Lithium-ion batteries are long-established, tried-and-tested solutions for grid-connected applications, resulting in other battery types rarely—if ever—being used nowadays in battery solutions to increase self-consumption. However, the situation is different in areas without access to a utility grid. Headquartered in Berchtesgaden, Elektro-Mechanik Meisl GmbH began specializing in solutions designed especially for mountain cabins and isolated islands more than 20 years ago and, in a close development partnership with SMA, has been building off-grid systems in extreme locations ever since.
Open all year round, the Ostpreußenhütte is located 1,630 m above sea level close to Werfen in Austria and offers overnight accommodation for up to 48 mountain hikers. Located in the middle of Salzburg’s Limestone Alps, the area has no access whatsoever to the utility grid. Because of the cabin’s remote location the access roads that could potentially be used for transporting diesel are tricky to navigate—not to mention the fact that diesel generators are noisy and generate emissions that pollute the environment. These disadvantages in using diesel coupled with the remote location of the cabin and the high levels of solar irradiation in the area make it ideal for a solar hybrid system with integrated battery storage.
The PV system with integrated battery storage ensures a year-round, eco-friendly electricity supply. Due to their chemical structure, conventional lead-acid batteries quickly reach their natural limits in the extreme temperatures that prevail in the mountains and under high cycle loads. As part of collaboration with Sony and SMA, the concept of lithium-ion batteries for large, three-phase systems in off-grid applications quickly took shape.
Sunny Island and lithium-ion batteries ensure a year-round energy supply
By June 2014, it was time to put the concept into practice. Following comprehensive load testing on both the SMA test bench in Kassel and Meisl’s test bench, the world’s first three-phase off-grid system with a Sony lithium-ion battery began operating in the Ostpreußenhütte.
The system comprises three Sunny Island 8.0H and four battery blocks with a total battery capacity of 38.4 kWh. Two PV systems (8.6 kWP) and a vegetable oil combined heat and power plant (20 kW) deliver clean electricity. The average electricity demand per day is around 60 kWh.
The system has performed very well, with the only problem so far being that when the temperature in the battery room fell below 0°C during the winter, a software error caused the system to fail. The manufacturers, Sony and SMA, responded immediately by updating the software to prevent a recurrence of this problem.
Hybrid energy supply sets a precedent
Due to excellent feedback received so far, Meisl has already installed a number of other three-phase, off-grid systems with a Sony lithium-ion battery. The largest system to date can be found in the perennially popular Rotwandhaus, which is located at an altitude of 1,737 m in the foothills of the Bavarian Alps. The electricity demand, which at times can exceed 150 kWh during the peak season, is covered by a PV system (15 kWP), a small wind station (5 kW) and a vegetable oil combined heat and power plant (25 kW).
In the past, the Rotwandhaus experienced serious problems with the installed lead-gel battery due to very high power peaks and the associated large number of cycles. To minimize the system’s frequent failures, the battery was replaced with four Sony lithium-iron phosphate blocks with a total storage capacity of 76.8 kWh. Experience has also been consistently positive here, even with frequent load cycles.
Outstanding cell technology and high level of modularity
The Fortelion lithium iron phosphate cell from the Japanese manufacturer Sony offers a high level of resilience during load cycles, a high depth of discharge and large number of cycles. And as early as the cell and system design phase, particular attention was focused on system safety. The Sony-developed system also offers a high level of modularity, which enables an almost unlimited number of system configurations—and, in turn, optimum overall system design.
Off-grid systems for the highest peaks and remotest islands
In addition to SMA inverters and battery banks, Elektro-Mechanik Meisl GmbH also installs combined heat and power plants, PV systems, water treatment systems, fire alarm systems and much more. These components are also used in on-grid applications and are complemented by an energy management central unit developed in-house to complete on-grid battery sets.
The company also provides iron hardware and electrical engineering services for industrial plants, customized switch cabinet construction, retrofitting and machine original equipment. Upcoming scheduled projects involving three-phase Sunny Island systems with lithium-ion batteries include a large-scale Multicluster project in the depths of the Colombian Amazon, various smaller-scale off-grid projects in the Indian Ocean and a project to supply energy to a German Antarctic research station.
Hubert Deubler (guest author)
Hubert works as a planning engineer for Elektro-Mechanik Meisl GmbH in Berchtesgaden and specializes in off-grid electricity supply. Since completing a Master’s degree in “Renewable energies” in Kassel, he has worked closely with SMA, where he has also made many friends. Until 2003, he worked as a forester as part of a development aid program in Latin America and Asia. In his free time, he markets luxury chocolate produced by the indigenous small agricultural cooperative Kallari from the Ecuadorian Amazon.