Load Management

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MICRO CHP
MICRO CHP
the big picture
By Jeremy Harrison
Photo book

 

Electrical Storage | Thermal Storage | Load Management | Metering

Management of electrical loads has been practiced in domestic applications for decades.  The most familiar application is the use of electric storage heaters to shift heating load from daytime periods when electricity is expensive, to night time (or other off-peak period) when electricity is relatively cheap.  The same concept can be applied to other loads, and washing machines, for example, often have time switches on the control panel, in order to delay operation of the appliance until a suitable off peak period.  However, the ability to match loads to the period of  micro CHP generation is significantly more complex as it operates dynamically to meet heating requirements.  In the case of storage heaters, electricity price depends on time of consumption, whereas with micro CHP, value depends on whether generated electricity can be used within the home (where it avoids purchase at a high price) or whether it is exported to the network (where it attracts a relatively low price).  Less than half the cost of electricity supplied to the home is for the energy content, the remainder being transport and other system costs.  Suppliers cannot, therefore, logically offer to purchase power at the same price they sell it.  Early studies showed that the value of micro CHP generation could be enhanced by load matching, although in practice utilisation can still only be increased by about 10% to 80%, however good the control system for a typical home.  Indeed the level of utilisation was, not surprisingly, found to be more influenced by the amount of power used in the home.  It is questionable whether the cost and complexity, and even lifestyle impacts of such controls is worth the enhanced generation value.

From a suppliers point of view, however, the ability to understand, influence and possibly control demand and generation within the home is of significant value. Furthermore, both generators and network operators can benefit from the ability to manage loads and generation embedded within the distribution networks to optimise utilisation, and hence cost recovery, of their asset investments.

 LOAD MANAGEMENT  GENERATION MANAGEMENT

Electricity was initially supplied on an unrestricted basis, with no account taken of the time of day.  In the 1960's, however, the high daytime demands which resulted in redundant capacity during the night was addressed by encouraging consumers to adjust their demand to take advantage of reduced night-time tariffs.  These tariffs were provided in conjunction with space and water heating devices which converted electricity into heat at night, which was then released during the day time and when hot water was required.  Initially this was achieved using simple clocks, but later evolved using radio tele-switching both to allow remote adjustment of start/stop periods and to stagger the changeover to avoid short term spikes in demand.  These tariffs remain in place in many EU countries; in the UK the most familiar is "Economy 7" which provides 7 hours of cheap electricity normally between 23.00 and 07.00.

In response to a growing awareness of the further potential for load shifting in the early 1990's, a consortium of UK electricity companies developed and trialled a sophisticated system (CELECT acronym for "Control Electric") which integrated day ahead CRM (Cost Reflective Messages), day ahead temperature forecasts, customer programmed heating demand and a self learning algorithm which predicted the thermal response of the home to heat input.  The customer programmed the desired temperatures for each zone (or room) throughout the day and the programmer then integrated the relevant inputs to provide the desired temperatures at the lowest possible cost, using a combination of storage and direct electric heaters.

In 1996, an EU funded project (ETHOS) took the concept a stage further by including other domestic appliances into the load management system and a number of manufacturers included the necessary functionality within their appliances should a common standard be agreed at some future date.

The UK based TAHI project incorporates load management and the potential for generation management, but as yet there is no common standard and the need for each appliance to contain compatible intelligence is something of a barrier to implementation.  The EU funded TAHEA consortium continues to develop the concept on a European scale.

Given the increasing provision of electricity from intermittent renewable generators such as wind and solar, there is naturally a corresponding demand to align demand with available supply.  Thus considerable effort continues to be expended in this area under the guise of "smart homes", although the limited amount of electrical loads which can be effectively shifted is of questionable benefit.

Rather than attempting to modify the behaviour of each individual appliance within the home (or even of the consumers themselves), it is possible and arguably preferable to modify domestic generation patterns, either to better match the consumers' pattern, or to modify the diversified demand profile of a number of conterminous consumers.

Clearly this can only be achieved if some form of energy storage is applied, most likely as thermal inertia of the system or with a dedicated thermal store.  The section on thermal storage deals with products for individual homes, but an EU funded project using the Vaillant fuel cell in conjunction with a substantial thermal store and supplementary boiler serving a small apartment block, operated successfully as a Virtual Power Plant (VPP) as early as 2003.  Since then there have been a number of pilot VPP projects although generally using somewhat larger generators.

However, it is clear that the ability to influence the operation of a single generator with a capacity of say 1kWe operating for several hours every day is significantly easier and more effective than attempting to implement load management of numerous diverse and lower energy impact appliances, particularly when each of those appliances needs to be a "smart" appliance, requiring the replacement of all domestic appliances in one go.

Of course, once a suitable system has been installed to provide generation management, it is a relatively simple step to address the load management.  One such system which is capable of doing just that is the HOMA product which has been demonstrated by a number of European utilities including E.ON in conjunction with engine and fuel based micro CHP systems in UK and Germany.

For further details on the ongoing (2014) European project click here.

Page update 22nd December 2013
 

MICRO CHP
MICRO CHP
the big picture
By Jeremy Harrison
Photo book

 

 

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This site was (partially) last updated on 12th August 2017 Jeremy Harrison