Sustainable Solar Dynamics

25 Oct, 2006 By: Kenneth Wong

Energy consultant uses SketchUp to analyze solar panel installations

John Humphrey, who cofounded the San Francisco-based consulting firm Sustainable Energy Partners, is devoted to clean energy pursuits in more ways than one. First and foremost, he's married to a scientist studying solar hydrogen production at Stanford University. He usually pedals his bike from his house near Golden Gate Park to the Mission District across town. From his office in a cafe-lined Bohemian neighborhood, he scrutinizes his clients' building plans and figures out cost-efficient methods to incorporate sustainable energy.

"I rarely receive 3D models from the architects I've worked with," observes Humphrey. "I'm often surprised at how much stuff gets done in 2D in the construction world, even today. ... What we usually do is take a floor plan and extrude up, or an elevation and extrude sideways, then fill in the gaps."

Suppose an architect wants to add photovoltaic panels on the roof of a project. Sustainable Energy Partners might be hired to design the panel layout that goes on top of the structure, then oversee the installation process. "Ideally we will get digital drawings," says Humphrey, "but if all we get is a printout, we'll take measurements, then recreate the basic roof dimensions pretty quickly."

So what can undermine a solar panel installation? "Crazy rooflines always kill me," says Humphrey. "What you really want is a big, flat, south-facing roof at an angle that will provide good solar exposure. There are some more specific, preferred angles for different types of solar technologies, but as long as the roof is south-facing and there's no shading issues, we're in the money."

Here Comes the Sun

One of the reasons Humphrey likes to build the 3D model as early in the process as possible is that it lets him analyze those all-important shading issues. "I usually work in SketchUp," he says. "It is so much faster than any other 3D tools I've used." SketchUp makes sun study possible through an interactive heliodon, a sun-angle simulator. "If you're putting up several rows of tilted solar panels," Humphrey observes, "you need to make sure there's enough gap between the rows so they're not shading one another." These studies can also reveal whether nearby objects, such as trees or utility poles, might impact the panels' operation.

The Mission Plaza's hybrid solar thermal and solar photovoltaic system. (Courtesy of Sustainable Energy Partners.)

SketchUp Pro 5, the latest commercial version, includes revised DWG/DXF Import and Export functions, allowing someone like Humphrey to use his clients' 2D AutoCAD drawings as foundation. According to Google, "Using the latest DWG direct libraries, you get access to more DWG/DXF entities for a smoother translation into and out of SketchUp."

Some users are experimenting with ways to import the terrain data from Google Earth into SketchUp for more sophisticated sun studies. Others use SketchUp's Ruby application programming interface to write scripts to display the sun positions in altitude and azimuth as they view shadows. For more, see the Solar Orientation for Google Earth Plugin and the Display Sun Angles threads on the SketchUp Pro user forum.

For indoor energy analysis, Humphrey uses the in-house tools developed by Sustainable Spaces, a partner company of Sustainable Energy Partners. For calculating financial data, he uses OnGrid Solar, an Excel-based solar panel sales tool.

Direct Communication

In addition to using technology efficiently, Humphrey has also learned the importance of interfacing with the decision makers in each client company. "We were hired by the facilities manager to design a system that the building owners didn't really know about," he recalls. "When the time came to build the system and get the contracts signed, the owners were not on board. It's always important to be dealing with the decision-makers. Eventually we managed to get the right people in the room so that a consensus was reached."

Humphrey urges CAD vendors to continue developing better and better tools that integrate the different aspects of a building's energy systems. "Some of the more exciting renewable energy systems could involve solar electric systems, solar heating (for space heating and hot water), and solar cooling," he suggests. "Being able to tie the performance of the systems to other parts of the building -- like the building envelope, duct design and insulation values, as well as lighting and other loads -- will allow us to design buildings that have lower and lower energy loads."

Royal Petroleum Fuel Station, Petaluma, California, with a 30-KW photovoltaic array. (Courtesy of Sustainable Energy Partners.)

What can any company do to make a serious positive impact on sustainable energy? According to Humphrey: Ask employees to ride bikes to work.

Guilty Pleasure

Humphrey admits to one indulgence that's not entirely consistent with his green energy philosophy: a hot tub installed in his office. Because it's heated with natural gas, this apparatus, dubbed the "Think Tank" by its users, does contribute to fossil fuel consumption. But Humphrey points out that it provides relief for the consultants' muscle tension from the unavoidable computer work.

About the Author: Kenneth Wong

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