I was contacted by a local Sri Lankan PV engineer who wanted his company to make a decisive move into off-grid systems. Previously they had successfully installed grid connected solar systems, but with no experience in off-grid they felt the safest option was to partner with a high profile foreign company and make a competitive tender bid for the project.
From that point on we worked together as one to prepare the bid documentation. As it turned out, our Eluvaitivu Island PV and Wind micro-grid proposal won and we set about procuring the components and having them delivered to the remote location by planes, trains and automobiles and a local small boat service. There are no vehicles on the island but for a uniquely Sri Lankan machine called a “Landmaster,” which is a small agricultural rotary hoe converted to utility vehicle of sorts.
The system configuration is AC coupled and consists of a 46kWp PV array, six 3.5kW wind turbines, twelve SMA Sunny Island 8kW inverters and a 100kWh lithium-ion battery bank. The purpose of the off-grid system is to reduce the consumption of diesel at the existing power plant.
There are 180 families living on the island all of whom rely on fishing for their income. The people of Eluvaitivu have received assistance previously for the construction of the local fish market building and more recently a fish drying facility. Their solar power project is a fine example of disruptive technology reaching even the remotest of islanders.
System Technical Features
The system is built around a bank of 20 6.4kWh (5kWh usable) lithium-ion battery cabinets. For three-phase power, SMA Sunny Island inverters are installed in clusters of three, one inverter per phase. Using 12 inverters, a total of four clusters were installed, each one requiring five battery cabinets. The batteries have an inbuilt battery management system, with software that enables the required parallel configuration in addition to the communications with the inverters.
The AC coupled concept allows for the PV and wind inverters to inject power to the micro-grid formed by the SMA battery inverters. Control of the battery charge current is achieved by shifting the AC frequency of the micro-grid higher as less charge current is required. The AC coupled inverters sense the frequency shift and ramp down the power from the solar panels and wind turbines.
In addition an Allsolus energy monitoring system connects directly to the battery, wind and PV inverters as well as the back-up generator, weather sensors and the feeder to the island loads. This allows the detailed remote monitoring of the entire system for operations and maintenance. The Allsolus remote monitoring is a crucial feature and is arguably the single most important factor in the ongoing success of such a complex system.
Construction and Commissioning
Despite the extreme heat and difficult conditions on the island, the Sri Lankan installation team was highly motivated to build what is the largest off-grid system in their country. With technical support and guidance from me and the local’s gritty Sri Lankan determination, the construction phase was completed by the end of April 2016.
The commissioning phase commenced with the paralleling of the battery cabinets. Firstly the latest firmware from the manufacturer had to be loaded as the paralleling capability had only just been developed and not yet factory tested by the battery manufacturer. Without any manuals or procedures the method to synchronise and equalise the 20 battery cabinets was worked out by trial and experimentation. Once the batteries were all functioning perfectly, the battery inverters could be fully set up, followed by the PV inverters and then the wind inverters.
Over a period of 10 days working 20 hours a day, the system was then tuned and matched to the island load profile. The system was then handed over to its new owners after two weeks of specialised operator training.
It was a profound experience for me working at Eluvaitivu Island on this job. Sleeping on the concrete floor where the local installers used the solar panels cardboard packing as a mattress, eating food with your hands, drawing water from a shallow well with a bucket, all these things are reminders of just how easy we have it in the West. Solar and wind power adds so much to the basic conditions of remote villages, I look forward to commissioning many more such systems.
(by Peter Bulanyi - onestepoffthegrid.com.au)