Sweden’s target for the proportion of electrical energy from renewable sources in 2020 is 49%, according to the European Union’s targets for inclusive growth. Therefore, the production of energy from renewable sources needs to increase in order to achieve this target.
The existing networks have been designed for central, adjustable electricity production, but there is now a need to modernize the grid to handle energy generated from wind and solar power resources. The existing energy system in Gotland is similar to a future energy system, which makes it possible to upscale the system.
Gotland, the largest island in the Baltic Sea, is located some 90 km (56 miles) from mainland Sweden. The island has a population of almost 60,000, of whom some 20,000 live in Visby. Because of the favorable weather conditions, Gotland has a large and growing number of renewable energy sources, the majority being from wind power but more recently from photovoltaic (PV) installations. During periods of strong winds and low energy consumption on the island, the surplus energy is exported from Gotland to mainland Sweden via the 150-kV, 260-MW direct-current subsea interconnector.
Limits and Solutions
In addition to all the usual challenges linked to volatile energy production and variable energy consumption, reversed polarity of the high-voltage direct-current (HVDC) interconnector results in vulnerable system operational conditions. The current situation is that Gotlands Energi AB (GEAB), the distribution system operator, despite having a keen interest to establish new wind power plants on the island, has been forced to limit the installed capacity on the island in order to ensure the power quality and reliability is not adversely affected. The limit imposed is based on a risk analysis that considered maximum energy production and minimum energy consumption on the island. Hence, the capacity of renewable energy sources is currently limited to 195 MW. A more conventional solution to this problem is the installation of a new high-voltage interconnector between Gotland and Sweden — a project that requires a huge investment that is already in the planning stage.
Therefore, a smart grid project is planned for Gotland that is designed to achieve a small but not insignificant increase in the capacity of the renewable energy sources. The project will take advantage of the available information technology, and in comparison to a new high-voltage link, it will be executed on a limited budget.
Smart Grid Gotland
Smart Grid Gotland is a full-scale research, development and demonstration pilot project designed to upgrade an existing rural distribution network in a deregulated market to a modern smart grid. The project has three main goals. The first goal is to provide a cost-efficient increase in the capacity of the renewable power connected to the existing distribution network by use of load shifting from active customers and battery-based energy storage. The second goal is to demonstrate that new technologies can improve the power quality and reliability for the customers supplied by a rural network with large quantities of installed wind power. And finally, it will create customer opportunities to participate in demand side management to shift load from peak demand hours to peak energy production hours.
Furthermore, these goals have five measurable objectives:
• Increase the installed wind power capacity from 195 MW by 5 MW by use of load shift from active customers and battery-based energy storage
• Reduce by 20% the system average interruption duration index (SAIDI) on the distribution network between Källunge and Bäcks substations
• Obtain the active participation of 30 industrial companies
• Attract 2000 residential customers to participate in a market test under market-driven conditions
• Ensure active customer participation contributes a load shift of ±10%.
The project is a cooperation between GEAB, Vattenfall, ABB, Schneider Electric, Svenska Kraftnät (the Swedish transmission system operator) and KTH (Royal Institute of Technology). This project is partly funded by the Swedish Energy Agency. The project has an estimated cost of 25 million euros (US$32 million).
Main Activities on Gotland
The two main activities are linked to the existing 10-kV distribution network between Källunge and Bäcks 70/10-kV substations. The network updating now includes the use of smart supervisory control and data acquisition (SCADA) systems installed in 2014 to operate the updated smart grid between the two substations. The research SCADA system is identical to the existing SCADA system, but it is equipped with some additional high-end functions — such as demand response management system — installed for network operations, experiments and studies in a safe environment.
The Market Test is referred to as “Smart Customer Gotland” to separate it from other activities in the project. Planned to be conducted over the whole island, it is different from the rest of the project as it is not restricted to the test area. The setup differs slightly between residential customers and businesses, but the initial idea was to attract customers to participate on the electricity spot market by offering a technical system for control of (electric) heating systems and a specially designed price signal.
The technical system is based on a combination of existing products, which was adjusted to enable control of heating systems (water boilers, electric heating and heat pumps) according to a price signal. The price signal comprises the spot market price on electricity and a time tariff in combination with a wind component (cheaper during windy days). The installation also includes a temperature sensor with override functionality for personal safety. Smart Customer Gotland started in October 2013.
Wind Power Integration
The general idea is to use the load shift from household customers and industry (the market test) to limit the number of situations with vulnerable system operational conditions, thus justifying an increase in hosting capacity. Besides the use of a price signal to incite a load shift, the project examines the need for additional systems — such as battery-based energy storage, ancillary services for voltage and frequency control (such as synthetic inertia), and other market models — needed to adjust the consumption to a volatile energy production.
Other solutions that could facilitate integration of large inputs of wind power, such as standardized connection and communication across all system voltage levels, although theoretical, are studied within this project.
The Smart Grid Gotland PV installation is located just east of Visby, comprising an area of 1000 sq m (10,760 sq ft) for the ground-based PV plant. The complex consists of three single-phase installations each of 3.2 kW and one three-phase installation that consists of two installations that each have a rating of 2.5 kW. The single-phase installation represents a house-roof installation while the three-phase installation symbolizes the PV installation on a barn roof.
The plant is connected to GEAB’s distribution network with the objective to investigate and verify how micro energy production affects the power quality, and also to determine how the new smart meter, which is installed in the test area, can be used to identify and preclude power-quality problems. The results emerging from this installation will provide an important input into how GEAB can use PV installations to reinforce the network and improve network reliability on Gotland. The PV installation that has now been in operation since October 2013 will be dismantled at the end of the project.
Phase 2 of the project, which includes updating the distribution substations and installing sectionalizers and sensors on the overhead line networks to create a self-healing grid, was initiated in winter 2015/2016.
Additional Project Objectives
This project consists of nine different sub-projects. Three of the sub-projects are associated with the specific objectives of wind power integration, power quality and the market test. The other six sub-projects consist of the technical installations required to establish a smart grid, namely smart meters, smart substations and rural networks, energy storage, smart SCADA and ICT and market installation.
Smart Grid Gotland is a research, development, demonstration and pilot project with the overall ambition of upgrading an existing distribution system into a modern smart grid. This will increase the hosting capacity of renewable power generation and it will improve power quality. Finally, it will enable active participation on the electricity market for household and enterprise customers.
The ambition, to upgrade an existing grid, addresses challenges that are especially interesting and demanding for an operator of mature distribution systems with relative few new installations. The island setting having only one distribution system operator and a singular interface to the transmission grid is ideal location for this project.♦
This work is a compilation of applications, research reports and articles, which means that every person and company that is, or has been, involved in the project has contributed to this article.
Erik Segergren was awarded a Ph.D. from Sweden’s Uppsala University and worked on the management of various projects in the interface between research and commercialization of emerging technologies within the power sector. Since 2011, Segergren has been employed solely on Smart Grid Gotland, especially focused on attracting funding from domestic authorities and the European Union.