To PV or not to PV?

What is the carbon impact of manufacturing renewable energy technology and how does it affect Zero Carbon pathways? Design Director Marie-Louise Schembri examines how the carbon savings of renewables compare to the embodied carbon of the system.

Theoretically, we need over 50 million photovoltaic (PV) panels (over 800km2) to replace all of the energy generated by fossil fuels in the UK. The UK has committed heavily to use offshore wind farms to decarbonise energy, planning to increase the current 11GW capacity to 40GW by 2030, which equals approximately 30% of electricity demand.

While this is all very positive for reducing carbon emissions from energy use, it is important to remember that everything we manufacture has a carbon footprint, resulting from the extraction of raw materials, transportation across supply chains, the manufacturing process and delivery to a final destination. So how do the carbon savings of renewables compare to the embodied carbon of the system?

Historically, embodied carbon emissions have been mostly ignored by government and business policy and have only recently started to get the attention they need. Buildings in the UK contribute 49% of the UK’s overall greenhouse gas emissions, and about 20% of this can be attributed to embodied carbon.

Policy in the built environment has so far focussed on reducing energy consumption and generating as much renewable energy as is feasibly possible. There is nothing wrong with the latter part, but in the face of a Climate Emergency we need to keep an eye out on unintended consequences of focusing too much on energy consumption.

Over the past 15 or so years, local planning policy has driven new developments to install renewable energy systems. In dense urban settings – office buildings for example – the result is typically a relatively small array of roof photovoltaic panels that generate approximately 1% of a building’s annual energy requirement. They are a lot more effective where the ratio of PV area to floor area is more balanced, such as on the tops of houses, logistics buildings and sports stadia, but commercial developers have begun to question the value of PV and small scale renewables, labelling them as tick-box symbols of greenwash.

So, are they worth the carbon impact?

Figure 1 Carbon balance of a 217m2 roof-mounted photovoltaic array (kgCO2e) installed in 2025

To answer this question, we mapped the carbon balance of a PV array over 60 years, assuming 2 replacement cycles based on real life FM activity. If you apply the carbon savings as an offset of carbon in the national electrical grid (best case scenario), the initial embodied carbon is displaced at a third of the array’s first lifecycle. But as electricity in the grid decarbonises (because of planned investment in large scale renewable energy on a national level) the panels offset progressively less carbon over time. In fact, from 2035 onwards, the carbon in grid electricity may be so low that installed PV will barely offset any of the embodied carbon, even if their efficiency increases by, say, 20% and embodied carbon decreases by 25%!

For the next 10 years, however, small scale generation still makes sense where technically feasible. In fact, their value is growing because of large scale battery deployment, which will make it possible to store renewable energy for later use on site, instead of dumping it into the grid (exporting it). Batteries and 5G also make aggregating, sharing and trading of renewable energy over a city, regional or broader level a possibility, so a building’s array becomes part of something much better and more efficient. This is referred to as Virtual Power Plant (or Station) and a few have already been deployed in parts of the UK in the past five years.

Over time, renewable energy systems will cost less carbon to produce, but it is key for our industry to continue to review the situation and keep our eyes open to the wider effects of procurement decisions. PV will continue to be an important part of the carbon puzzle for the foreseeable future, but it is imperative each case is studied on its own merits – in terms of both operational and embodied carbon.

Get in touch with Design Director Marie-Louise Schembri if you would like to find out more.

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