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Solar Inverters: A Niche Market

published: 2011-07-06 16:08

As more and more large-scale solar farms have been leaving the drawing board to go into construction, manufactures of photovoltaic (PV) solar cells and concentrated PV units have not been the only companies that have seen an increase in orders.

PV installations, whether large-scale utility farms or small-scale business or residential installations, all need an obscure piece of electronic equipment that continues to see a surge in new developments: the solar inverter.

While solar PV market for residential has crept along for decades, utility-scale installations over 1MW are finally taking off. This new market has changed the technological needs of developers of solar power and both established and start-up inverter manufacturers have been racing to meet this challenge.

Power Inverters

Inverters take DC power from the PV panels and “invert” it to the AC power required for residential use, and so it can be fed into an electric utility grid. Being tied to the grid though requires additional electronics that synchronizes the power’s frequency (50 or 60 Hz) and limits its voltage and current to match that of the grid.

For multi MW utility-scale solar farms, these inverters are much different from the small, wall-mounted units used for individual residential solar applications that only handle about 100kW. The more sophisticated electronics for large capacity utility installations includes computers that constantly monitor the grid’s AC waveform and adjusts the solar farm’s output voltage to consistently match the grid. This means touch screens that display the power production, multi-level 24-hour diagnostic monitoring, data collecting and remote Internet access to all functions. The largest solar array installations require multiple inverters, with the largest inverter units requiring liquid cooling.

Because of their complexity, inverters can make-up about 10 percent of the total cost of a large-scale solar power project. To insure that these inverters maximize the power output while maintaining the cost-efficiency of the entire solar power plant, inverter operating efficiency is crucial.

Inverter Efficiency

As crucial as the efficiency of a PV panel, the efficiency of an inverter will determine how much energy that a solar array creates is actually converted to power and delivered to the utility. Every single incremental increase in inverter efficiency leads to additional energy output produced, and therefore a greater rate of return.

For inverter manufactures, the current selling point is the bragging rights for each small percentage their new inverters can achieve. For example, Colorado-based Advanced Energy Industries Inc. has held the utility-scale solar inverter efficiency industry benchmark of 97 percent and then 97.5 percent. Then in June 2011, Advanced Energy introduced its Solaron 500kW inverter with a 98.7 percent EU weighted efficiency, and a 99 percent peak efficiency.The company says its inverter's peak efficiency is 0.3 to 0.25 percent higher than any other inverter in its class.

That efficiency rating came from the California Energy Commission (CEC), which is the leading North American agency for reviewing and approving inverters for commercial use. The CEC posts rating for hundreds of inverters and other solar equipment on their website.

Advanced Energy had announced in May 2011 that its Solaron 500kW inverters will be part of a 150MW PV project in Arizona that is slated to be operational in 2013. When completed, it will be one of the largest PV installations in North America. The company has also been chosen by Cupertino Electric Inc. in San Jose, California, to supply inverters for another 35MW PV project.

North America’s Inverter Needs

As this utility-scale solar market continues to develop in the U.S., inverter manufacturers that have done well in the European market are working to establish themselves in North America. The U.S. Energy Information Administration predicts that solar generation in the U.S. will expand more than fourfold over the next decade.

Grid-connected PV installations in the U.S. for Q1 2011 grew 66 percent over Q1 2010 to reach 252 MW, according to the U.S. Solar Market Insight report released by the Solar Energy Industries Association on June 16, 2011. Cumulative grid-connected PV in the U.S. has now reached over 2.3 GW.

Meanwhile, North American utilities, solar engineering designers and construction firms have been attempting to move to the next level by shedding the 600V PV grid standard for a 1,000V design to increase efficiency while lowering costs. This industry evolution had been slowed by the lack of a certified 1MW, 1,000V inverter.

But in late June 2011, Houston-based American Electric Technologies Inc. announced it had received word from TUV Rheinland that its 1MW, 1,00OV Integrated Solar Inversion Station (ISIS) had passed the UL 1741-2010 inverter tests. AETI says their liquid-cooled ISIS is the first 1MW inverter unit tested at 1,000V.

Meanwhile, French-based Converteam is now working into the U.S. market for inverters. Less than eighteen months after entering the inverter market, the company announced it had reached cumulated orders equal to 100MW of inverter capacity for the utility-scale PV market. That company’s inverters range from 45 kV to 1.5 MV, all of which use air-cooled or liquid-cooled technology.

Converteam has supplied inverters for projects in Germany, France, the UK and Italy. The largest project is a 12MW solar farm in Sietzsch, Germany. It is one of Germany’s largest PV installations, using 52,200 PV modules on a 33-hectare site in Saxony-Anhalt and connected to the grid using 21 Converteam inverters installed in eight separate stations.

Another firm moving into the U.S. market is Woodward IDS. Though Woodward is headquartered in Fort Collins, the company recently acquired Integral Drive Systems AG to form Woodward IDS, headquartered in Zurichwith operations in Bulgaria and China. Woodward IDS' solar inverters, which have been used in PV installations in Europe, are being introduced for the first time in the United States at the Intersolar North America exhibition July 12-14, 2011 in San Francisco. Among the inverters they supply are units with output ratings up to 1000kW.

In April 2011, Israel-based SolarEdge opened a new production site at the Ontario, Canada, Flextronics factory. Because they will be produced locally, the SolarEdge inverters will comply with Ontario’s “Domestic Content” requirement that allows installers of private and commercial installations using the units to benefit from the Ontario Power Authority Feed-in-Tariff programs. The company’s inverters have a 98 percent maximum efficiency and include 3kW, 3.5kW, 4kW, 5kW and 6kW single-phase inverters, and 7kW, 8kW, 9kW, 10kW and 12.5kW three phase-inverters. From the Ontario facility, SolarEdge plans to supply inverters to the entire North American market in a way that allows faster delivery, according to the company.

Low Inverter Competition

There are several factors that make competition within the solar inverter market different from the PV market.

What makes the utility-scale solar inverter manufacturing sector unique is that it is not a “one size fits all” product. Solar installations not only each have their own unique design requirements, but those requirements also vary depending on what country the construction takes place. While inverters do come in various sizes for utility applications, inverter manufactures do need to be flexible enough to supply any unique orders based on a customer’s requirements for each site. This includes supplying electronics that may be subject to harsh, outdoor conditions.

Another difference between PV and inverter design and manufacturing is that PV makers not only strive to compete among themselves, they must also compete with other forms of energy by finding technical ways to quickly lower their costs. To do that, PV manufactures must continue to work to increase by many fold the conversion efficiency of their PV cells. Since inverters only amount to roughly 10 percent of the total cost of building and running a solar power facility and have already reached nearly 100 percent efficiency, the pricing is not under such pressure.

But the competition is starting to grow as orders increase rapidly due to the growing number of the utility-scale PV projects being planned and constructed since 2010. The continued high growth for solar installations forecast for the North American market is not only benefiting the domestic suppliers, such as Satcon and Advanced Energy - the largest non-European suppliers, the growth continues to attract European companies and new start-ups.

But the inverter market remains global.

According to the International Energy Association, global solar PV capacity is expected to provide 11 percent of global electricity production equaling about 3,000 gigawatts of installed capacity by 2050. Since inverter manufactures also measure their potential market in watts, this means there will be a need for nearly an equal amount of inverter capacity.

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