which could
be electricity storage) and at least one gateway to the outside.
Electricity storage may or may not be present. Electricity sources
are not part of the nanogrid, but often a source will be connected
only to a single nanogrid. Interfaces to other power entities are
through gateways within the nanogrid controller. Nanogrids implement
power distribution only and not any functional aspects of the devices
(or loads) that connect to the nanogrid. Thus, the components of a
nanogrid are a controller, loads, storage (optional), and gateways.
Figure 1 is a schematic of a nanogrid. A nanogrid manages the power
distributed to its loads. All power flows are accompanied by
communications and all communications are bi-directional.
Communication - either wired or wireless - is used to mediate local
electricity supply and demand using price, both within the nanogrid
and in exchanges across the gateways. The nanogrid controller
receives requests for power, grants or revokes them, measures or
estimates power, and sets the local price. Loads take the price into
account in deciding how to operate. Controllers negotiate with each
other across gateways to buy or sell power. Battery storage is
optional - batteries can increase the reliability and stability of a
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nanogrid.
Grid or local renewable power
|
| +---------------
| | More connections
+----------------+---------+----+ to other grids
| Nanogrid Controller +
+---+----------+-----------+----+
| | |
| | +----+----+ All connections
| | | Battery | include power and
| | +---------+ communications to
| | (optional) mediate power supply
+---+---+ +---+---+ to demand
| Load | | Load |
+-------+ +-------+
Figure 1: Conceptual diagram of a nanogrid
Controllers may resemble existing Power over Ethernet (PoE) switches,
however unlike PoE they need not be limited to one device per port.
To set the local price, the controller takes into account the price
of any utility grid electricity it has access to, as well as the
quantity and price of any local power sources. A nanogrid can
exchange power with other nanogrids or with microgrids whenever
mutually beneficial (as indicated by relative price). This enables
optimal allocation of scarce and/or expensive power among loads and
among local grids. A price will typically be a current price and
non-binding forecast of future prices, up to one day in advance.
Devices that connect to a nanogrid will ship with default price
preference functions that make sense given typical grid prices. When
a nanogrid is connected to the grid, the grid price will be a strong
influence on the local price, though local generation and storage can
dramatically change that dependency. When not grid-connected, the
local price will reflect the local supply/demand condition, the
estimated replacement cost for battery power (which may be future
grid power), and an assessment of battery capacity. Nanogrid
policies establish the local price and load policies establish the
price a given load is willing to pay.
A core principle is to separate power distribution technologies from
functional control technology. Power distribution is envisioned to
have three layers: layer 1 is power; layer 2 is power coordination;
and layer 3 is device functionality. Nanogrids implement layer 2 to
improve the efficiency and flexibility of power distribution and use
(layer 1), and isolate power distribution from device functionality
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(layer 3). Separating power coordination from functionality has
several purposes. In future usage, devices that are in the same room
or otherwise need to coordinate functionally will often be powered
differently, and devices that share a power infrastructure may not
have functional relationships. Separating power distribution into
different functional layers allows each function to evolve
separately, greatly easing and simplifying the development of new
technologies and deploying them alongside existing products.
To develop useful nanogrid technology we need standards for
communication internal to nanogrids, and for communication between
them via gateways.
Nanogrids use price to mediate their internal supply and demand with
attached loads, and to determine how power is acquired from external
grids and exchanged between nanogrids. They require energy price
information, common communications protocols and interfaces, and
standardized semantics.
3. Benefits
Nanogrids could offer many benefits, broadly including:
o Local Renewables
o Storage and Reliability
o Security, Privacy, and Reliability
o System Reliability
o Demand Response
o Smart Grid
o New Electricity Users
o Disaster Relief
o Military Applications
o Reduced Capital Costs
o Reduced Energy Use
o Mobile and Off-Grid
Nanogrids could provide smart grid benefits at the small (local)
scale, a capability we lack today; smart grid efforts only address
grid connected and large scale contexts. Nascent nanogrids are
common today in digitally managed forms (technologies including USB
and Power over Ethernet (PoE)), and unmanaged ones (vehicles,
emergency circuits, etc.). However, they all lack the ability to use
price as the core prioritization mechanism and lack the ability to
exchange power with each other; a fully functioning "managed"
nanogrid can do both. Such future nanogrids could be connected in
arbitrary and dynamic networks to each other, to microgrids, and to
the utility grid.
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Nanogrids are a new mechanism for managing power at the local level,
useful in a wide variety of applications. They particularly enable
more and better use of local generation (including intermittent
renewables) and local storage, as well as facilitate "Direct DC" -
powering loads with local renewable power without converting to and
from AC. Recent studies have estimated 5-13% electricity savings
from Direct DC in residences [DIRECTDC], and local renewables also
avoid transmission system losses. Many people value local renewable
energy more than grid power and value the reliability and certainty
of local storage and off-grid capability.
Nanogrids offer the possibility of moving to a less reliable large-
scale grid, providing increased quality and reliability locally, and
saving capital and energy in a distributed, bottom-up manner. While
the smart grid will better match supply and demand at the large
scale, we lack mechanisms to do this at small scales. Nanogrids fill
this gap. Microgrids are important and necessary, but lack near-term
potential for dramatic scale-up of deployment, lack standards-based
plug-and-play technologies, lack comprehensive visibility into
individual loads, and lack pervasive use of price. Nanogrids build
on standard semiconductor and communications technologies already
produced at mass-scale, and can be deployed incrementally and at low
capital and installation cost. This will enable them to spread
rapidly and quickly become a standard fixture in buildings.
While existing nanogrid technologies enable only relatively small
loads, there is no power limit to nanogrid loads or controllers.
While nanogrids work best with communicating loads, for legacy
devices, with one device per port, the controller can implement the
load control function itself for on/off loads, as well as variable
loads like lights and motors.
By being directly and correctly responsive to the most local
conditions of energy supply, storage, and demand, nanogrids can
provide price and other control abilities not possible with other
technologies which treat electricity distribution at a more
aggregated and abstracted level. Nanogrids are also inherently more
flexible and should be less capital-intensive than alternatives, and
provide a more nimble infrastructure for local generation and
storage.
4. Implications for EMAN
The concept of power interface in the current EMAN drafts is
consistent with the interfaces that nanogrids have, both those from
controllers to loads, and those at gateways between nanogrids. A
load could report via EMAN protocols directly, or a controller could
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report information about loads on their behalf; these are both basic
EMAN functions. The role that batteries play in nanogrids is
consistent with EMAN's treatment of them.
Nanogrids enable bi-directional exchange of power between grids;
recent versions of EMAN documents acknowledge this as a possibility
and support it (of course, the power flows in only one direction at
any given time). Two existing power distribution technologies, UPAMD
and HDBaseT, support bi-directional power flows.
Nanogrids have two characteristics that could be challenging for EMAN
to handle and deserve further consideration. The first is that grids
can be arranged in any topology and may lack a single "root" as the
utility grid generally provides. The second is that connections
among grids and connections to loads may be intermittent and dynamic.
Accommodating these does not seem contrary to the goals of EMAN, but
EMAN semantics could be defined in a way which makes doing so
difficult or impossible.
5. Other Implications
Communication internal to a nanogrid will be specific to the
particular physical layer technology. USB, for example, could add
nanogrid capability by simply extending the existing protocols it
provides for coordinating power distribution on USB links. For PoE,
it would be possible to do this with LLDP, or with some higher-layer
protocol. Communication between nanogrids will require standards for
gateways between them that cover both electrical and communications
aspects. IEEE is a likely choice for at least most of this. Some of
these may benefit from using IETF protocols, though core to the
concept of local power distribution is that it only requires
communication between immediately adjacent (electrically-connected)
grids - just one hop.
Whether or not the IETF is involved in power distribution protocols,
most of the devices in future that are on nanogrids, and the
controllers themselves, will likely also implement IETF protocols, so
that semantic consistency between the two domains would be extremely
beneficial. Just as EMAN provides visibility into device power
(measurement and control) at the network level, the IETF may want to
in future support management protocols for small (microgrid or
smaller) grids (that is, not intruding into the utility grid space
where other standards organizations are active).
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6. Terminology
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
document are to be interpreted as described in RFC 2119 [RFC2119].
7. Security Considerations
This mechanism introduces no information security vulnerabilities. A
security advantage of nanogrids is that they only need to communicate
with other grids (or power sources) to which they are directly
electrically connected. This requirement for physical connection
greatly reduces their vulnerability, and is in sharp contrast to many
grid architectures which require communication across many network
links.
8. Privacy Considerations
Nanogrid gateways need only communicate information about the price
and quantity of electricity, not about their internal structure or
electricity-consuming loads. This makes them exceptionally
protective of privacy.
9. References
9.1. Normative References
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, March 1997.
9.2. Informative References
[NG-2009] Nordman, B., "Nanogrids: Evolving our Electricity Systems
from the Bottom Up", Darnell Green Power Forum , May 2009.
[CIGRE] Marnay, C., Nordman, B., and J. Lai, "Future Roles of
Milli-, Micro-, and Nano- Grids", presented at the CIGRE
International Symposium, Bologna, Italy LBNL-4927E, 2011.
[DIRECTDC]
Garbesi, K., Vossos, V., Sanstad, A., and G. Burch,
"Optimizing Energy Savings from Direct-DC in U.S.
Residential Buildings", LBNL-5193E , 2011.
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Authors' Addresses
Bruce Nordman
Lawrence Berkeley National Laboratory
1 Cyclotron Road
Berkeley, CA 94720
USA
Email: BNordman@LBL.gov
Ken Christensen
University of South Florida
4202 East Fowler Avenue, ENB 118
Tampa, FL 33620
USA
Email: christen@csee.usf.edu
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