Growing advantage for off-grid storage in grid-tied applications


From pv magazine International

When you power a back-up system, it is not only necessary to have sufficiently high AC power but also to provide excess power. Why is this? And what is a good value for power and duration of the possible excess power?

Pierre-Olivier Moix: We consider a back-up system as an off-grid system for a limited period. The system should be able to power the required demand and not the opposite – just having limited demand that can be supplied by the system. And this is why it is not possible to fix a value, it depends on every project and specific demand. The good news is that the value can be adjusted with the time, depending how the demand is evolving. In our case, there is no limit, because you can even add units in parallel if the demand increases heavily.

You have launched a new product, which you say provides such “real autonomy and back-up power,” also for grid-connected single family houses in northern and southern Europe. Which customers do you think will be willing to pay the surcharge for this advanced back-up performance?

We are all now aware of the trends in electricity prices. The sector is transforming, from a centralized and heavily subsidized market towards a multi-actor, dynamic scenario. The electrical demand for single family houses is also shifting, especially with the arrival of electric mobility. People looking to drastically reduce their carbon footprint without sacrificing autonomy or independence will rely even more on storage systems in the future. A storage system without ‘small print’ limitations will provide the freedom to decide the electrical model based on their own circumstances without considering external factors.

You not only emphasize the quality of the back-up power, but also the energy management functions. What do customers want, in that respect?

Everything is becoming smarter, and this is also happening with electrical devices. To centralize and control all of the intelligence available is still a challenge and far from being standardized. We have incorporated straightforward energy strategies that can easily be implemented to have the first layer of smart energy management without any additional controller. These strategies will have a real impact on the energy profile, making it possible to increase energy self-sufficiency by between 20 and 50%.

What are the typical dimensions of a solar and battery home system that you would recommend, when one wants to profit from the performance of the next3?

The next3 architecture has been conceived for a three-phase demand, with a lot of flexibility. In terms of power, we can supply up to 24-30 kW peaks and 10 kW peaks in a single phase. The flexibility is also available on the storage type, not only in terms of battery technology, as our inverter can work with lithium, lead-acid and many other battery technologies. In terms of storage capacity, our flexible charge and discharge profile makes it possible to configure the profile for each battery storage system, so the client, and not the system, is responsible for deciding their own autonomy.

Technically, what are the main design differences of your new product compared to standard solar and energy storage home systems?

It is not fair to directly compare existing energy storage home systems with our solution. We propose to apply the off-grid model in grid-tied applications, we are a step ahead in terms of autonomy and autarky. In our case, the battery is a must and the grid is an accessory that we could use as an asset. Our device requires a battery to work, the system architecture is different. This is why we offer solar autarky without conditions. For designing such a system, we advise to focus on the demand and autonomy required. Solar, if available, is often the most interesting energy source, in terms of maximizing the output. Other variables, especially the battery capacity, will depend on the autarky rate desired. The system should be able to match the energy requirements foreseen in the next 10-20 years. The battery capacity, however, is a modular asset that can evolve with the system.

To provide advanced back-up performance, do you have to pay the price of reduced efficiency, due to an over-dimensioning of the components? How important is efficiency for such a product? How have you measured and quantified your system’s efficiency?

Based on our long experience with energy storage, the efficiency is important but is not a critical element compared to the demand and energy management. However, with our innovative system architecture based on a DC link, we are able to reach efficiencies from solar to loads and from solar to the grid, that are at the same level or even higher. The main impact in system performance comes from smart management not only of the solar resource available, which is pretty well managed by all, but also the storage asset. Efficient use of the storage can lead to a huge boost in the total system efficiency and the autarky rate.

Would you also use this system for pure off-grid solutions, or do you have other products for these cases?

In off-grid most of the time, we need to handle an AC source as well (generator, hydro turbine, etc). In fact, we consider the grid as another AC source that should be integrated in the system. The device can therefore perform for both off-grid and on-grid applications and the main advantages of integration, flexibility and smart energy management are very useful in both cases. Our well known Xtender battery inverters were also a very important factor in the beginning of the self-consumption industry. Different regulations and simple applications were a hurdle. With the next3, we believe that we provide a very relevant solution for solar autarky, and are well prepared for the challenging future trends.

Which off-grid applications are present in Europe that installers should keep in mind?

Agricultural and field applications, mobile applications, C&I [commercial and industrial] portable and temporary applications, remote set-ups. There is an off-grid sector that will remain off-grid.

Questions from pv magazine. The questions were answered in written form.

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