In addition to the technical lessons learned, the project team expects to draw conclusions regarding the changes necessary to the current regulatory regime that will enable the optimum usage of energy storage in unbundled power systems.

Venteea Project Shows a Fair Wind for Distribution Network Energy Storage

Michael Lippert | Saft

 

Venteea is France’s major smart grid field demonstration project to develop the best approach for the economic and technically efficient integration of renewable energy sources into rural medium voltage (MV) distribution networks. Among the various technologies and grid management systems under evaluation is a megawatt-scale lithium-ion (Li-ion) battery system commissioned in 2015.  Michael Lippert of Saft describes the multi-service control approach designed for this system and provides some operational feedback from its first eight months of operation.

The Venteea project, running over three and a half years, is led by a consortium of eight industrial and two academic partners (ERDF, Saft, Schneider Electric, General Electric, EDF R&D, Boralex, RTE et Made), supported by the French Agency for the Environment and Energy Management (ADEME).

Venteea’s goal is to validate the key solutions that will ensure reliable/efficient operation of future MV distribution systems and allow the integration of a larger proportion of renewables at the best possible cost. A distribution grid with a high penetration of wind generation was selected to test industrial pilots of new technologies and control approaches that include primary substation digital management, real-time network state estimation, a Volt VAR Control scheme and a Distributed Energy Storage System (DESS).

The network selected for the Venteea project is located in Chervey, in the Champagne-Ardenne, which is France’s main region for wind generation with over 15 percent of the country’s installed base. This network has remained in commercial operation throughout the project and comprises a 20 MVA primary substation and six 20 kV feeders. It serves 3,200 customers and hosts two wind farms rated at 6 and 12 MW.

The storage element of Venteea has focused on the design, construction and operation of a 2 MW / 1.3 MWh battery system. The main aim of the project team is to understand the potential of DESS to facilitate the integration of renewables and enhance the operation of power systems in the future.

 

This covers two key objectives:

1 - to evaluate the ability of the DESS to provide a multitude of services as well as its operational performances under various conditions

2 - to assess the practical feasibility of a multi-service/multi-stakeholder scheme to improve the business case for storage through the addition of several revenue streams. Some existing regulatory barriers in the French unbundled power system (e.g ownership) were relaxed intentionally within the framework of the project.

 

DESS components and system architecture

The Venteea DESS is shown in Figure 1, while its complete architecture is presented in Figure 2. It consists of a 1.3 MWh Li-ion battery connected to the MV grid through a 2.16 MVA Power Conversion System (PCS). The battery comprises two Saft Intensium® Max IM+20M systems housed in 20-foot containers, each containing 12 strings of 28 Synerion® 24M modules. The Schneider Electric PCS comprises two 20-foot ES Box RT 1080 containers, each containing two 540 kVA full 4-quadrant inverters and a 3-winding MV/LV transformer.

A - Saft Storage Solution
B - Schneider ES Box
C - 2 wind farms connecting point
D – Storage connecting point

Figure 1: the DESS designed, built and operated within the Venteea framework

 

Figure 2: architecture of the Venteea installation

 

The storage unit is located in the immediate vicinity of the points of interconnection of the two wind farms operated by Boralex.

To demonstrate the potential of multi-service operation, the DESS can be connected either to the MV feeder hosting the 12 MW wind farm or to the MV feeder hosting the 6 MW wind farm and customers. The required switchgear and the MV/LV transformer powering the storage unit auxiliaries are located in a dedicated MV substation. The storage unit was commissioned in the second half of 2015 and this article reports on 8 months of operation up to March 2016.

 

The need for multi-service DESS operation

Energy storage assets can provide various services such as management of voltage and current constraints in distribution grids as well as participation in power system security and reliability, etc.

However, when considered individually, most of these services do not:

1 – mobilize continuously 100 percent of the power/energy capacities of a DESS (so there is scope for improved utilization)

2 - generate sufficient revenue to achieve profitability (hence the economic need to improve utilization.

 

For these reasons the project is investigating the combination of services, i.e. the use of storage units for multiple functions so that they can be operated at their full potential and harvest more income from one or more stakeholders.

Field deployment of this concept is already within the reach of vertically integrated utilities but is more challenging in an unbundled power system, where its feasibility remains unproven. This is one of the key focuses of Venteea’s storage element.

Table 1 shows the DESS services tested within the framework of the project. For the optimum analysis of storage benefits and their aggregation, these services concern three stakeholders: TSO (Transmission System Operator), DSO (Distribution Service Operator) and DG (Distributed Generation) operator.

 

Stakeholder

Service

TSO

TSO1 - Participation in frequency control

DSO

DSO1 - Distribution peak sheaving

 

DSO2 - Local voltage control

 

DSO3 - Contingency grid support

 

DSO5 - Reactive power support

 

DSO9 - TSO fees optimization

DG operator

DG1 - Support to the provision of ancillary services

 

DG2 - Smoothing of short-term output fluctuations

 

DG3 - Generation peak shaving

 

DG4 - Energy time shifting

 

DG5 - Capacity firming

DESS operator

ARB - Time of use energy arbitrage

Table 1: overview of the storage services tested during the first 8 months of operation


Figure 2 shows the dedicated control system comprising two complementary levels developed to enable multi-service operation:

 

The Storage Scheduler is a remote supervision layer that plans the DESS services in advance to maximize profitability while satisfying both requests from stakeholders and a set of constraints (power/energy capabilities or the plant, current/voltage limits of the network, etc.). The Storage Scheduler is run every 30 minutes to:

1 - estimate the headroom available in the grid to operate the DESS using load and generation forecasts

2 - calculate an optimized plan for the next 36 hours.

These functions provide the required level of visibility for the next day of operation to interact with the stakeholders/ markets, and they also enable intraday adjustments if required to limit the impact of any deviation from the initial program. The program set by the Storage Scheduler can be manually overridden if needed - this was used largely used over the first phase of the tests to send custom schedules to the battery system.

The Storage Master Controller provides local supervision of storage services that:

1 - autonomously execute the optimized schedule received from the Storage Scheduler

2 - take appropriate actions if a contingency occurs.

It features a library of control algorithms developed within the Venteea framework. These manage the provision of each service in real-time based on set points included in the optimized schedule (such as the primary reserve allocated to the DESS at a given time) and local variables related to the grid (such as the measured frequency) or to the DESS itself (such as its State of Charge, SOC).

 

Results from the first 8 months of operation

Test overview

In the first 8 months of operation the storage unit spent a total 222 days (92.5 percent) in perfect working order or with only minor issues that had no impact on operation. Most of the downtime occurred shortly after commissioning, including upgrades of some control routines and the replacement of small parts. From then on, the unit achieved a satisfactory level of availability for a field demonstration featuring new generation storage systems that were the first of their kind. - only one day of complete outage was recorded from the end of October 2015.

The DESS has drawn/injected 310/226 MWh and 326/63 MWh from/to the grid - the battery has performed 170 equivalent full cycles. Table 2 presents some statistics regarding the modes of operation activated over the whole time period. As planned from the beginning of the tests, the Storage Scheduler was active - to gain experience - but it was bypassed intentionally during the first phase, with the program of services established manually ahead of time according to the testing priorities of the project team. This phase aimed mainly to assess the provision of all the potential services available from the storage unit, either individually or combined.

 

Mode of operation

Cumulated activation time as on March 06 2016

Days with activation

Total activation time

TSO1

83 days

1384 hours

DSO2

111 days

1924 hours

DG1

55 days

944 hours

DG2

58 days

902 hours

DG3

19 days

108 hours

DG5

7 days

38 hours

Table 2: cumulated activation time of some of the services tested during the first 8 months operation

 

Key performance indicators were defined and finely monitored to track both the behavior of the DESS (such as efficiency) and the quality of the delivered service (such as meeting grid code requirements).

The second phase of the tests started at the beginning of 2016 with a progressive increase in the time spent by the DESS in full self-scheduling mode. A ramp-up trajectory has been defined in terms of the number of services handled by the Storage Scheduler and the complexity of the multi-service/multi-stakeholder scenarios under consideration.

 

Insights into the DESS operation.

Participation in primary frequency control.

In primary frequency control mode the storage unit is controlled to respond proportionally to any frequency deviation from 50 Hz, without any intentional deadband. In a typical example, the Storage Master Controller was set so that the battery system delivered its full assigned reserve of 2 MW for a deviation of 200 mHz (+2 MW at 49.8 Hz and -2 MW at 50.2 Hz). In addition to the frequency response, active SOC control ensured high availability of the service.

The quality of the service supplied by the Venteea DESS is verified according to the specifications defined in the French "Régles services systeme " (system services rules).

To date, the 1,400 hours of operation achieved has confirmed the ability of the battery unit to participate in primary frequency control.

A question that remains open at this stage is the risk for power system security and reliability when using limited energy resources to provide frequency control services. Specific tests are currently being carried out under the supervision of RTE to address this.

 

Generation peak shaving.

Generation peak shaving is carried out according to load and generation forecasts available. In typical cases where a risk of constraint on the distribution grid was anticipated the SOC of the DESS was adjusted to 10 percent. It was then dispatched to shave any peak above the calculated limit of 10 MW. The quality of the provision of this service is quantified by the proportion of power peaks above the assigned limit that can effectively be shaved - this strongly depends on the accuracy of the generation forecasts.

 

Participation in local voltage control.

In addition to the services detailed above, for local voltage control the Storage Master Controller is set so that the reactive power of the storage unit responds to the voltage variations according to the desired Q(U) characteristics. In a typical case the Q(U) control would be utilized up to its allocated power of 1 Mvar during the high wind period at night and then remain activated, but not utilized in real-time, for the rest of the day. The performance of the DESS for this service is quantified by the proportion of time spent within its preset tolerance range (usually > 95 percent).
 

Summary

The 2 MW storage unit designed, built and commissioned within the framework of the Venteea project had been in operation for 8 months at the time of writing. So far, the first phase of the tests has made it possible to demonstrate the ability of the DESS to:

  1. provide all the targeted services, individually or combined

  2. to handle complex programs established ahead of real-time with up to 48 changes daily in the mix of activated modes of operation.

The second phase, which started at the beginning of 2016, focuses on the assessment of the self-scheduling process included in the Storage Scheduler to ensure optimal multi-service/multi-stakeholder operation. In addition to the technical lessons learned, the project team expects to draw conclusions regarding the changes necessary to the current regulatory regime that will enable the optimum usage of energy storage in unbundled power systems.

 

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