Acronyms in wind farms construction

I’ve been informed by one of my most affectionate reader that some acronyms that I’m using in the blog are not immediately clear.

Therefore I’ve started a first list of the most used ones - special thanks to Janos for helping expanding the list:

AEPAnnual energy production.
BoPBalance of plant. All civil (roads, foundations, crane pads) and electrical works (cables, substation, etc.) in the wind farm.
CapExCapital Expenditures
CODCommercial operation date
COECost of energy
EISEnvironmental impact sudy
EPCEngineering procurement and construction. A type of contract (also known as "turnkey")
FIDICInternational Federation of Consulting Engineers  (Fédération Internationale Des Ingénieurs-Conseils)
HSHealth and safety
HVHigh voltage
IPPIndependent power producer
IRRInternal Return Rate
LDLiquidates damages
MLAMechanical Load Assessment
MVMedium voltage
O&MOperation and maintenance
OEMOriginal equipment manufacturer. Here, the company producing the wind turbine.
OMAOperation and Maintenance Agreement (sames as SMA)
OpExOperation expenditures
PCCPoint of common coupling
PPAPower purchase agreement
RoWRight of way. The legal right to use a certain route.
S&ISupply and installation
SCADASupervisory control and data acquisition
SMAService and Maintenance Agreement (same as OMA)
SoWScope of work
TSATurbine supply agreement. The contract between the wind turbine manufacturer and the wind farm developer.
W&SWind and site. Usually, either the assessment of the wind farm (W&S study) or the department doing it.
WFWind farm
WTGWind turbine generator

Technical due diligence of a wind farm

It is a hard task to compress in a blog post the reasons behind the technical due diligence of a wind farm and the several points that must be evaluated.
In a nutshell, in the clear majority of the wind farms developments are built using borrowed money.
The equity (cash at risk) is put by the developer, while the debt (money given against some form of security) is provided by a financial institution, or more commonly by a pool of institutions.
There are obviously exceptions to this rule, that is wind farms developed only with cash coming from the books of the company investing in the project. Nevertheless, these are exception and what is common is to have most the budget (up to 70%) provided by a financial institution such as a bank.
The lenders will be obviously interested in being sure that the financial model behind the project is solid.
Therefore, they will ask for a due diligence to identify, quantify and (if possible) mitigate technical risks.
In general, the lender will check what he considers appropriate.
Normally 3 macro categories are checked:

Financial due diligence, including for instance

  • Hypothesis
  • Budgets
  • Financial models

Legal due diligence, including items such as

  • Land lease
  • PPA
  • Contracts (e.g. TSA) & subcontracts

Technical due diligence

There is obviously an overlap between the various categories – for instance, some items are not purely “technical” or “legal”.
The technical due diligence should investigate in detail several key points.
A short, non-exhaustive list would include at least the following items:

  • Site suitability (wind resources, turbulence, data solidity)
  • Choice of WTG model (track record and match with the wind resource, power curve, certification, etc.)
  • Archeological y environmental constrains (impact on flora and fauna, such as birds and bats)
  • Access to the area (road survey and works outside the wind farm)
  • Geotechnical survey (ground risk)
  • Noise study (a big problem in inhabited areas)
  • Shadow flickering & visual impact
  • Grid connection
  • Electrical losses (are they calculated correctly?)
  • Projects for the BoP (foundations, MV, substation, etc.)
  • Congruence of the time schedule of the project
  • Interface between subcontractors
  • Allocation of risk

EWEA 2016

Some days ago I’ve had the opportunity to spend an afternoon at the EWEA summit, the European Wind Energy Association main event.
It was held in Hamburg, city where I have the pleasure to live since December 2015, and it was simply HUGE.

This year, both onshore and offshore were held together, resulting in an impressive amount of stands.
Unfortunately, I wasn’t able to meet too many new company specialized in onshore EPC (my main business).

However, I was able to enlarge the list of contact in engineering companies – coming from several years in Madrid I know fairly well who is who in southern Europe, while I still have to familiarize more with northern Europe consultancies (mainly Danish, but also German or French).

All in all, it was a very interesting experience and a great occasion to meet a couple of old friends.

Unmanned aerial vehicle (UAV) topography

This is a new technology we are going to use in a wind farm we are going to build in Chile.

The area that we need is too small to make LIDAR topography cost effective, but too big to use standard field topography: with this new solution we can have the needed data for a reasonable price.

The vehicle comes in 2 shapes: airplane like (fixed wing) and helicopter like (rotatory wing). The fixed wing plane is launched with a sling.

The vehicle weight around 3 kilos, and it can fly for about 1 hour at a height of a couple hundred meters, with a speed of about 75 Km/h.

It is possible to obtain several useful outputs:

  • Cartography
  • Digital Model of the Terrain
  • Aerial pictures
  • Thermography
  • Multispectral images
  • Video

It normally flies alone without any input, but it can be used with a remote control as well.

The main advantage is that it is clearly cheaper: you don’t need to book a flight, wait for a days without clouds (because you can fly lower) and it’s quick and safe.


Wind farms projects using Google Earth topography

One of the biggest problems in wind farms preliminary projects is the lack of a reliable topography.

Due to the tight budgets developers are often working with, it is often impossible to obtain a good topography (like the ones you can get with a LIDAR instrumented flight) or at list a decent one (as the standard field topographic surveys).

One of the possible solutions is to work with the Google Earth topography. Software like AutoCAD civil 3D makes it possible to download a cloud of points with coordinates and elevations and work with them.

The question is: how good is this info?

Unfortunately it’s impossible to answer univocally. The base grid, covering almost all the inhabited surface of the planet, has been obtained with a space mission (the NASA SRTM, Shuttle Radar Topography Mission).

The points are approximately spaced 50 meters, so it is a very rough starting point.

This base has been integrated with a “mosaic” of different DEM (digital elevation models) freely available material, so there are states in the US with a 1 meter contour line, or even cities with a very dense cloud of points (even a point every 20 centimeters).

It is currently impossible to know from where the points you are using are coming from, and if a point is “true” or interpolated. It is possible to have an impression seeing the shape of the contour lines (if you “zoom out” from the topography you will often see a pattern of squares coming from the available points).

This data is normally reasonably acceptable for a somehow preliminary project. Several commercial plug in are available to enhance the results.

For instance Plex Earth allows you to import Google Earth data (pictures and points) in different coordinates systems, importing contours in an area with any shape specified. It can also be used for preliminary volume calculation, to export objects from AutoCAD to visualize them inside Google Earth or doing the opposite (that is, importing a Google Earth KML file).

Wind power plant concepts and performance indicators

Wind turbines are usually placed in clusters called wind farms, with sizes ranging from a few MW (sometimes even a single wind turbine is sold, for instance to a private investor or to give power to an energy intensive factory like a cement plant) up to several hundred MW.

These clusters are connected to the grid as single generation units, therefore the term wind plants is the best suited. Whereas initially the emphasis on wind farm design was mainly on efficient and economic energy production that respected the rules of the grid operators, nowadays, with increasing wind power penetration, the demands of the grid operators have changed.

In response to these demands, modern wind turbines and wind farms have developed the concept of the so called “wind energy power plant”. The concept is essentially a wind farm with properties similar to a conventional power plant, with the exception that the fuel injection is variable. The operation of a wind energy power plant is designed in such a way that it can deliver a range of ancillary services to the power system.

Its control system is designed such that the power can be actively controlled, including ramping up and down similar to conventional generation plants. Wind power plants can and do positively contribute to system stability, fault recovery and voltage support in the system.

The properties described above greatly enhance the grid integration capability of wind power. In order to achieve high penetration levels, active control properties are essential to optimally share the power supply tasks together with other plants and to enhance network security.

An essential difference between wind plants and conventional power plants is that the output of wind plants very strongly depends on the characteristics (mainly the local wind climate) of the site where they are installed. The rated power, also known as the nameplate power, is the maximum power, which is reached only 1% to 10% of time. Most of the time wind turbines operate at partial load, depending on the wind speed. From the point of view of the power system, wind turbines can be regarded as production assets with an average power corresponding to 20 to 40% of the rated power, with peaks that are three to five times higher.

Wind power performance indicators are related to the principal wind turbine specifications, that is rated power, and rotor diameter. The specific rated power is in the range of 300 - 500 W/m2, where the area is the "swept area" of the rotor. Wind turbine electric power output will vary with the wind: it is measured according to IEC and is graphically represented in a power curve (a graphical representation of the power output at several wind speeds).

This energy output can be standardized to a long-term (20 years) average energy output and to derive the power output in short-term forecasting from 10 minute average wind speed values produced by forecast models.


Here you have an example of range and typical values for several relevant technical characteristics both for wind turbines and wind farms:


Wind Turbine characteristicRangeTypical value
Rated power (MW)0.850-6.03
Rotor diameter (m)58-13090
Specific rated power (W/m2)300-500470
Capacity factor onshore18-40Varies
Capacity factor offshore30-45Varies
Full load equivalent onshore1600-3500Varies
Full load equivalent offshore2600-4000Varies
Specific annual energy output (kWh/m2 year)600-1500Varies
Technical availability onshore95-9997.5



Wind Farm characteristicRange
Rated wind farm size (MW)1.5-500
Number of turbines1-hundreds
Specific rated power offshore (MW/Km2)6-10
Specific rated power onshore (MW/Km2)10-15
Capacity factor (load factor) onshore18-40
Capacity factor (load factor) offshore30-45
Full load equivalent onshore1600-3500
Full load equivalent offshore2600-4000
Technical availability onshore95-99


Sources for this post:

Powering Europe. Wind energy and the electric grid (EWEA, November 2012)

IEC, 2005 Power performance measurements of electricity producing wind turbines

TradeWind 2009. Integrating wind – developing Europe’s power market for the large-scale integration of wind power.



LEGO and Vestas: The unlikely duo

As you probably know if you are in the wind sector both LEGO and Vestas are Danish companies, so it is not a big surprise to discover that several wind turbines related products are produced by LEGO.

Not only the “standard” LEGO City 7747 Wind Turbine Transporter, but even a personalized, limited edition set (known as “LEGO Vestas 4999”) fully working (with battery, not with wind) and with a shining Vestas logo on the nacelle.

It was a Christmas present given to all employees several years ago - unfortunately I was not in the company at that time, so my only alternative is to buy one on eBay, where it is selling between 300 and 400 euros(!).

In the following pictures, an exposition of LEGO wind turbines in a Danish airport in 2010 (I think it was Billund).

There are several scenarios: wind farm in the desert, in the mountain, offshore… very cool.

What is this BoP?

BoP is an English acronym that stands for Balance of Plants. In the wind farms sector, it means everything but the wind turbines.

Balance of Plant

Basically there are 3 types of Wind Farm contracts commonly used:

  • Supply only. It include WTGs, SCADA, Installation supervision and Commissioning.
  • Supply and Installation, including all the items in Supply only plus WTGs transport and cranes for the installation (basically, it adds the assembly of the machine).
  • Turnkey (full EPC), including all the above plus civil and electrical works.

The sum of wind farm civil works and electrical works are usually called Balance of Plant (BoP).

Often it is done by a company different from the wind turbine supplier, and sometimes even 2 separate contractors are used, one for the civil works and one for the electrical works.

BOP civil engineering scopes of work include roads and drainage, crane pads, turbine foundation, meteorological mast foundations, cable trenches and buildings for electrical switch gear, SCADA equipment, and a maintenance/spare part facility.

BOP electrical work scopes include underground cable networks (medium voltage cables, copper cables and optical fibre cables) and sometimes even an overhead transmission lines, electrical switch gear to protect and/or disconnect turbines or other equipment from the system, and grounding and connections for control rooms, maintenance facilities and point of connection equipment to feed the wind farm’s power generation into the electrical grid. Transformers and switches for individual turbines are normally located within the turbine and they are provided by the turbine supplier.

In the EPC wind farm contract, three phases can be distinguished:

Engineering: A detailed engineering project is developed to fit the machines to the actual conditions of the site. Conditions can vary dramatically, depending on topography, geotechnical conditions, grid connection requirements, permits, local regulations an so on. In this phase technical choices are made, and drawings are produced together with the bill of quantities.

Then comes the Procurement phase, where civil and electrical works are subcontracted to one or more companies. Potential subcontractors are contacted, their quotations are received and compared.  Short listed contractors are screened and the work is finally awarded to the company with the best price/quality ratio.

Finally, the phase of Construction begin, where the works of the subcontractors are monitored to see if they comply with the technical specification and if there are delays respect to the signed chronogram.



Industrial Archeology

These are several pictures that I took in 2010 during a trip to Tarifa, southern Spain.

It is one of the best spot for wind surf, kite surf and of course for wind energy production.

The WTGs are about 20 years old, but they look like remnants of a faraway past, with their lattice tower and noisy turbines.

Regarding the drainage system, very effective concrete ditches and a complete network of transversal drainage pipes has been used.

Also, the exit of the drainage pipes has been “hidden” using an interesting mix of concrete and local stones.

Why this blog


My name is Francesco and I am a newbie in the word of blogging.

Being an engineer working in a big sector in the wind sector, I decided to start this page to share with colleagues and other whoever may be interested what I learn projecting and building wind farm worldwide.

I work in a team dedicated to Balance of Plant (also called “Bop”): it means everything in the wind farm that is not the wind turbine, for instance the roads, crane pads, foundations for the civil part and the substation and medium voltage cables for the electrical part.

I'll try to post pictures, video and info regarding wind farm and wind farm construction, a job that I find really interesting.