Remote Herefordshire Cottage

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Wind & Sun design and install electricity system for rented property that was entirely off-grid – with the requirement to be automatic and independently controlled

A Sunny Island system with 3.5 PV array were installed as part of a house renovation where the cost of grid connection was prohibitive. The system owner is able to claim Feed In Tariffs for the solar generation at the same rate as if they were grid connected.

The system was designed to tie in with a diesel generator using a 14kWh 48VDC Rolls deep cycle battery store and a 5kW Sunny Island SI-5048 battery charger/inverter connected to a 3.5kWp Photovoltaic (PV) array. Smaller loads can be run using the battery & inverter with the generator used for larger loads and backup battery charging. This avoids, for instance, a 7.5kVA generator running late at night to run a TV and a light bulb - giving increased efficiency and lower running costs and allows power to be available 24hr/day without having the generator running constantly.

Loads are normally run from the inverter (up to inverter capacity), if the loads increase or the battery becomes low the generator will be started and supply transferred. Whilst the generator is running it is controlled via the central management system operating as apowerful battery charger.

Often sufficient charge is put into the battery so that during times of high use (eg. when using washing machine) loads can be run without using the generator except for occasional battery recharges. Generator efficiency is maximised by always being run fully loaded and so fuel & maintenance costs are minimised.

The PV array in the system further reduces engine use cutting down times that the generator is run purely for battery charging. The generator then becomes a back-up for times of unfavourable weather and to meet peak load requirements.

The 3.5kWp PV system consists of 20 BP Solar BP4175 175Wp modules combined with an SMA SB-3300 Sunny Boy inverter which is connected to the AC output side of the Sunny Island.

Because of this a conventional AC generation meter was used to enable the system owner to claim Feed In Tarriffs for the solar generation at the same rate as if they were grid connected.

In operation, the generator is barely used from Spring until Autumn but is automatically controlled to provide additional battery charging during the winter months when there is less hours of sunlight.

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