Wednesday, 30 October 2019

Upgrading our electricity distribution networks.

Electricity North West plans to reduce the voltage of their customers' electricity supply which will reduce bills by up to £60/year - and be hardly noticeable except it will take a little longer to boil the kettle [1]. In this post I take a look at the Smart Street trial they have run to test out their concept [2]. As well as energy savings a key purpose of the trial was to evaluate new voltage regulation equipment that could delay the need to upgrade the distribution network. Reducing the voltage reduces the delivered energy and peak load, so the existing infrastructure can cope for longer.

Savings on customers bills are welcome but even more importantly (for climate change) we need to be able to install more distributed generation and run bigger loads due to heat pumps and electric vehicles. How much will that cost? A case study on low carbon heating in a town in Scotland has some answers to that [3]. The cost of the network was much less than I expected - much less than the heat pumps anyway.

Reducing the voltage brings real energy savings - 5% to 8%.
Reducing the voltage to save energy is called Conservation Voltage Reduction (CVR) The effect varies between appliances. In some there is an overall energy saving, others not.
  • Things with a motor (such as the compressor in your fridge or vacuum cleaner), may run more efficiently at lower power, especially if they have been designed for European countries where the voltage is 220V. This is a genuine saving.
  • Most electronic devices such as TVs and computer equipment are constant power devices - they will take more current to offset the lower voltage and there will be no savings.
  • Lighting may be less bright - old fashioned incandescent lights definitely will be. LEDs and CFLs are may or may not be constant power [4].
  • Heating devices such as your kettle and the heater in your washing machine will take longer to get to the required temperature but there will be no overall energy savings.
A study on the impact of CVR to 220V on domestic homes conducted in 2011 found savings of around 5% [5]. However, there have been substantial changes in usage patterns since then - more energy efficient lighting, lower temperature washes and more efficient appliances in general. Some of these changes will increase and some decrease potential savings. As it turns out the Smart Street project did even better, with energy savings in the region of 5% to 8%. There were also savings from reducing losses on the network.

Typical bill savings were £30-£40 but up to £70/year.
According to the report, the first objective of the Smart Street project was to to reduce customers' energy consumption and bills without noticeable adverse effects on their experience. Overall bill savings were found to be £30-£40 /year but up to £70 in some cases. The supply company says there were cost savings from 'market imports, balancing services, transmission charges, distribution charges and taxes'.

Improved support for distributed generation and less need for upgrading the copper.
The next objective is about delaying upgrading capacity and integrating low carbon technology. It is to show that 'The Smart Street method is faster to apply than traditional reinforcement, supports accelerated LCT [low carbon technology] connection and reduces network reinforcement costs'. Low carbon tech is a problem because it massively increases (electric heating, charging electric vehicles) or decreases (solar panels) load. High loads decrease voltage and solar panels increase it. Solar panels on a sunny day can generate enough to get power flowing in reverse, back into the substation! The voltage management equipment used by Electricity North West was designed to smooth out these issues, controlling both under-voltage and over-voltage.

Electricity North West is not the only network operator exploring interesting ways to eke more out of our existing supply network. Installing network storage at key points is another approach, and also demand side response, where customers turn down demand on request. (Individual household customers are too small to be useful but there are savings to be made if aggregators can recruit enough in the right places where the network is constrained.)

Electric heating could triple peak demand or more.
Increase in electricity demand due to installing
heat pumps in a case study town in Scotland [3]
However, reducing our GHG emissions is going to require many households to switch over to electric heating. An 8% power saving due to voltage management is as nothing compared to a three or four times increase due to heat pumps. How are we going to manage that? We are going to need more electricity substations and more connections, splitting existing supply links and loops so that each cable supplies fewer customers.

Cost of upgrading the network could be just £600/person.
The costs for this are likely to be substantial but not eye watering. A case study (funded by BEIS) comparing costs for alternative low carbon solutions for an example town in Scotland (Cowdenbeath) showed that peak demand would increase from about 10 MW to about 27 MW (reading off the chart right). However, two thirds of the increased demand could be met with relatively minor enhancements to the low voltage network. After that however, the increase required a new primary substation and increased cabling and the overall cost would be £8.4M. This is for a town with 14,000 people so about £600/person. This is considerably less than the cost of the actual heat pumps.
This chart shows how the cost of upgrading the distribution network (Y-axis) increases with the increase in peak demand (X-axis). There is a big jump in cost with the first new primary substation (PSS). Subsequent ones cost less. The final large jump is for a new grid supply point (GSP) which is a new connection to the transmission system. Chart from [3]

A hybrid heat pump/gas solution is cheaper but the carbon savings are less.

In common with other studies, the Cowdenbeath study found that a hybrid heat pumps solution (90% heat pump, 10% gas) was cheaper. The grid required far less reinforcement (costs down by 40%) but the main savings were from the smaller heat pump. However there were less carbon savings because of the methane gas still being used.

Should we pay for peak demand on the network, as business customers do?
The cost of upgrading the distribution network was less than I had feared but there is still the question of how it should be funded. We pay for the network via our electricity bills. Currently the average household charge for maintaining the network is £86/year [6]. If you install a heat pump or an EV charging point your electricity bill will increase and your network charge with it. It will take a few years for your payment increase to pay for the upgrade.

However, with smart meters it is possible to measure your peak demand as well as the overall demand. You have some choice about this - for example you can choose how fast to charge you electric vehicle. Also heat pumps run most efficiently when run steadily all the time; configuring them this way also reduces peak demand. Since the overall network costs are related to peak demand would it makes sense for your network charges to be based on this too (as they are already for larger businesses? Or you could opt to allow remote management of your system by an aggregator so they can turn down your power usage when the network is close to capacity.

[1] Wait eight seconds longer for your kettle – and cut your carbon bill (Guardian) Oct 2019

[2] Smart Streets Project Closedown Report (Electricity North West) 2019


[4] Impacts of Conservation Voltage Reduction on Customer Power Quality in Future Networks (Mcorn et al, Conference: 51st Int. Universities' Power Engineering Conference (UPEC)At: Coimbra, Portugal) 2016

[5] Energy Saving Trial Report for the VPhase VX1 Domestic Voltage Optimisation Device (OFGEM) 2011

[6] UK Power Network Annual Review 2017/2018 (UKPN) 2019

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