When the economy of scale with wind power led to larger and larger wind turbines, opponents of these installations took to referring to them as "industrial wind power." Whenever I see a letter to the editor or news story that uses this identity I can tell that it’s going to be a letter or article with an anti-wind bias.

Whether its marring their views of pristine mountains, or blighting their night sky with blinking red lights, or causing bird and bat fatalities, or the somewhat mythical "infrasound" of large wind turbines, opponents almost universally refer to these wind farms using an industrial moniker.

So, I’m becoming troubled by recent reference to "industrial solar" in describing the larger photovoltaic (PV) installations that are cropping up in Vermont and nationwide. There’s a 500-kilowatt (kW) system being planned in Westminster, and a two-megawatt (MW) array proposed for Brattleboro, along Interstate 91, to mention just a couple.

The economy of
scale with solar

As with wind, there is an economy of scale with solar-electric systems. Bulk purchase of solar modules brings the costs down some and, more significantly, larger inverters (the devices that convert direct-current electricity produced by PV modules into the alternating current that can be fed into the utility grid) and other balance-of-system components are a lot less expensive per kW or MW of capacity than the residential-scale components we use for PV systems we install on our houses.

But the differences in cost between large and small systems isn’t nearly as great with PV systems as it is with wind turbines. This means that the incentives for building very large solar systems ("industrial-scale" if you must) aren’t as great as they are with wind.

Advantages of smaller
PV systems

Despite the (relatively minor) economy of scale that argue for larger PV systems, there are some benefits of small systems.

For starters, small systems are well-suited to rooftops. A typical house, if it has a reasonable orientation, can hold a four to six-kW solar array, enough to handle a significant fraction of that home’s power consumption (as long as it’s reasonably energy-efficient). And commercial buildings, with large flat roofs can often hold hundreds of kW or even a MW or two of solar -- which can provide a significant fraction of those buildings’ electrical demands.

Putting solar modules on roofs creates headaches with roof maintenance, and poor-quality installations can result in roof leaks, but rooftop mounting allows us to preserve land area for agriculture, recreation, and wildlife habitat. Whenever possible, I prefer to see PV systems installed on rooftops or carports rather than ground-mounting though, I recognize that that isn’t always possible or practical.

Small PV systems also put electricity generation close to where it is being consumed. Such "distributed power" is changing the face of the utility grid. From a resilience standpoint, generating power close to the point of end-use of electricity also opens up an opportunity for incorporating either some battery storage or capability to use power from the solar system even when the grid is down--something that most grid-connected solar systems can’t do today. (For more on that, refer back to my column, "Beating the Achilles Heel of Grid-Tied Solar-Electric Systems"-- archived at BuildingGreen.com.)

Is big solar bad?

Not in my book. As I look toward the future and a growing imperative to dramatically reduce our fossil fuel consumption and carbon dioxide emissions, I’m convinced that we need a mix of facility sizes with renewable energy systems. There will be many places where large, ground-mounted megawatt-scale solar systems make sense, such as along highways and utility corridors where the land is already degraded and agriculture may not be feasible.

In arid places with lots of open land it should be possible for large solar systems to be developed responsibly -- as long as enough open space is maintained for wildlife.

This isn’t to say that huge arrays make sense everywhere, just as wind turbines don’t belong everywhere. Having served as a trustee of the Vermont Chapter of The Nature Conservancy for nine years, I am well aware of the need for natural, undisturbed habitat.

But I’m also aware that if we don’t address our greenhouse gas emissions, we will be doing far more damage to ecosystems than the solar arrays (and wind farms) that are coming under more widespread attack.

Alex Wilson is the founder of BuildingGreen, Inc. and the Resilient Design Institute (www.resilientdesign.org), both based in Brattleboro. Send comments or suggestions for future columns to alex@buildinggreen.com.