Brecht Zwaenepoel

Smart microgrids and virtual power plants in a hierarchical control structure

In order to achieve a coordinated integration of distributed energy resources in the electrical network, an aggregation of these resources is required. Microgrids and virtual power plants (VPPs) address this issue. Opposed to VPPs, microgrids have the functionality of islanding, for which specific control strategies have been developed. These control strategies are classified under the primary control strategies. Microgrid secondary control deals with other aspects such as resource allocation, economic optimization and voltage profile improvements. When focussing on the control-aspects of DER, VPP coordination is similar with the microgrid secondary control strategy, and thus, operates at a slower time frame as compared to the primary control and can take full advantage of the available communication provided by the overlaying smart grid. Therefore, the feasibility of the microgrid secondary control for application in VPPs is discussed in this paper. A hierarchical control structure is presented in which, firstly, smart microgrids deal with local issues in a primary and secondary control. Secondly, these microgrids are aggregated in a VPP that enables the tertiary control, forming the link with the electricity markets and dealing with issues on a larger scale.

Solar Commercial Virtual Power Plant

Installed photo voltaic energy grew exponentially during the last decade. One of the driving forces was the often generous governmental support. In Belgium (Flanders) for example, investors could acquire green power certificates worth €450/MWh during several years. However, due to the large boom of solar plants and hence rising subsidy cost, governments are dropping this support (eg. €450/MWh in 2009 to €90/MWh in 2012 for Flanders). In this paper the authors investigate if solar energy can become more profitable if forces are joined in a Commercial Virtual Power Plant to sell the solar power on the wholesale market. The numbers are based on the Flemish region, however, the same procedure can be applied to other markets as well. It turned out that for existing installations the potential benefits are marginal due to the small share of the energy revenue compared to the subsidy revenue in the total income of a solar plant. However, lower subsidies and coupling with other production resources and (flexible) consumers promise to be more profitable, although this needs more investigation.

Congestion-induced wind curtailment mitigation using energy storage

Allowing the connection of additional renewable energy sources (RES) in areas with limited transmission capacity is becoming of a serious concern. Building new transmission lines only provides a long-term solution to cope with this issue due to the fact that it takes much longer time (up to 5-10 years) compared to time needed to build new wind farms (about 1 year). Storage is proven to be an effective solution to make maximal use of existing grid infrastructures in the short-term. This paper proposes a cost-benefit optimization formulation for optimally sizing the storage in a wind-storage system which is connected to an external spot market via limited transmission lines. A small test system is studied in order to find the optimal size of storage to avoid congestion by allowing revenue to be generated only via reducing the congestion-induced wind curtailment. Additional revenue streams can be also included to maximize the monetary value of the wind-storage system.

Solar commercial virtual power plant day ahead trading

During the past years, a large amount of photovoltaic (PV) capacity has been installed in Belgium. The main driver for this was the abundant government support (Green Power Certificates). However, during the last few years, the support for new installations has been withdrawn and new PV capacity ceased. In previous research, it has been proven that selling PV energy of existing plants directly on the wholesale market is not feasible due to the large share of green power certificates awarded to these plants. However, the price of green power certificates has dropped significantly and hence the balance between certificate and commodity revenue is restored. This paper investigates the risks and challenges of leaving the fixed rate system and trade directly on the more volatile day ahead markets while facing penalties resulting from wrong forecasts. It will be proven that nominating to much or not enough energy can be positive, but also yield large risks.

Use of energy storage for Belgian power network

The intermittent and fluctuating nature of output power of renewable energy sources (RES) can lead to serious security concerns such as congestion in the transmission system. Incorporating storage devices with RES is technically an effective means to mitigate this concern by allowing fluctuating RES to be as stable as traditional power plants. Storage is an even more consumer-friendly solution with greater control over electricity consumption time and price compared to e.g. demand-side management which offers limited control over the price for end users. It can also contribute to lower the electricity price, peak-shave the demand, defer upgrade investments, provide ride-through solution for (momentary) faults, contribute to voltage/frequency control, increase the share of green energy and thus reduce overall greenhouse gas emissions, improve power quality by reducing harmonic distortions and voltage sags/surges, facilitate utilization of more efficient off-peak generation units, etc. This paper assesses the technical applicability and economical viability of different storage devices to the Belgian power network, focusing on the structure of the Belgian electricity market. A high-level overview of widely-used storage technologies, their benefits and shortcomings are also provided.

Renewable Energy Balancing with Thermal Grid Support

Waste heat valorisation in process industry is a common strategy today. The residual heat is converted to electricity by using steam turbines or organic Rankine cycles. As this energy conversion is likely constructed as an integral cooling capacity for the primary process, loss of electricity production will result in reduced process cooling and hence production capacity loss. This restriction prevents these generators to deliver supporting services to the electrical grid. In this paper, it is proven that coupling waste heat recovery with a district heating network provides flexibility to the electricity generation while ensuring cooling capacity to the process. This flexibility can be utilised by a Virtual Power Plant (VPP), e.g., to compensate for the variable output of renewable energy sources. Today, the power fluctuations are only compensated by traditional power plants (gas, coal) due to the scale and flexibility of these power plants. In this paper, a strategy is defined to balance variable (renewable) production with industrial waste heat. As such, some grid support tasks can be transferred from the central power plants to decentralised generation units. The backup of the variable sources is provided by utilising the local available capacity, while maintaining or improving energy efficiency of exothermal industrial processes. Operational boundaries are defined and new challenges identified. In this paper, firstly, the heat sources available for this concept are identified. Secondly, the properties of the different conversion technologies are described. Thirdly, the benefits of a virtual power plant utilising waste heat are determined. Finally, this VPP concept is verified by means of a case study in Belgium, Ostend Energy port. Available heat from biomass, chemical processing and waste incineration is used as primary energy source to balance local renewable production.

Increasing Economic Benefits by Load-shifting of Electrical Heat Pumps

Electrical heating is still widely used in the process industry. While the use of immersion heaters for the production of hot water or steam is declining, the adoption rate of electrical heat pumps is increasing rapidly. Heat pumps show great flexibility and potential for energy savings, e.g. through low temperature waste heat recuperation. In combination with thermal storage they also allow for load shifting. Because their main power source is electricity, which up to now cannot be stored efficiently, heat pumps can transpose their thermal load shifting ability to the electrical grid. Today, more and more industrial electricity consumers are adopting energy supply contracts with variable pricing parameters strongly coupled to the energy trading market. Some large consumers even buy and sell on this market directly. In this paper it is proven that for customers with (hourly) variable electricity pricing, the use of electrical heat pumps can lead to additional cost savings without influencing the industrial process. The yield of the heat pumps can be increased during hours with low energy cost, with the thermal buffer absorbing the heat surplus. During hours with high energy cost the heat pump yield is lowered and stored heat is used by the industrial process. Considering that heat can be stored much more efficiently than electricity, the load shifting ability of heat pumps can also be utilised to provide stability on electrical smart grids and to increase electrical self-consumption on microgrids. This paper will also explore the potential of thermal storage through heat pumps for these electrical smart grid applications.

Thermal systems in process industry as a source for electrical flexibility

The need for balancing services in the European electricity grid is increasing. The reason is twofold: renewable energy sources (RES) are still in up rise, meanwhile the classical power plants — commonly used to provide balancing — are economically pushed out of the market. This results in less available balancing resources but increasing balancing needs as RES are less predictable and controllable. The decline of the balancing volume provided by classical power plants can be counteracted by the concept of Demand Side Response (DSR). Balancing services are shifted towards the electricity consumers instead of traditionally being an electricity producers responsibility. The concept of DSR is well documented as it was already introduced in 1973 at the time of the first energy (oil) crisis. Now, the DSR concept gains again momentum as electricity markets rapidly change to adopt RES. New insights and incentives are to be investigated as the electrical landscape has changed tremendously since the first introduction of DSR. This paper will focus on the concept of DSR in process industry.

Potential of domestically provided ancillary services to the electrical grid

In this paper we explore some methods to offer ancillary services by domestic demand response on a low voltage grid. These grids are becoming more and more inundated with decentralized renewable energy production, often leading to congestion issues. We show how domestically provided ancillary services can mitigate these problems. While demand response is already becoming established on large-scale installations, integration on a residential level poses some challenges toward cost and ease of integration. We present a solution that is both economic and non-intrusive and apply it on domestic electric water heaters. A project are where these solutions will be tested and verified is presented.

Virtual sector profiles for innovation sharing in process industry : sector 01: chemicals

Production data in process industry are proprietary to a company since they are key to the process design and technology expertise. However, data confidentiality restrains industry from sharing results and advancing developments in and across process sectors. Using virtual profiles that simulate the typical operating modes of a given process industry offers an elegant solution for a company to share information with the outside world. This paper proposes a generic methodology to create sector blueprints and applies it to the chemicals industry. It details the profile of a typical chemical site based on essential units and realistic data gathered from existing refineries and chemical plants.