Letters

The Cost of Solar Editor's note: Don Nolte, P.E., of Progressive AE, Grand Rapids., Mich., and author of the story "Solar Roofing: Seamless Integration of Architecture and Engineering," CSE 10/03 p. 59, responds to Donald Parham's letter in last month's issue asking for specific cost information associated with photovoltaics.

12/01/2003


The Cost of Solar

It is always good to get feedback and openly discuss our projects and engineering solutions. First, my write-up did not mention [the U.S. Green Building Council's] LEED (Leadership in Energy and Environmental Design) certification because we did not submit the building for LEED certification, as the program was not fully in place at the time of design. The benefactor who financed the PV system desired to have it installed so as to raise the general awareness of students and the community of emerging alternative energy sources. Progressive AE's challenge was to make this system functional and fully integrated into the overall architectural structure. That being said, here are some answers to your questions:

What is the installed cost of the photovoltaics, including all of the metering options? The numbers we received from the general contractor were about $135,000 for the complete PV system. This includes the standing seam metal roofing that the PV panels were adhered to. We have not received the net metering cost breakout as supplied by the utility.

What is the payback in an economic cost analysis? I did not perform a full-blown economic analysis, as a simple payback indicated that there was no way to cost-justify the system. This is precisely why I wrote about the benefactor of the college in the article. The simple payback was 60 to 70 years.

How much power has been sold back to the utility company? The primary use of PV generation is to offset the utility supply to the building and not for resale to the utility. Most likely, it will have a minimal kWh sold back to the local power company. At only 2 cents per kWh for buy-back power, the return would be minimal, as the building uses a minimum of 10 kW, even on weekends. I do not have a kWh number, as the meter does not register a separate outgoing flow.

Is this included in the $2,500 per year savings? No.

At a 35,000 kWh per year savings, what percentage of the total electrical power usage does this represent? A good question. Looking back at my estimates, my projections showed a total of about 2.5% to 2.8% of the total demand and roughly 5% of the total kWh per year.

What is the cost impact (if any) of designing the roof at an angle of 42 degrees? Another good question, which I put to our architectural and construction staff. Their estimate is that it added roughly $30,000 to the structure's cost. But it did add the benefit of providing attic space and the ability to easily access the underside of the roof for wiring and future maintenance.

I hope this helps. I agree that engineers must continue to question published, generalized statements from USGBC or any other source to strive for excellence in our profession.

Donald Nolte, P.E., Progressive AE, Grand Rapids , Mich.

EMI Bus Duct Concerns

Regarding the M/E Roundtable, "Computer Room Power: Up or Under?" CSE 11/03 p. 35 , you failed to mention the problem of EMI/RFI issues. I have been involved in projects where power bus duct in a mechanical space affected adjacent office area computer monitor displays, ultimately requiring the installation of an Mu-metal partition wall covering. [Mu-metal is a nickel-iron alloy—77% Ni, 15% Fe, plus Cu and Mo—which has extremely high magnetic permeability at low field strength.]

The problem arose when office occupants expressed concern over their wavering monitor displays. They were also worried about possible health effects of the magnetic fields generated by bus duct. Although it was determined that the field strength did not present a health hazard, the expensive Mu-metal covering was installed to allay office occupant concerns and restore proper monitor display.

From a data communications standpoint, bus duct emanations are low-frequency (60 Hz) magnetic field noise that generally should not interfere with data room communications and cabling systems. However, communications systems are becoming more and more sensitive to high rate-of-rise type noise. Placing power wiring in conduit helps abate power system noise, because of both the shielding effect of the conduit and the ability of three- phase wiring to self-cancel noise emanations. However, bus duct generally has less noise-cancelling ability than conduit and wire systems.

This is a concern in that as data rates push higher and higher, more signal processing is needed to detect and remove noise. Network systems are vulnerable to smaller and smaller noise levels. This represents both a problem and an opportunity. The problem is the folks who understand—IEEE 802.3 Ethernet folks, who are even trying to write a standard for 10Gbps over copper—aren't the folks who can recommend abatement solutions: namely, power engineers.

The opportunity is to develop some guidelines for how to design power distribution in buildings and offices to best support the coming higher data rates over copper. I kind of understand the problem, but I don't know what the answers are. It's an area we've managed to ignore for now but promises to become more crucial.

Perhaps the manufacturing community, IEEE and TIA can marshal forces and generate some answers. In the meantime, possible noise effects should be analyzed with IT personnel before installing bus duct in computer rooms.

Debbie Ryon, P.E., RCDD, The Cube Corporation, Wallops Island, Va.





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