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Effect of distributed energy systems on the electricity grid

Ecotricity is an ethical energy company, being both an independent generator of renewable electricity and an electricity and gas supplier to circa 40,000 domestic and business customers. The company's business has been concerned with building wind turbines and connecting them to the grid. It has built 15 wind parks across the UK, including a wind turbine on the outskirts of Cardiff at G24i (a solar panel manufacturer).

Ecotricity wants to develop a distributed energy storage system, a black box to store electricity at consumer level. Consumer demand and wind-generated energy have peaks and troughs that do not match. Currently, Ecotricity sells electricity at low value during high wind generation and buys it at high value to fill the gaps, hence peak demand is met by the dirtiest power generation and Ecotricity cannot maximise its profits. A distributed energy storage system could flatten the demand curve and sell power on demand, enabling better value for Ecotricity. Flattening the grid/consumer demand profile would reduce need for dirty power capacity, furthering Ecotricity's ethical stance and supporting the UK's green agenda, possibly even helping it cope with the loss of the 8GW of coal red power stations that were earmarked for closure by 2015.

Ecotricity will seek the approval of the industry regulator and others before introducing energy exporting black boxes into the market (and into customer's homes), and is currently carrying out a feasibility study into the idea as a whole. To assist in doing all of these, a number of questions need to be answered. Assuming technology is available to store and then distribute energy locally, what is the effect on the stability of the National Grid of introducing hundreds of thousands of black box energy stores? The AC output from all the large generators currently has to be synchronised anyway, in terms of peak voltage, frequency and phase angle. Are the current standards (G83) for Grid Tied Inverters (that convert DC into AC) sufficient to ensure the introduction of an unprecedented number of energy stores or micro generators onto the grid will not affect its stability?


Problem presented by:
James Parrott (Ecotricity)


Study Group contributors:

Chris Budd (University of Bristol)

Paul Dellar (University of Oxford)

Christopher Hodge (University of Bristol)

Hossein Hassani (Cardi ff University)

Yi-Ming Lai (University of Oxford)

Matthew Lettington, (Cardi ff University)

Sean Lip (University of Cambridge)

Nikolai Leonenko (University of Cardi )

John Ockendon (University of Oxford)

Colin Please (University of Southampton)

Matthew Weber (University of Oxford)

David Wood (University of Warwick)

David Allwright (Industrial Mathematics KTN)


Related resources:

Problem brief

Initial presentation

Final presentation

Final report

Other energy projects

Other Study Group projects



Archived Discussion

Post by Industrial Mathematics KTN on April 4, 2011 at 4:21pm
Here is the initial presentation from Ecotricity
Attachments: Ecotricity Energy Storage Problem.pdf, 86 KB

Reply by Melvin Brown on April 5, 2011 at 11:05am
So we are looking to model the connection of household battery storage systems to the local grid. Our present aim is develop an aggregate model of number of households and start to look stability and feedback issues are, if any. Since the battery output is DC we need an inverter to convert to AC on the local network. We are working in complex power-flow notation, (ie real P and reactive power Q), but we need a SIMPLE inverter model to suit this modelling need, and which captures the input -output mapping in the P,Q space. This is proving tricky to find, and is holding us up at the present. The are quite complex models out there, but a simple model is required. If anyone has a good reference for such a model, please would you post here... Thanks.

Reply by Melvin Brown on April 5, 2011 at 1:28pm
A simple inverter model has been found. See

Reply by Dave Wood on April 7, 2011 at 9:34am
Don't know if this is of any use for the synchronisation problem: Renato et. al. "Synchronisation of pulse coupled biological oscillators" SIAM J. Applied Maths 50, 1645-1662, 1992... mentione it to DA yesterday.

Reply by Paul Dellar on April 7, 2011 at 11:41am
Along the same lines, there's the Fermi-Pasta-Ulam work on a lattice of nonlinear oscillators coupled by nearest-neighbour interactions, or more recent work on coupled Lorenz systems. Both show complicated quasi-periodic behaviour.
N. J. Balmforth, C. Pasquero & A. Provenzala (2000) The Lorenz–Fermi–Pasta–Ulam experiment, Physica D 138, 1-43 doi:10.1016/S0167-2789(99)00193-1

Reply by Dave Wood on April 7, 2011 at 5:48pm
Leech heart paper attached.
Essentially rings of coupled oscillators have classic solutions of synchronised or phase locked but out by equal phases around the ring (eg three oscillators at phases 0, 2pi/3 and 4pi/3. Periodically forcing then can lock them into the same frequency as the forcing term.
Think of individual batteries as oscillators, coupled them in rings and force with signal from generator? Need to be careful synchronise rather than waves of phase differences. Can provide better info for report!
Attachments: leech heart.pdf, 970 KB

Reply by Melvin Brown on June 14, 2011 at 12:12pm
Draft report is circulating participants for comment, and presently with Chris Budd.

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