Chicken Shed Electricity Demand

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This double sided shed houses a total of 32,000 free range laying hens. During the day they have extensive shaded external areas to run out but at dusk they return to the shed for warmth and safety.

All operations within the shed are electrically powered which includes the muck and egg belts, feeders and drinkers, lighting and pop-up doors. The ridge has axial flow fans to assist ventilation in hot weather. An egg packing room and a chiller room complete the installation.

Whilst the client would have preferred a 150kW solar PV array, the DNO imposed a limit of 100kW maximum export capacity unless the client agreed to pay a substantial sum for "grid strengthening measures" which were required some distance from the clients property. As the client had already paid a considerable sum for an upgrade from a single to three phase supply the additional cost could not be justified.

In accordance with the connection agreement Westflight designed and installed a 100kW solar PV array on the South facing pitch of the shed. The array uses 5 x SMA 20000TL-30 3ph inverters which feed into an enclosure containing MCB and RCD protection together with the G59 protection relay and generation meter. An export meter is also fitted so that the self consumption can be accurately recorded over any defined time period.

Initial calculations indicated that self consumption during the winter period would be 65 - 75% whilst in summer this would increase to between 80 and 90% when the ventilations fans would be used more frequently on sunnier / hotter days. These forecasts have so far been reasonably accurate but the client wanted to see if this could be improved.

To record the electricity consumption within the chicken shed we use a Rogowski coils around each of the L1, L2 and L3 tails supplying the main distribution board connected to our data Logger. To record the solar PV generation we use a second logger with its Rogowski coils around each of the L1, L2 and L3 tails leaving the G59 enclosure. With a separate lead connected to our common earth we can then start the data collection process which will continuously record for typically five days and nights. At the end of the data collection period we can download the data and compare the solar PV generation against the electricity demand within a defined period.

In the graph shown below, the red line shows the electricity demand over a 24 hour period in November, averaged over the three phases, L1, L2 and L3.  The blue line shows a typical solar PV generation profile for a day in November whilst the green line shows a typical solar PV generation profile for a day in June.

The electricity demand is quite low between 8pm and 4am when lighting is at its minimum and only basic services are running. Around 4:30am the load increases substantially as the lights come on and the feeders start to run. At 8:00am the load increases again as the egg belts are started and the egg packing operation begins. By 10:00am the load is beginning to decrease as the egg packing is almost completed and most of the birds are now outside. At the same time the solar PV generation is increasing towards its peak around midday meaning that a lot of the on-site generated electricity is now being exported. From the graph it can clearly be seen that there is the possibility to more closely align the period of solar PV generation with the electricity demand from the shed by re-scheduling some of the operations which will then substantially reduce the cost of purchased electricity. However, this will not cover all of the electricity demand during the evening, night and early morning periods. Using intelligent battery storage to store the excess solar PV energy generated during the day to power the house overnight would further reduce the energy costs.

Prior to calculating the size of battery storage required to run a shed of this size we first analyse the load on each phase over a 24 hour period to see if all of the single phase loads which include all of the lighting and most of the electric motors is correctly balanced. If they are not then it is possible that during daylight hours the shed could be importing electricity on one heavily used phase whilst at the same time exporting excess electricity on an under loaded phase.



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