An electricity supply network that uses digital communications technology to detect and react to local changes in usage. - Oxford English Dictionary Smart Grid is a concept describing the evolution of the power system. Among the desired future power system attributes would include the following:
- an increased application of modern communication methods,
- renewable power generation,
- distributed or bulk energy storage,
- distributed generation,
- incorporation of power electronic devices, etc.
How these technologies are deployed is subjective and thus subject to biases of the stakeholders. Stakeholders are interested in having increased observability of the system in order that efficiency, network design decisions, power quality, load forecast quality, and power system reliability can be improved. This can allow for savings in capital expenditures and operation and maintenance costs as well as revenue gains due to a potentially increased system efficiency.
Consumers would be interested in having increased power reliability and being able to reduce their energy rate. This could be achieved through the implementation of a time varying energy rate system.
Having a power system capable of integrating large amounts of renewable energy is an example of consumer or social benefits that the Smart Grid would allow.
Benefits of Smart Grid
The key drivers for the change to a modern electrical grid are:
- Increase in operational efficiency,
- Increase in energy efficiency,
- Added customer satisfaction, and
- Increased renewable energy integration.
The stakeholders in the electrical grid benefit from these positive changes as illustrated in Figure 1.
The utility experiences reduced capital expenditures, reduced operations costs, and increased flexibility in generation and control. Consumers have lower energy bills, reduced outages, and more information about their energy usage. The societal benefits are decreased carbon emissions, added environmental information and energy efficiency initiatives based on real-time information.
Operating an electrical grid, whether large or small, is a complex task. There are strong market and regulatory pressures on a utility to keep electrical rates low. By adding control and monitoring points throughout the system, connected back to a common control point, the information can be used from a single point to operate the system to maintain proper voltage and frequency throughout the network. As control and monitoring points are added to the system, advanced asset management techniques can be used to increase system reliability.
There were an estimated 67 billion kWh in distribution losses in Canada in 2015. Xcel Energy (an American utility) estimates that advanced electrical grid control and operation could reduce these losses by 30%.
The losses in the system are reduced with specialized equipment including capacitors, static compensaters and advanced storage control. This equipment is used for volt/VAR control to maintain an optimal power factor and optimal power flow.
Smart meters on customers homes allow the customers to have real-time information about their energy usage. Understanding how your energy usage compares to others in the community, the utility can suggest customized upgrades to your home that have known ROI. These could include new windows, better insulation, etc.
Better distribution system managements are associated with improved power quality, reducing inconvenience to the customer. This is done with improvements in the following:
- Voltage/current harmonics
- Voltage magnitude
- Number and length of outages,
Renewable Energy Integration
Integrating variable renewable energy generation assets such as solar, wind, tidal, etc requires a different paradigm for overall system control as its percentage of total generation increases. With historical load profile information and detailed forecasting, a modern grid can manage the variable nature of the renewable energy integration. This is further enhanced with a distributed demand side management system and electrical storage.
Figure 2 - Traditional power system
The electrical utility system was designed for energy flow in one direction (Figure 2), from the utility generation facilities to the customer.
With advances in solar, storage, electric vehicles, etc; there is a growing demand for a bi-directional system (Figure 3), where the customer is an active participant in the electrical grid. The increasing complexity of bi-directional current flow requires investment in communication, protection and control, and monitoring of the electrical distribution system.
With power flow in one direction, a utility knows all sources of voltage and current flow. Equipment protection and personal safety require simple isolation techniques with the existing distribution grid design. When there are multiple sources of voltage on the distribution grid, proper isolation requires coordination with non-utility entities such as customers and independent power producers (IPP).
Figure 3 - A "smarter" grid
Available Technologies Associated With Smart Grid
Smart Grid technologies require grid connected assets to be integrated with information technology infrastructure so that they can be monitored and controlled in an active fashion.
An example is modern electrical meters (smart meters) at the home, connected to the internet and reporting the real-time data to the utility, while being made available to the consumer. When a customer's electricity meter is connected and communicating in real-time to the utility, it can be used to automatically generate an outage report. Resources can then be dispatched immediately rather than requiring the customer to report the outage to start the restore process.
Utilities can start to use the customer to build intelligence into the system during an outage. One method is to use social media and have customers report outages, potential problems, etc with pictures. The utility can then correlate this information (typically a username, location, picture, etc) with real-time grid telemetry (metering, protection devices, etc) to dispatch crews with the correct gear immediately.
An example could occur when a tree falls on a line near a homeowner. The utility meters alarm at the control room on a loss of communication, triggering an SMS to the customers affected. The customer replies to the SMS with a picture of the tree on the line. Now the crew can gear-up and go directly to the cause of the outage and make a repair with minimum downtime. This decrease in total downtime by:
- no waiting for a customer to report,
- no surveying the line for the damage, and
- the correct crew with the correct gear are dispatched the first time.
On topology for the Smart Grid is a distribution of smaller interconnected grids, typically called microgrids. These microgrids would be connected to distribution systems in a similar way that distribution systems are connected to the transmission system.
These micro grids could vary in size from entire towns, and large campuses down to a small community or single home. The idea of a home microgrid is something that we are thinking about here, and building designs and technology to make this work. If we can do it at a home level, it can be scaled to larger communities.
What are the parts of a microgrid?
A microgrid will has the same components as any interconnected utility grid, it will have:
The generation can be anything from small diesel or co-gen plants, to solar and wind. For the Home Microgrid system we will be focusing on small scale solar.
The distribution system will be as simple as what you have in your home, to what is needed to run a university campus. Now much changes here.
The loads don't change much in a microgrid system. However, these loads may be more controllable based on changes in the optimization parameters based on the system state.
Which takes us to the protection and controls. This is where the system looks vastly different from a typical home or campus. The controls of the system has to work with the greater utility grid to ensure that it doesn't increase the strain, and can seamlessly connect and disconnect without disturbing nearby customers. The control system has to be able to operate the system in an islanded mode, and then re-connect without distrubance.
What this type of protection and control system looks like isn't standardized, but I will be investigating it as part of my Home Microgrid Newsletter. This newsletter is in addition to the other scheduled emails I send out on Electrical Safety and the main newsletter. It is focused entirely on the home microgrid concept. If that interests you, please check it out.