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Home battery enables off-grid and fully sustainable living

by Bouke van der Weerdt, Solutions Manager, Huawei, 19/3/2021

Energy storage will play an important role in the energy transition. Many companies are busy developing systems. Bouke van der Weerdt, solutions manager at Huawei, talks about the LUNA2000 smart string Energy Storage System (ESS).

Huawei started with the production of an internet router and then became widely known for their smartphones. Solution manager Bouke van der Weerdt: “Our R&D department came up with the LUNA2000 smart string ESS system. This home battery works with a single-phase inverter or small three-phase inverters up to 10 kW each, optimizers, and an app to monitor the energy flows.”

Battery connected to up to three battery modules

This home battery is modular type, with the power module on the top connected by a DC coupling to one, two and a maximum of three battery modules with built-in energy optimizer. “We call the device a Smart String ESS,” explains Van der Weerdt, “because you could put batteries in a string, just like solar panels, with a maximum of three battery modules. Each battery module contains an energy optimizer that regulates the charging and discharging process inside the module. This prevents unwanted balancing currents from arising, and also ensures that risks of overcharging, deep discharge or overheating cannot occur. The system is scalable from one power module with one battery module (5 kWh) to two power modules with a total of six battery modules and a capacity of 30 kWh.”

Inverter capacity

A battery makes it possible to use the generated power from the solar panels efficiently. Self-consumption always comes first, what is left of electricity is temporarily stored. And only when the battery is fully charged, it is fed back into the grid. “The great thing about a battery is that the capacity of your inverter is no longer the maximum capacity of your installation,” says Van der Weerdt.

Peak load is a thing of the past

“Suppose you have one 5kW inverter, which gives the opportunity to install a quantity of PV panels with a peak capacity of 10kW. The system is then enormously over dimensioned, so you would normally have a large cap loss. We call that clipping losses. By connecting a battery to the inverter, the inverter can simultaneously supply 5kW to the grid and store 5kW in the battery. The total output capacity of the inverter is then twice as original AC-rated power. The peak load on the grid is therefore a thing of the past, and the surplus is stored. So two birds with one stone.”

Lithium iron phosphate is ideal for this application

Because it is a lithium battery, the energy from the battery can actually be used and thus optimally used. Van der Weerdt: “Lithium batteries have gotten a bad name because of some incidents in the past, but there are many different types of lithium batteries, and we have done extensive research into the composition of our battery. The lithium iron phosphate type is ideal for this specific application. This technology is the most chemically stable and cannot self-ignite. So nothing can really happen. However, the battery is quite heavy due to this type of cathode composition. That would be a major disadvantage for an electric car, but for a non-mobile application such as a home battery it does not matter. However, it is wise to protect the battery against excessive temperature fluctuations, as these will adversely affect its performance. A good place would be a garage or utility room.”

An inverter can work in reverse

An inverter can also work in reverse by charging it at night during the off-peak tariff and releasing that energy during the day during the peak tariff. The system can therefore function without PV panels, and can be used purely for charging the battery at night and discharging it during the day. However, the efficiency is of course higher with solar energy, which is, after all, completely free.

System linked to backup box

This ESS system can be connected to a backup box that automatically supplies certain groups with power in the event of a power failure. A backup box is not the same as a UPS. It is therefore not a no-break supply and therefore it gets dark in the house for a few seconds before the backup box starts functioning. The backup box can also be started manually to power an isolated system.

Overview of the functioning of the system

Van der Weerdt: “The inverter is the heart of the system, with the PV panels on one side and the power module with the battery module(s) on the other. The components of the system are automatically recognized and configured by an app. That takes one and a half to three minutes, and for an installer it is very useful and efficient. Within a short time you have a complete overview of how the entire system is functioning, and you can therefore see where a possible problem lies."

One type per component

There is only one type per component. This applies to the inverter, the optimizer, the app, the ESS etc. The user/installer doesn’t need to choose, it is just a matter of connecting. The system is compatible with almost all poly and monocrystalline PV panels on the market.

Completely off-grid is possible

For a single phase connection, for example a tiny house, a home battery such as the Luna2000 makes it possible to be completely off-grid. "You have to watch out for peak loads," warns Bouke van der Weerdt. “Air conditioners, for example, draw high peak currents when the compressor starts up, and heat pumps can also cause peaks. But anyone who is aware of this and takes it into account can do without a grid connection. This is a good prospect in the context of energy transition.”

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