Lunar Energy ($300M for home solar energy storage)

Lunar Energy designs and engineers the home battery system of the next generation to electrify all homes and connect communities to form clean, resilient virtual power plants.

Challenges: home solar energy

Solar energy is a clean and renewable source of energy, and its use can reduce reliance on fossil fuels and the carbon footprint. Solar cells, also known as photovoltaic (PV) cells, convert sunlight into electricity. The installation of solar panels on rooftops is one of their most common uses. Solar panels installed on home roofs can reduce energy costs, lower carbon emissions, and promote sustainability.

To connect the solar panels to your home’s electrical system, a solar power system with DC-to-AC converter (or inverter) and other necessary equipment are required. The inverter converts the DC power generated by the solar panels into AC power, which is then fed into the electrical grid.

A PV disconnection system is an essential safety feature of a solar power system because it can help prevent accidents and protect people and equipment in case of emergencies. There are several reasons why this system is so critical:

Electrical hazards: Solar panels generate electricity when exposed to sunlight, and this electricity can be hazardous to workers and others who come into contact with the system. The PV disconnection system can rapidly disconnect the solar panels from the rest of the system, thereby reducing the risk of electrical shock or other accidents.
Fire hazards: Solar panels can also pose a fire hazard if they are damaged or become overheated. In case of a fire, the PV disconnection system can quickly shut down the solar power system, reducing the risk of the fire spreading and making it easier for firefighters to safely extinguish the flames.
Maintenance: Solar power systems require regular maintenance, which often involves working on the system’s electrical components. The PV disconnection system can disconnect the solar panels from the rest of the system, allowing workers to safely perform maintenance without the risk of electrical shock or other accidents.
Regulatory requirements: The National Electric Code (NEC) requires that all solar power systems be equipped with a PV disconnection system. Compliance with these requirements is essential for the safe and legal operation of a solar power system.

Most existing PV disconnect systems have multiple boxes made by various manufacturers. These distinct components each have their own controls and may be incompatible with one another. This adds complexity to installation and control of a power system’s various components. This fragmented PV disconnection system may cause homeowners and installers to become confused.

Lunar Energy Technology

Lunar Energy develops a solar power system with a single integrated PV disconnect switch to facilitate multiple types of disconnections, including rapid shutdown, PV disconnect, and energy storage system disconnect. Compared to most existing PV disconnect systems, Lunar Energy’s single integrated PV disconnect switch is compact, elegant, and super easy to install. The operation of the Lunar Energy’ solar power system is controlled by Lunar Gridshare software.

PV disconnect switch

The diagram below depicts Lunar Energy’s solar power system, which connects the energy storage system (e.g., battery), receives input power from solar panels, and supplies AC power to users. The inverter (or DC-to-AC converter) of the solar power system comprises a battery connector, CAN (Controller Area Network) isolator, an inverter power board, and three switches in series connection: PV disconnect switch, emergency stop switch, and a local on-off switch. The opening of any of the switches actuates rapid shutdown, PV disconnect, or energy storage system disconnect.

Lunar Energy's solar power system with a single integrated PV disconnection (ref. US11522366B1). — Lunar Energy’s solar power system with a single integrated PV disconnection (ref. US11522366B1).

Battery connector

Battery connector connects the energy storage system to the inverter circuit.

CAN (Controller Area Network) Isolator

CAN (Controller Area Network) isolator provides the differential physical layer interface between the data layer link, hardware protocol, and the physical wiring of the CAN bus.

Inverter power board

Inverter power board comprises an AUX power supply, a microcontroller, a DC-to-AC converter, and a latching AC relay. The microcontroller is controlled by Lunar Energy’s software.

The AUX power supply and three switches (a PV disconnect switch, an emergency stop switch, and a local on-off switch) are connected to the microcontroller via a sense line. The AUX power supply provides a voltage signal (12 V or 24 V) that is received by the microcontroller via the unbroken sense line (i.e., no switches are open).

Through the AC enable line, the microcontroller sends signals to the latching AC relay to control the on/off state of the inverter’s power output of the inverter. The latching AC relay is used because it can maintain its state (either open or closed) without a continuous electrical signal. An example of a latching AC relay is the Omron G9TA.

The microcontroller is a centralized processor that coordinates and controls the actions of various components in the power system, such as relays, PV optimizers, etc., to effect a sequence of actions that facilitate multiple types of disconnect in response to activation of a single switch.

PV disconnect switch

The PV disconnect switch is integrated into the inverter, eliminating the use of field wiring to connect them. It is a service disconnect switch that disconnects the PV power source from the inverter.

The PV disconnect switch is coupled to a switch that is inline with the sense line.

Local On-Off Switch

The local on-off switch is also used by a user to turn off the power system. It is inline with the sense line.

Emergency Stop Switch

Emergency stop switch is an external or remote activation switch for rapid shutdown. It is inline with the sense line. If the power system is installed in a home, a remote e-stop switch is provided on the exterior or outside of a building for a firefighter to interact with.

The working mechanism of the PV disconnection

The opening of any of the three switches (PV disconnect switch, the e-stop switch, the local on/off switch) first causes the sense to break, and the voltage on the sense line goes low (e.g., to 0 V). The microcontroller detects the voltage signal and performs a set of actions, including lowering PV DC bus voltage and disconnecting the power output of the inverter by opening AC relays, thus turning off the inverter output. Dropping PV DC bus voltage and disconnecting the output of the inverter fulfill rapid shutdown and energy storage system disconnect requirements, respectively.

The PV disconnect switch is a multi-stage switch to fulfill the PV disconnection. The PV disconnect switch is coupled to a switch that is inline with the sense line.

Prior to opening the PV disconnect switch to disconnect the PV source from the inverter, the switch that is coupled to the PV disconnect switch and inline with the sense line is first opened. This in turn causes the sense line to break, and the voltage on the sense line goes low (e.g., to 0 V). The microcontroller detects the voltage signal and performs a set of actions, including dropping PV DC bus voltage and disconnecting the power output of the inverter by opening AC relays, thereby turning off the inverter output.

In this way, the PV system is powered down before the PV disconnect switch is actually opened.

By having such a two-stage disconnect in which the PV power of the power system is turned off prior to opening the PV disconnect switch, the arcs that the PV disconnect switch would have to handle would be smaller, allowing for the use of a smaller switch with reduced size packaging. This is in contrast to the use of an off-the-shelf PV disconnect switch, which is included in a variety of types of installations and must assume that, in any given installation, it could be required to break a current/voltage load at its maximum rating in order to break any arcs that occur when opening under load.

Lunar Energy Patent

US11522366B1 Photovoltaic disconnect

Lunar Energy Products

Lunar Energy’s products include affordable hardware and software products for the residential sector to help homeowners generate, store, and manage energy. These products are designed to transition homes to 100% clean energy, making electricity greener, air cleaner, and energy more safe, secure and reliable.

Lunar Gridshare is a cloud-based software platform for distributed energy resources (DERs) that enables connected, smart, all-electric homes. It connects with 3rd party devices, creates detailed predictions of household and fleet energy behavior, and maximizes value for customers and the grid. Lunar Gridshare is currently deployed at scale across 35,000 homes (330MWh of batteries) in Japan via ITOCHU and is being used by Sunrun to operate its VPP network in the US.