Distributed Generation-Integration in to the Smart Grid

Since renewables and distributed generation are developing fast and don’t appear to be going anywhere, grid operators have the responsibility to integrate them into the existing transmission and distribution network operations systems.
Published: Thu 20 Feb 2014

While this integration can pose a myriad of problems, innovative and cost-effective solutions are available to the utility to resolve or mitigate the problem.

In the past, electricity was transmitted in one direction and grid operators had to ensure that there was enough supply to meet demand. But this scenario has changed significantly-energy consumers are now becoming energy producers. Now, grid operators have to be aware of current and forecasted distributed energy production and distribution, explains Gene Zimon, president of EDGE Advisers.

Forecasting

Currently, utility load control systems forecast how much energy to buy based on prior period usage adjusted for forecasted weather conditions. But, as distributed energy resources develop, utilities have to forecast their electricity production, local consumption and power fed back to the grid. Grid operators have to gain an understanding of the current state of the transmission and distribution network, and must take into consideration the condition of distributed energy plants and the transmission lines to their grid interconnection points.

This is an immediate problem that many progressive utilities are attempting to address. Solar, wind and other distributed generation plants are generally located in isolated areas, calling for the construction of new transmission lines to connect to the grid. In the US, the integration of the flow of electricity from distributed energy units is being addressed through state-enacted interconnect standards ( Virginia, Maine and Utah). Thirty states have comprehensive standards which assign the responsibility and the cost of the interconnection to power producers and ensuring that specific technical and safety measures are established. Most of the state standards require that any distributed site go offline within two seconds of detecting a power outage on the grid. This is typically done by protective relays internal to the generating facility or by a direct transfer trip signal from the substation.

Solutions for protection and islanding are expensive and can negatively affect the return on investment of building a distributed generation facility that is compliant with state interconnect standards. Lower cost solutions, that meet regulator standards, should be explored.

Data integration

Utilities are also developing solutions that integrate information flows between the utility and the distributed generation plants. Complementary to the physical integration of distributed generation into the grid is the need to maintain a two-way flow of information between distributed facilities and the utility’s SCADA, EMS and load forecasting systems.

The SCADA system requires a real time view of the current and projected flow of electricity throughout the grid. Access to the unit’s condition and to its projected production and distribution is key for the utility to ensure grid reliability.

Load management and forecasting systems

Similarly, load management and forecasting systems estimate how much supply to bring in on a daily basis. Without knowledge of current production or forecasts of distributed energy production, the total day-ahead load supplied to wholesale purchasers could have an increasingly widening margin of error as distributed capacity increases. This will increase the wholesale cost of energy, as overestimated base load will result in purchasing too much energy and underestimated base load will require more reliance on spot market purchases.

Unfortunately solutions for data communications from distributed generation plants located in remote areas are difficult to justify since conventional communication mechanisms such as fiber, dedicated telephone lines and microwave links are costly. In response to this, utilities should explore cost-effective alternatives such as wireless and B-PLC technologies to transfer information from the distributed site to the substation.

Fortunately, software vendors such as Draker and Locus Energy are deploying products that not only manage solar performance and asset conditions, but also predict production, measure actual production and control energy flows back to the grid. Both companies have the capability to provide this information in real time to the utility SCADA systems.

Based on conservative estimates, renewables and distributed generation is predicted to double every ten years.. Grid operators should recognize that this supply must be treated as any other supply source and be fully integrated into their transmission and distribution network operations systems. Rather than apply existing solutions to a new problem, utilities must apply innovative and cost-effective solutions which are designed to solve a problem.