May 2013

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Electricity MeterAlthough the ‘smart grid’ means different things to different people, there is the general idea that it all means big change.  But the smart grid isn’t all about brand new technologies.  Managing and storing electricity from the intermittent renewables, our electric vehicles charging in the garage and our incredibly efficient appliances at the other end can just mean using what we already have in a better way.

Demand Side Management (DSM) is about managing intermittent supply with flexible demand but it sounds like something right out of a textbook – so what does it really mean?   It means that instead of making sure there is enough electricity in the system to meet your demand for kettles and fridges and phone chargers, in the future we will have to match the demand to the available supply.  That’s what DSM is all about.  It isn’t new and can be as simple as turning things off when the supply is low, when it is less windy for example.  But how simple is that, in practice?  Well, as many researchers will tell you, not very!  Being able to reduce demand on cue involves predictions of supply and demand in order to know when you need to drop demand – you can’t just ‘turn off the lights’.   So how else can we manage the levels of supply and demand?

Another aspect of DSM is to generate electricity and export it to the grid when supplies are low.  That’s where the humble diesel generator comes in.  They exist up and down the country as back up for companies in case of power cuts.  We have research being undertaken in the SEE ERL discussing the financial and technical benefits to using these generators in a more effective manner.  It can be as simple as moving pre-existing maintenance schedules to peak electricity consumption periods in the day which can help with network management and make the companies who own the generators money!   Generating more locally to the peaks in demand could assist in reducing transmission losses as well.

The principle of using what we have in a better way has to be a core principle of moving to a more sustainable society.   We can’t replace everything we have every time there is a new technological breakthrough.  You can’t knock down the 25million households in the UK because we have found a more energy efficient way to build them.  Instead we add insulation, advise residents on how to use them in the best, most ‘intelligent’ way possible.

The smart grid is about enabling consumers to use electricity more ‘intelligently’ – when there is enough supply available – as well as generating and transmitting it more ‘intelligently’ as well.  Consumers aren’t just in the home but in the commercial and industrial sectors too and here there is more scope to change electricity consumption patterns.  Some enablers may well be brand spanking new technologies but don’t underestimate the contribution of what we already have.  Let’s get teaching our old grid system some new tricks!

batteryMuch of our research within our lab has a focus on the low-voltage distribution network, the copper that runs through towns and cities across the UK and delivers energy into businesses and peoples homes. Along with other energy stakeholders talking about the use of energy storage, the distribution network operators (DNOs) are also considering how energy storage could be used to support the network at the street-level. DNOs are primarily concerned with keeping the lights on whilst avoiding exceeding operational constraints on voltage and current within their networks. If the volts vary, lights flicker; if the current gets too high, things start melting…

The impact that energy storage systems have on the voltage and current along a electricity feeder down a typical street is not immediately obvious and we have been running some simulations using an open source package OpenDSS to find out what might happen. In our relatively simple early tests, it appears that the location of the energy storage device has a big impact on the subsequent improvement of voltage and current along the feeder. For example, if you install a battery on a feeder and give it the simple instruction to charge in the middle of the night and discharge during the evening when everyone is at home cooking and watching TV with the lights on, then there is a pretty good chance you are going to reduce the peak energy that must be supplied from the grid to that feeder during that evening period –  it comes from the battery instead. Great. However, if what you are really worried about is whether the section of cable half-way down the feeder is going to fail because the houses connected just beyond that point have very high demand, then the battery ideally needs to go just beyond that point in the feeder… If you put it at the beginning of the feeder near the substation then you will reduce the power flow through the substation at peak time, but the same currents will still flow down the rest of the feeder to those houses with high demand and your high-risk section of cable will still see the same current and may fail.

Two things occur to me:

  1. In some contexts worrying about peak power through a LV substation, and increasing the associated headroom, is the right thing to do. However, from the point of view of the distribution network, and when primarily worried about voltage and current violations along a feeder, then (perhaps no surprise) it is important to think about the actual voltages and currents.
  2. The location of an energy storage system on a feeder, and in particular the location with respect to energy users with high demand or distributed generation, has a significant impact on the ability of that storage device to help the network.