Solar arrays continue to outshine that of wind farms when it comes to stable and predictable power output, said financial ratings agency Fitch as it released latest analysis of the global portfolio of plants it monitors.

Fitch – which rates debt attached to 57 renewable energy projects – said the PV plants it tracks “are consistently outperforming wind on a global scale”.

Fitch director Andrew Joynt said: “Solar projects are demonstrating lower operational risk, better generation performance and lower volatility. Solar projects also tend to meet or exceed initial volume estimates while wind projects more often underperform against expectations.”

The ratings agency revealed it had downgraded 12% of the 41 wind projects it rates – a portfolio heavily geared to Latin America and the US – all due to underperformance against expectations.

Fitch’s report, Renewable Energy project Rating Criteria, reckons 85% of wind project observations fell below their initial P50 forecasts – the level of production the plant is expected to beat 50% of the time, as determined by independent third-parties – with 53% more than 10% below.

That’s worse than the last time Fitch released similar analysis in 2017, when the agency said 75% of wind project's data showed they missed P50.

Solar projects managed a 79% rate of observations at above P50 level when the data was analysed – covering output since 2010 for wind and 2011 for solar, but excluding ramp-up phases.

The report says “wind project underperformance is often attributed to overestimation of power production due to the greater technical challenge in forecasting relative to solar projects”. And Fitch makes it clear that resource, rather than equipment performance, is at the heart of the issue.

“Aside from some ramp-up issues during the first years, few of Fitch’s rated wind and solar projects were negatively affected by operational underperformance not related to renewable resource levels,” said the report. “Most projects employ proven technologies and there now exists a pool of well-known operators with established track records.”

Fitch reserves a note of caution for offshore wind, which it says “is relatively new and the rated transactions are in their early years of operations. These projects have more complex operations than onshore peers due to the more challenging operating environment offshore and face the risk of outages of the offshore transformers or transmission cables that connect wind farms to the onshore grids.”

The ratings agency also concedes that the limited size and scope of its sample means only limited conclusions can be drawn for the sector as a whole.