How important are hybrid systems to your customers?
Mathias Grässl: Self-reliance is becoming ever more important, and hybrid systems allow our customers to take themselves off the power grid. Just now we have provided the equipment for a building near Berne which is being built without a main power supply. It has photovoltaics on the roof, a small wind turbine generating one kilowatt and a gas generator in case sun and wind are not sufficient. The gas generator runs on bottled gas as is commonly used for camping. Those three generators feed into a 24 kilowatt-hours battery.
What kind of a building is that?
A private home. The owner also decided on solar-thermal heating, for which a 9,000 litres solar buffer is provided. In my opinion, a heat pump would have made it even more efficient since the PV array also generates during the winter months, but at least some of the surplus from the solar is stored in the buffer via an electric heating element.
How difficult was it to integrate the two additional generators?
That is also taken care of by the management system of the Powerball battery. We can actually integrate any conceivable energy source into the building.
How important are fuel cells or cogeneration plants in hybrid systems for comprehensive energy supply?
Fuel cells are not yet significant, but we occasionally integrate a cogeneration plant. These are still exceptional cases, but we can tell that our customers are increasingly interested in truly self-sufficient systems. To supply this need, we offer a great storage unit with a large capacity that can charge or discharge at low output. Also, the storage capacity can be extended at any time when the operator’s needs require it.
Why is there no need for high charging outputs with cogeneration plants?
Cogeneration plants tend to have electrical outputs between two and five kilowatts and usually operate for longer periods of time. A battery of 24 kilowatt hours can actually be charged at 2.4 kilowatts. However, that requires adapting the electronics, selecting the right charge controller and, of course, the battery has to match.
Real self-sufficiency is known as being in island mode. Is this the future of the solar and storage sectors?
I can see a trend in that direction. Most suppliers of lithium systems do not offer emergency power or island mode. Once the grid fails, the battery also shuts down. We can do both: emergency power and island mode. And we are giving that to our customers. Since April 2017, all Powerball storage units are set up for full emergency power supply and last summer we also presented our first self-sufficient systems.
How did the customers react?
We have two product lines. In the first consultation, customers often focus on the price – because they have not yet understood the value of emergency power and self-sufficiency. We generally start out showing our line of storage units that do not have this functionality. But eventually, the customers tend to want the full package, even if it costs 1,000 euros more. Because it will keep them in power even if the grid fails.
How do you control the switch from grid operation to island mode?
Our systems make that switch within fifteen to 100 milliseconds, depending on the complexity. The storage unit then specifies a three-phase current grid, which makes it possible to manage the house grid. We can also use the contacts of the ripple control receiver on the inverter to manage the system. To disconnect the building from the grid, an emergency power box is required, which we can easily connect to our versatile system. This system can be retrofitted for emergency power and off-grid operation
Are there different demands from your customers in Switzerland and Germany?
Yes, there is much more demand for genuine self-sufficiency in Switzerland than in Germany. The German customers often say: We will retrofit this later, let us start with an eight-kilowatt hour storage unit. In Switzerland, we sell more storage units with 24 kilowatt hours, with all functions and add-ons. Photovoltaics and storage units are often combined with heat pumps. In Switzerland, yields from solar panels are generally higher than in Germany, especially in the southern regions.
What difference does that make?
In January and February las year we achieved a degree of self-sufficiency of 95 percent with such a plant, which had surprised me. On bad days, the yield one can get from an array of 20 kilowatts can be as little as one tenth, or 2,000 watts, which can then be put into the storage battery. This is sufficient to run the heat pump. There have been maybe five or six days when the heating system had been running low. Generally speaking, solar yields in Switzerland are higher than in Germany: about 100 kilowatt hours more per kilowatt installed. Of course, we also have more snow than in Germany, but once that has melted off the roof and the sun is shining, the light reflections from the white snow in the surrounding area add to the sunlight coming directly onto the solar panels. (HS)
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Read more on energy storage in Europe:
http://www.pveurope.eu/News/Energy-Storage/Storage-advice-Island-inverters-are-key-to-system-speed
http://www.pveurope.eu/News/Energy-Storage/Installed-lithium-ion-battery-costs-below-USD-200-per-kWh
