Metering

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

 

Electrical Storage | Thermal Storage | Load Management | Metering

Metering, although initially appearing to be a minor issue, is turning out to be one of the most complex issues within the UK competitive market.  The metering and settlement infrastructure has evolved to meet the needs of traditional energy flows from central generating plant down to domestic consumers who have always been "demand only".  Competition in the UK started with large industrial customers and then progressed to the 100kWe (peak demand) sector requiring the use of HH (Half Hourly) metering to match the consumption profile of customers against the variable wholesale cost of the electricity they consumed.  The infrastructure developed to meet this market included up to 50,000 potential customers with relatively high transaction costs appropriate to the high value of such customers.  Unfortunately, the need to extend HH trading to 23 million individual domestic customers is not compatible with such a system and the industry faces considerable challenges in resolving the issue of attributing value in the supply chain without incurring prohibitive transaction costs.
NON HALF HOURLY  HALF HOURLY  ADVANCED METERING  COMMUNICATIONS

Traditional domestic meters simply record cumulative kWh totals and have no facility to record consumption within a specific period.  Even two-rate meters, such as those used with Economy 7 tariffs, simply record cumulative totals during the on-peak and off-peak periods respectively.

In 2003, the UK implemented a standard known as P81, which permits the use of Non Half Hourly (NHH) metering for export as well as import, avoiding the high cost of recording, analysing and "settling" kWh for each of the 17520 HH periods each year.

In order to correlate the consumption of domestic consumers using NHH meters, it is necessary to apply "settlement profiles".  These make statistical  assumptions based on historical load research and, in most instances bear no relation to the actual consumption of any given household.

Currently, the assumed profile for export comprises two "chunks", one two hour period in the early morning and another for five hours in the evening, based on the assumption that all micro CHP generation will occur within the standard seven hour daily heating period, itself an assumption of a typical household's heating pattern.  Although it is recognised that this is a crude assumption, it is considered accurate enough for the very small number of systems currently in operation. 

Extensive trials undertaken by BEAMA for the UK government concluded that such deemed profiles were inappropriate for microgeneration given the widely varying nature of the technologies.

BEAMA project

As outlined above, Half Hourly (HH) meters are used in commercial installations where the significant amounts of kWh exported in each half hour period, justifies the cost of such metering and the underlying settlement process.

In many cases these are provided with Advanced Meter Reading (AMR)functionality to facilitate readings and minimise errors.

These are available from numerous manufacturers but are not included here as the related infrastructure is not currently considered suitable for micro CHP.

HH metering is, however, essential to capture the true value of a specific microgeneration installation; it allows consumption to be accurately attributed to the relevant cost period and hence optimises the value of each customer.  It also incentivises operation of the microgeneration system to deliver optimum value to either the end user or the energy system as a whole.

For many years, the cost and effectiveness of manually reading meters has been under scrutiny. There are clear advantages to being able to remotely access meters, including accurate start/end reads with change of tenancy and change of supply and to avoid the need to estimate readings when access to the property cannot be obtained.

However, within the current UK market, the structure of the industry acts as a disincentive to the implementation of advanced metering.  The meters are owned by the metering company which charges a daily rental to the energy supplier.  If a customer changes supplier (which can in theory take place every 28 days!), the new supplier may not wish to pay the higher rental for an advanced meter, particularly if they do not support the related infrastructure.  The meter company then has a stranded asset with no means of recovering the investment.

Regardless of this, meters are being developed which can provide a higher level of service.  Indeed, some meters are being developed which provide the functionality not only to remotely read meters, but also to communicate additional information.

However, the current UK roll out of "smart meters" is anything but; it simply provides the minimum functionality of remotely accessible aggregate kWh readings.

Fundamental to the control and metering of domestic consumers with micro CHP (or any other form of generation) is the ability to receive and in some cases send information.

A number of options for communication within the home are being considered including:

1) Power Line Carrier (PLC) which attaches a carrier signal to  the mains cabling and hence has connectivity to all electrical appliances without the need for additional wiring.  This is probably the simplest and cheapest system, perfectly adequate for the bandwidth required for load management.

2) LAN

3) Wireless

From the home to the central control, the options include:

1) PLC up to a sub-station from whence the data is transferred to radio. This has the disadvantage of requiring high penetration levels to achieve economies of scale and although successful in countries with monopolistic (Italy, France) or mandated (Sweden) common infrastructure, is unsuitable for the UK.

2) GSM and GPRS allow the implementation of incremental capacity, but currently suffer from very high operational costs, although there is no reason that the structure of charges could not be changed to reflect the low bandwidth and use of off-peak communication network capacity.

3) Fixed (telephone) using PSTN or broadband.

Page update 23rd December 2013
 

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

 

 

Contact : info@microchap.info

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