Introduction to a Power Control System (PCS)

The maximum size of a home residential solar system with energy storage has historically been limited by the rating of the home's main electrical service panel.

Learn more about electrical codes for solar here.

SunVault® now has Power Control Systems (PCS) functionality. With PCS, SunPower can increase the amount of solar and storage that can be installed with your home's existing main service panel. The PCS feature uses software to dynamically control solar and storage operation based on the main service panel rating.

What are the Benefits of Power Control Systems?

Having PCS functionality has two key benefits.

First, PCS enables SunPower to install more powerful SunVault® systems without installing a new, larger main service panel. This avoids additional equipment cost to the project and the requirement to extend permit and interconnection approval associated with service panel upgrades.

Secondly, it will circumvent the need for additional interconnection equipment required by California investor-owned utilities (IOUs) such as PG&E, SCE, and SDG&E, when installing a storage system larger than 10 kW. SunVault's PCS functionality helps qualify more projects for installation and avoids additional equipment costs. Additionally, there is less equipment to install on the wall (such as a Net Generation Output Meter (NGOM)), as well as helps with solar and storage system size limitations.

PCS Operation for Utility Compliance

When PCS is enabled for utility compliance, the SunVault PCS system will operate in "Import-Only" mode. While your solar system will continue to export excess power to the grid when available, this mode does not allow the export of stored power from the battery to the grid. The SunVault will only discharge only to meet the power needs of the home.

PCS Operation for Main Service Panel Protection

When a PCS system is used to protect the Main Service Panel(MSP), it will monitor the total loads in the home and limit the PV and the Storage if the power draw on the MSP exceeds its rating. This will appear as a loss of solar and storage, if the LED panel on your Energy Storage System (ESS) are not on or an ESS alert that will last as long as the home loads and the solar and storage are higher than the MSP rating. For example, if you are charging an electric vehicle this increase of energy use may cause the PCS to either stop incoming power from your solar panels or SunVault storage unit. Therefore, in your mySunPower app, it may look like your solar panels aren't producing or your SunVault isn't supplying power, but really, PCS is protecting your home from too much electrical current flowing through your main service panel. Once you stop charging the vehicle, your system will return to its normal operation.

Examples as seen in the mySunPower® online web portal:

Examples as seen in the mySunPower online web portal

Fig. 1: SunVault system in Cost Savings mode with PCS enabled for Import Only

In Cost Savings mode with PCS, SunVault will discharge power equal to the home loads during high time-of-use hours (system default: M-F, 5-8pm), up to your Reserve Charge. The SunVault will not discharge additional power to the grid for net energy metering (NEM) credit.

SunVault system in Self Supply mode with PCS enabled for Import Only

Fig. 2: SunVault system in Self Supply mode with PCS enabled for Import Only

In Self-Supply mode, the system maximizes your use of solar energy and minimizes the amount you import from the grid during the day. With PCS enabled, SunVault maintains up to a 100 W grid-imported power and may also require grid-imported power depending on the types of loads active. In the chart above, the SunVault and the grid support home power needs from 6-12pm.

For more information be sure to read our Resource Article which discusses the different operating modes for SunVault Storage.

FAQ about Power Control Systems

  1. When is PCS included in the design of a SunPower Equinox® solar system with SunVault storage?

    1. As a standard, SunPower includes PCS functionality in SunVault system designs for:

      1. Systems in 26-2, 39-2, or 52-2 configurations

      2. Systems interconnected to utility grids operated by Pacific Gas & Electric (PG&E), South California Edison (SCE), and San Diego Gas & Electric (SDG&E) to eliminate the needs for the additional NGOM metering equipment

      3. Systems that benefit from using existing electrical equipment when using PCS.

  2. Can I turn PCS (Power Control System) off?

    1. PCS may not be turned off, as this functionality is integrated into the design and operating controls of your solar and storage system. There are two reasons for this: PCS is enabled at your home either as an electrical code requirement from an Authority Having Jurisdiction (AHJ) and, in some cases, as a utility requirement for systems with over 10 kWh capacity.

  3. For a SunVault with PCS enabled, why is my home using grid electricity when I have stored energy in my batteries?

    1. The simple answer: The PCS tracks and responds to home energy use based on the power drawn on each electrical phase, while maintaining up to a 100 W import from the grid. All homes have two electrical phases. PCS requires the storage system to discharge at the minimum load on either phase. For example, if Phase 1 only has room lights on (low power: ~500 W) and Phase 2 has the microwave running (high power: ~1000 W), for 1500 W total home load, the storage system will discharge the Phase 1 load of 500 W on both phases, for a total of 1000 W, while the grid will support the remaining 500 W. This operation control is required for compliance by the product certification (UL standard UL 1741 CRD).

    2. The technical answer: When PCS is active and there is a load imbalance between the phases, some of the home loads will be powered by the grid. This ensures that the energy storage will not discharge to the grid on either phase, due to the "Import Only" as required by SunVault product certification. Therefore, the battery will only discharge to the lower of the two phases and will subtract an additional 100 W buffer. The remaining power needed will be covered by solar energy if available, then by the grid.

  4. What is net energy metering (NEM)?

    Net energy metering is a grid electricity billing arrangement that enables homes which generate their own electricity to export excess energy back to their local power grid and receive credit applied to future electricity bills Learn more here.

    Note: A SunVault system will occasionally reboot itself during normal operation. If this reboot happens while operating off-grid you may experience a brief loss of power to the home. The SunVault system will recover on its own. If the system does not recover, please call SunPower Support at 1-833-410-2382.