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Alasdair Donn

By Alasdair Donn, Principal Energy Solutions Engineer at Willmott Dixon Energy Services Ltd

When we’re all working hard to reduce the performance gap on operational energy and carbon emissions for new projects, a helping hand from some effective low/zero carbon energy technologies would be very welcome….

On recent projects at Willmott Dixon we have looked in detail at how a few of the renewable/low carbon energy systems we have installed are performing in-use. Do we have a clear idea of what performance they should be giving, can we reliably measure this, what issues are our clients having operating these systems, and how are they delivering against expectations on output, cost, efficiency, carbon ?

In terms of our recent experience across monitored projects there is a clear leader in the performance gap ‘league table’ of technologies that ‘do what it says on the tin’. We have monitored several solar photovoltaic (PV) systems on a variety of buildings from offices to schools and housing – in all cases the monitored actual performance, in terms of electrical generation, has achieved the projected as-built performance. We even have a few that are outperforming targets…that kind of performance gap is a welcome benefit.

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For PV systems on buildings we have the benefit of piggy-backing on technology developments that have led to a huge global industry in PV manufacture and installation at grid-scale in large ground-mounted solar parks – even in the moderately sunny UK we now have over 5000 MW of installed PV generating capacity. All of this investment and  technology is based on performance, accurately predicted and delivered in practice. For any PV procurement you may have on your project the supply chain can provide a pretty accurate and validated projection of future performance based on system design, shading, longevity etc allowing a tracking of actual vs target performance to be easily carried out.

As a performance-based product, the industry also offers very low cost and simple monitoring and analysis packages that give web-based access to live and historic energy output data. These packages are at the ‘plug and play’ level of software compared to a complex BMS system, and offer some great benefits too in terms of feedback of information to clients.

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How about costs ? The massive increase in global manufacturing for PV panels and inverters in the last 10 years has led to large reductions in installed costs. Typical commercial systems for medium-scale buildings can be procured for £1000-£1200 per kWp of capacity, and with current feed-in-tariffs and displaced electricity costs, payback on investment is typically 6-8 years.

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So where’s the catch and what are the pitfalls ? As long as you work with supply-chain partner with a sound track record and quality technology the risks with PV are low. Performance data from some of their operating systems is a great place to start. In our experience we have seen inverter failures on some systems, but if reliably monitored these can be easily rectified. Planned maintenance needs are low and panel cleaning regimes if required can also be managed via monitoring performance and cleaning when demanded.

Solar PV is not for every project, but if you want to provide a reliable and low-risk element to your future building energy delivery and operating cost budget it’s well worth a look….