Could Solar Inverters Moonlight As Grid Stabilizers?

July 13th, 2011 by Susan Kraemer





All utility-scale solar farms use inverters that turn the DC power that solar panels make into the AC power that is used on our electrical grid. But, so far, these solar farms’ inverters only work days, converting each day’s sunshine into AC electricity for the grid.

But it turns out, that because we are adding so much renewable energy to the grid, there is a new job that solar inverters can do, by working nights as well as days. By moonlighting, solar inverters could actually help stabilize the renewable energy grid.

What if solar inverters on large solar farms could stay busy, and cut solar farm costs, by earning their keep working all night long as well?







That is the question that was asked by a researcher with 20 years of experience with devices that perform as flexible AC transmission systems (FACTS) and are used by utilities to keep the grid stable.

Rajiv Varma, Associate Professor of electrical engineering at the University of Western Ontario in Canada has just patented the very exciting answer, and done so five months ahead of GE, that is also hot on the trail of this brilliant and timely idea.

Via PV Magazine: Varma has come up with an inexpensive way to modify solar inverters so they can be used at night to help stabilize distribution and transmission capacity on the grid.

Utilities already use a regulating device on electricity transmission networks called a STATCOM (Static Synchronous Compensator) which is a kind of FACTS device to provide voltage control that can improve grid capacity where distribution and transmission constraints emerge. In addition to voltage control they can reduce power system oscillations that cause system instabilities, which is becoming more common as utilities move to integrate more large-scale renewable systems, such as solar and wind farms, into the grid.

At the heart of every FACTS device is an inverter. What Varma has patented is a way to modify a solar farm inverter by programming it to perform the work of stabilizing the grid at night. Ontario, where Varma lives is a test bed of sorts. It is rapidly adding renewable power, because of its extremely generous Feed in Tariff rates. But this is leading to oversupply, of wind power especially, that is threatening grid stability.

Wind power companies in the province are increasingly having to offer to supply their own FACTS devices to regulate their unruly wind energy offerings in order to be allowed access to the grid. Wind power can be tremendously disruptive to the grid, overwhelming it during stormy weather, and FACTS devices like STATCOMs can reduce that inconsistency by reducing the power oscillations that destabilize the grid, by operating as either a source or a sink.

By marrying a solar farm to a wind farm nearby (ideally within about five kilometers) Varma thinks the two could work synergistically supplying daytime and nighttime power that is regulated and smoothed out by the solar farm inverter at night, and even working part time on cloudy off-peak days on an as-needed basis. He estimates that the inverters used within a 4.5 MW solar farm for example, would expand distribution line capacity enough in the night to allow an additional 7 MW of wind power onto an otherwise congested area of a network.

A $7 million dollar Canadian research effort led by Varma and his team has just proved through sophisticated computer models that solar PV inverters could be modified to work as STATCOMs. The team worked closely with Ontario’s transmission system operator, Hydro One, and the Canadian division of First Solar, the US thin-film giant which has an 80 MW solar facility in the area.

Having proved the concept, the next step for Varma’s team is to build several 10 KW prototype inverter systems, test them in the lab, and then try them in the field, with funding from two local utilities, London Hydro and Bluewater Power.

If that field test works as Varma thinks, look for an exciting new company: SMG Night Solar, that has been spun out from the university research, that will be commercializing the imaginative idea, likely through licensing it.

The idea is a win-win-win, benefitting solar farms (night time income possibilities), wind farms (built-in power stabilizers to make their unruly power more acceptable) and utilities (that must add more renewable energy, but must also keep the grid stable too).

And of course we all win, too by finding yet another creative way to power our economy off clean energy so we can continue to enjoy a livable climate on our one dear planet, hopefully for as many centuries into the future, as we have in the past.

Susan Kraemer @Twitter









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