Learning from the Experts – Managing High Penetration PV in Hawaii
With a goal of 100% renewables by 2045 in its Renewable Portfolio Standard (RPS), Hawaii is under pressure to figure out how best to integrate renewables. For Hawaii Electric (HE), electric savings from renewable technologies at customer sites have grown to 643,060 MWh in 2015, up 25% from 2014, according to HE’s 2015 Renewable Portfolio Standard Status Report. On Oahu, 16 percent of residents have rooftop solar, according to GreenTech Media. Intermittent renewable resources, like Photovoltaics (PV), effect the operation of the low voltage grid, causing voltage spikes or dips and lowering power quality. HE has taken a disciplined approach to test the application of one smart technology on vulnerable portions of the grid.
At utilities with pockets of PV concentration, engineers understand the potential for problems. As early as 2011, 72 percent of utilities were concerned that their grids would face challenges or require upgrades even before the penetration of solar PV reached 24 percent, according to a study conducted by Accenture and IDC Energy Insights, Achieving High Performance with Solar Photovoltaic (PV) Integration. HE saw the solar impact on feeder loads on cloudy and sunny days as early as 2009. The company set out to identify the feeders where PV was having an impact and to field test a technology to mitigate high/low secondary voltages.
Despite the growth in distributed PV, most utilities do not have a model of the distribution network that captures PV at the feeder level. In fact, most utilities do not even keep electronic records of PV installations that could be tied to to the GIS. HE needed to have a better understanding of the penetration of PV geographically, but did not have the time and resources to capture every installation. Instead, the company modeled the distribution grid using known installations and patterns of impact to identify the sites where PV is likely to be installed. The idea was to identify the penetration (installed MW/gross minimum daytime load). Feeders with penetration of over 75% have potential for back-feed. In some cases, circuits with only 16 customers with PV, could push the penetration to over 120%.
The power electronics-based low voltage regulator (LVR) has been put forward as a smart technology that could provide benefits to grid operations. LVRs have been tested to compensate for current harmonics on the supply side. On the load side, could an LVR regulate load voltage to the customer, smoothing the effects of intermittency on voltage?
HE decided to test out the LVR in a field demonstration. The company wanted to evaluate what benefits LVRs could deliver, document lessons learned, and develop a process and screening standard for pro-actively deploying LVRs without the need to monitor all circuits. Gridco System’s In-Line Power Regulator (IPR) was chosen for the field demonstration. The project included the following stages:
- Circuit Selection: Circuit selection was done based on a combination of customer complaints and known or modeled areas of high penetrations of PV exhibiting voltage, back feed and power quality issues.
- Verification: HE deployed monitoring devices that would provide data for performance evaluation.
- Pre-deployment modeling: A simulation model, using circuit data, was used to identify where IPRs would be installed on the circuit
- Field deployment: Units were deployed on circuits with moderate and high levels of PV penetration. IPRs were set-up in by-pass mode to monitor grid operations as a baseline and then activated for controlling local conditions (voltage, VAR and harmonics)
- Analysis: The device was evaluated for performance given site conditions using data from real-time monitoring of grid conditions for a period of one year.
After one year of testing (HE met its timeline for this project!), LVRs were found to work for high penetration areas. The LVRs installed proved to be capable of regulating load voltage, when source voltage was changing, at a lower cost than traditional measures such as tap changes. HE also learned that it did not have to install the LVRs everywhere. The company could reduce their initial investment by selectively targeting installations. LVRs can be precisely located to address voltage for customers affected by high or low voltage – say those in the midst of PV installations or at the end of the line. Based on the data, HE was also able to refine LVR settings to maintain voltage at the optimal level.
The LVR field test is part of a broader operations and planning initiative. HE wants to be able to strategically locate “smart” technologies to enable reliable system, regional and local control. There are a host of technologies to review – advanced distribution management systems, distribution line sensors, smart inverters, storage, etc. Many utilities are testing whether the technologies are technically able to meet requirements. To get a complete picture, utilities will need to address the economics as well.