Download The Grid and its Future - Companion Piece to Summer 2015

 The Future of the Electrical Grid, Distributed Generation and Energy Storage Danny Tosolini, P.Eng June 2015 About the Author Danny Tosolini received his Bachelors of Engineering Science Degree at The University of Western Ontario and got his start in the electrical utility industry in Alberta working for TransAlta Utilities. After seven years in Alberta, Danny moved back to Ontario where he has worked for several south western Ontario Local Distribution Companies including: St. Thomas Energy, Norfolk Power, Erie Thames Power and is presently employed at Woodstock Hydro. Danny is a registered professional engineer in the provinces of Alberta and Ontario and has been working in the electrical utility industry as an engineer for over 30 years in areas such as distribution, substations, generation and metering. Danny would also like to thank Jay Heaman, Operations Manager at Woodstock Hydro for his comments and input and for allowing the engineering time to prepare this review. Some Electrical Grid History The electrical grid was primarily designed to have multiple large scale generating stations spread out over large service areas (which could be an entire country or continent) and interconnected with high voltage transmission lines forming a grid to transmit and deliver power. If a section of transmission line is damaged or has to be taken out of service for maintenance, the power could be routed around it using other parts of the grid. Similarly if a generating station became unavailable, other generating stations connected to the grid could be used to generate the power required. With multiple generators separated by hundreds of kilometers all connected together with a transmission system grid, redundancy and reliability over a very large service area can be achieved. All generators have control systems to match power output based on the changing load requirements. When large scale generators connected to the transmission system grid reach maximum output power, Operators can dispatch (connect) more generation to the transmission system grid. During the day as power requirements increase, Operators connect more generation and during the night when power requirements decrease, Operators disconnect generators. Some generators always remain connected to supply the “base load” (load that always remains connected). Although many generators can be connected to the transmission system grid, the transmission lines have limits on where the power from the generators can be routed or delivered. Some large industrial facilities that require large amounts of power are connected directly to the transmission system grid, however, to distribute power in local areas distribution systems at lower voltages with radial feeders are connected to the grid with transformer stations. Distribution system feeders are not interconnected in a grid pattern, they are supplied radially from one end only. Redundancy is achieved by designing distribution feeders with loops and tie points between feeders. The feeders can be laid out in a grid pattern, but they are not connected as a grid. They just have tie points at the intersecting grid points. At points along the distribution feeder where power is delivered, transformers are connected to further reduce voltage for the secondary system. Although some secondary systems have been connected in a grid pattern with multiple transformers connected in parallel, most of the secondary systems are radial with only one transformer connection point to the distribution system. Some industrial and commercial facilities may be connected directly to the distribution system. On a distribution system, if there is a fault on a feeder, the protection is designed to only disconnect the portion of the feeder that is faulted, leaving the feeder up to where the fault is operational. Because of the “grid like” layout of the feeders and loop design (being able to supply a feeder from either end), the faulted portion of the feeder can quickly be isolated minimizing the outage times for the majority of the feeder until the faulted portion can be repaired. With large scale generators connected to the transmission system grid, there was no need to have generation connected to the distribution system nor to the secondary system. Distribution systems and secondary systems were intended to only have loads connected with the power supplied from the generators on the transmission system grid. Distributed Generation The idea behind distributed generation is to have generators also connected to distribution systems and secondary voltage systems. In Ontario, the Independent Electricity System Operator (IESO) also refers to generation that is connected to the distribution system and secondary voltage systems as “embedded generation”. The generation is “embedded” with the loads whereas the generation connected to the transmission system grid is remote generation that uses the transmission system to transmit power to the loads that are connected to the distribution system. With the advancements of renewable energy generating technologies along with the continued advancement of automation and control systems, the ability of connecting smaller generating units at the distribution system level has become technically and economically possible. Further advancements in computer and internet communications technologies with the ability to process massive amounts of data and information (including energy usage and billing information) is also facilitating the installation of distributed generation and the term “Smart Grid” is now being used. Automation and control systems such as: generator governors able to match generation with load, under frequency relays able to dump load (see note 1), or protection relays able to isolate faulted sections of the transmission or distribution system to minimize outages or to automatically restore power have been part of the grid from the beginning. Although “Smart Grid” may be a new name, the concept has been around since the first grids were built. Grids are probably getting smarter, but they have always been smart! Distributed generation connecting to the distribution system or secondary systems have different operating requirements. There may also be some limitations as to where these generators can connect and to the size and quantity of these types of generators on the distribution system. Bidirectional meters are required to keep track of the energy flows. Distributed generation is not intended to be used as back up generation. When there is a power interruption or outage either on the transmission system grid or on the distribution system, the distributed generation has to automatically disconnect from the distribution system or secondary system. The reason is to avoid back feeds during faulted conditions or to avoid a portion of the distribution system or secondary system that is disconnected from the rest of the system to remain energized. Generators that are intended to be used as back‐up power must be connected to loads with a transfer switch such that the load can either connect to the distribution/secondary system or the backup generators but not both. If distributed generation is also intended to be used as backup generation, it has to be designed such that it can be physically disconnected from the distribution/secondary system when there is a system power outage. Primarily, distributed generation is sized only to supply power to the local distribution system. Distributed generation is not intended to supply power back onto the transmission system grid for it to be transmitted to other parts of the transmission system grid. Distributed generation connected to the secondary system is normally sized only to supply power to the localized secondary system and not back up to the distribution system. Having said this, there may be scenarios where power generated on the distribution system flows back up to the transmission system and power generated on the secondary system flows back up to the distribution system. Distributed generation can be “self dispatching”. That is, distributed generators can automatically connect to the system whenever they are available to generate (ie. the sun is shining or the wind is blowing) and automatically disconnect when the energy supply is not available. As part of the “self dispatching” capabilities of distributed generators, their control systems can also be set up to detect small changes in frequency. If there are too many generators available, the frequency increases a little bit and the distributed generators (normally solar inverter type generators) can automatically be disconnected (see note 1). Distributed generation can also be used only to displace load referred to as “load displacement generation”. This type of generation is normally connected on the secondary system at a specific load point with the intent to “displace” a percentage of the load that is normally supplied from generators connected to the grid. The power from this generation is not intended to flow back up to the secondary system or to the distribution system. It is only intended to supply the specific load where the generation is connected. It is important to recognize that when there are power outages on the transmission system grid that result in power outages on the distribution system, all distributed generation on the distribution system which includes distributed generation on the secondary voltage systems, must be disconnected. To restore power to the distribution system, all the power that was coming from the distributed generation will initially have to come from generators connected to the transmission system grid until conditions allow for distributed generation to come back on line. Also, when distributed generation is immediately cut off by cloud cover for solar generation or the wind stops for wind turbines, the lost power has to come from other sources typically the generators on the transmission system grid. To account for this, there may need to be additional generation connected and available on the transmission system grid. This is also one of the reasons why there are limitations to the amount of distributed generation that can be connected to the distribution system. Even though there may need to be some additional generation available on the transmission system grid to account for some of the distributed generation, since power outages usually only affect certain areas or regions and rarely occur for the entire transmission system grid, it may be possible to replace some of the large scale generation connected to the transmission system with distributed generation. Reducing the generation on the transmission system grid also reduces the power flowing on the transmission system grid. Having more capacity available on the transmission system grid may provide opportunities for distributed generation that can generate more economically or with lower environmental impact to have its power allowed to flow back to the transmission system grid and transmitted to another part of the grid where it may be required. Having said this, large capacity renewable energy generation such as wind is also being connected directly to the transmission system grid. Hydro generation has always been considered renewable energy generation which can account for a large part of the generation on the transmission system grid. With the availability of distributed generation connected to the distribution system, it may also be possible to supply additional load on the distribution systems without increasing the generation requirements or capacity requirements of the transmission system grid. When generating locally, or for load in the same location as the generator, there are much lower system losses. By the time energy leaves a generator on the transmission system and is delivered to a load on the distribution system, as much a 10% of the energy can be lost as heat in the wires and transformers used deliver the energy. About 25% of the energy presently delivered from generation on the transmission system grid in Ontario is renewable energy generation (hydro, wind, solar and biofuel). Hydro is the lions share with wind presently providing less than 5% of the renewable energy and biofuels and solar less than 1%. Even though distributed generation presently produces less than 3% of the energy in Ontario, almost all of the distributed generation is renewable with 85% of solar generation connected as distributed generation (see note 2). Whenever possible, renewable energy generation, whether it is on the transmission system grid or it is distributed generation is being given priority over non‐renewable generation. Although adding distributed generation increases the complexity, it also provides many more options and opportunities to supply power. There will certainly be a balancing act involved in trying to manage what generation can be used and in determining where the optimum paths are for the power to flow without compromising the safety and reliability of the entire system and at the same time trying to provide the most economical and environmentally friendly operating scenarios and conditions. Energy Storage There is no lack of ideas for energy storage systems such as batteries, mechanical fly wheels, or compressed air (just to name a few). Energy storage systems can also be used to supply power to the distribution system or secondary system and is basically just another type of generation. Energy storage systems can store energy from renewable energy sources when they are available and deliver the energy when required. Energy storage systems can be re‐charged during off peak times (at night or during weekends) to help balance power flows. Energy storage systems can also be used for back‐up power requirements. Furthermore, with the development of electric vehicle technology, the batteries from electric vehicles can also be used as an energy storage device connected to the distribution or secondary system and used for distributed generation. Micro Grids Along with “Smart Grid”, the term “Micro Grid” is also being used. The idea behind the Micro Grid is that a small area such as a university campus or other small group of buildings, plants or facilities can be supplied with distributed generation completely isolated from the main power grid. The Micro Grid, with a collection of generators and loads, can be a private small grid operating independently from the main power grid or it can be tied to the main power grid but able to operate independently when separated from the main power grid. A Micro Grid would be tied to the main power grid at the distribution level or secondary voltage level. Using bi‐direction metering at the interconnection point, a Micro Grid can supply power or draw power either from the distribution system or secondary voltage system depending on where it is connected. A Micro Grid can also be defined as distributed generation with a collection of generators and loads connected to the main power grid at one point. Because several distributed generators and/or energy storage systems can be connected to a small interconnected grid, a micro grid can have some of the same reliability benefits as the main power grid. Economies of scale in terms of costs and efficiencies usually come into effect with large scale integration. With the advancements in generating technologies along with advanced automation and control systems including large scale data collecting and data processing capabilities coupled with advanced communications capabilities available from the internet, small scale integration may be competitive with the larger scale integration. Small scale integration may also be in a better position to take advantage of the advancements in renewable energy and energy storage technologies or can enhance or assist the main power grid to take advantage of renewable energy and energy storage technologies. Transactive Energy Ever heard of Transactive Energy? Apparently, it is a concept so new that it does not yet have a formal definition (see note 3). The basic idea is that Transactive Energy is based on the economics of the energy market and the value of energy. Smart Grid technology includes the ability to communicate between generator and load and with many devices in between. Transacvtive Energy is automation and control system software that also takes into consideration energy value. Basically, Transactive Energy is more smart grid sophistication, control and automation utilizing advanced computer and software systems that include large scale data collecting and data processing capabilities. Coupled with advanced communications capabilities available from the internet, decisions are made on how to operate the entire electrical system. The vision appears to be that Transactive Energy systems will make the electrical grid even smarter! We already have planes that can fly themselves and automobiles that can drive themselves, so an electric system grid that can operate itself is not too farfetched of an idea! However, cars and planes cannot design themselves, build themselves, maintain or repair themselves, which is also true for electrical system grids. Some may say not yet, but I certainly will not be around if and when this ever happens. Note1: The majority of the generation connected to the grid is rotating machine type generators. When the grid becomes heavily loaded or there is not enough generation available, the generators which are all synchronized slow down a little bit. This slow down (typically in the 0.5% range or 0.3 Hz) can be detected in the rotating frequency of the generators which are synchronized to 60 Hz. Certain types of loads can be automatically disconnected by relays when the frequency drops below a specified set point. When the system becomes lightly loaded or there are too many generators available, the generators speed up a little bit. Once again this speed up (typically in the 0.5% range or 0.3 Hz) can be detected and distributed generators (normally solar inverter type generators) control systems can automatically disconnected the generation. Note 2: Bruce Campbell President and CEO of the IESO, during his January 26th, 2015 Ontario Energy Network Luncheon Speech said; “Here in Ontario, we expect to have over 2,000MW of solar power connected to Ontario’s system by 2016 – 85% of which will be embedded in our distribution systems”. Note 3: In 2013, Carl Imhoff, manager of electricity infrastructure for the Pacific Northwest National Laboratory summed it up by saying, “Transactive energy is a means of using economic signals or incentives to engage all the intelligent devices in the power grid—from the consumer to the transmission system—to get a more optimal allocation of resources and engage demand in ways we haven’t been able to before.”