SunSpec Alliance v. Tigo Energy Inc

1. Case Identification

• Case #: IPR2021-01286
• Patent #: 8,933,321
• Filed: July 20, 2021
• Petitioner(s): SunSpec Alliance
• Patent Owner(s): Tigo Energy Inc.
• Challenged Claims: 1, 5, 6, 7, 12, and 13

2. Patent Overview

• Title: Safety System for a Solar Array
• Brief Description: The ’321 patent discloses systems for automatically or remotely rendering a solar array safe during emergencies or maintenance. The system uses a "watchdog unit" at each solar module to monitor communications from a central controller and disconnect the module from a power bus if the communication is interrupted.

3. Grounds for Unpatentability

Ground 1: Anticipation of Claims 1, 6, 7, 12, and 13 by Moine

• Prior Art Relied Upon: Moine (French Patent Application Publication No. FR2894401A1).
• Core Argument for this Ground:
  • Prior Art Mapping: Petitioner argued Moine discloses every element of the challenged claims. Moine's system includes a transmitter (7) that sends a periodic signal to a receiver (5) controlling a switch (4), which connects or disconnects a solar module (3) from the main circuit (1). Petitioner asserted that Moine's transmitter (7) is the claimed "central controller," the receiver (5) is the "local controller," and the receiver (5) and switch (4) together constitute the "watchdog unit." When the receiver fails to detect the periodic signal from the transmitter for a "set timing," it opens the switch, disconnecting the solar module to ensure safety, thereby anticipating the limitations of independent claims 1 and 12. Dependent claims 6 and 7 were allegedly met because this process inherently involves determining an irregularity in periodicity that surpasses a time-based threshold.

Ground 2: Obviousness of Claims 1, 6, 7, 12, and 13 over Moine and Kronberg

• Prior Art Relied Upon: Moine and Kronberg (Patent 5,054,023).
• Core Argument for this Ground:
  • Prior Art Mapping: Petitioner contended that to the extent Moine's receiver (5) is not considered a "watchdog unit," Kronberg explicitly discloses a "smart watchdog safety switch" that performs the required functions. Moine provided the overall solar power system with a central transmitter and local receiver/switch for safety disconnection. Kronberg taught a specific, well-known watchdog circuit that monitors a periodic input signal ("heart beat signals") using an event detector and a counter. If the signal is not received within a specified time, the counter triggers an output to indicate a malfunction. Petitioner argued a POSITA would integrate Kronberg's watchdog circuit to implement Moine's receiver function, using Kronberg's output to control Moine's switch (4).
  • Motivation to Combine: A POSITA seeking to implement the safety shutdown function of Moine, which relies on detecting the absence of a periodic signal, would be motivated to use a well-known, dedicated watchdog timer circuit like that taught by Kronberg. Kronberg's device was designed for the exact purpose of "protecting critical processes in the event of controller failure," aligning perfectly with Moine's goal of safely shutting down the solar array during a malfunction.
  • Expectation of Success: The integration was presented as straightforward. Watchdog timers were a common and predictable technique for detecting malfunctions. A POSITA would have a high expectation of success in using Kronberg's standard electronic safety circuit to reliably detect the absence of Moine's periodic signal and trigger a switch.

Ground 3: Anticipation of Claims 1 and 5 by Adest '055

• Prior Art Relied Upon: Adest '055 (Patent 8,531,055).
• Core Argument for this Ground:
  • Prior Art Mapping: Petitioner argued that Adest '055, which relates to the shutdown of photovoltaic power systems, anticipates claims 1 and 5. Adest '055's "power module 405" was identified as the claimed "watchdog unit," which includes a "detector/receiver 207" and a "controller 306" (the "local controller"). This unit monitors a periodic 100 Hz signal from an inverter or "signaling block 420" (the "central controller"). If the signal is lost for a period longer than one cycle (a "skip"), the controller initiates a "safety mode," disconnecting the solar panel from the power bus using a switch (FET 330). This allegedly met all limitations of claim 1.
  • Prior Art Mapping (Claim 5): Petitioner further argued that Adest '055 explicitly discloses the bypass circuit required by claim 5. When FET 330 disconnects the solar panel, other switches (FETs 328, 348, and 350) are configured to form a path that allows current to bypass the solar panel, thus meeting the limitation.

4. Key Claim Construction Positions

• "the location controller" (Claim 1): Petitioner argued this term, which lacks an antecedent basis in the claim and does not appear in the specification, is an obvious typographical error. Because the claim first recites "a local controller" configured to perform a specific task, and later recites "the location controller" as making the determination for that task, Petitioner contended the term should be construed to mean "the local controller" to correct the error.

5. Arguments Regarding Discretionary Denial

• Petitioner argued that discretionary denial under §314(a) based on the Fintiv factors would be inappropriate. The core argument was that since no parallel district court litigation involving the ’321 patent was pending, the Fintiv factors do not apply.
• Petitioner further contended that even if the factors were considered, they would favor institution due to the early stage of any hypothetical litigation and the strong merits of the petition. It was also argued that denial under §325(d) was unwarranted because the prior art references were not considered during the original prosecution and a prior IPR petition (IPR2021-00541) was terminated before institution or a preliminary response.

6. Relief Requested

• Petitioner requested institution of an inter partes review and cancellation of claims 1, 5, 6, 7, 12, and 13 of the ’321 patent as unpatentable.