Energy Efficiency and Distributed Energy Resource Hosting
May 4th, 2023
The Synergies Between These Important Goals
Utility goals and initiatives aimed at energy savings and clean energy are a constant on our industry radar, with a strong interest in related power delivery challenges, best practices, and technology solutions – all with good reason.
According to the Environmental Protection Agency (EPA) website, 27 states have some type of energy efficiency requirements or goals. And according to the Center for Climate and Energy Solutions, 30 states have developed standards for use of carbon-free energy generation sources, including renewables.
Distributed solar generation will be a key component of reaching renewables goals, as is made clear in a recent statement in Wood Mackenzie’s 2022 Year in Review Solar Market Insight – “Nationwide, the residential segment installed just shy of 6 GWdc in 2022, growing by a staggering 40% over 2021. A record 700,000 homeowners installed solar in 2022.”
Electric vehicles (EVs) are also considered distributed energy resources (DERs). Strong consumer adoption of EVs in some geographies will require utilities to manage EV charging loads without negatively impacting power quality.
Given the heightened focus on energy savings and DERs, it makes sense that larger utilities have separate teams managing distributed energy resource integration and energy efficiency programs, such as Volt-VAR optimization (VVO).
In certain cases, however, synergy between energy efficiency and DER hosting can prove to be beneficial for both energy efficiency and DER team goals. Take for example, low voltage VAR control. Low voltage VAR control improves power quality at distribution transformers, enabling conservation voltage reduction (CVR) and energy savings, while also increasing distributed energy resource hosting capabilities.
What follows is a look at how low voltage VAR control works and how it enables significant progress toward both energy efficiency and distributed energy resource goals.
Low Voltage VAR Control for Energy Efficiency
To meet energy efficiency goals, utilities typically implement demand response programs and conservation voltage reduction (CVR), intentionally operating their distribution system within the lower end of the acceptable voltage range for achieving energy savings and demand reduction. Importantly, these minimum voltage levels must be monitored at the grid edge to ensure they are 114V or higher.
CVR programs focus on medium voltage assets like capacitor bank controllers, voltage regulators, and load tap changers. Low voltage VAR control extends volt-VAR optimization further downstream and enables incremental savings beyond traditional CVR by raising low voltage points at the distribution transformer.
Under normal operating conditions, as shown in the graph below, the orange minimum voltage curve dips to 114V at its lowest points – leaving little margin to decrease voltage at the substation without causing low voltage problems at end points. But when you add low voltage VAR control like Sentient Energy’s Grid Edge Control (GEC) solution, the minimum voltage profile at the distribution transformer is boosted, resulting in a 2.7% voltage margin above the lower limit.
The newly created margin enables utilities to use CVR to drop feeder or substation voltage by 2% – saving energy while maintaining a 0.7% margin from the lower limit.
Low Voltage VAR Control for Solar Hosting
When the goal for utilities is hosting more distributed generation like rooftop solar, attention must be paid to maximum voltage and the upper voltage limit of 126V. This focus is essential because when rooftop solar is feeding power into the grid, voltages rise.
To host more solar on distribution feeders, utilities need to create more margin from the 126V upper limit. They may not think to use VAR control because it raises voltage levels, but this is where synergy between distributed energy resource hosting and energy efficiency comes into play. When VAR control is combined with CVR voltage reductions, greater margins at the upper voltage limit of 126V are created – enabling more hosting capacity.
The graph below shows both orange minimum voltage and blue maximum voltage curves. When VAR control is added, a large margin of 2.7% is created between the minimum voltage curve and the lower 114V limit. The maximum voltage curve is not changed much with VAR control, and the top end margin is measured to be 1.3%.
When the utility applies a 2% CVR reduction, the upper margin increases to 3.3% – leaving room for additional solar hosting.
Low Voltage VAR Control for EV Hosting
Potential power quality issues associated with EV charging is another area utilities and their DER teams may have on their radar. In some scenarios, EV charging can cause voltage decreases below the 114V minimum, particularly along longer, rural circuits.
The graph below shows a simulated 9.8-mile distribution circuit with 30% EV charging penetration distributed along the feeder. EV charging causes minimum voltage to decrease from 114.4V to 108.5V, a drop of 5.9V. However, with low voltage dynamic VAR control, the minimum voltage is boosted to 114.0V – just meeting the lower limit.
Dynamic VAR control addresses the undervoltage caused by EV charging.
Leveraging the Synergies
Considering what each utility team must achieve, it’s understandable that energy efficiency teams and DER teams need to focus on separate programs. Utility energy efficiency or volt-VAR optimization teams are tasked with finding incremental energy savings and maintaining the 114V lower limit. DER teams have multiple challenges. They must address overvoltage caused by high levels of solar integration and ensure that the 114V minimum is met on circuits with high EV charging penetration.
What these teams must not overlook, however, are the synergies between improving energy efficiency and distributed energy resource hosting, as well as the technology solutions that enable enhanced outcomes for both.