Nuclear has highest investment risk; solar shows lowest, say US researchers

Nuclear power plants exceed construction budgets by an average of 102.5%, costing $1.56 billion more than planned, according to a study by Boston University’s Institute for Global Sustainability.

A new study by the Institute for Global Sustainability at Boston University found that energy infrastructure projects exceeded planned construction costs in more than 60% of cases. Researchers analyzed data from 662 projects across 83 countries, spanning builds from 1936 to 2024 and totaling $1.358 trillion in investment.

The study covered a wide range of project types. These included thermoelectric power plants fueled by coal, oil or natural gas, as well as nuclear reactors, hydroelectric facilities and wind farms. It also examined large-scale PV and concentrated solar installations, high-voltage transmission lines, bioenergy and geothermal plants, hydrogen production sites, and carbon capture and storage systems.

Researchers modeled projects with minimum thresholds: power plants with more than 1 MW of installed capacity, transmission lines over 10 km, and carbon capture systems processing more than 1,000 tons of CO₂ per year.

In the study, “Beyond economies of scale: Learning from construction cost overrun risks and time delays in global energy infrastructure projects,” published in Energy Research & Social Science, the authors found that energy infrastructure construction takes 40% longer than planned – on average, a delay of roughly two years.

Nuclear power plants had the highest cost overruns and delays, with average construction costs exceeding estimates by 102.5%, or $1.56 billion. Hydroelectric projects followed at 36.7%, then geothermal (20.7%), carbon capture (14.9%), and bioenergy (10.7%). Wind projects averaged a 5.2% cost increase, while hydrogen projects came in at 6.4%.

By contrast, PV plants and transmission infrastructure recorded cost underruns of 2.2% and 3.6%, respectively.

Construction delays also varied by technology. Nuclear, hydro, and geothermal projects experienced average delays of 35, 27, and 11 months, respectively. PV and transmission builds had the best performance, typically completing ahead of schedule or with only minimal delays – averaging one month if delayed at all.

The study concluded that projects exceeding 1,561 MW in capacity face significantly higher cost escalation risks, while smaller, modular renewable builds may lower financial exposure and improve forecasting. Once construction delays surpassed 87.5%, cost increases rose sharply.