Performance of US wind farms

LBNL reported the following comparative performance numbers for wind turbines.  The comparison is between 1998-99 and 2015:

- Average capacity of WTG has increased by 180%

- Average hub height has increased by 47%

- Average rotor diameter has increased by 113%

As a result of these, the capacity factor of WTGs has increased from 26% to 41%.

In 2015, the average prices of wind projects had fallen to $1,690/kW (which is 20% to 40% below 2008 prices)

With these efficiencies and cost reductions, PPA for wind projects in US are averaging about $0.02/kWh in 2015.

4 hour energy storage flywheel

I thought I would never see a flywheel with 4 hours of energy storage.  Amber Kinetics has managed to develop a 6.25 kW flywheel with 29 kWh of energy storage.  The traditional flywheels I was aware of stored less than one minute of energy.

Here is what we know:

- Weight of flywheel = 5,000 lbs

- Speed of rotation = 8500 rpm

- Flywheel is a monolithic steel rotor

- Flywheel is also used as rotor for the motor/generator

- Stator is 8 pole permanent magnet

- Full power conversion to get 60 Hz AC

Although no cost is mentioned, one of their key objectives is low $/kWh cost and second is low self discharge rate.

Details are available at:

Hawaii Electric seems to be the first customer.

Reaching for the sky ... 166m hub height of onshore wind turbines

Vestas has introduced onshore wind turbines with hub height of 166m.  It is the V126-3.45MW model.  They also offer hub heights of 87m, 117m, 137m, 147m and 149m.  The tall hub heights are made possible by the large diameter steel tower (LDST) sections that are below the standard 3 sections of the tower.  LDST is made in 3 sections for ease of transportation.  The claim is hub height of 166m versus 117m results in 20% higher annual energy production.

This approach has some advantages over an alternate approach adopted by suppliers like Enercon who build a concrete base tower onsite, and then place the 3 sections of the steel tower on top of the concrete base.  The advantages of LDST is faster installation (2 days) and 99% recyclable (after decommissioning).  

Wind turbine integrated with pumped hydro

I just saw an innovative concept from GE: Storage of water below the wind turbine. Details are not very clear, but it looks like, there will be a 40m tall water storage unit below the wind turbine. The tower of the WTG is 138m and it sits on a 40m high water storage unit for a total hub height of 178m. GE is using the 3.4 MW WTG with rotor diameter of 137m. So the total height to tip of blade is 246.5m, which GE claims is the tallest wind turbine. There will be 4 such WTGs in the hybrid park. What is really unique is tight integration with hydro ... storing water under each WTG.

A 16 MW hydro generator sits 200m below the wind turbines; there is also a lake to store the water after it has gone through the hydro-generator. So the concept is when there is excess wind energy, water will be pumped from the lake to the water storage unit below the wind turbine, and when the electricity prices are high hydro power will be generated. An alternative concept may be more important--use of this scheme for secondary frequency response for grid stabilization during ramping and other random events caused by varying WTG output or varying load that would otherwise require expensive ancillary services.

It would be interesting to compare cost of wind-hydro versus wind-battery. Obviously this wind-hydro hybrid requires the stars to line up in terms the right location with good wind, hydrology and contour/elevation, while the wind-battery hybrid does not need any of this. Nevertheless, it would an interesting cost comparison.

For more details see

Flexible generation with Wind and Solar

City of Denton, TX has a goal of using 70% of electricity from wind and solar by 2019.  In order to achieve this goal it is buying 12 highly flexible Wartsila internal combustion-based gas generators with a total capacity of 225 MW.  These generators have quick start/stop times and high ramp rates, which are required when balancing wind and solar.  The claim is this allows wind and solar to act like base-load generators and the fossil-fuel generators to fill in the gap.  Interesting narrative.

For more information, see

However, i suspect, this configuration may not work for island grids, because of low overall grid inertia.  Denton must be getting its primary frequency control from ERCOT, but an isolated grid would need inertia--possibly from wind generators with synthetic inertia.

Solar energy prices: Low and going lower

I wrote about the falling price of wind energy, see  

Here are amazingly low prices of solar PV (

  1. Chile awarded a contract for 2.91 c/kWh for a 12 MW solar plant in the Atacama desert
  2. Dubai awarded a contract in May 2016 for 2.99 c/kWh for an 800 MW solar plant

An update on wind prices, the 2015 Wind Technologies Market Report from LBNL reports that wind PPA in interior of the US dropped to around 2 c/kWh in 2016, which is based on a sample of 2 projects totaling 207 MW.  Note this does not include the 2.3 c/kWh of production tax credits for 10 years.  So with the incentive the levelized revenue of these wind projects is below 4.3 c/kWh.

Wind PPA prices, cost and other 2015 data in US

The 2015 Wind Technologies Market Report from Lawrence Berkeley National Lab was released this month.  My takeaway from the report are:

  1. 8.598 GW of wind power was added in 2015. which amounted to $14.5 billion investment
  2. Wind power was 41% of electricity generating capacity additions in 2015
  3. Wind penetration is slightly above 5% of total electricity generation
  4. Project finance environment was strong in 2015: After-tax Tax Equity yield was about 7.5% and after-tax 15-year debt interest rate was about 2.5%
  5. In 2015, average rotor diameter crossed 100m.  Average hub height was slightly above 80m.  Average nameplate capacity was slightly above 2 MW
  6. Average specific power of wind turbines was about 250 W/m2
  7. Average capacity factor of wind plants in 2014 was close to 42%
  8. Average 2015 price of wind turbine was $1,100/kW
  9. Average 2015 total installed cost of wind power plant was $1,690/kW
  10. Average 2015 O&M costs were close to $8/MWh for projects built in 2014
  11. Average 2015 PPA was $38/MWh, based on sample of 6 projects of total capacity of 401 MW.  It was much higher than 2014 PPA of $23/MWh and 2016 PPA of below $20/MWh.  The 2016 sample was based on 2 projects.
  12. The forecasted amount of wind power additions until 2020 is 8 GW per year.