Dairy farmers are early risers. When they drive their cows into the milking stalls at 6 am it is usually still dark and gloomy outside. At night, too, when the animals return with full bellies from the pasture, the sun is already dipping toward the horizon. That is why the large PV systems on the rooftops of dairy operations have to feed most of the power they produce into the grid. After all, the high-consumption tasks of milking and pasteurizing the milk are largely done outside the sunny hours. But this equation changes for a dairy equipped with a storage system.
Just recently, MBT Solar equipped a local dairy farmer in the northern German state of Schleswig-Holstein with a 40 kilowatt hour (kWh) storage system. He re-registered his PV system from 2012 for self-consumption and now uses most of the solar-generated power himself. He is counting on a self-consumption rate of about 80%.
For Mathias Zdzieblowski, an account manager at Tesvolt, the company that provided the storage system, this installation shows a trend. Storage systems in industry and agriculture are on the rise, he says.
The impetus for the installation of a storage system came from the dairy farm itself, said the Managing Director of the installation company Karl-Heinz Rautenberg. It wanted an emergency backup power supply to ensure that in the event of a power failure the milk of the 200 cows would continue to be cooled and not spoil. Until now, this meant acquiring a PTO generator, which would be hauled out of the barn in an emergency and hooked up to a tractor. The farmer opted for a more modern solution. The new storage system is programmed sothat there is always enough power in reserve for emergency purposes. In daily use, it avoids the use of power from the grid. Once it is charged up during the midday hours, it supplies the farm with electricity for evening milking, through the night, and again for morning milking the following day.
The installer believes that economically the concept is worthwhile, once the benefits of self-consumption is coupled with the benefit of the emergency generator no longer being required. Moreover, the solution offers the company more security. For other farmers as well, security was crucial. Imagine the costs involved if the ventilation in a chicken coop failed and the animals suffocate. Or what would happen to newly born piglets if the heat lamps failed because of a power outage, says Rautenberg.
We design our battery systems based on specific customer requirements, and combine that with charging technology from SMA, explains Zdzieblowski. It is a modular system. Up to 60 kWh of storage capacity can fit inside a cabinet. Several cabinets can be combined, if necessary, in a connection-ready container. Some clients only need an emergency power reserve for sub-areas. Others want a private, standalone network that allows them to continue working, uninterrupted. Once the power outage is over, the emergency reserve can also be replenished from the grid if no solar power is available. That eases a lot of anxieties, Zdzieblowski says. At Tesvolt, there is a department dedicated solely to project calculations.
The company says that it trained more than 100 trade partners last year in how to determine the current state of commercial and industrial customers operations, and also determine the initial data for a correct design. Although the situation in agriculture is financially difficult, Tesvolt and MBT Solar were overwhelmed this summer with requests for battery storage systems, report Rautenberg and Zdzieblowski.
Keeping cool with a battery bank
A good friend of Tesvolt Founder Lothar Kohl offered another example. He is the Managing Director of Eis & Friends in Morxdorf in the German state of Saxony-Anhalt and in May invested in a storage system. He, too, was faced with the choice of purchasing a new emergency power supply for 20,000 or completely revamping his energy concept for 200,000. Now he has a new 110 kW peak PV plant and a containerized storage system for 120 kWh of electricity. In the event of a power failure, fridges and
freezers can be supplied with power for another five to six hours, depending on weather conditions. Because the storage system is topped up as early as 1 p.m. in the summer, he is now planning to reduce the temperature of his cold storage a further two degrees during the day to consume even more solar power himself.
A battery storage system that provides backup power also has the advantage that it is rarely subjected to a deep discharge. With such gentle treatment, the system could last 20 years, said Zdzieblowski. Kohl is satisfied with his decision, because it still possesses plenty of potential. In his minds eye he can already see electric company vehicles refueling for free and vans that are directly charged with icy air, rather than using an energy hungry mobile cooling unit. Annual power consumption at Eis & Friends is at least 90,000 kWh and is higher in summer than in winter, which makes PV an obvious choice. Kohl expects a payback in the form of saved electricity costs and the feed-in tariff of around 25,000 per year. In the best case, the system could pay for itself in eight years.
Discussion of economic efficiency
Why is it, then, that numerous experts still warn of the high cost of storage systems and advise business owners to hold off on purchasing them? Theo Remmersmann of the Chamber of Agriculture for the German state of North Rhine-Westphalia is one of those skeptics. For years he has been advising farmers on the installation of PV systems and has already reviewed many offers for storage systems. He says: Ive never seen one that wasnt prettied up. He points out that self-consumption is also burdened by the pro-rata EEG surcharge. This also affects the part of the electricity that is not even consumed, but rather lost during storage and discharge. He asserts that the assumptions for the rise in electricity prices over the next 20 years are often exaggerated. To outsiders, this difference of opinion is difficult to understand because owners and installers keep a close hold on their financial planning. Tesvolt says that the economics of its projects are very good (see box below).
Furthermore, self-consumption is just one of several items that business owners have in mind when they do their cost accounting. The manifold other options that storage offers, such as providing backup power, smoothing the load profile or for regulating feed-in power or
peak shaving, make it attractive in the eyes of the investor. However, these considerations make it more complicated to perform a precise calculation in cents per kWh for stored electricity as a one-size-fits-all scenario for all cases.
Reducing the connected load
Another way to save costs with stored power is to cap peak loads reliably, says Winfried Wahl of RRC Power Solutions. His company develops power supply solutions for customers, and incorporates storage batteries into its concepts. Customers with low base loads and brief peak loads benefit, says Wahl, because they can scale down their power connection with the help of the storage system.
Each year, depending on the network operator, that could amount to 100 per kilowatt of connection power. Thus, depending on the situation, storage systems pay off at different rates. But eight years has been [a] realistic [forecast] in individual cases, he says.
The Saarland town of Homburg is one of RRCs customers, for instance. In their case, it would even be possible to provide control power, said Wahl. That also has a positive effect on the economics.
It is still difficult to assess just how strong the trend towards storage systems in agriculture and industry is; it can be tough to estimate because companies are careful about not revealing their revenue figures. The seasonal load distribution is better-suited to pig and chicken farming, which requires air conditioning, than it is to dairy operations. This evens out again when power comes from several sources, such as wind farms, which has a strong influence on storage use.
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