Off grid PV and Wind Turbine system for a farm
Wind & Sun designed and installed this off grid PV & Wind Turbine system in 2003
- Module type: BP Solar BP3160S (8 x 160Wp)
- Inverter: 1 x SMA SWR-1100 (1.1kW)
- Wind turbine; Proven WT2500 (2.5kW)
- Inverter 1 x SMA WWR-2500 (2.5kW)
- Sunny Island system: 1 x SMA SI-4500 (4.5kW)
We were approached to provide a design for a renewable energy system for a small organic hill farm on the Welsh borders.
The existing electricity supply was an ageing 6.5kW diesel generator which ran the house and smallholding. Existing electrical loads were limited to times of diesel generator use but included bore-hole pump, lighting, HiFi, TV, vacuum cleaner & washing machine. The owners wanted to add to this a fridge & freezer (they farm cattle & sheep) and so a continuous electricity supply was needed. Running costs were very high and naturally being surrounded by the peace and quiet of the beautiful Welsh countryside they kept operation of this generator to a minimum but now wanted more of the convenience and comforts of modern living.
Various grants have been introduced to promote the uptake of renewables in the UK in order to help with the country’s commitments to reduce CO2 emissions so now seemed like an opportune time to improve their situation. The 2.5kW windturbine and a photovoltaic array system backed up by a generator, incorporates features of both grid-connect & off-grid systems and has the advantages of high renewables penetration and AC coupling that can potentially run up to 8kW of loads without back-up generator in right weather conditions.
The Wind Turbine System
Although situated in an area of high windspeeds the farmhouse itself was surrounded by trees and hills so it did not make a good site for a wind turbine. After looking at all available parts of the farm an optimum site for the wind turbine was decided upon – this was located at approx. 350-400m from the farm with 270º exposure to prevailing winds. This is an ideal site for a 2.5kW Proven windturbine – a machine we were confident would give long-term high performance. Remember, twice the windspeed gives eight times the power!
However, using a typical 48V system and wind turbine this distance would have required using very heavy 120 sq mm output cable costing over £3000 and still result in approx. 8% power losses for a 2.5kW machine. To overcome this a high voltage version of the wind turbine and a Windy Boy inverter and the ‘Sunny Island’ was proposed. To overcome the problem of voltage & power losses between wind turbine and battery a 300V version of the Proven wind turbine was used and power taken down the hill at this voltage. This allowed more manageable three core 25 sq mm cable to be used reducing costs to approx £850 and power losses to approx 1%.
The PV System
In addition to the wind turbine we proposed using a photovoltaic (PV) array to charge the battery in order to give a balanced supply throughout the year. As the house had tall trees located to the south mounting of the PV array on the roof was not suitable due to shading. A nearby location was found which received direct sunlight for most of the day & year and it was decided to locate a freestanding PV array here. Because of the Sunny Island approach already decided on for the wind turbine distance from this location to the battery location (30m) was not an issue.
This consists of 8 x BP Solar BP3160S 160Wp polycrystalline modules (1.28kWp) used with an SMA SWR 1100E 1.1lkW Sunny Boy inverter. The modules are 24VDC nominal and wired in one series string using integral Multi-Contact connectors. This array was mounted on the 45 º pitch south-facing roof of a purpose built shed in which were mounted inverters and switchgear for both PV array & wind turbine. The shed was built by the owner based on some sketches we provided so was ready when we came to install the PV’s. This was done using a BP Solar Solar Energizer mounting system. DC disconnects rated for 750VDC 16A labelled ‘ PV Array main isolator – contains live parts during daylight’. No charge controller is required and the MPPT features of the Sunny Boy are utilised allowing maximum output from the PV’s to be obtained.
The battery was located in a lean-to building adjacent to the farmhouse protected from the cold and the Sunny Island inverter was also located here. The battery consists of 24 600Ah deep cycle traction cells to give a 48VDC 600Ah (approx. 23kWh useable capacity battery bank). A wooden enclosure was built around this with ventilation to the outside.
The Sunny Island works as both a high quality sine wave 4500W 230V 50Hz power source and as a powerful battery charger. The Sunny Island inverter can start the generator if battery gets low or loads exceed inverter capacity. It is designed to work with all types of generator with the capability to preheat and cool down engines. The generator at this property is of the ‘Startomatic’ type – this means it includes a control panel so that it automatically starts when a load is switched on and stops once all loads are switched off. In order to allow the Sunny Island to start this generator a 60W heater ‘dummy load’ was included – when the generator is required the Sunny Island switches on this load which in turn starts the generator. An extra three-core armoured cable was put in between the Sunny Island and the generator shed in case the generator was replaced with another type in the future.