We got a call from a North Wales farming family in a very remote location who were in some difficulty with their off-grid power supply. A local company had installed a Sunny Island together with 16 x Rolls S600 batteries and 3kW of solar PV. This system was initially supported by an Iseki 9kVA diesel generator which was possibly more 20 years old and difficult to start in cold weather. When they experienced a lot of starting problems they were advised to purchase a new Hyundai 3kVA generator. Within a very short period of time the new generator suffered a catastrophic failure with its piston through the side of the cylinder block.
A site visit and investigation confirmed that the Sunny Island had been set up with a number of incorrect parameters which included the battery capacity, max generator charge current, and battery charging voltages. Rolls batteries are probably the best deep cycle batteries available but they have specific values which must be set in the Sunny Island if they are to charge and discharge correctly and provide a full service life in excess of 10 years. The max generator charge current was set far too high for the air cooled single cylinder Hyundai generator which meant that it was running continuously in an overload condition which rapidly led to its demise.
We spent some going through all of the Sunny Island settings and correcting them as required before leaving the site running on a manually controlled 3kVA petrol generator backing up the solar generation. At the clients request we will shortly be specifying a replacement Stephill 3 cylinder water cooled generator together with a wind turbine and an extension to the battery capacity which will then ensure that their system is fully automated, their batteries are charged and discharged correctly and their lights never go out again.