Looking at conventional forms of power generation, we see that as segments of an industry mature, operational experience grows and technological advances are achieved.
Owners and operators of older equipment seek to apply this new knowledge to improve the performance and reliability of their assets, reduce O&M costs and extend operating life to derive increased value from those assets.
Rebuilding, overhauls and repowering are common in more traditional generation technologies. These days, assessing the remaining useful life and life extension of equipment is also receiving greater attention in a maturing wind industry.
This goes beyond routine efforts with gearbox and generator systems. It evaluates the entire turbine system, all key structural elements, the site-specific operating environment and wind conditions, historic operating data, O&M records and other information to estimate fatigue accumulation and compare it with the machine’s design capacity.
This process enables informed technical and business decisions on options to meet the operator’s specific objectives.
According to Navigant’s World Market Update, 22,932 wind turbines were installed last year. Over the past five years, the global industry has installed an average of 22,750 units a year. That works out at about 62 turbines being installed every day, or more than 2.5 per hour.
An estimated 220,000 units are in operation around the world, of which half were installed before 2007. These older fleets will increasingly become a focus as the industry tries to sustain or improve performance, lower O&M costs and extend operating life.
Given that modern turbines are multi-million-dollar investments, the historic approach of removing an older unit and replacing it with the most recent (and larger) technology may not always be practical.
Local ordinances on height restrictions, setbacks and environmental considerations may have been enacted or expanded since a project was built. These constraints, while enabling the installation of, say, 1.5MW turbines, may prevent the introduction of modern 3MW-plus units on 120-metre towers — or require the project to go through the permitting process again.
In addition, repowering may trigger the renewal of power-sale and interconnection agreements, which can pose additional business, legal and financial risks. So, beyond simply repowering a project, assessment of the remaining useful life and routine estimates of fatigue accumulation, combined with inspections and proper O&M, can offer additional benefits, including:
*Increased energy production over the planned turbine’s life, where site conditions and design margins allow;
*Maintaining current production levels, but extending a turbine’s operational life;
*Reducing structural loads through advanced controls and monitoring equipment such as Lidar to bring down O&M costs and extend the unit’s life; and
*Technical and economic assessment of performance retrofits such as blade extensions, control-system adjustments, drivetrain refurbishment/enhancement or installing modern power inverters as part of a renewal programme.
Taking a risk-based approach to a turbine’s life extension can offer an attractive compromise between the potential for enhanced revenue and the possibility of increased financial and safety risks.
DNV KEMA has developed cost models for three life-extension methodologies, comparing the internal rate of return against a base case of a 20-year life. The modelling approach considers costs and revenue over the life of the turbines, including the cost of preventing or predicting structural fatigue failure and the cost of normal component wear-out.
We also perform field inspections, O&M assessments and analysis of control and data-acquisition systems to inform judgments on specific modifications.
As this issue grows in importance, we will be helping the industry to provide estimates of fatigue accumulation, comparison statistics and confidence levels to give owners a basis for technical and economic decisions, maximising project value and ultimately enabling a lower overall cost of energy.
Bjørn K Haugland is executive vice-president and chief technology and sustainability officer at DNV Group, the classification and verification organisation
This piece was published as part of the Thought Leaders series. Recharge’s Thought Leaders’ Club brings together leading thinkers and participants from the renewable-energy sector to examine the key challenges facing our industry