PowerMatching City demonstration in The Netherlands
The need to integrate more distributed generation is clear. Here, Frits Bliek discusses the background to Europe’s first ‘living’ smart grid demonstration project, in which homes in The Netherlands use various microgeneration technologies within an intelligently-controlled smart grid environment.
Today’s climate and energy problems call for alternative solutions, such as distributed generation and renewable energy sources. In the future, systems which produce both heat and power are likely to have a big role to play at every level, right down to the individual household. A trial is therefore underway in the Netherlands, with the aim of identifying reliable, cost-efficient ways of integrating such distributed systems into the public grid. Known as PowerMatching City, the trial involves twenty-five homes.
|Overview of the PowerMatching City scheme|
As we move towards a more sustainable energy economy, an increasing proportion of our energy will come from combined heat and power (CHP) units, wind turbines and solar cells. At present, the power from such systems is normally fed into the high-voltage and medium-voltage grids. However, there is a clear trend towards decentralization at every level, with individual neighborhoods, buildings and even homes producing their own energy. In parallel with the rise of micro-generation technologies, the search for sustainability is driving demand-side electrification: the use of electricity to power heat pumps, cars and so on. Such systems are usually connected to the low-voltage distribution network.
|Gas turbine CHP plant|
These developments imply a shift away from traditional power grids, with their hierarchical top-down structure, towards more diffuse bi-directional networks capable of accommodating major fluctuations in both supply and demand. Market players will also take on new roles – consumers will become ‘prosumers’ (producer-consumers), for example, and new commercial and non-commercial actors will enter the market.
Energy companies, network operators and governments consequently face a variety of new social, technical and economic challenges. How can the demand for electricity be met without compromising comfort and convenience, cost-efficiency or security of supply? What is the best combination of technologies? Can local network overloads be prevented by using smart standardized techniques?
Satisfactory answers cannot be found without implementing intelligent solutions throughout the grid, and even inside the consumer’s home. The creation of a ‘smart grid’ is now possible using sophisticated information technology (IT). In a smart grid, IT forms an essential control mechanism, matching supply and demand in the most economical way.
Computer models and lab tests enable researchers to demonstrate how a smart grid or an innovative generating system or application will work, and to optimize the design. However, the best way to take smart grids to the next level is by bringing them to life. This requires detailed engineering and testing of concepts … because the proof of the pudding is in the eating.
Working with Dutch research center ECN, software company HumiQ and utility Essent, KEMA has created a ‘living lab’ smart grid environment. ‘PowerMatching City’ is part of the European Integral Project. The project is looking at how future smart grids will be managed under normal, critical and emergency conditions, with the aim of defining a single IT and communications infrastructure for all circumstances. The ultimate goal is to build and demonstrate an industry-quality reference solution for the aggregation, control and coordination of distributed energy resources, renewable energy and smart appliances, based on cost-effective, generally available IT components, standards and platforms.
The field test involving normal operating conditions is taking place in the Dutch city of Groningen. Twenty-five interconnected homes have been provided with micro-CHP units, hybrid heat pumps, PV solar panels, smart appliances and electric cars. Additional power is produced by a wind farm and a gas turbine. The underlying coordination mechanism for this demonstration project is based on ‘PowerMatcher’, a software tool used to balance energy demand and use. The project got underway in March 2010.
Consumers won’t accept smart power if it means reduced comfort and convenience. System designs therefore have to ensure that, no matter how a smart grid utilizes the available flexibility, people can continue their lives as normal. The field tests will investigate prosumers’ willingness to sacrifice some comfort and convenience for flexibility, if there is a financial incentive.
|Hybrid heat pump – view inside the house|
The hi-tech generating technologies used in this project include two heating systems designed by KEMA. Twelve homes have been fitted with small micro-CHP units. The other 13 have electric air-water heat pumps, plus external high-efficiency gas heating.
Whispergen is a micro-CHP unit developed in KEMA’s own laboratories. It is a gas-fired system that produces both heat and electricity. The heat is stored in a buffer, thus getting round the problem that heat and power aren’t always wanted at the same time. Whispergen uses the principle of the Stirling engine, a 200-year-old maintenance-free gas engine concept with an external combustion chamber. Each unit has an electric power output of 1 kWe and a thermal power output of 6 kWth. There is also an internally gas-fired auxiliary heater, which can boost thermal power output by 6 kW to ensure comfort. The auxiliary heater can run independently from the micro-CHP.
To separate the production of heat and electricity, the micro-CHP is connected to a 210-litre hot water buffer. The top section of the buffer holds approximately 90 litres of hot water with a temperature of between 60°C and 80°C, which is used primarily as hot tap water. This tap water is taken directly from the top of the buffer, without the use of a heat exchanger. The buffer is replenished from the bottom with cold water at about 10°C -15°C. The bottom section of the buffer holds a further 120 liters of water, whose average temperature ranges from 10°C to 60°C. This water is used for spatial heating and, in contrast to what happens with the tap water, heat extraction involves the use of a heat exchanger. The top and bottom halves of the buffer can be heated independently or simultaneously.
What’s more, as its name suggests, Whispergen is very quiet. Its noise output is just 45 dB – about the same as a refrigerator.
HYBRID HEAT PUMP
The other innovative technology used in the project is the hybrid heat pump. Combining an electric heat pump with a high efficiency boiler results in a system capable of producing base load energy in a highly efficient way, while also catering for demand peaks on a network-friendly basis. The efficiency of a heat pump is very high, because for every kW of electrical power, 3 kW to 5.5 kW of thermal power is produced.
For peak-demand activities such as taking a shower, or providing heat during extreme cold snaps, the hybrid heating system uses the same type of hot water buffer as Whispergen to store energy that isn’t needed right away. This heat pump is used for spatial heating only, because it cannot reach high temperatures (>45°C) without a significant drop in its coefficient of performance (COP). So the heat pump heats up only the bottom section of the buffer. Depending on the outside temperature, this section can reach temperatures between 35°C and 45°C. When the temperature outside is too low below the freezing point, the COP of the heat pump drops to far to be used efficiently. Then, the 14 kW external high-efficiency gas-fired heater is used. The gas-fired heater also heats all the tap water.
COMFORT, SAFETY AND RAPID RESPONSE
Monitoring and direct control of the heating system is provided by a custom-designed programmable logic controller (PLC), ensuring that the homes remain comfortable and that the system operates safely. Data from the PLC – information about parameters such as the temperatures in the buffer sections –can be sent to an external control point. It’s also possible to send a command to the PLC, telling the unit what temperature to maintain in the bottom section of the buffer.
|Whispergen unit being installed|
A PowerMatcher agent has been interfaced with the PLC to make intelligent use of the flexibility provided by the hot water buffer. The agent can receive monitoring signals from the PLC and use them to calculate the best temperature for the bottom section of the buffer. However, it is ultimately up to the PLC whether a buffer temperature command is implemented. This failsafe arrangement means that consumer comfort and system safety aren’t compromised.
In PowerMatching City, the micro-CHP units and integrated heat pumps are part of a virtual energy chain. Additional energy is provided by solar cells, wind turbines and a gas turbine. On the demand side, PowerMatching City’s residents have fully electric cars and plug-in hybrids. The homes are also fitted with smart washing machines and other intelligent appliances. The smart grid provides both physical and logical integration.
Fluctuations in the output from wind turbines and solar cells make it necessary to have a rapid-response power supply system. At the same time, the large-scale introduction of electric heat pumps and electric vehicles will significantly increase the peak load on the grid. This will lead to (local) congestion of the network at peak times. Smart grids can provide flexibility by rapidly shifting the demand for energy associated with the use of electric vehicles, heat pumps and smart appliances to match production peaks. Distributed energy resources, such as micro-CHP units, can also be used to plug production gaps when the wind drops.
In PowerMatching City, the key to obtaining flexibility of the kind described is the PowerMatcher agent. All the city’s cars are fitted with the agent, which spreads the charging process out over the night, smartly utilizing the peaks in wind power production and ensuring that the batteries are recharged at the lowest possible cost.
The same mechanism is used in the smart appliances. Smart freezers and washing machines help to reduce peak loads on the electricity network and enable energy from renewable sources to be utilized when it is available. So, for example, a smart washing machine is programmed to finish its cycle by a given time; the machine’s PowerMatcher then picks the most efficient start time that fits in with the desired end time. This might involve doing the washing when electricity is cheaply available.
In the smart freezer, the temperature is allowed to fluctuate within programmed limits, with the PowerMatcher choosing when cooling will take place. In all cases, the PowerMatcher makes sure that the user is not inconvenienced in any way.
The technological side is just one part of the story. We assume that prosumers will only invest in sustainable generating technologies and smart appliances if they have an economic incentive for doing so. Economic optimization for the prosumer is therefore one of the project’s primary goals. Energy can be exported from the home to the network, or imported from the network to the home, as the prosumer’s economic interest dictates. Each prosumer has a local PowerMatcher agent, which works in the background to optimize the power flows without user interaction. The efficiency of the new installations brings the added benefit of reduced energy consumption and therefore smaller energy bills.
Prosumers can access their real-time energy consumption profiles anywhere, any time via an internet portal. The necessary data is gathered by smart meters connected to each individual installation and placed in a central database. Peer group comparison ranks prosumer performance and prompts people to cut their energy consumption. There is also an operator portal for system maintenance, which monitors the performance of the whole system and allows maintenance personnel take action – and potentially prevent failure – even before the consumer notices that his or her system isn’t performing as it should.
For suppliers and the parties with programme responsibility, the biggest cost items are imbalances and imbalance reduction measures. The cluster can be operated as a virtual power plant, adding value from different perspectives. A trading objective agent will provide price incentives, so that the cluster’s energy demand can be controlled. This control mechanism is, in principle, limited to shifting the load of the whole cluster, since consumers will not produce or consume more energy but will only provide flexibility. Furthermore, the predictability of the cluster will be improved by price optimization and internal balancing, allowing better day-ahead forecasting.
Smart metering will increase the readout frequency, so that data on the whole cluster’s energy demand is available on a near-real-time basis, and will allow validation of the internal balancing point of the cluster itself. With a view to building up a clear picture of these processes and their interaction with a supplier’s regular trading and dispatching activities, the cluster is controlled from the trading room of the Dutch utility Essent. Dispatch activities take place in near real time and various trading strategies will be tested.
Frits Bliek is the Project Leader from energy consulting firm KEMA, Arnhem, The Netherlands
Contact the project at: firstname.lastname@example.org
PowerMatcher technology is a distributed energy system architecture and communication protocol, which facilitates implementation of standardized, scalable smart grids that can include both conventional and renewable energy sources. Through intelligent clustering, numerous small electricity producing or consuming devices operate as a single, highly flexible generating unit, creating a significant degree of added value in electricity markets. PowerMatcher technology optimizes the potential for aggregated, individual electricity producing and consuming devices to adjust the way they operate, thus improving the overall match between electricity production and consumption through dynamic, real-time pricing. The real-time prices provide incentives for off-peak electricity usage and on-peak electricity generation, improving the load factor of the grid.