Bergey Excel 10 vs Excel 15: Which Residential Workhorse Fits Your Site

The Bergey Excel 10 and Excel 15 share the same battle-tested three-blade upwind rotor design, both engineered for grid-tied residential and small-farm applications in the United States. The Excel 10 produces a rated 10 kW at wind speeds around 11 m/s (24.6 mph), while the Excel 15 scales output to 15 kW at similar wind speeds thanks to a longer blade diameter. Both turbines use permanent-magnet alternators, include Bergey's GridTek-10 inverter for seamless NEC Article 705 interconnection, and carry the same twenty-year warranty on the rotor and alternator. The decision hinges on your site's average wind speed, available tower height, permitting constraints, and whether the 50-percent jump in capital cost justifies the roughly 40-percent gain in annual energy production.

Rotor diameter and swept area drive output differences

The Excel 10 sweeps 7 meters (23 feet) across with its three fiberglass-reinforced blades, capturing 38.5 square meters of wind. The Excel 15 stretches that diameter to 8.6 meters (28.2 feet) and sweeps 58 square meters—a 51-percent increase in capture area. Because wind-turbine power scales with the square of blade length, that extra meter of radius translates directly into higher energy harvest at any given wind speed.

Both rotors spin at variable RPM controlled by the permanent-magnet alternator's load curve, typically ranging from 80 RPM at cut-in (around 3.5 m/s or 7.8 mph) to 310 RPM at rated wind speed. Neither uses hydraulic or mechanical pitch control; instead, blade airfoil design and rotor geometry provide passive stall regulation above rated wind, limiting shaft torque and protecting the alternator from overspeed. Maximum design wind speed is 60 m/s (134 mph) for both machines, and both employ an electromagnetic disk brake that can stop the rotor during maintenance or emergency shutdown.

The Excel 15's larger swept area becomes decisive in Class 2 and Class 3 wind regimes (annual average 5.5–7.5 m/s at hub height). At a steady 7 m/s, the Excel 10 typically generates around 1,200 kWh per month under ideal conditions, while the Excel 15 approaches 1,700 kWh. Over a year, that gap compounds to roughly 6,000 kWh of additional output—enough to cover an extra all-electric household's baseload or offset a heat-pump heating season in a mid-latitude climate.

Tower height and wind shear magnify the performance spread

Bergey specifies both turbines for towers between 18 and 43 meters (60–140 feet), with the company strongly recommending at least 24 meters (80 feet) for the Excel 10 and 30 meters (100 feet) for the Excel 15 to clear surface turbulence and reach laminar flow. Wind speed increases logarithmically with height above ground; in typical open terrain with scattered obstacles, each doubling of height adds 10–15 percent to average wind speed.

Installing the Excel 10 on an 80-foot tower in a site averaging 6 m/s at that height might yield 14,000 kWh annually. Mounting the Excel 15 on a 100-foot tower at the same site—where wind speed climbs to approximately 6.4 m/s thanks to the extra height—can produce 21,000 kWh. The taller tower alone contributes about 7 percent more wind energy, and the larger rotor captures that energy more efficiently. The combined effect widens the output gap beyond what swept-area math alone suggests.

FAA Part 77 notification applies to both turbines when total structure height (tower plus blade tip) exceeds 200 feet above ground level, or when the site lies within certain distances of airports. In practice, the Excel 10 on an 80-foot tower with a 23-foot rotor diameter reaches roughly 92 feet at the highest blade tip, well below notification thresholds in most locations. The Excel 15 on a 100-foot tower with a 28-foot rotor tops out near 114 feet, still comfortably under 200 feet but closer to the limit if taller towers are contemplated.

image: Bergey Excel turbine mounted on tubular lattice tower in open farm field with clear sky

## Grid interconnection and inverter capacity remain identical

Both turbines ship with Bergey's GridTek-10 inverter, a 10 kW continuous-rated unit that converts the turbine's wild three-phase AC to grid-synchronized 240 V single-phase AC compliant with IEEE 1547 and UL 1741. The inverter includes integrated anti-islanding protection, automatic disconnect for utility outages, and programmable power-factor correction.

The Excel 15's peak output exceeds the inverter's continuous rating during high-wind events. When rotor power surpasses 10 kW—common in gusts above 13 m/s—the inverter clips the excess, holding grid export at 10 kW and dissipating surplus energy as heat in the inverter's internal resistive dump load. This clipping reduces the Excel 15's theoretical annual yield by 5–8 percent in very windy sites (Class 4 or higher), but Bergey engineers the system this way to use a proven, field-tested inverter platform rather than a larger, less-proven unit.

Owners who require full 15 kW export capability can request a custom GridTek-15 inverter during order configuration, though this adds approximately $3,200 to the system cost and extends lead time. In Class 2 and Class 3 sites, clipping events remain rare enough that the standard GridTek-10 captures more than 95 percent of the Excel 15's available energy, making the upgrade hard to justify on return-on-investment grounds.

NEC Article 705 requires a dedicated breaker in the main service panel, sized at 125 percent of inverter continuous output (12.5 A for a 10 kW inverter on 240 V). Both systems need a grounding electrode system separate from the building ground when the tower-to-building distance exceeds 250 feet, and lightning-arrestor devices on the AC and DC sides of the inverter. Local jurisdictions often impose additional requirements—setback distances, noise ordinances, shadow-flicker studies—that affect permitting timelines but apply equally to both turbines.

Capital cost and available incentives shift the breakeven calculation

Manufacturer-specified pricing for the Excel 10 turbine and GridTek-10 inverter starts around $32,500; the Excel 15 with the same inverter begins near $48,700. These figures exclude towers, which add $18,000–$35,000 depending on height and foundation requirements, and installation labor, which typically ranges from $8,000 to $15,000 for crane rental, electrical hookup, and commissioning. All-in installed cost for an Excel 10 on an 80-foot tower averages $65,000; an Excel 15 on a 100-foot tower approaches $95,000.

The federal Residential Clean Energy Credit under IRC §25D covers 30 percent of total installed cost through 2032, stepping down to 26 percent in 2033 and 22 percent in 2034. A $65,000 Excel 10 system qualifies for a $19,500 tax credit, reducing net outlay to $45,500. The $95,000 Excel 15 system earns a $28,500 credit, netting $66,500. Taxpayers claim the credit on IRS Form 5695 for the year the turbine enters service; unused credit carries forward to subsequent tax years if current-year tax liability is insufficient.

State-level incentives vary widely. The DSIRE database shows rebates and performance payments in states including Massachusetts, New York, Oregon, and California, although many programs cap small-wind incentives at turbines under 100 kW and require pre-approval. Property-tax exemptions for renewable-energy equipment exist in roughly half of U.S. states, shielding the added assessed value from annual property-tax bills. Sales-tax exemptions on turbine purchases apply in states such as Iowa, Kansas, and Oklahoma.

Net metering policies determine how excess generation credits against future consumption. Full retail net metering—available in states including New Jersey, Vermont, and Maryland—values every exported kWh at the retail rate, maximizing system payback. Avoided-cost net metering (common in Georgia, Idaho, and parts of the Carolinas) credits exports at wholesale rates, which can be 40–60 percent below retail and significantly lengthens return-on-investment timelines.

image: Close-up of Bergey GridTek inverter installation showing AC disconnect and utility meter interface

## Annual energy production and simple payback under typical conditions

Assume a residential site in central Iowa with 6.2 m/s average wind speed at 80 feet, rising to 6.6 m/s at 100 feet due to wind shear. Retail electricity costs $0.14/kWh with full net metering and no demand charges. The Excel 10 at 80 feet would produce approximately 15,500 kWh per year; the Excel 15 at 100 feet would yield roughly 23,000 kWh.

After the 30-percent federal tax credit, the Excel 10's net cost of $45,500 divided by $2,170 annual savings (15,500 kWh × $0.14) gives a simple payback of 21 years. The Excel 15's $66,500 net cost divided by $3,220 annual savings (23,000 kWh × $0.14) yields a 20.7-year payback—nearly identical despite the higher upfront expense. The slightly shorter payback for the Excel 15 reflects better capacity-factor utilization at the higher hub height.

If the same site adds a state rebate of $1.50/watt (not uncommon in historically generous wind states), the Excel 10 receives an additional $15,000 (10 kW × $1,500/kW) and the Excel 15 gains $22,500. Net costs drop to $30,500 and $44,000, respectively, shortening payback to 14.1 years for the Excel 10 and 13.7 years for the Excel 15. The Excel 15 edges ahead because the incremental cost per incremental kWh produced falls below the Excel 10's ratio once tower-height gains compound with rotor-area gains.

In lower-wind sites—say 5.5 m/s average at 80 feet—the Excel 10 might produce only 11,000 kWh annually while the Excel 15 at 100 feet (experiencing roughly 5.9 m/s) yields 16,000 kWh. Even with incentives, payback stretches beyond 20 years for both machines, and the Excel 15's higher capital cost becomes harder to justify. Below Class 2 wind regimes (under 5.5 m/s annual average), neither turbine makes economic sense without exceptional electricity rates or unique off-grid requirements.

Maintenance schedules and long-term reliability considerations

Bergey specifies an initial inspection at six months, then annual inspections thereafter. Each service includes guy-wire tension checks (for guyed towers), bolt torque verification on tower sections and turbine mounting flanges, alternator-bearing greasing via zerk fittings, brake-caliper inspection, and inverter filter cleaning. Bergey's design eliminates gearboxes, hydraulic systems, and yaw motors—common failure points in larger turbines—so maintenance labor typically runs 2–4 hours per year.

Bearing replacement intervals depend on site conditions. The main shaft uses sealed cartridge bearings rated for 100,000 hours (roughly 11.4 years of continuous operation). In practice, bearing life extends to 15–20 years in low-turbulence sites but may shorten to 10–12 years in high-turbulence environments with frequent wind-direction changes. Replacement requires lowering the turbine with a gin pole or crane, a task that adds $2,500–$4,000 in labor and equipment rental.

Both turbines use the same alternator architecture and bearing sizes, so parts commonality simplifies inventory for dealers and reduces lead times for replacements. Blade sets retail for approximately $3,800 (Excel 10) and $5,200 (Excel 15) as of late 2024. Lightning strikes represent the most common cause of unscheduled repairs; even with grounding and arrestors, a direct hit can damage the inverter's power electronics. Inverter replacement costs roughly $6,500 for the GridTek-10.

Insurance riders for wind turbines vary by carrier. Homeowners policies sometimes exclude wind turbines taller than 60 feet or require separate endorsements. Standalone turbine insurance—covering fire, lightning, windstorm, and mechanical breakdown—costs 0.5–1.0 percent of insured value annually. A $95,000 Excel 15 system might carry $700/year in additional premium, while a $65,000 Excel 10 adds around $500/year.

Zoning and permitting realities favor the smaller footprint

Many rural counties and townships regulate wind turbines through height limits, setback multipliers, and noise ordinances. Height limits of 100–120 feet remain common; the Excel 10 on an 80-foot tower easily complies, whereas the Excel 15 on a 100-foot tower approaches or exceeds limits in more restrictive jurisdictions.

Setback requirements typically mandate a distance equal to 1.1–1.5 times total height (tower plus rotor diameter) from property lines. The Excel 10's 92-foot total height requires roughly 138-foot setback under a 1.5× rule; the Excel 15's 114-foot height demands 171 feet. On five-acre parcels (467 feet per side if square), the Excel 10 fits comfortably with margin for other structures. On smaller lots—common in exurban subdivisions—the Excel 15 may violate setbacks unless lot geometry allows placement far from boundaries.

Noise ordinances cap sound pressure at property lines, often at 50–55 dBA during daytime and 45 dBA at night. Both Bergey turbines measure below 45 dBA at 100 feet distance under rated wind speeds, so compliance is straightforward when setbacks place the tower well inside property boundaries. The Excel 15's slightly higher tip speed (marginally louder aerodynamic noise) rarely triggers violations, but neighbors sensitive to low-frequency hum sometimes file complaints. Pre-installation community outreach and clear sight-line documentation reduce friction.

Shadow flicker—the strobing effect when rotating blades pass between the sun and a window—affects properties to the north (in the Northern Hemisphere) during morning and evening hours. Both turbines generate comparable flicker patterns at equivalent distances; mitigation involves siting the tower to keep the flicker zone away from occupied structures, or accepting seasonal flicker in exchange for optimal wind exposure.

image: Bergey Excel wind turbine installation with crane lifting nacelle onto tower section

## Off-grid and hybrid-system suitability for both platforms

Although Bergey markets the Excel series primarily for grid-tied installations, both turbines adapt to battery-based off-grid systems using Bergey's DC controller in place of the GridTek inverter. The DC controller rectifies three-phase AC to charge 120 V or 240 V battery banks, with dump-load regulation to prevent overcharge.

In off-grid configurations, the Excel 15's higher output can shorten generator runtime during calm periods if paired with adequate battery storage. A 48 kWh lithium-ion battery bank (roughly $18,000 installed) combined with the Excel 15 might eliminate generator use for days at a stretch in windy seasons, whereas the Excel 10 requires a larger battery bank or more frequent generator cycling to maintain the same autonomy.

Hybrid systems that combine wind with solar photovoltaics leverage the seasonal offset between peak solar (summer) and peak wind (winter in many U.S. climates). The Excel 10 pairs well with a 6–8 kW solar array; the Excel 15 balances a 10–12 kW array. Both require a charge controller capable of handling simultaneous wind and solar input, such as the Midnite Classic or Outback FlexMax series, and a bidirectional inverter/charger like the Schneider Conext or Victron Quattro.

Off-grid economics tilt toward the Excel 10 when total energy demand remains below 30 kWh/day and space for solar panels is limited. The Excel 15 justifies its cost in high-consumption off-grid homes (50+ kWh/day) or small commercial sites like remote telecom repeaters, fish hatcheries, or research stations where generator fuel transport is expensive.

Which turbine fits which site profile

The Excel 10 makes sense for:

• Residential properties with average wind speeds between 5.5–6.5 m/s at 80 feet
• Sites where zoning caps tower height at 80–90 feet
• Homeowners whose annual consumption ranges from 12,000–18,000 kWh
• Budgets constrained to $70,000 all-in installed cost or less
• Locations with restrictive setbacks that limit tower placement options

The Excel 15 suits:

• Properties with sustained wind speeds above 6.5 m/s at 100 feet
• Sites with minimal zoning restrictions allowing 100–120 foot towers
• Households or small farms using 20,000–30,000 kWh per year
• Buyers who can finance $90,000–$100,000 and access both federal and state incentives
• Off-grid or hybrid systems with high energy demand and space for battery storage

Neither turbine performs economically below 5.5 m/s annual average wind speed, and both require professional site assessment before purchase. Bergey offers a free wind-resource screening using GIS data and NREL wind maps, though on-site anemometry over 6–12 months provides the most reliable forecast of actual production.

Frequently asked questions

Can I upgrade from the Excel 10 to the Excel 15 later if wind speeds are better than expected?

No practical upgrade path exists. The tower foundation, base section, and guy anchors (if applicable) are sized for the specific turbine's thrust load and weight. The Excel 15's larger rotor generates higher dynamic loads, requiring a foundation redesign and potentially a complete tower replacement. Reselling the Excel 10 and installing the Excel 15 as a separate project involves nearly the same total cost as a new installation. Accurate wind assessment before purchase eliminates this scenario.

Do both turbines require the same tower type, or can I use a monopole for one and a guyed lattice for the other?

Bergey certifies both turbines for tubular monopole towers and guyed lattice towers within the 18–43 meter height range. Monopole towers offer cleaner aesthetics and no guy-wire land footprint but cost 30–40 percent more than equivalent-height guyed lattice. The Excel 15's heavier nacelle (approximately 485 lb versus the Excel 10's 350 lb) increases foundation and tower-section steel requirements on monopoles, widening the cost gap. Guyed lattice towers distribute load through guy anchors set 50–70 percent of tower height away from the base, reducing foundation size but consuming more land area.

How does winter icing affect the two turbines differently?

Both turbines experience similar icing behavior in freezing-rain and wet-snow conditions. Ice accumulation on blades disrupts airfoil shape, reducing lift and causing vibration. Neither turbine includes active ice-shedding (heating elements or vibration systems). Bergey recommends allowing the turbine to shut down naturally when ice load triggers the overspeed brake, then resuming operation after ambient temperature or sun exposure melts the ice. The Excel 15's larger blade surface area accumulates slightly more ice mass, and centrifugal shedding during startup poses a marginally larger debris-throw hazard within 150 feet. Sites with frequent icing (more than 20 days per year) may see 10–15 percent annual production loss for either turbine.

Will either turbine work with a battery-backup system that keeps essential loads running during grid outages?

The standard GridTek-10 inverter shuts down immediately when grid voltage drops, meeting IEEE 1547 anti-islanding requirements. Bergey offers an optional automatic transfer switch and battery-charge controller module that switches the turbine to charge a battery bank during outages, then powers an off-grid inverter supplying essential loads. The module adds approximately $4,800 to system cost and requires a dedicated battery bank (minimum 24 kWh usable capacity recommended). Both the Excel 10 and Excel 15 support this configuration; performance during outages depends on wind availability at the time rather than turbine model.

Which turbine handles high-turbulence environments like forested hills or coastal bluffs better?

Neither turbine tolerates high turbulence well; both are engineered for open terrain with turbulence intensity below 15 percent. Bergey specifies minimum clearance of 30 feet above any obstacle within 300 feet to reduce turbulence-induced fatigue. The Excel 15's larger rotor diameter makes it slightly more sensitive to vertical wind shear and direction changes common in complex terrain, potentially shortening bearing life by 10–20 percent compared to the Excel 10 in the same high-turbulence site. If site assessment reveals turbulence intensity above 18 percent, Bergey recommends a taller tower to reach smoother flow, or consideration of a different site altogether.

Bottom line

The Excel 10 delivers dependable grid-tied performance for moderate-wind residential sites where tower height and budget constraints favor the smaller machine, while the Excel 15 rewards owners with stronger, more consistent winds and the tower height to exploit them. Calculate your site's true wind resource at the proposed hub height, model annual production with both turbines, and compare net cost after incentives to verify which system crosses breakeven before the warranty period ends. Consult a NEC Article 705-compliant licensed electrician for interconnection details and secure all required permits—including FAA notification if tower-plus-blade height approaches 200 feet—before finalizing turbine selection.