Black start energy storage: Are hybrid inverters and energy storage systems black start capable? Protection against temporary power outages and blackouts

Most inverters are not capable of a black start. With some inverters, it is possible to perform a black start by charging a separate battery before switching on the inverter. However, this is not always possible and depends on the type of inverter.

The new generation of black-start capable hybrid inverters features a backup power transfer switch, allowing selected loads to continue receiving emergency power during a grid outage. This backup power enables the hybrid inverter to be black-start capable. Solar recharging is also supported, allowing the battery to continue charging during a grid outage to supply power to loads.

Fronius Prim GEN24 Plus Hybrid Inverter Series

The Fronius Prim GEN24 Plus hybrid inverter series is black start capable – Image: Xpert.Digital / Sergey Nivens|Shutterstock.com

The Fronius Prim GEN24 Plus hybrid inverter series is capable of black start.

GoodWe Hybrid Inverter 5-10KW ET Plus Series

Hybrid inverter for home and energy storage – from GoodWe – Image: Xpert.Digital / Sergey Nivens|Shutterstock.com

The GoodWe Hybrid Inverter 5-10kW ET Plus series features a high-voltage backup power (UPS) function. In the event of a power outage, switching over within 10 milliseconds ensures an uninterrupted power supply for connected devices.

The GoodWe ET-Plus series of three-phase hybrid inverters is designed to guarantee a stable power supply for connected loads. These devices feature a three-phase emergency power output with three-phase current and a power range of 5 kW, 6.5 kW, 8 kW, and 10 kW.

The wide battery voltage range of 180 V to 550 V allows for flexible compatibility with several lithium battery systems on the market.

The incoming PV generator output can exceed the nominal output by up to 30%. This results in better energy yield on both hot and very cold days. The UPS (uninterruptible power supply) function enables switching over within 10 milliseconds in the event of a power outage. The inverter also features an open battery management interface, which meets the requirements of some energy providers.

The GoodWe hybrid inverter is equipped with a high-voltage battery connection and two separate, independent MPP trackers, thus offering a complete package. This device can be kept up-to-date via the GoodWe PV Master app, and the data is transmitted to the free GoodWe SEMS portal via the integrated Wi-Fi interface.

Are HUAWEI inverters capable of providing emergency power?

No, at the moment we have no information about whether and when anything will be released in this regard.

Is the Enphase solar system technology with microinverter capable of providing emergency power?

Unlike a string inverter, which centrally monitors all connected solar modules, in a decentralized solar system each solar module is combined with an Enphase micro-inverter.

More information here:

• New & innovative: Decentralized and modular plug & play solar system – unlike the others

The Enphase IQ System Controller is not yet available in Germany, but is expected to be released this year (2023). It detects when the power grid fails and seamlessly switches the house from grid power to backup power.

Furthermore, with the new Enphase IQ8 microinverter, the solar system is able to supply emergency power in the event of a power outage without the need for a battery storage system.

The microinverter is available in four versions: a solar-only version without emergency power, a Sunlight Backup version capable of off-grid operation without battery storage, a Home Essentials Backup version with a small battery storage unit, and a Full Energy Independence version with a large battery storage unit. All three of these off-grid solutions require an Enphase System Controller to supply the house with solar power during a power outage.

A black start is the restoration of operation of a power plant or part of a power grid after a complete or partial shutdown, without having to resort to the external power transmission network.

The energy required to restart a power plant can come from an on-site standby generator. Alternatively, if a large amount of electricity is needed, a connection line to another power plant can be used to bring the plant online. Once the main generating units are operational, the power transmission grid can be reconnected and electrical loads restored.

Black start power can be ensured through an agreement in which a specific energy supplier is paid to provide black start power when needed. Not all power plants are suitable for providing black start power to a grid.

Black start capability is particularly important during a widespread power outage to restore the energy grid. Normally, the power required to start a generating unit is drawn from the grid. The energy from black start-capable generating units can then be used to start generating units that are not black start-capable.

Unlike hydroelectric power plants, thermal power plants require a high level of (electrical) energy for their own use before they can provide electrical or thermal output. By adding a black-start capable unit with sufficient capacity to a coal-fired or nuclear power plant unit, black-start capability can be achieved for the entire system. This usually involves gas turbines that are started using energy from batteries or diesel generators during a black start. Diesel generators are often present in nuclear power plants anyway for redundancy reasons, as residual decay heat is generated even after a reactor scram in an emergency (or even during a regular shutdown), which must be dissipated by the coolant. The failure of this system was one of the factors that led to the Fukushima reactor accident. Every power grid must be equipped with a sufficient number of black-start capable power plants to ensure a rapid grid restart after a grid failure.

A black start capable power plant should have special characteristics:

• It should be able to start quickly: If the black start takes a long time, then the power plant cannot help restart a collapsed grid; other power plants could already help it during the start-up – its black start capability is then useless.
• It must be able to operate independently of external power sources: Not only the pure power generation process, but also other ancillary requirements must function independently of the grid (control center, telephone and communication systems with grid operator and management, substation, etc.). If necessary, island operation with a sub-network is possible (supplying critical consumers such as police, hospital, fire department, THW [Federal Agency for Technical Relief]).
• Furthermore, a black start capable power plant should be able to withstand a high starting current if it was not possible to disconnect it from the grid beforehand.
• It should have a flexible startup behavior.

Examples of power plants used in Germany that are capable of (direct) black start are:

• Hydropower plants, including run-of-river plants, storage plants, pumped-storage plants, and
  gas turbine power plants, also in combination with other power plant types such as nuclear or coal-fired power plants.
  According to monitoring under Section 35 of the German Energy Industry Act (EnWG), there are (as of 2020) 174 black-start capable plants (power plant units or turbines) in Germany, each with a net rated output of at least 10 MW.
• In Austria, there are a total of 32 confirmed black-start capable power plants and an unknown number of unconfirmed black-start capable power plants. For many of the confirmed power plants, however, the specific models are not publicly known. The best-known and largest of these are the Malta and Kaprun pumped-storage power plants with capacities of 850 MW and 813 MW, respectively.

Not all power generation facilities are suitable for a black start. Wind turbines are not always suitable for a black start because the wind may not be available when needed. Wind turbines, mini-hydropower plants, or micro-hydropower plants are often connected to induction generators that are unable to supply power to restore the grid. The black start system must also be stable when operating with the large reactive load of a long transmission line. Many high-voltage direct current (HVDC) converter stations also cannot feed into a "dead" grid because they require commutation power from the grid on the load side. A pulse-width modulation (PWM)-based HVDC system with a voltage source converter does not have this limitation.

A major reason why thermal power plants are rarely capable of black starts is the contraction and shortening of the turbine shaft when it cools from its operating temperature to ambient temperature. It then jams in the casing and can neither be rotated nor removed; to restart the power plant, it must first be preheated so that it can rotate freely again before the hot steam can flow through it.

When a thermal power plant is shut down, the turbine shaft is heated up in time so that the power plant can be restarted at the planned time.