Reducing winter electricity charges by generating power

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Part of the responsibilities that the Christchurch City Council assumes is that of Civil Defence Emergency Management and maintaining essential services in an emergency, including water and waste water pumping. In order to ensure that minimum service levels are maintained, the Council has installed generators in the principal pumping stations and key buildings, capable of delivering 10,000 kVA.

While these embedded generators are installed primarily for emergency services the Council uses these assests to reduce electricity costs.

The embedded generators that are permanently installed at a site may be set up to be switched on automatically by a signal received from the local electricity network company, Orion. The signal indicates that electricity consumption in the city is too high and that consumers with embedded generation may use their generators to reduce the demand to lower levels.

In the graph on the right we have illustrated an approximation of electricity use as might occur on a cold winter’s morning in Christchurch. The temperature on this particular day was minus five degrees and it remained cold all day. More graphs showing additional detail and with greater accuracy are available on the Orion website.

The first indication of high demands in the city is a ripple control signal that switches off domestic hot water cylinders. If switching off the hot water cylinders does not sufficiently lower the levels of electricity use, then a signal is sent to the major customers. The brown line indicates where generation was requested from embedded generation across the city, this request is called a Control Demand Period. Once the embedded generation started to supplement the electricity supply, you can see how the blue line of actual electricity demand stays below the maximum limit set by Orion.

The query that might arise is that surely the diesel used to run the generators is more expensive than the power that we draw from the grid? Usually the answer would be yes, but during a Control Demand Period, there is a penalty of $143,30 per kVA demand , averaged over demands recorded in Control Periods over that winter. The value of using the generators far out weighs the cost of running them for the short periods requested.

Use of installed generators in Council owned properties and pumping stations has reduced the electricity account of the Christchurch City Council by over $1 million.

The benefits of the project include:

• A reduction in the running costs of buildings and services operated by the Christchurch City Council by over $1 million a year.
• Secondary use of Council assets.