Balance of Station Costs

Balance of Station (BOS) costs include foundations, control/electrical hardware , site preparation, electric collection system and transmission lines, substation, windfarm control and monitoring equipment, O&M facilities and equipment, initial spare parts, shipping, resource assessment, surveying, legal counsel, project management and administration, permits, construction insurance, and engineering services. Since land cost is listed on Table 1 as a percent of revenue and not an initial capital cost, it is discussed in the O&M section.

A range of approximately 25%-33% of total project costs was estimated for BOS costs in a recent design study based on a 50 MW windfarm using 275 kW wind turbines [21]. Other recent estimates are that BOS costs account for approximately 20 percent of the cost of energy from windfarms [20,36]. This indicates that BOS costs are approximately 25% of the total project cost. Therefore, using the TC 1996 FOB cost of $750/kW yields the BOS value of $250/kW (250 is 25% of 750+250). The range of +5/-20 shown on Table 1 reflects the possibility that developers may be able to reduce BOS costs for current projects well below the level of $250/kW [21].

The majority of BOS costs for utility scale windfarm projects are directly dependent on the number of turbines installed. While important, turbine rating has a smaller impact on BOS cost. Since the number of turbines is fixed for all years in this characterization, the primary drivers of B OS cost changes are increases in turbine size in years 2000 and 2005 (BOS cost increases 20% from 1996 to 2005), and from learning effects resulting from increasing cumulative volume after year 2005 (BOS cost decreases by 13% between 2005 and 2030). Learning effects apply to the design, construction and management of projects. The small increase in BOS cost per turbine in years 2000 and 2005 reflects a relatively small amount of additional capacity- and size-related costs, e.g., higher cost power transfer and conditioning equipment, heavier foundations, that are incurred for each turbine. That is, for a 50-turbine windfarm, the absolute cost increases per turbine are small relative to the increase i n rated capacity. As expected, the tables show that costs decline significantly on a per-kW basis in both periods.

Project Size Impact on Cost - BOS cost estimates in Table 1 account for costs related to increasing turbine size, and associated increases in per-kW-related costs, for a fixed number of turbines. However, factors to adjust total windfarm project cost for increased numbers of same-size turbines are not included in Table 1. Wind turbines are a modula r technology. A wide range of capacity may be installed within a short construction period simply by varying the number of turbines added to an installation. There are two primary sources of potential cost reduction resulting from increasing the number of turbines in a windfarm. First, the manufacturer may be willing to set a lower price for a larger number of turbines. Second, some windfarm costs are fixed or exhibit diminishing costs per turbine for each additional turbine . Examples of these include infrastructure-related costs for roads, grading, and fences, O&M facilities and equipment , project administration and permits, surveying , and legal fees. As a preliminary guide, Table 9 taken from the 1993 EPRI Technical Assessment Guide [37], may be used to scale project costs for various project sizes.

Table 9. Project size impact on cost.

Plant Size (MW)

Percent of 50 MW Cost











Renewable Energy Eco Friendly

Renewable Energy Eco Friendly

Renewable energy is energy that is generated from sunlight, rain, tides, geothermal heat and wind. These sources are naturally and constantly replenished, which is why they are deemed as renewable.

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