Assessing the Ability of Smart Inverters and Smart Consumer Devices to Enable more Residential Solar Energy

Evaluating advanced inverter functionalty to enable higher penetration of photovoltaics on the grid

Electric Power Research Institute, Inc.


Palo Alto, CA

Recipient Location


Senate District


Assembly District



Amount Spent



Project Status

Project Result

This project focused on understanding advanced smart-inverter functions, as defined in California's Rule 21 tariff, to effectively enable higher use of solar PV to customers and on the grid. Specific residential smart load management algorithms and communications architecture were developed for smart loads and inverters to enable higher PV penetration. This approach increases the solar PV value to the homeowners, while adhering to distribution grid requirements. Field testing demonstrated that optimization of residential smart loads could consume excess solar PV. Solar PV generation capacity and the availability of flexible or demand-responsive loads play a pivotal role in determining the amount of increase in the hosting capacity. Results from this project will help regulators and grid operators evaluate regulatory changes needed to scale deployment of Rule 21-compliant inverters and assess the outcomes that are relevant to their DR programs and reliable grid operations.

The Issue

Transformers are a key limiting component for the installation of solar generation on California's distribution systems. Transformer constraints together with distributed solar may result in voltage issues or inhibit permitting of solar. Smart inverters can help mitigate these issues. However, it is not known whether multiple inverters can operate side-by-side in stable conditions when each one is performing smart-inverter functions. High PV penetration on a distribution feeder may contribute to local over-voltage, variability, and equipment stress on the customer side, limiting PV deployments and production.

Project Innovation

The purpose of this project is to resolve the limiting conditions that occur on California distribution systems when many PV systems are installed behind a single residential distribution transformer by evaluating advanced inverter functionality with the specific goal of enabling higher penetration of photovoltaics on the grid. The project is identifying, implementing, and testing (both in lab and field) optimal methods by which smart inverters can mitigate the issues that otherwise would limit local high penetrations of residential PV. The process will identify how California Rule 21 functions can be used and configured so that multiple smart inverters work in harmony and will also identify how other naturally-occurring consumer devices, such as electric vehicle chargers and other smart loads, can serve to further enable high-levels of solar PV.

Project Benefits

As the penetration of autonomous (Rule 21) inverters increases, their interactions will grow in importance. This project will help provide a clear understanding of inverter characteristics and of their potential interactions that may help preserve the stability and reliability of the grid, benefiting both consumers and operators. Consumers who invest in solar PV systems (and utilities that provide incentives or expect benefits from PV) wish to maximize the power they can realize from their system. Sharing excess PV generation with local loads may increase the utilization of such systems without negatively impacting the distribution grid.

Lower Costs


The use of smart inverter functions, together with smart (PV-optimized) behavior of loads, can increase production (KWh) of residential systems by 15%. For an affected consumer on a constrained distribution circuit, this means more annual savings.

Greater Reliability


The testing and evaluation of smart inverter functions and smart management of consumer loads under this project can help minimize stress on grid equipment and further improve reliability.

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