Consumer information – building the Solar PV revival Blog Post

Consumer information – building the Solar PV revival

March 15, 2021

Colin Meek:

Will the Solar PV market surge again?

When the Government announced the closure of UK’s Feed-in-Tariff there were dire predictions for UK’s Solar PV installation sector. Yet even though installation numbers are well down compared to 2015 there are signs of optimism. MCS has noted a 5% increase in installation numbers in the latter part of 2020 compared to the same period in 2019 and that trend accelerated in the autumn. Consumers generally know that, given the demise of the Feed-In-Tariff, a quick financial ‘payback’ and promises of healthy ‘returns on investment’ are a thing of the past. Although welcome, the Smart Export Guarantee (SEG) makes only a marginal difference to the financial payback period: the period of time needed before the energy savings match the cost of the installation.


So, what is driving current domestic uptake and will the market stabilise and expand?

Clues lie in the wider economic context and the reaction to climate change. A recent study of public attitudes to low carbon generation technologies carried out in Scotland found that the small minority who have taken the plunge are primarily motivated by the environmental benefits they deliver (Climate Exchange, 2020). While that study was focused on renewable heat, it is likely to reflect current attitudes to other forms of low carbon generation. The news service Edie notes that broader Government and popular support for net-zero targets may be promoting demand for microgeneration (Edie, 2020).

At rb&m, we are convinced that building domestic markets for low carbon solutions means giving consumers the ability to make informed choices  and, as the focus on financial payback wanes, the case for Solar PV installation can and should start to focus on two other critical issues:

  • CO2e mitigation; and
  • Solar PV as part of a smart package of solutions that can help families become more resilient by becoming more energy independent.

This analysis crunches the numbers and, while a typical household would struggle to justify the outlay necessary for Solar PV on its own, the economics are transformed when it is combined with other low-carbon technologies. We might be seeing the early signs of a Solar PV revival.


We are saving the planet when we install Solar PV …… right?

A recent study published by Nature calculated the Solar PV energy and emissions debt (or burden) associated with Solar PV deployment and sought to identify when that debt was repaid through clean energy generation. In other words, the point in time when the cumulative disadvantages of Solar PV deployment are outweighed by the benefits. That date, they said, was most likely to have occurred at some time between 2011 and 2017 (Louwen et al., 2016).

There are good reasons why it is impossible to be more certain about the environmental benefits. The life-cycle analysis (LCA) of Solar PV is complex and study results vary dramatically (Raugei et al., 2017). One meta-analysis reported a 10-fold variation in results for the assumed embedded energy involved in PV panel production (Bhandari et al., 2015). A 2014 report by the Grantham Institute for Climate Change found that the carbon cost of crystalline silicon Solar PV deployed in Europe can double if the carbon intensity of the grid used for the manufacturing is typical of China. In 2014, the Intergovernmental Panel On Climate Change (IPCC) said the carbon cost of Solar PV ranged from between 18 to 180 gCO2eq/kWh (IPCC, 2014).

While the Solar PV industry has historically placed emphasis on the likely annual financial outcome of a domestic-sized installation, a lot less certainty is expressed about the ‘carbon payback’ for UK Solar PV installations: the period of operational time needed to save the CO2e as emitted during the manufacture and distribution of the system.

The production of Crystalline Solar PV units is very energy intensive, but it is usually assumed that this ‘embodied carbon’ is quickly ‘paid back’ once the units actually generate electricity. In fact, the energy payback is often not straightforward and depends on range of factors such as:

  • the crystalline silicon technology used;
  • the location of manufacture and the location of installation (the carbon intensity of the grid electricity that the Solar PV generation displaces);
  • the rated efficiency of the panels, and
  • critically, the suitability of the installation site.

Of pivotal importance here is the dramatic fall in the carbon intensity of UK’s grid electricity. In 2010, every kWh of grid electricity displaced by solar electricity saved 0.458kgCO2e. As more low carbon generation has been added to the grid that figure obviously falls. In 2019 it fell to just 0.255kgCO2e and 0.233 in 2020. The more electricity supply grids decarbonise, the more important the Solar PV system’s life-cycle impact becomes when calculating the net environmental gain of that system. As the grid decarbonises further this scrutiny of the Solar PV industry can only intensify.


But what do these figures actually mean for a small domestic-sized installation?

Two estimates are needed to calculate the ‘energy payback’ (EPBT) of a Solar PV system: an estimate of the initial energy used to produce and distribute the system and an estimate of the generation it will deliver during its whole operational life.

The life-cycle carbon cost of Solar PV can be expressed as MJ/m2 which enables a comparison with the expected output of a system in kWh. For example, a systematic review of life-cycle analyses found the average embedded energy for mono-Si installations to be 3532MJ/m(Wong, Royapoor and Chan, 2016).

For an estimate of generation, rb&m use a model based on measured solar irradiance at a site in the north of the UK combined with data from the PVGIS service and correlated with figures from NASA to estimate the potential output of a UK domestic-sized system. This model provides an irradiance curve giving monthly generation and we can test a range of variables and their impact on the financial payback and EPBT. For our examination of EPBT, we assumed the system had an optimum angle and orientation, no shading and degradation of 0.7% per year.  Forecast generation for 4m2 mono-Si panels (rated efficiency 17.85%) is given in Figure 1.

Solar PV Consumer Information Generation Curve

Fig 1: Forecast generation from measured data correlated with PVGIS: 4m2 from north of UK

We can use the best estimated generation (Figure 1) and embodied energy of the panels to build an energy payback graph (Figure 2) and, using the embodied energy requirement of 3532MJ/mas cited above, the energy payback (or EPBT) was calculated to be 7 years.

Solar PV Energy Payback Consumer Information

Fig 2: Forecast energy payback assuming 3532MJ/m2 energy debt


The energy payback calculation can be used to estimate and understand the system’s CO2e mitigation using two further values:

  • the carbon intensity of the grid electricity that the system displaces; and
  • the carbon intensity of the electricity used in the system manufacture.

For example, if we assume the carbon intensity for both reflects the recent carbon intensity of UK’s grid (in 2018) then the lifetime net CO2e saving is under 1 tonne per m2 (and the carbon payback also about 7 years).


Seven years sounds OK but is there a catch?

That’s an optimum outcome and there are huge uncertainties. If we assume the carbon intensity of UK’s electricity remains at around  0.225kgCO2e, and we also assume that the panels were manufactured in China where the carbon intensity of the grid is much higher (around 0.650kgCO2e) then the lifetime carbon saving drops dramatically and there is no energy payback until the end of the second decade. Circular Ecology has carried out a similar exercise for a much larger commercial-scale office installation and reached similar conclusions (Circular Ecology, 2020). And estimates provided by the Energy Saving Trust for domestic PV also show that the CO2e savings do not occur until the second decade of operation (Energy Saving Trust, 2021).

Another key uncertainty here relates to the reliability of life-cycle estimates to capture all of the embodied energy involved in Solar PV production. One meta-analysis (Bhandari et al., 2015) used a ‘cradle to gate’ system boundary that encompassed the embedded energy (raw material through all manufacturing stages) for the module, the other ‘balance of system’ components (such as the inverter) and all supporting infrastructure. The average embedded energy for mono-Si ranged from around 3500MJ/m2 to 9,000MJ/m2 with an average of just over 6,000 (embedded energy for multi-Si ranged from 2,000MJ/m2 to 6,000). Again, when applied to our model above, that 6,000MJ/m2 average for mono-Si panels extends the energy payback into the second decade of operation.

As stated above, life-cycle estimates of embodied energy vary but there can be no question that the energy (and carbon) payback period of systems imported into the UK that have a high embodied energy will be significant. Additionally, the above analysis assumes that the panels have an optimum angle and orientation and no shading. Badly positioned panels will erode CO2e savings further.


Discussion: Is there any good news?

At first glance, it would be easy to assume that the rapid decarbonisation of UK’s grid will inevitably stall the roll-out of Solar PV. There are at least three factors that can help remove that roadblock to further mass deployment.

Firstly, domestic Solar PV installed as part of a smart bundle of energy efficiency offers households the potential for dramatic carbon and financial savings. A typical consumer’s demand for electricity does not correlate well with the periods when solar irradiation is at its peak – in the middle of the day. Household electricity use tends to peak at breakfast time and then in early evening. Consequently, a typical Solar PV system with no battery storage will export at least half of the solar generation. A simple way to use more of the generated electricity is to use diverters to heat hot water in immersion tanks.

Other solutions, however, are not only transforming the economics of Solar PV they are transforming the financial case for a range of other low carbon technologies. For example, the Zappi car charger diverts Solar PV generated electricity (that would normally be exported to the grid) to the EV battery – cutting car running costs to almost nothing for large parts of the year. If an EV owner is out during the day, she can store Solar PV generated energy in batteries which then charge the EV in the evening. The economics of heat pump installation can be similarly transformed using stored solar generated electricity to power the heat pump when it is most needed.

Those investments are not cheap but a household that can stretch to those sums (without taking on the burden of finance interest) will be more financially resilient and dramatically cut transport fuel and energy costs as well as CO2 output.

Secondly, the lessons from the above energy payback analysis underline the importance of site optimisation, the EPBT and transparency. Governments, local authorities and consumers should place more emphasis on the embodied carbon of Solar PV to put pressure on producers and importers via installers to improve production methods. As Circular Ecology argues, transparency is key: “Until manufacturers produce detailed embodied carbon footprints of their products, procuring a lower embodied carbon crystalline PV panel becomes a challenge.” Better data on embodied energy would raise awareness and help consumers at all levels make an informed choice. And those choices will build pressure on producers to cut the embodied energy involved. Consumers might tolerate a financial payback that extends beyond 10 years but, for a sustainable long-term market that consumers can trust, better reporting standards are needed and product declarations will ultimately help the supply chain respond positively to the decarbonisation of UK’s grid.

Thirdly, with increased scrutiny comes innovation and better practice. Louwen et al., show that for every doubling of installed PV capacity, the greenhouse gas output falls by between 17 and 24% depending on the technology. The more focus there is on embodied carbon, the faster the industry will clean up its act. For example, there are signs that some UK-based companies such as Naked Solar are placing more emphasis on the low-carbon credentials of their own choice of panel and First Solar have announced plans to power all of its manufacturing with renewable energy (First Solar, 2020).

And, with innovation comes new technology. Solar PV cell efficiencies are improving which means more generation for every square meter of panel improving the case for installation. Typical efficiencies of commercially available silicone panels are around 17% with the best offering slightly over 20%.  Recent lab results show that 25% may not be too far distant. Perovskite crystal technology is also showing promise when layered onto silicon in hybrid cells. While some claim that perovskite technology still has a series of technological road-bumps to overcome (Nature, 2019) others claim perovskite represents a genuine step change in the solar market (Oxford PV, 2020).


What next?

While it is clear that domestic Solar PV will have an important role to play in helping households maximise the benefits of other technologies such as EVs and heat pumps, there are dangers that may yet derail the market. Smart home energy efficient technologies offer huge benefits but, when bundled together and hyped through aggressive selling, the potential for confusion and miss-selling is obvious. At rb&m, we see a range of bad practices but one of the worst tactics deployed is confusion marketing used to camouflage high interest payments that have the potential to nullify the financial benefit of the renewable technologies. Consumers can also be locked into contracts using electricity supply agreements that effectively transfer most of the financial benefits.

Our next post on Solar PV in this series will focus on:

  • Solar PV’s potential to transform the case for several low carbon technologies;
  • how consumers can extract the maximum benefit of a Solar PV installation by boosting the financial and carbon savings available; and
  • what more can be done to prevent miss-selling and confusion marketing.


References and Further Reading

Bhandari, K. P. et al. (2015) ‘Energy payback time (EPBT) and energy return on energy invested (EROI) of solar photovoltaic systems: A systematic review and meta-analysis’, Renewable and Sustainable Energy Reviews. Elsevier, 47, pp. 133–141. doi: 10.1016/j.rser.2015.02.057.

Circular Ecology. (2020). Embodied Carbon of Solar PV: Here’s Why It Must Be Included In Net Zero Carbon Buildings. Available at: (Accessed: 3 February 2021)

Climate Exchange. (2020). Public awareness of and attitudes to low-carbon heating technologies. Available at: (Accessed: 10 January 2021)

Edie. (2020). One year on: How has the solar feed-in-tariff closure impacted renewables in the UK? Available at:–What-impact-has-the-solar-feed-in-tariff-closure-had-in-the-UK-/ (Accessed: 10 December 2020)

Energy Saving Trust. (2021). Solar Panels. Available at: (Accessed: 5 March 2021)

First Solar. (2020). First Solar Commits to Powering 100% of Global Operations with Renewable Energy by 2028. Available at: (Accessed: 5 March 2021).

Intergovernmental Panel on Climate Change. (2014). Climate Change 2014: Mitigation of Climate Change. Working Group III Contribution to the Fifth Assessment Report of the Intergovernmental Panel on Climate Change. Available at:

Louwen, A., van Sark, W., Faaij, A. et al. (2016). Re-assessment of net energy production and greenhouse gas emissions avoidance after 40 years of photovoltaics development. Nat Commun 7, 13728 (2016).

Nature. 2019. The reality behind solar power’s next star material. Available at: (Accessed: 5 March 2021)

Oxford PV. 2020. IN THE NEWS: The Guardian: “UK firm’s solar power breakthrough could make world’s most efficient panels by 2021”. Available at: (Accessed: 5 March 2021)

Raugei, M. et al. (2017). ‘Energy Return on Energy Invested (ERoEI) for photovoltaic solar systems in regions of moderate insolation: A comprehensive response’, Energy Policy. Elsevier Ltd, 102(June 2016), pp. 377–384. doi: 10.1016/j.enpol.2016.12.042.

Wong, J. H., Royapoor, M. and Chan, C. W. (2016). ‘Review of life cycle analyses and embodied energy requirements of single-crystalline and multi-crystalline silicon photovoltaic systems’, Renewable and Sustainable Energy Reviews. Elsevier, 58, pp. 608–618. doi: 10.1016/j.rser.2015.12.241.


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