Tag Archives: Renewable Energy

Industry Developments: Cooling Electronics in Wind Turbines

By Norman Quesnel, Senior Member of Marketing Staff
Advanced Thermal Solutions, Inc.

(This article will be featured in an upcoming issue of Qpedia Thermal e-Magazine, an online publication dedicated to the thermal management of electronics. To get the current issue or to look through the archives, visit http://www.qats.com/Qpedia-Thermal-eMagazine. To read the preceding post on Cooling Solar Power Inverters, click https://www.qats.com/cms/2016/11/21/industry-developments-cooling-solar-power-inverters.)

Wind power systems capture natural air currents and convert them, first to mechanical energy and then electricity. Windmills have long harnessed natural, renewable wind currents to grind grains and pump water. Now those windmills have evolved into highly engineered wind turbines, with very long, highly-engineered blades spinning on steel towers some that are tens of meters high.

There are some relatively small wind turbines that power individual houses or businesses. They can generate around 100 kW of power. But most of today’s wind turbine industry is for utility-scale power generation. These are large, tall wind turbines, in fields of dozens or hundreds, delivering high levels of electricity to power grid systems that reach thousands of end users. More than a quarter million of such turbines are in use around the world.

Cooling Electronics in Wind Turbines

Fig. 1. The Alta Wind Energy Center in California has more than 600 wind turbines and can produce more than 1.5 GW of power. [1]

Most utility-scale wind turbines are built on open, naturally windy land or off-shore. Each turbine can produce 1.0-1.5 MW, enough energy to power hundreds of homes. The United States has about 75 GW of installed wind power capacity. And, despite some local resistance, the U.S. has begun to join other countries with off-shore installations. China has by far the most installed wind power capacity at about 150 GW. Globally, the combined power capacity from wind turbines is forecast to nearly double between 2016 and 2020 to 792 GW. This would be enough to power 220 million average homes in the U.S. [2, 3]

Mechanics of Wind Turbines

When natural wind blows past a turbine, its blades capture the energy and rotate. This rotation spins a shaft inside the rotor. The shaft is connected to a gearbox that can increase the speed of rotation. The gearbox connects to a generator that produces electricity. Most wind turbines consist of a steel tubular tower. On top of this is a nacelle structure, housing the turbine’s shaft, gearbox, generator and controls.

On the wind-facing end of the nacelle is a hub to which the turbine blades are attached. Together, the blades and the hub are called the rotor. The diameter of the rotor determines how much energy a turbine can generate. The larger the rotor, the more kinetic energy is harnessed. Furthermore, a larger rotor requires a taller tower, which exposes the rotor to faster winds. [4]

A wind turbine is equipped with wind assessment equipment, including weather vanes. These send data to a computer to automatically rotate the turbines into the face of the wind and to a pitch system that can angle the blades to further optimize energy capture. [5]

Cooling Electronics in Wind Turbines

Fig. 2. The major components of a wind turbine. [6]

Turbines and Fire

Hundreds of wind turbines catch fire each year. The most common cause is lightning strikes, but overheated equipment can also be responsible. Highly flammable materials such as hydraulic lubrication oil and plastics are in close proximity to machinery and electrical wires inside the nacelle. A fire can ignite from faulty wiring or overheating. The results are catastrophic. The rush of oxygen from high winds can quickly expand a fire inside a nacelle. Once a fire starts, it is not likely to be deliberately extinguished. Water hoses can’t reach a nacelle’s height and wind turbines like these are typically set in remote locations, far from emergency aid. [7]

Cooling Electronics in Wind Turbines

Fig. 3. A wind turbine’s blazing nacelle and hub at a wind farm in Germany. Lubricating oil is often the fuel when these fires occur. [8]

Electronic Devices in the Nacelle – and Heat

Most wind turbines don’t catch fire, of course. Yet, despite all the surrounding wind, the electronics in their nacelles still need significant thermal management to function continuously. The most important electronics are the generator and power converting devices.

The generator is the heart of a wind turbine. It converts the rotational energy of the wind-spun rotor into electrical energy. It generates the electric power that the wind turbine system feeds into the grid.

Generating electricity always entails the loss of heat, causing the generator’s copper windings to get hot. Larger capacity generators are even further challenged. The thermal losses will increase with the generator in proportion to the cube of its linear dimensions, resulting in a serious decline in generator efficiency.[9]

Excess generator heat must be dissipated to maintain efficiency and avoid damage. On most wind turbines this is accomplished by enclosing the generator in a duct, using a large fan for air cooling. Some manufacturers provide water-cooled generators that can be used in wind turbines. The water-cooled models require a radiator in the nacelle to void the heat from the liquid cooling matrix.

Wind turbines may be designed with either synchronous or asynchronous generators, and with various forms of direct or indirect connection to the power grid. Direct grid connection means that the generator is connected to the (usually 3-phase) alternating current grid.

Wind turbines with indirect grid connections typically use power converters. These can be AC-AC converters (sometimes called AC/DC-AC converters). They change the AC to direct current (DC) with a rectifier and then back to usable AC using an inverter. In this process, the current passes through a series of Insulated Gate Bipolar Transistor switches (IGBTs). These convert direct current into alternating current to supply to the grid by generating an artificial sine wave. The more frequently the switch is turned on and off, the closer to a true sine wave the current flow becomes, and the more sine-like the flow, the purer the power. The resulting AC is matched to the frequency and phase of the grid. [10]

However, the faster these switches actuate, the more heat they develop and given a wind turbine’s variable inputs, IGBTs for this application need to cycle very frequently. This generates large amounts of heat that will dramatically decrease overall efficiency unless properly cooled. [11]

Cooling Electronics in Wind Turbines

Fig. 4. An active air cooling system inside a wind turbine nacelle features an air-to-air heat exchanger for managing heat in the generator (Vensys). [12]

Even with efficiency improvements, a wind turbine’s power generation systems and subsystems must manage ever increasing heat within its limited nacelle space. In addition, even if incurred power losses are as little as 3-5 percent, thermal management systems would have to dissipate 200-300 kW and more of heat.

Air cooling has been used effectively in small-scale wind turbines, but it is not practical for removing the heat produced in MW-scale units. Its thermal capacity is so low that it is difficult to blow enough air across a motor or through the converter to maintain reliable operating temperatures. That is why water cooling is used more often than air for larger wind turbines.

Cooling Electronics in Wind Turbines

Fig. 5. Electronics in a medium voltage (Up to 12 MW) wind turbine converter. Cooling is provided by a closed-loop unit with a mix of deionized water and glycol (ABB).[13]

However, water cooled systems are relatively large, and their thermal efficiency limitations force the size and weight of power generation sub-systems to essentially track their power throughput. Due to the thermal performance limitations of water, the power-generation equipment for a 10 MW wind turbine is nearly twice the size and weight of a 5 MW model. This is largely because water cooling cannot adequately remove additional heat loads without spreading them out.

One supplier of liquid cooling systems for wind turbine electronics is Parker Hannifin. Its Vaporizable Dielectric Fluid (VDF) system provides heat transfer capability significantly greater than that of water. The VDF system requires less fluid and lower pump rates. The same dissipation rates provided by a 6 liter/minute water flow can be achieved by 1 liter/minute VDF flow, thus allowing for a smaller system.

The hermetically sealed VDF assembly is designed to be leak proof, but if a leak occurs the non-conductive fluid will not damage electronic components. The cooling system’s efficiencies and lack of thermal stack-up provide an additional advantage in that the system maintains a fairly tight temperature range. The lack of thermal cycling removes a strain on the turbine’s electronics, which extends their useful life. [14]

Cooling Electronics in Wind Turbines

Figure 6. Dual-phase liquid cooling method for converters has a circulating refrigerant in a closed-loop. Vaporizing coolant removes heat from devices and re-condenses to liquid in a heat exchange (Parker). [15]


Heat issues in wind turbine electronics mainly concern the generator and the power conversion electronics. The heat load of the generator comes from copper wire resistance and from iron loss from the rotation of the core. Further heat loss is mechanical due to friction. These energy losses become heat energy that is distributed into the wind turbine nacelle.

The excess heat from the nacelle-based power conversion systems is mainly due to impedance from electronic components such as capacitors and thyristors. Higher temperatures will reduce the system’s life and increase failure rate. Thermal management methods such as liquid cooling can be effectively adapted for nacelle electronics. [10]

1. https://en.wikipedia.org/wiki/Alta_Wind_Energy_Center
2. https://en.wikipedia.org/wiki/Wind_power_by_country
3. http://www.ozy.com/fast-forward/how-twinning-tech-will-power-our-future/71993
4. Layton, Julia, How Wind Power Works, HowStuffWorks.com.
5. http://www.awea.org/Resources/Content.aspx?ItemNumber=900&navItemNumber=587
6. https://www.linkedin.com/pulse/smart-grid-energy-harvesting-martin-ma-mba-med-gdm-scpm-pmp
7. http://www3.imperial.ac.uk/newsandeventspggrp/imperialcollege/newssummary/news_17-7-2014-8-56-10
8. https://www.youtube.com/watch?v=sYoQ6mS2gss
9. http://ele.aut.ac.ir/~wind/en/tour/wtrb/electric.htm
10. Jian, S., Xiaoqian, M., Shuying, C. and Huijing, G., Review of the Cooling Technology for High-power Wind Turbines, 5th Intl Conf on Advanced Design and Manufacturing Engineering, 2015.
11. http://www.windpowerengineering.com/design/mechanical/cooling-electronics-in-a-hot-nacelle/
12. http://www.vensys.de/energy-en/technologie/generatorkuehlung.php
13. https://library.e.abb.com/public/430f5f2493334e4ead2a56817512d78e/PCS6000%20Rev%20B_EN_lowres.pdf
14. http://www.windsystemsmag.com/article/detail/60/cool-system-hot-results
15. http://buyersguide.renewableenergyworld.com/parker-hannifin-renewable-energy-solutions/pressrelease/parker-to-launch-converter-cooling-systems-for-1mw-wind-turbines-at-husum-wind-energy-2012.html

For more information about Advanced Thermal Solutions, Inc., its products, or its thermal management consulting and design services, visit www.qats.com or contact ATS at 781.769.2800 or ats-hq@qats.com.

Industry Developments: Cooling Solar Power Inverters

By Norman Quesnel, Senior Member of Marketing Staff
Advanced Thermal Solutions, Inc.

(This article will be featured in an upcoming issue of Qpedia Thermal e-Magazine, an online publication dedicated to the thermal management of electronics. To get the current issue or to look through the archives, visit http://www.qats.com/Qpedia-Thermal-eMagazine.)

Traveling across the U.S. one will find the widening use of renewable energy systems, including large scale solar and wind farms. The power from these installations is clean, emission-free and relatively low cost. Their own energy sources are free and endless: the wind and the sun.

Wind energy has become a cost-effective power source, competing with installations of coal, gas and nuclear power. So too has solar power, which is the focus of this article.

Solar power is doing more than ever to help meet energy demands for local power and for feeding power back to the electric grid. Today’s U.S. solar installations exceed 3,100 megawatts, enough to power more than 630,000 homes. The price of solar panels has dropped by nearly a third since 2010 and costs continue to fall. Manufacturers in the U.S. are also exporting billions of dollars worth of solar products. [1]

Solar Power Inverters

Figure 1. Wind and Solar Power Installations Share Some Thermal Management Issues with Other Electronics Systems. [2]

Most thermal management issues in solar power systems occur with their inverter systems. Here, the solar-generated DC power is converted to AC for power grids or local use. While these inverter systems can be very efficient, some excess heat must be managed so it doesn’t affect the inverter’s life or performance.

Cooling Solar Energy Inverters

Some solar power systems produce steam to spin turbines and generate electricity. But the more common solar systems are photovoltaic (PV) solar power facilities. In these, solar panels absorb and convert sunlight into electricity with the use of inverters. One or more solar inverters, or PV inverters, converts the sun-sourced, variable DC output of the PV panels into alternating current, AC. This is then fed into a commercial electrical grid or used by a local, off-grid electrical network. AC is the standard used by all commercial appliances, which is why many view inverters as the gateway between the photovoltaic (PV) system and the energy off-taker. [3]

Inverters are standard in PV solar systems whether they’re kW range residential systems to MW sized power plants. Larger installations may use a central inverter or a series of string inverters.

In a central inverter set up, the DC power from multiple solar panel arrays runs to combiner boxes and then to the inverter which converts it to AC. In a string inverter scheme, there are smaller, individual inverters for several panel arrays. The DC power runs directly into a string inverter rather than a combiner box and is converted to AC. While string inverters are used in residential to medium-sized commercial PV systems, central inverters are common to large commercial and utility-scale sites. [4]

Solar Power Inverters

Figure 2. Photovoltaic Solar Panel Installations Can Feature a Central Inverter or a Series of String Inverters. [4]

There are also solar microinverters that convert the DC generated by a single solar module to AC. The output from several microinverters is combined and often fed to the electrical grid. Microinverters are an alternative to conventional string and central solar inverters, which are connected to multiple solar modules or panels of the PV system. The main advantage of microinverters is that small amounts of shading, debris or snow on any one solar module, or even a complete module failure, do not disproportionately reduce the output of the entire array. [5]

Whatever its configuration, the PV inverter determines the amount of AC watts that can be distributed for use, e.g. to a power grid. For example, a PV system comprising 11 kilowatts DC (kWDC) worth of PV modules, connected to a 10-kilowatt AC (kWAC) inverter, will be limited to the inverter’s maximum output of 10 kW. [6]

There is also some power loss in the DC-AC conversion process. At the MW scale this could significantly impact a plant’s capacity (and revenue). But fortunately, inverter technologies have been advancing and expanding. The efficiency of state-of-the-art converters is more than 98 percent.

In addition to converting DC to AC, today’s inverters provide other services to help ensure their systems operate at optimal performance level. These include data monitoring, advanced utility controls, applications and system design engineering. Some inverters provide maximum power point tracking (to maximize power extraction), and anti-islanding protection (automatic shutdown). [7]

Cooling PV Solar Inverters

All inverters generate excess heat, especially utility-scale central inverters. Solar inverters used in the kW range are typically contained in finned metal housings that provide cooling via natural convection. Large-scale PV inverters are typically between 1 and 2 MW and the heat they generate directly correlates with their conversion efficiency. For an example, a 1 MW inverter with 98 percent conversion efficiency is generating about 20 kW of thermal energy. This is enough heat to comfortably warm 10 homes. [8]

Cooling solutions are typically needed inside inverters to protect their IGBT (insulated-gate bipolar transistors) modules. These solid state power semiconductor devices are electronic switches and consist of many devices in parallel. The design of the IGBTs and their cooling systems are among the most important aspects in protecting inverters and improving their conversion efficiency.

Improper IGBT design results in lower efficiency with higher heat exhaust. Cooling this heat requires a more complex and powerful cooling system. Better thermal management for the switching devices is essential to entering the next era of PV inverter efficiency, beyond 99 percent.

The recently-introduced PVS980 1500 VDC outdoor central inverter by ABB is optimized for large multi-megawatt solar power plants. The PVS980 features a self-contained cooling system to ensure outstanding endurance in tough environments with minimal maintenance. The cooling system uses phase transition and thermosiphon technology to prevent external air from entering the critical compartments of the inverter. This reduces the risk of corrosive gases or sand entering the inverter and causing damage. [9]

Solar Power Inverters

Figure 3. The Cooling System in ABB’s PVS980 Outdoor Central Inverter Uses Phase Transition and Thermosiphon Technology. [9]

The PVS980 inverter can operate from below freezing to extreme heat in 100 percent humidity without jeopardizing functionality. With the simplicity of air cooling and with the power density of a liquid cooled inverter, ABB’s inverter has very high total efficiency and low maintenance. There are no fillable liquids, pumps, valves, inhibitors and thus no leaks. All this makes the PVS980 suitable for any outdoor utility-scale PV plant.

Solar Power Inverters

Figure 4. The LV 5 Series Solar Inverter from GE Power Conversion Features a Liquid Cooling System. [10]

Some of the recent advancement in the inverter cooling system, such as an advanced hybrid cooling solution, requires significantly less air-flow in the system without an auxiliary fan power load. This lower load condition allows the inverter to further increase conversion efficiency. [11]

Solar Power Inverters

Figure 5. Outdoor Central Solar Inverter Whose Power Semiconductors, Inductor and Internal Ambient Air are Cooled by a Two-Phase System. [10]

Parker provides utility scale inverters with two-phase refrigerant cooling systems. The have a high efficiency design that integrates proven insulated gate bipolar transistor power conversion and magnetics with Parker cooling technology. No air conditioner is required. Power semiconductors, inductor, and internal ambient are all cooled by the integral two-phase system. Multiple access panels simplify installation and scheduled maintenance. [11]

The small footprint and high reliability of Parker’s outdoor central solar inverter is made possible by an advanced cooling system that uses a non-conductive, non-corrosive liquid to cool critical components. The refrigerant requires only 13 percent of the flow rate of an equivalent water/glycol based system. The cooling system runs efficiently by capitalizing on the tremendous amount of heat that is transferred as the refrigerant vaporizes, then releasing the heat through a condenser. No compressor is needed. Redundant system components allow inverter operation even after loss of a pump or a fan

Solar Power Inverters

Figure 6. IGBTs Mounted on a Cold Plate Inside a Central Solar Inverter. [11]

Compared to air cooling, with Parker’s solar inverter design IGBT temperatures are kept more constant over time. Advanced cooling is used on both the IGBT devices and the high efficiency inductors, as well as with a unique cool door feature that circulates temperature controlled air inside the sealed enclosure. Heat from the coolant loop is removed by an isolated heat exchanger, with no air exchange from the enclosure interior to the outside environment. Heat exchanger fans are variable speed for maximum efficiency. They are designed for redundancy and are monitored for rotation. In the event of a fan or coolant pump malfunction, the inverter will continue to operate, folding back power if necessary. The cooling system is designed for a minimum of maintenance, and there are no air filters to change.

Solar Power Inverters

Figure 7. Fan-less Heat Pipe Cooling is Used Up to 50% Load in This Toshiba 1500VDC PV Inverter. [12]

Another producer of large scale PV inverters is TMEIC (Toshiba Mitsubishi-Electric Industrial Systems Corporation). Their Samurai inverter series has power ratings up to 2700 kW. Each model has an advanced hybrid cooling system that uses heat pipe technology. The heat pipes allow the system to operate up to 50 percent load without turning on fans. The heat pipe cooling uses fewer parts and a slow speed fan. The fan-less mode runs when the inverter is below 50 percent load at 50°C. Natural convection provides the necessary cooling. Cool air enters from the bottom, flows through the heat pip, and hot air is exhausted from the top. [12]


A PV solar power system’s current inverter determines the amount of AC watts that can be distributed for use, e.g. to a power grid. For systems operating in the megawatt output range, the inverters will require some level of thermal management to cool their IGBT systems. Many of these large inverter systems have custom cooling solutions that can differ from each other (e.g. air cooling vs. liquid cooling) but all methods have their origins in cooling electronics other than those found in the solar power industry.

[1] http://www.cleanlineenergy.com/technology/wind-and-solar
[2] http://www.ucsusa.org/our-work/energy/our-energy-choices/our-energy-choices-renewable-energy#.V_bXoeUrJpg
[3] http://www.solarpowerworldonline.com/2013/04/how-do-solar-inverters-work/
[4] http://cenergypower.com/blog/string-vs-central-inverters-choosing-right-inverter/
[5] https://en.wikipedia.org/wiki/Solar_micro-inverter
[6] http://www.solarmango.com/scp/solar-inverter-the-brain-of-a-solar-power-plant/
[7] https://en.wikipedia.org/wiki/Photovoltaic_system
[8] http://www.solarpowerworldonline.com/2015/02/new-age-solar-inverter-conversion-efficiency-99/
[9] http://www.abb.com/cawp/seitp202/db94b0aa1e8655a9c1257fdb0043680e.aspx
[10] http://www.gepowerconversion.com/sites/gepc/files/downloads/Solar_Single_Pages.pdf
[11] http://www.parker.com/literature/Renewable%20Energy/Parker_RenewablesBrochure__NA_7-2_spreads_lr.pdf
[12] https://www.tmeic.com/Repository/Others/Solar_Ware_Samurai_brochure_Rev-T-July2016.pdf