When it comes to advancing technologies for alternative energy, there are many issues to consider. Those that impact the system’s efficiency, reliability and life-cycle cost should be at the top of the priority list. For example, it’s important to be sure that the cables specified for the wind farm align with the standards of the larger grid. To specify anything less is short-term thinking that could result in lost revenue due to downtime, expensive repairs and negative publicity.
Companies should invest significant resources in developing materials that ultimately help distribute power more efficiently and reliably over the life of the entire system. They should also look at projects from a holistic standpoint because everything is interdependent. The success of one component certainly influences the performance of the other components and ultimately impacts the productivity of the entire system.
And that’s why we at Dow Electrical & Telecommunications recommend looking at the cable specification process from the perspective of total life-cycle cost rather than the short-term cost of components and installation. Without proper specifications, potential failures must be anticipated right up front. And because wind energy failure costs are higher than similar voltage utility outages, the wind energy industry may warrant even more demanding specifications than the traditional utility infrastructure.
A reliable, long-lasting power cable collection system can improve the return on investment for the entire system. Benefits include:
- Enhanced consistency of revenues
- Lower operating and maintenance expenses
- Fewer forecasting penalties
- Maintained public image/goodwill
- Deferring or even eliminating the need for future capital expenditures
In fact, the life-cycle cost model we’ve developed can be used to help determine the impact cables can have on a wind farm’s return on investment. Variables include:
- Wind farm specifics like electricity generation size, number of turbines, etc.
- Cable length and cost
- Installation cost
- Predicted cable life
- Number of expected cable failures
- Cost per failure
- Dielectric losses of the cables
- Discount rate and tax rate
As part of the life-cycle cost evaluation of the collection system, cable materials must be considered the primary driver of performance. The use of sub-standard cables ultimately puts the owner/operator of the wind farm at risk for certain system-wide failures.
In order to specify the best materials for wind farm applications, some background information on cable insulation materials may be helpful. Medium voltage (MV) power cable insulation can be made with cross-linked polyethylene (XLPE), ethylene propylene rubber (EPR) and water tree-retardant XLPE (TR-XLPE), just to name a few materials. There are many performance variables that vary widely between these materials, the most important of which is cable life expectancy.
TR-XLPE insulation is now widely utilized for MV underground (UG) power cables for reasons of quality, cost competitiveness, longevity and lower long-term operating costs. Studies have shown that cables made with DOW ENDURANCE™ TR-XLPE materials in UG applications have shown little electrical aging after nearly 30 years in the field and have a forecasted lifetime performance of more than 40 years. It’s important to note, however, that not all TR-XLPE materials are created equal and premature failures are possible without properly specified cables.
Our recommendation is that the wind energy value chain should create cable specifications that require a minimum cable electrical performance AND the use of TR-XLPE insulation. Owner/operators should partner with an experienced high-quality cable manufacturer who will help balance the need for low life-cycle cost with specific performance requirements.
Installation is also an essential part of the overall cable collection system performance and should be completed by trained installers who are experienced in handling, splicing and terminating these high performance systems. A diagnostic test should be performed at commissioning to ensure that the system is in peak working order. Ultimately, this work will pay off. Modeling based on field data suggests that a 5% upfront investment in quality cable materials and installation can save as much as 600% over the life-cycle of the wind farm.
The Need for Cable Performance Standards
Longevity and reliability are critical considerations for cables that support the traditional utility power infrastructure. These performance characteristics are equally as important for the cables that support wind farms. The industry needs to develop and implement standards that will provide efficiency and reliability to owners and customers alike. Specification of the cable insulation material makes all the difference in long-term performance and overall reliability.
Until cable standards for wind farms are developed and field-tested, specifiers and end users should require cables to meet or exceed the current power industry minimum standards. This will help ensure the use of excellent materials, quality cable manufacturing processes and world-class performance, which contribute to system reliability and achieving the highest return on investment.
Collaboration also will help the forward progress of the industry. Groups like AWEA and ICC are certainly important as they support the sharing and distribution of information. But it will take a bigger effort from all involved – investors; developers; independent power providers; utilities, equipment, cable and material suppliers; and others – to achieve the energy goals that are likely to be legislated soon.
Dow Electrical & Telecommunications experts look forward to working on this challenge and encourage our colleagues and industry leaders to join us in this effort.