C6 - Local network management and distributed generation curtailment avoidance through domestic demand response

Summary

In the UK, renewable energy capacity is set to grow by 26 GW and this growth is critical to reach the decarbonisation objectives set out for the Net Zero ambitions. As renewable energy capacity increases, the cost of curtailment is also set to rise, with energy consumers potentially facing an estimated £1 billion per year of curtailment payments in the UK. The most cost-effective outcome would be to help grid operators manage network stress while increasing the amount of utilised renewable energy. Domestic demand is an untapped resource which could pose a potential solution. Prior work has explored the potential for households to provide reliable support to the network through aggregated energy flexibility (demand shifting, and load turn up). This paper summarises a demand shift trial conducted by SP Energy Networks (a distribution system operator) and Octopus Energy (a retailer). The trial area selected has over 3 GW of connected and contracted distributed generation against a local demand of approximately 500 MW. The cumulative firm capacity of Grid Supply Points (GSPs) in the region is around 1.8 GW. Significant proportion of generation capacity would need to be curtailed during certain network operating scenarios. As a demand shift trial, six separate events were created; these lasted for two hours between either 5:30 am – 7:30 am or 7:30 pm – 9:30 pm covering weekdays and weekends. The outcome of the six trial events showed households used more energy when requested to do so to help balance generation. Households who successfully reached the 10 % increase target were deemed to have participated in the trial and were rewarded with free electricity or with their credits doubled. A total of 20 MWh demand response was secured with a maximum turn-up per event recorded at 2.84 MW and an average turn-up per event being 1.7 MW. Participation was also higher in the evening, approximately 20 % more than in the early morning. This shows that it is key to know when the best moment is for demand shifts. In addition, survey showed that 98 % of customers were satisfied with the demand shift trial, with over 46 % wanting to participate in this initiative 5 days a week. In summary, domestic flexibility method like this trial will support the move towards Net Zero, through reducing the need for expensive curtailment payments or grid rebalancing interventions.

1. Introduction

The energy landscape is evolving with how electricity is generated, transported, distributed and used. This means that distribution system operators will need to rethink their role in order to plan, design, operate, maintain and manage the network more efficiently. This is particularly critical considering how the electrical infrastructure is key to tackling the climate emergency and realising Net Zero carbon targets.

With the UK Government targeting carbon-free power generation by 2035, within a relatively short period of time, it is forecasted that a significant proportion of transport and heating will be electrified. A five-fold increase in distributed energy resource (DER) is also anticipated in the electrical networks where the main authors work in. Coupled with the rapid rise of digitalisation, this will precipitate a revolution in how both domestic and commercial customers interact with the electricity distribution system.

These changes will result in higher distribution network utilisation, more dynamic and volatile power flows, more complexity in network operation, and a greater need for whole system coordination.

Figure 1 depicts the transformation of the present distribution networks from being passive and predictable to more dynamic and complex networks.

2. DER Penetration and growth

In the next ten years, the generation and storage capacity on the main authors’ network is likely to triple and by 2050, a five-fold increase in generation is anticipated [1].

Figure 2 shows that significant growth is expected across the two network licence areas owned by the main authors. The growth will be particularly from renewable generation. The majority of the increase in capacity is expected to come from wind, solar PV, and storage.

Given that wind and solar PV generation output is weather-dependent, it is unlikely to always occur at the same time as periods of high demand. This means that the distribution network may need intervention to accommodate wind and solar PV generation capacity. It also means that there may be a greater export of power from the distribution network up onto the transmission network, and greater transfer of power across the transmission network, at times when generation output is high, and demand is low.

To accommodate renewable generation growth, new technologies have been developed and implemented, such as Active Network Management (ANM) [2], to offer quicker and lower cost connections and accommodate renewable generation growth.

3. Curtailment and demand side flexibility

The level of renewable generation curtailed across Great Britain (GB) in 2020 due to network constraints was a total of 3.5 TWh [3] with an estimated curtailment cost of £299 million. These costs increased to £507 million in 2021, mainly due to the impact of high gas prices at the back end of 2021. Renewable generation from Scotland represented most of these curtailments and associated costs.

As renewable capacity penetration increases, the cost of curtailment is also set to increase and the consumers in Scotland and England may face an extra cost which is estimated to be over £1 billion per year through curtailment payments.

Demand Side Flexibility

Studies have found that demand-side flexibility can be used to reduce renewable generation curtailment by better matching demand with supply. The International Energy Agency (IEA) has found that demand response and storage could reduce the need for curtailment of renewables in the EU from 7 % to 1.6 % in 2040, leading to 30 MtCO2e emissions reductions in 2040 [4].

Another study from the National Renewable Energy Laboratory (NREL) shows that renewable energy curtailment in low demand-side flexibility scenarios has a rate of 6 % to 9 % compared to scenarios with high demand-side flexibility with curtailment rate of 2 % to 3 % [5].

Domestic demand is an untapped resource which could provide a potential solution. Prior work has explored the potential for households to provide reliable support to the network through aggregated energy flexibility (demand shifting, and load turn up).

4. Demand shift impact assessment

Dumfries & Galloway and Ayrshire region has over 3 GW connected and contracted DER against a local demand of around 500 MW. The cumulative firm capacity of Grid Supply Points (GSPs) in the region is around 1.8 GW due to which significant proportion of generation capacity would need to be curtailed during certain network operating scenarios. To assess the impact of the shift in domestic demand, this region was chosen for the demand shift/demand flexibility trial.

The authors (a distribution system operator and a retailer) reached out to customers in the Dumfries & Galloway and Ayrshire region and sought interest from over 8,500 domestic customers who were willing to participate in the trial. The cumulative capacity secured from the customer was 10.6 MW.

Network Modelling

The main authors have developed Engineering Net Zero (ENZ) model which comprises a full connectivity of complete LV network combined with HV and EHV network connectivity model. The ENZ Model allows for complex modelling and is a significant advancement on vectorised geographic information systems (GIS). It has been designed to operate with large data sets and provides access to full asset data including conductor types, ratings etc. It enables the tracing of the network and aggregating of demand, including the effects of demand diversity at any point in the network.

This ENZ Model which can run comprehensive programme of power flow analysis for every half hour for every forecast scenario – 175,000 iterations per network asset, was used as part of this trial. The model systematically identified the location, magnitude, and timing of every network constraint in the electricity network. An example is shown in Figure 3.

This precise knowledge meant the authors could reach out to domestic customers to enable demand side flexibility for every constraint. This identified the optimum approach for providing the required network capacity.

Impact Assessment

For the demand shift trial impact assessment, the ENZ model was used to determine network performance and number of constrained customers. The base data considered within the study area is shown below:

Network impact assessment from ENZ model-based system studies indicated that, by considering the existing network operational scenario, the anticipated 10 MW shift in customer demand does not cause any adverse impact on the network. However, with the forecasted Electric Vehicle and Heat Pump uptake by end of regulatory price control period (2028), the anticipated shift in customer demand at the time of peak would lead to overloading of 3 secondary substation transformers above the cyclic rating.

A detailed sensitivity study considering time profile based half-hourly data and 17,520 simulation was performed to determine the opportunity for demand shift considering seasonal and time of the day variations which is shown in Figure 4.

The assessments indicated that the demand shift opportunity ranges between 15-50 MW for the existing network without triggering a network constraint and the demand shift capacity erodes by 10 MW with future low carbon technology (LCT) uptake.

5. Demand shift trials

With extensive engagement with the retailer, the distribution system operator developed six separate events that lasted for two hours between either 5:30 am – 7:30 am or 7:30 pm – 9:30 pm covering weekdays and weekends.

The dates for the trial were determined based on consumer behaviour and their usual trends. For the events between 7:30 pm to 9:30 pm, the aim was to observe if the domestic customers were able to shift their usual peak consumption to later in the evening. The morning 5:30 am to 7:30 am on the weekends was chosen due to the lower demand and high generation period.

Trial Process

The trial process can be divided in three steps:

1. Pre-Event: The retailer emailed participating customers in the Dumfries & Galloway / Ayrshire area with the trial information and an opt-in request. The customers, both with and without smart meters, who accepted the opt-in request became part of the “trial group”.
    
2. Event: In each of the six events the process was as follows:

• The distribution system operator’s control room conducted assessments to identify the networks needs day-ahead of each event.
• Once confirmed that there are no constraints in the network, the distribution system operator sends an email to the retailer confirming the viability of the event.
• The retailer sent a day-ahead reminder email to all domestic customers in the trial group with their turn up target.

3. Post-Event: The retailer calculated the demand shift response as the difference between the actual and forecasted demand. Customers who successfully reached the 10 % increase target were deemed to have participated in the trial and were rewarded with free electricity / double the credit if they turned up by 100 % of their usual consumption.

6. Trial results

The outcome of the six trials indicated that domestic customers turned up a total of 20 MWh with maximum turn-up per event recorded at 2.84 MW and an average turn up per event being 1.7 MW.

The pre-trial and post-trial results are shown in Figure 5.

Figure 6 shows the percentage of consumers who increased their consumption by more than 10 % in the trials period.

As anticipated, for the evening events, the consumption was higher with a participation of around 20 % more than in the early morning events. This greater participation and in turn the almost doubling of the consumption confirmed the hypothesis that it is important to determine when the best moment is to carry out the trial event.

The detailed assessments indicated that demand shift participation and customer response were highest in the Thornhill (DG3) and Moffat (DG10) postcode areas. Figure 7 below shows the demand turn up participation from each post code area with the trial region.

Customer Survey

The retailer carried out a satisfaction survey and 71 % of the customers were happy with the participation and with over 46 % indicated that they would have been keen to participate 5 days a week.

7. Conclusion

Renewable energy capacity in the UK is set to grow by 26 GW and this growth in renewable energy generation is critical to reach the decarbonization objectives set out for the Net-Zero ambitions. As renewable capacity increases, the cost of curtailment is also set to increase and the consumers in Scotland and England may face an extra cost which is estimated to be over £1 billion per year through curtailment payments.

Studies have found that demand-side flexibility can be used to reduce renewable generation curtailment by better matching demand with supply.

Customers across Dumfries and Galloway participated in a six-week demand shift/flexibility trial. Customers were instructed to power up their usage when green energy supply was highest, households used more energy across the six two-hour trial windows. Trials concluded that a total of 20 MWh demand response was secured with maximum response per event recorded at 2.84 MW and an average turn up per even being 1.7 MW.

Households who increased their usage by more than 10% were credited back all the energy they had used during the two-hour timeframe. Those who used more than 100 % extra were credited double the amount they had used. Participating customers were rewarded with an average of £5 of free energy, with some saving up to £73.
Domestic flexibility methods like this trial will support the move towards a greener energy system – balancing the grid and bringing down the costs for everyone by reducing the need for expensive grid rebalancing interventions.

References

1. SP Energy Networks, Distribution Future Energy Scenarios (DFES), 2022
2. SP Energy Networks, RIIO-ED2 Business Plan, Annex 4A.3 - DSO Strategy, 2021
3. Lane Clark & Peacock LLP, Renewable Curtailment and the Role of Long Duration Storage, Report for DRAX, 2022
4. L. Vickery, Digitalization & Energy, International Energy Agency, 2017
5. National Renewable Energy Laboratory (NREL), Electrification Futures Study: Operational Analysis of U.S. Power Systems with Increased Electrification and Demand-Side Flexibility, 2021

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• Contact Author: K. SINGH