Understanding the Complexities of Connecting Customer Rooftops to the Grid – Part 1
As governments continue to invest in green technologies and encourage the use of renewable energy sources, more and more households are installing solar panels on their rooftops. In many countries, local and national regulations stipulate that any household that wants to install rooftop panels can do so, and that the utility must connect the rooftop system to the grid.
From the utility's perspective, the transformation to a multi-directional energy grid represents a paradigm shift. This post discusses some of the operational complexities related to connecting customers' rooftop systems to the electrical grid.
Not All Inverters Are Created Equal
Connecting a customer's rooftop equipment to the grid requires an inverter, which converts the direct current (DC) generated by the solar panels to alternating current (AC) that can be used by the home and/or "sold" back to the grid.
There are many different types of inverters available at varying levels of quality. The challenge for utilities is that the quality of the electricity coming back to the grid depends on the quality of the inverter. With millions of homes using rooftop systems, the ramifications of quality issues for even a small percentage of these installations translates into countless sources of "noise" and a major problem for grid operators.
The variations in quality among inverters can affect the quality of the generated electricity, both in terms of frequency and voltage amplitude. Similarly, installation quality also varies depending on the relevant contractor. This is another risk that utilities need to mitigate in order to improve rooftop integration with the grid.
Utilities are trying to address these issues by taking a more proactive approach with their customers:
- Recommending one type of inverter for all rooftop systems (avoiding problematic products) and even assisting in inverter installation
- Offering subsidies or incentives to encourage customers to use the "right" inverter and to achieve uniformity throughout the grid. Some utilities offer a customer portal where customers can buy the recommended type of inverter at a discounted price.
- Providing consulting services to advise customers/installers which inverters to use, as well as the advantages and disadvantages of each type of inverter.
In parallel to these customer-facing activities, utilities also understand the need for central management systems to control and fine-tune the frequencies and voltages of the inverter fleet.
Dealing with Two-Way Energy Flows
The traditional power grids used today were built to flow in one direction – from the power plant (generation) over the transmission and distribution networks and to the homes. These grids and their equipment assets were carefully planned to deliver low-voltage at the edge (i.e., adjacent to the home), taking into consideration the energy drop across the feeder. Now that consumers are also generating electricity from the rooftop, storage batteries and other distributed energy resources (DERs), this fundamental balance has been disrupted. The changes in voltage levels can damage service transformers and feeders, as well as affecting home appliances.
Another key challenge stems from the volatile changes in energy levels flowing towards the grid from these large numbers of rooftop systems. Imagine, for example, what happens to energy levels when a large cloud rolls in during the middle of the afternoon on a sunny day. Traditional grid assets, such as transformers and feeders, were not built for these types of sudden changes and need to be protected by a more advanced and comprehensive solution for managing energy flow.
Bottom Line: Take a Proactive Approach
The high adoption rate of residential rooftop systems requires utilities to take a more proactive approach with respect to integration of solar panels and other DERs. To protect their grid assets and ensure high-quality electricity across the grid, utilities need better control over customers' rooftop systems. Through marketing campaigns, online portals, educational activities and even installation services, utilities can help customers choose the right equipment for optimal grid integration.
In upcoming blogposts, we'll be examining additional challenges related to the management of DERs, battery storage, smart meters and demand response solutions. Stay tuned!