The owner of a large farmhouse re-employed Worcester Renewable Energy to install a ground mounted photovoltaic system to generate renewable electricity to help run his ground source heat pump system which it had previously installed for him. Six ground mounted PV arrays have been sited along the boundary of an agricultural grazing field adjacent to the main farmhouse. The arrays have been staggered to keep them close to the boundary whilst ensuring that they still face directly south with a pitch of 30 degrees to optimise the yield from the system, estimated to be 14,105kWh/year, about the same as the average consumption of four domestic dwellings. The system is also estimated to save 8,012kg of CO2, or the equivalent of 8 tonnes of sugar!. Prior to installing the system planning permission was first sought from the local authority and a connection offer obtained from the Distribution Network Operator (DNO). A three phase electrical supply was not available to the site which limited the system size to 16.92kW, the maximum size permitted on a single phase supply. A new transformer upgrade was also required as the existing transformer was only rated at 15kVA.
Mr Thorpe said: “Installing a photovoltaic system to generate renewable electricity towards the running of my ground source heat pump system as well as the general electricity for the property makes perfect sense, and me and my wife are pleased to be continuing to do our bit to reduce our carbon emissions.”
“We were extremely pleased with the ground source heat pump system Worcester Renewable Energy installed for us so we decided they were right company for us to continue our renewable energy journey with by having them install a ground mounted photovoltaic system for us.”
Mr Thorpe, Owner.
One of the fields in ownership of the farm was designated by the owner as the preferred location for the PV array as the boundary hedge line faced in a southerly direction. It also screens the installation from view when approaching the property up the main driveway as well as screening it from the nearest passing road, which although a significant distance away, helped with obtaining planning permission being granted.
With the orientation of the PV arrays being of paramount importance for maximum generation from the system, before commencing excavation, the site was set out using laser levels to ensure that the concrete bases required for the panel mounting system faced precisely South.
An interconnecting service trench to lay the armoured AC electrical cables from the three inverters was excavated from the PV array electrical enclosure in the field to the property existing meter box where the system is connected into.
Before excavating to depth for the concrete footings for the PV mounting system, the top soil was first removed and set aside for later reuse. Keeping the top soil separate from the excavated substrata ensured that when the site was re-levelled following completion of the works that the surface could quickly recovers to its original condition or be re-seeded.
Because the boundary line of the field was not perfectly South facing, in order to keep the panel arrays facing directly South, but still keep them close to the hedge row, the total array was divided into six smaller arrays allowing each to set back from the proceeding one. This avoided the array protruding into the field away from the hedge line which would otherwise have been the case.
Trenches were excavated between each panel array and back to the electrical enclosure allowing the DC strings from the panel arrays to be connected together and wired back to the inverters. All cables were laid in conduit for protection with electrical warning tape laid just below the backfilled finished ground level to warn anyone excavating in the future of their presence.
To allow for ease of maintenance around the panel arrays the perimeter of each base was edged in timber to allow grass and brambles to be strimmed neatly up to and around each array.
Two concrete foundations sit within each panel array base designed to support the PV mounting system containing the panels. The bases act to cantilever the wind loads imposed on the arrays by their exposed location. The accurate design of the foundations and associated mounting system ensures overall structural stability of the system.
With the formwork and DC cable ducting in place, delivery and pouring of the concrete to form the foundation bases for the PV mounting system commenced.
Although the concrete foundations sit below the finished ground level and are therefore not visible, each pair were laid exactly level with one another with a smoot surface finish ensuring that the PV mounting system uprights are perfectly perpendicular and at exactly the same height thus ensuring that the horizontal mounting rails accommodating the PV panels are true and level between them.
Once the concrete foundations had cured an impervious membrane was laid over the panel array base to prevent vegetation from growing up under the panels. This assists in the easy maintenance and inspection of the arrays in the future and negates the time consuming and difficult job of having to strim and cut grass and brambles from under the panels and around the uprights.
Bark chippings were laid over the impervious membrane to conceal its presence and blend the panel array bases into their natural surroundings.
Once all below ground work was complete and the panel array bases finished with all the AC and DC cables brought up into position through the concrete slabs work could begin on the assembly of the PV mounting system and installation of the electrical enclosure. This was the point at which the installation started to quickly take shape and where the rewards of the exacting work below ground were borne out.
The PV mounting system was designed specifically for the installation and ordered well in advance of works commencing on site to allow for manufacturing lead times. It was then delivered to site when required in kit form ready for on-site assembly. Made of lightweight aluminium transporting and manoeuvring components into position was carried out with ease.
Each of the horizontal mounting profile rails was accurately spaced and fixed into position ready to receive the PV panels.
Each panel was placed in position and fixed to the profile rails using purpose designed mid and end clamps. These also act to create vertical and horizontal expansion gaps between the panels for thermal expansion preventing the panels from coming under stress and potential fracture. The gaps also allow for a small amount of air flow through the array reducing the total wind loads.
The last few panels were installed and connected completing the arrays allowing the final wiring up of the system to be carried out.
With the six panel arrays complete wiring of the system commenced. This involved wiring each of the DC strings to their corresponding input of the appropriate inverter through DC isolators. The DC isolators allow each sting to be isolated for maintenance and safety purposes. Once all DC wiring was compete, wiring of the AC cables took place from the inverters and AC isolators into the property incoming electrical supply. Cable sizes were designed to ensure that minimum power loss along the cable length to maximise system output.
The ducting containing the three AC armoured cables from the three inverters in the electrical enclosure was taken under the customers garden and patio to the new meter box position adjacent to the existing meter box where the PV system could then be connected into the customers incoming electrical supply.
Before taking up the patio slabs each is numbered to ensure that they could be returned to their original position once the ducting containing the AC cables has been laid.
A trench under the patio was excavated to accommodate the ducting containing the AC cables and then backfilled ready to relaying of the patio slabs previously removed and set aside.
A secondary meter box containing a sub-consumer unit was installed adjacent to the existing primary meter box containing the main incoming electrical supply and Distribution Network Operator (DNO) main fuse/cut out for the property so that the new system could be connected into the main supply.
The completed installation which has been fenced off from grazing cattle.