Top innovation meets giant installation on a PV array described as London’s largest yet, as Imtech’s Paul Burnett explains.
Imtech was appointed as an energy services company to all of the London boroughs within the West London Alliance via the Greater London Authority’s RE:FIT framework.
As part of this, and in consultation with Hounslow Borough Council, Western International Market was identified as an opportunity to install a solar photovoltaic array as part of a £2.2m redevelopment.
Largest PV array yet
This has culminated in what is claimed to be the largest solar PV array in London, incorporating ground-breaking battery storage technology and innovative demand management controls.
Western International Market is located in Southall, west London, and is one of the capital’s principal wholesale markets of fresh produce. Heathrow Airport is a nearby neighbour and the market acts as distributor for goods flown in from around the world.
Under Hounslow Borough Council’s ownership, the market was purpose-built in 2008 and houses about 75 independent wholesale businesses.
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The site is one of the council’s largest and consists of two main buildings: the Produce Hall and Flower Hall. The combined roof area is approximately 11,000 sq m.
The buildings were one of the biggest users of electricity within the council’s portfolio at about 3.6 MWh a year. Consequently, it was well suited to the installation of solar PVs that can provide savings from both the reduced consumption of grid electricity and feed-in tariffs. This means a revenue stream for the council over the next 25 years.
“The installation provides a peak capacity of 1.7 MWh, with an annual yield of approximately 1.5 MWh, representing more than a third of the total consumption of the facility”
Consisting of 6,069 PV panels across the two roofs of the facility, the installation provides a peak capacity of 1.7 MWh, with an annual yield of approximately 1.5 MWh, representing more than a third of the total consumption of the facility.
The PV panels are linked to 47 distributed invertors situated on the external facade of the facility below the main roof. The invertors are wired to the existing LV infrastructure at high level within the buildings. Excess energy is transmitted by the existing electrical infrastructure back to source – in this case, the two electrical substations situated on site.
Collaboration helped to establish that, due to the operating activities of the site, peak-load demand is in the early hours of the morning, when the PVs are unable to generate electricity.
Technology was developed by the team to meet this demand via two lithium-ion battery storage units, rated at 120 kWh each (240 kWh total) and with a usable capacity of 192 kWh.
Charging throughout the day, when demand is low and generation is at a peak, the batteries are discharged via invertors into the existing LV infrastructure, after the fiscal meter, to meet demand during peak times.
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Control is achieved by the installation of an energy meter within each of the substations, which is sensitive to flow direction, leading to optimised charge and discharge of the units. Each unit has a bi-directional management system that can charge and discharge at 36 kWh.
The storage batteries are housed in purpose-built enclosures adjacent to the substations and have optimised temperature controls; this ensures maximum capacity and life from the system.
A large part of the electrical demand is recharging fork lift trucks. To manage the load factor, dedicated timer switches have been installed to each charging circuit to move energy demands to when the PV generation is at peak. This still allows optimum charging times at 8-9 hours with no impact on the tenant’s operational activities.
Thanks to pre-accreditation, the client has obtained the higher feed-in tariff prior to the recent 87 per cent cut by the government.
This, along with 90 per cent of the solar PV generation being consumed on site (only 10 per cent is exported), has ensured the system installed will provide the council with an internal rate of return of about 9 per cent and a payback of 7.19 years, while reducing carbon emissions by approximately 780 tonnes every year.
The long-term guarantees delivered by Imtech through the RE:FIT framework mean the council can rest assured that its investment in the Western International Market will pay off.
Paul Burnett is group director at Imtech Low Carbon Solutions