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



   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.

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   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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                   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

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",
   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

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.

              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


   Ken Christensen
   University of South Florida
   4202 East Fowler Avenue, ENB 118
   Tampa, FL  33620


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