SMA Sunny Island Off-Grid System
Effective off-grid supplies can be provided and Feed In Tariffs claimed for the solar generation, by using a SMA Sunny Island inverter/battery system in conjunction with a diesel generator and a solar PV array.
The battery store is kept charged by the solar panels and normally supplies the loads. The generator is only needed if loads exceed inverter capacity or if the batteries need recharging in times of unfavourable weather. Whilst the generator is running it powers the loads and the Sunny Island inverter operates as a powerful battery charger to replenish the batteries.
Generator efficiency is maximised by always being run fully loaded and so fuel & maintenance costs are minimised.
The PV array is connected using a Sunny Boy inverter which directly powers the loads during the day. Over-charging of the battery is prevented by power limiting the Sunny Boy in response to frequency changes initiated by the Sunny Island based upon battery state of charge.
This consists of exactly the same components that are used in a grid connect system – PV modules, mounting system, Sunny Boy inverter etc. The only difference being that the Sunny Boy inverter country code grid parameter is set to ‘Off-Grid’ instead of G83/2 or G59/3.
A standard kWh meter is used to show the total energy generated by the PV system as a basis to claim Feed In Tariff credits per unit of electricity generated.
This is configured for 48V and sized to store power generated during the day and provide enough usable energy to meet anticipated demand with minimum use of the generator. It uses specific deep cycle batteries designed for this type of application.
Typically, everything would be sited in an outbuilding which needs to be well constructed and weathertight. The batteries need to be sited in a separate ventilated area from the inverter & controls.
This is a fully integrated part of the whole system controlled automatically from the Sunny Island inverter – simple ‘two-wire’ control is required ie. a generator which runs when contacts are closed and stops when they are opened. Other generators can be accommodated but at greater cost.
This can be included to allow owners and installers to see the performance of the system remotely over the internet. Ideally this is done via a broadband internet connection if available (which involves no running costs) or can be via a telephone or GSM connection.