SOLAR TODAY Blog

By Timothee Neron-Bancel
Guest "Ask Ms. Liz" columnist
Operation Manager for NABCEP

A note from Liz Merry: This is a timely column on the NABCEP Certificate of Knowledge program. This information is very helpful for those interested in earning the COK.

The North American Board of Certified Energy Practitioner's (NABCEP) Entry-Level Photovoltaic (PV) program has proven to be very popular since its inception in 2005. There are now more than 100 providers of the Entry-Level exam throughout the country, and more than 3,000 individuals have received notice of achieving a passing score as of July 15. In the last six months alone, the number of people who have successfully passed the exam has more than doubled, as more individuals consider solar-related careers.

Do national standards contain a consistent bias in favor hot-weather architecture? Specifically, do they favor passive cooling technology over passive heating technology?

Two experts have recently drawn attention to idiosyncracies in heating/cooling rules. First, architect Paul Hutton here in Colorado points out that LEED points are awarded for white or reflective roofs, even in snow country where a dark roof may provide solar gain and reduce load on the heating system. Moreover, a high-albedo roof can delay snow melt and therefore shorten the life of the roof material.

Second, Larry Schlussler at Sun Frost in Northern California noted that windows that shut out solar gain are now eligible for federal tax credits, but windows that encourage solar gain are not. In effect, you get a tax credit for windows installed in Phoenix, but not if you're building a passive solar house in Portland. Here's Schlussler's letter:

I recently read that President Obama's stimulus plan would promote more efficient windows with a rebate program. That sounded like a cost effective way of saving energy.
When I look at the specifications for the qualifying windows, I was distraught. The windows had to have a U value below .3 and a SHGC (solar heat gain coefficient) of less than.3. The SHGC is the fraction of solar energy admitted though a window of building. Solar gain is what is needed to passively heat a home. It was disappointing that after years of buildings and testing passive solar structures; passive solar strategies are being generally ignored. Perhaps we should start referring to windows as solar collectors to emphasize their ability to collect light and heat. Windows are by far the most common and lowest cost solar collectors. In addition to collecting heat they also can collect light; an attribute particularly valuable in commercial buildings.

Literature promoting more efficient windows by the window industry and Energy Star touts the low U value and the ability of a window to reduce summer heat loads, but not their ability to collect heat. A recent interview on NPR with scientists from the Buildings Technology Department at Lawrence Berkeley National Laboratory talked about how modern windows save energy by using coatings to "keep the heat out during the summer and in during the winter". However, they omitted passive heat collection.

Which windows coatings are appropriate on a particular face of a building depends on geographic location, orientation of the window, overhangs, shading from plants and neighboring buildings, how and when the building is being used, and interior window treatments.

Perhaps, the heat collection potential of windows is not emphasized because promoting this aspect of a window will not increase sales, or it could be because the effective use of a window collector requires some whole system thinking.

The limited implementation of windows for effective day-lighting strategies in commercial buildings may be the result of not having a defined product. Perhaps a window manufacturer could get the orientation and size of a window from the building designer. Then the manufacturer would provide the appropriate external shading, glass coatings, light shelves and internal window treatments, etc. in a single package.

If we are going to make an impact on global warming and conserve energy, low cost strategies like the effective use of windows must be a high priority.

Larry Schlussler, PhD

The role of clouds in climate change has been up in the air for years.

I'm sorry. This is very serious, so let's abandon the bad puns.

Climate change deniers have tried to paint cloud cover as a "negative" feedback, helping to control climate warming. The theory is that warm sea surfaces produce more water vapor, hence more cloud cover, hence more albedo (that is, reflectivity), hence less sunlight warming the ocean. It's a nice theory.

It's been going up to about 85 degrees F (30 degrees C) in Boulder recently, but indoor temp at the house rarely goes above a comfortable 71 F (21 C); we don't have air conditioning. I've explained this to friends as a combination of shade and "ground source cooling," but I now have some numbers that make sense.

My little 1400-sq ft house is 90 years old, and the big trees on the south side (in the front yard) are at least 50 years old. Ken Sheinkopf, SOLAR TODAY's home energy guru, points out that big shade trees can drop temperatures about 6 to 8 F (3 to 4 C).  This means that the south-facing slope of the roof, along with the front porch, front walls and windows, rarely go above 78 F (25 C).  

When I renovated the house 10 years ago, I stuffed the walls and ceilings with R-19 insulation, but didn't insulate the floor. The floor sits over a 30-inch crawl space and the soil underneath maintains about 55 F (13 C) year-round -- say 50 F (9 C) in winter and 60 F (15 C) in summer. In July, then, the air near my floors should split the difference between the roof and soil temperatures -- which would be about 69 F (20 C).  Ambient temperature at the middle of the room should be about 71 F (22 C), which is what we really experience most afternoons, with windows open for cross-ventilation. At night, indoor temp can go down to 64 F (25 C), cool enough that the fur-bearing quadrapeds want to snuggle.

Back home in Boulder after the week in Paonia, we're working on the garage again. It's going pretty quickly now that we finally have the space cleared out. On Sunday, I knocked out the original window on the south wall, and built a new frame for a larger, insulated window. It was up in time to seal out the evening storms that day.

On Monday, Cleo finished putting up the Tyvek, and I began running wire for the new GFI outlets on three walls. Tonight I'll pick up the first roll of fiberglass insulation and Cleo will staple it up on Wednesday. Then we'll start taking down  the garage door, so she can insulate the ceiling.

I'd like to panel three walls and the ceiling before we frame up the east wall, which is where the garage door was. Hoping to score some big insulated patio doors for that wall. It will be easier to move big panels in if we do it before the doors go in. Besides, it's more pleasant to work with the sun and breeze coming through the space.

Friday was graduation day for the 10-day basic course in PV design and installation. Most of the students have been here two weeks, and many are staying on for the advanced course next week. About a dozen took the two-hour NABCEP entry-level test on Friday evening.

The morning saw final wiring and adjustments on some of the lab projects. My group spent some time in the morning figuring out the voltage drop in the #8 AC line from the PV inverter to the Sunny Island microgrid emulator. Then we connected the Sunny Island to the 48-volt battery bank, the grid transformer, and the PV array inverter. We turned everything on and waited while the Sunny Island exchanged data with the other units and came on line.

After lunch, Ed Eaton convened a study group for students taking the NABCEP test, and the rest of our group put together a schematic of the Sunny Island rig, suitable for use in explaining the complex system to an inspector.

The graduation ceremony at 3:30 pm was a casual affair - Kris, Flint and Kyle handed out the diplomas and everyone promised to keep in touch.

By Liz Merry
SOLAR TODAY "Ask Ms. Liz" columnist

The Department of Labor has started accepting applications for energy training partnership grants (download the PDF). With approximately $100 million-worth of two-year grants up for grabs, hundreds of schools and for-profit providers are currently designing new solar installer training programs.

It may be a heretical statement, but we don’t need more solar training capacity as much as we need a wider pipeline to provide newly trained installers with on-the-job training from experienced installers.

The groups reorganized today and I went with instructors Brad Burkhartzmeyer and Brady Bancroft to learn about the elaborate Sunny Island system.

The weather started cool but heated up quickly. Happily, we didn't have to work on a roof. The system's DC side is fed by a 1.6 kilowatt ground-mount array, built as a single string of eight Sanyo bifacial modules. We got it up pretty quickly. Brendan Pattison and Dan Michelson wired up the DC and AC disconnects, while Scott Ostrin and I bruised the heels of our hands plumbing up the rack. I'd add a 10-foot straight-edge and a rubber mallet to the tool kit.

The Sunny Island is a pretty cool product, devised by SMA originally for isolated stand-alone power systems. If you lived on an island or on a mountain-top or in a remote village far from any grid, you might want a Sunny Island. The main box simulates a grid, imposing a sine-wave voltage on any power coming in. That means any peripheral inverter will see it as a grid and cooperate. You can send in power from a PV array, microhydro generator, wind turbine, battery array or straight from a real grid. Assuming more than one power source, if any one of them goes down, the Island keeps sending out "grid" power. I want one.

The laboratory has been adopted by a large gray tabby, who chose to join us for the day. As we moved from classroom lean-to to array to lunch tent to Sunny Boy shed, Tigger led us from shade to shade, invariably finding the coolest, breeziest spot to stretch out.

We had a chance to gloat a bit. Kris inspected the Enphase system we'd put together and gave us an A. "Not an A+," he pointed out. The only sloppy bit was the way I'd coiled the excess length of AC cable from the inverter string to the rooftop junction box. Too much cable to stuff into the channel in the rack rails, so I'd coiled it neatly and fastened it to the rails with wire ties. Perfectly safe and workmanlike, but if it was my roof I'd have attached a wire-mesh basket under the top row of modules and coiled the excess cable there. Or cut off the excess and crimped on proper new connectors.

After lunch we toured all the completed projects and got explanations from their construction crews. The guys who put up the pole-mount system seemed happiest: their system went up pretty quickly and they got to finish the wiring standing up straight in the shade of their own modules. The most complex system is the Sunny Island rig, designed to take power from any kind of source, charge a battery bank and exchange power with the grid. I signed up to work on that team on Thursday.

Then it was teardown time. The Enphase crew made short work of this: the system came apart even more quickly than it went up, because we didn't have to align anything. The only tricky bit was disengaging the locking connectors that hook each module to its inverter. You need a special tool to disengage the two hooks. One of the joints stuck and needed four-handed fiddling, using a hook-nosed pliers.

While all this was going on, the solar cookers did business. The social plan for the evening was a potluck, so the ovens were full of casseroles, ears of corn, and a broiling chicken. By 5:30 the non-chefs among the student body raided the local supermarket for desserts - I scored five quarts of sherbet and a bottle of local wine.

I've come to think of the Solar Energy International laboratory course as summer camp. On day two you've not yet made fast friends but you're beginning to figure out who's good at what and how the team will fit together.

My group of six built an Enphase system today, using 10 175-watt SolarWorld modules and 10 Enphase microinverters. We only had three safety harnesses, so Brendan Pattison, David Fuller and Mark Deazley hopped onto the roof and started bolting together the rack and the first row of modules. The rest of us handed up tools and made helpful comments, like "That doesn't look straight." Then Kyle Bolger, our instructor, pointed the groundlings at the conduit bits lying about and got us started on the under-roof wiring. Rick Basler wired up the disconnect box.

After lunch we traded places. Rick, Todd Bevington and I climbed onto the roof to bolt down the second row of five modules and complete the electrical connections. We later measured the temperature of the sun-blasted modules at 42 degrees C, and the asphalt shingles were not cooler. I spent an unpleasant 15 minutes lying flat on my back in the roasting pan, fishing around under the array to make the final connection to the junction box and tie up the last unruly loops of cable.

Then Kyle walked us through the commissioning and testing. Brendan, an electrician from Tennessee and by far the youngest and bravest of us, donned the insulated gloves to make the final connections and turn on the disconnect. Nothing smoked.