Since the advent of modern solar technology, common wisdom has always taught us that solar panels should face the equator. For those of us in the Northern hemisphere, that means south. Now, with falling panel prices, the South-facing paradigm may be falling by the wayside.
Photo Credit: NREL.gov
As we know, the suns relative position to any given location on earth changes not only throughout the day, but throughout the year. It rises in the East and sets in the West each day, while it rises higher in the sky during the summer and lower in the winter. The seasonal change is less drastic the closer you are to the equator. Solar collectors, be they Photovoltaic (PV) electrical generating panels or solar thermal collectors which create heat, perform best when they are perpendicular to the sun’s rays. For this reason, solar installations have traditionally been designed with a tilt toward the equator, relative to the latitude.
In the world of PV solar, high PV panel prices have always required optimum system performance for maximum economic benefit. In many cases, this meant seasonally adjusting the tilt of panels or using “trackers” to automatically adjust the tilt of the array though the day. For fixed arrays, like roof mounted systems, South has always been the required direction. Now, as panel prices are falling, we are seeing many more panels being mounted on roofs facing east and west. So what gives?
photo: http://jb-electrical.co.uk
The paradigm-buster in this case is more economic than technical. Your PV panel may lose a degree of performance by not facing south, but the value of the power during a given time of day may make other orientations more financially attractive. For instance, panels facing West will be exposed to less sun during the day than panels facing south, and will therefor make less power. But the power production by the west-facing panels reaches its peak in the late afternoon, at the same time that demand for utility power peaks. As people come home from work and school, air conditioning goes on, along with TVs, washing machines and other appliances. Utility companies rely on more expensive natural gas “peaking” plants to generate power during these times, and so the power produced costs more. That means that late afternoon solar generation is worth more, too.
According to a report from the Texas-based research firm Pecan Street: “residential solar systems, and particularly west-facing rooftop systems, may also act as a fairly impactful peak demand reduction device for utilities struggling to meet afternoon demand in hot summer months.”
Key findings from the report included:Counting only the electricity generated by a rooftop solar system that is actually used in the home (and therefore not counting electricity that was sent to the grid because it could not be used in the home), homes averaged a 58 percent peak demand reduction for electricity from the grid.
South-facing solar systems cut peak demand from the grid by 54%, while west-facing systems reduced their homes’ peak demand from the grid by 65%.
During peak hours, homes used 80% of the power generated from the rooftop systems and returned 20% to the grid. In the homes with south-facing systems, 78% of the power generated was used in the home; 22% was returned to the grid.
In homes with west-facing systems, 84% was used in the home; 16% was returned to the grid. Over the course of the full day, 64% of the energy generated by the rooftop systems was consumed on-site; 36% was returned to the grid.
Over the course of the full day, and not including surplus energy returned to the grid, the solar systems provided 36% of the average power used per home. Nearly a third (32%) of the power was generated during peak demand hours.
In the wake of findings like those of Pecan Street, The California Energy Administration has announced a new $500 incentive for new, West-facing solar arrays.
“We are hoping to squeeze more energy out of the afternoon daylight hours when electricity demand is highest,” said David Hochschild, lead commissioner for the agency’s renewable energy division, which will be administering the program. “By encouraging west-facing solar systems, we can better match our renewable supply with energy demand.”
In Europe, where solar installations far outpace those in the United States, the South-facing paradigm is rapidly becoming a problem for utilities. According the The Telegraph: “… Professor Ralph Gottshalg of Loughborough University…said Germany has too many solar panels which means that its grid is disrupted on sunny summer lunchtimes with a flood of solar power so cheap it has to be almost given away. He is urging to the UK to follow Germany’s recent policy of putting panels on east-west facing roofs to smooth the supply of power during the day and prevent spikes of power at midday.”
So, what about East? According to Professor Gottshalg, there should be more solar going in on East roofs as well. This is true, from the perspective of solar as an offset for a users overall demand for grid power. However, in most areas, the power generated in the morning will be worth less money than that generated in the afternoon. However, in some areas, morning usage might be higher, for instance in colder rural areas in the North. Also, shading can be an issue at individual locations, and a wide open Eastern solar window may be a more viable option than a partially shaded southern or western exposure.
So what about trackers? Don’t they still offer the most power throughout the day? Stated simply, yes. However, tracking system technology has not fallen in price as quickly as panel prices. In most cases, it is now cheaper to buy more panels and use them less efficiently than it is to use tracking technology to maximize panel output. The one glaring exception to this discussion is, of course, off grid-applications. When storing electricity on-site in a battery bank, utility time-of-day pricing does not apply. For everyone else, it looks like solar system designs may be looking to a new direction.
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