Keeping a community solar farm generating to 2036

The operating array, commissioned in 2016 and contracted under a Feed-in Tariff to 2036.

Arc Renewables advised a community energy society on the feasibility of replacing the ageing central inverters at a 4,998 kWp ground-mounted solar farm, setting out a route to protect output for the remainder of its Feed-in Tariff term.

The society owns and operates the solar farm on behalf of its members, with income underpinned by a Feed-in Tariff that runs to 2036. The modules remain healthy and within warranty, but the original central inverters are approaching the end of their serviceable life. One unit was already running on parts cannibalised from another, the operations and maintenance contract was due to expire, and data handover from the incumbent had been slow.

The board needed an independent view, free of any contractor's commercial interest, on whether and how the inverters should be replaced, what it would cost, and how to sequence the work so that generation income was protected through the remaining years of the tariff.

Arc grounded the study in evidence rather than assumption. Twenty-seven monthly operating reports and the society's own independent performance model agreed to within 2.6 percentage points across 71 months, giving a firm baseline against which any intervention could be judged.

A non-intrusive site visit confirmed the as-built plant and its condition. Arc personnel observed and photographed from outside the arc flash boundary, with all cabinet work carried out by the operator's staff under their own permit to work. The picture that emerged was clear enough to base a capital decision on.

The instinct on a site of this age is to repower to modern 1500 V inverters. The site's own electrical design ruled that out. The array operates at roughly 730 V DC, below the approximately 850 V minimum tracking voltage of current 1500 V inverters. They simply would not work without restringing the entire array, a repower-scale intervention that is not justified while the modules are healthy and in warranty, and one that would carry real subsidy accreditation risk under the tariff.

The recommended route is replacement with 1000 to 1100 V string inverters, reusing the existing site transformers and their established grid interface. Indicative all-in cost falls between £0.5M and £0.8M. Crucially, the inverter hardware itself is only 15 to 25 per cent of that figure; the substantial costs sit in DC re-termination, AC collection redesign, the medium-voltage interface and protection, the grid application, monitoring, and labour.

The recovered yield comes from three sources: a modular failure mode, where losing one string inverter costs a fraction of output rather than a sixth of the site; far finer tracking, moving from six zones to several hundred and recovering losses from per-string shading; and closing the monitoring blind spot at the second station so faults are seen and fixed sooner.

There is a strategic point too. The original central inverters are bespoke, with no commodity replacement market now that the manufacturer has left that business. String inverters carry standardised interfaces and commodity pricing, so any future discontinuation becomes a manageable replacement event rather than an orphaning risk. Extended warranties to 2036 and a small holding of on-site spares decouple uptime from the supply chain.

Arc carried the study as independent technical adviser, owing nothing to any supplier or contractor. The work ran across several strands, each feeding a single board-ready conclusion.

The study, with a standalone executive summary, was delivered ahead of the society's board meeting. It gives the directors a costed, evidence-based route to protect output for the remaining decade of the tariff, a clear understanding of why the obvious upgrade does not apply here, and a phasing plan that keeps the asset earning while the work is carried out.

The study is currently with the board for consideration. Arc's role throughout has been to give an honest, independent technical view, not to sell a solution.

A fifteen-minute call is enough to understand your asset, your objective, and your decision context and to tell you whether Arc can add value in your situation.

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