Now Hiring Engineers – Electrical & Structural

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Currently Available Positions:

  1. Senior Electrical Engineer – MV & SCADA
  2. Senior Electrical Engineer
  3. Solar Engineer
  4. Senior Structural Engineer
  5. Marketing Manager

Please send your resume to info@purepower.com

Join the team that produces the best value engineered and constructable drawings in the industry. You will be coming into a culture of constant education, improvement, and teamwork. As a Pure Power engineer, challenge yourself every day to make each design and drawing set the best one yet.

The 120% Rule Explained – 2011 NEC 705.12(D)(2)

Everyone knows about the 120% rule, but not everyone understands the situation it is trying to protect against. This article will explain Pure Power’s philosophy on the 120% rule.

The Code
In the 2011 National Electrical Code (NEC), the language in 705.12(D)(2) is straightforward:

“Bus or Conductor Rating. The sum of the ampere ratings of overcurrent devices in circuits supplying power to a busbar or conductor shall not exceed 120% of the rating of the busbar or conductor.

In the 2014 code, this one sentence has been revised to be several paragraphs long with different scenarios. However the philosophy holds true, and once you understand the philosophy of the simpler 2011 version of 705.12(D)(2) you will be able to understand NEC 2014’s more sophisticated version.

Example of a typical commercial facility electrical service equipment:
Below is a depiction of a typical commercial switchboard. It is very common for the sum of the branch circuit breakers to add up to more than the main circuit breaker. The engineer that originally designed the building and electrical system understood that the loads were intermittent, and very unlikely to be maxed out at the same time.
120 rule 1-Start

 

System without solar, under normal load:
This shows the system under a typical load. None of the branch breakers are pulling the full load, and the total current is less than the bus and main circuit breaker rating. Everything is perfectly fine in this scenario.
120 rule 2-Normal-Load

 

System without solar, under overload condition
If the branch breakers draw more current than the main breaker’s rating, the main will trip and protect the bus.

120 rule 3-Overload

 

System under overload condition with solar interconnected load-side.
The load breakers are drawing more current than the main breaker’s rating, however the main is not tripping to protect the bus. The solar is acting like a “backdoor”, allowing additional current to feed the loads. The loads are able to pull much more current than the bus is rated for, but the main breaker doesn’t “see” it. The bus will overload, overheat, and fail (possibly catastrophically). This is what the 120% rule is protecting against!
120 rule 4-Overload-with-PV

 

System under overload condition with solar interconnected line side (supply side)
How does a line (supply) side interconnection affect the overload scenario? Below is the example with the same load. Since the solar is on the line side of the main, it cant sneak anything past it to the distribution section. It doesn’t matter if the current is coming from the PV or the Utility, if it exceeds 800A the main breaker will trip to protect the bus. The main circuit breaker will continue to protect the switchboard just as it always has, nothing to worry about.
120 rule 5-Line-side

 

Conclusion
Real life examples are not always as cut and dry as the example above. You can have cold sequence metering, tapered buses, interconnecting at subpanels, etc, things can get very tricky. As long as you apply the philosophy above to the new language in NEC 2014, you can work through the problem and ensure a load side interconnection cant overload the bus.

Photo of the Month – December

Pure Power engineered a rooftop solar PV system with an innovative new method for mounting string inverters. The inverters are mounted on strut stands directly over cable tray, and the AC and DC wiring is all neatly and compactly run in the cable tray. The cable tray has barriers to provide the required separation between the AC, DC, and communication circuits. In addition to being clean and attractive, this value engineered solution saved the installer considerable time, money, and space compared to traditional conduit raceways.

Here are photos of the finished product. The electricians executed Pure Power’s plans perfectly.

AE-Inverter-over-Tray-1 AE-Inverter-over-Tray-2 Solar-Inverter-Tray-Details Solar-Inverter-Tray-Plan

 

Scary Photo of the Month – September

On this system, the installer stacked ballast so high that it shades the modules at noon of each day. Why would anyone use a hollow block for ballast?
Module interrow Shading

At the same site but on a different roof… There was ample space on the roof, but the installer placed the modules right up against the parapet wall where it would it would be heavily shaded in the afternoons year round.  Module Shading 2
Module shading 1

Photo of the Week: Improper Raceway

Sept 2 - Inproper racewayThis installer gets full points for creativity, but fails miserably for inappropriate construction means and methods. These cables are not protected from physical damage, and they are not outdoor rated so the UV rays will deteriorate the cables causing premature failure.

Pure Power Systems names Bill Chaney Director of Business Development

Pure Power Engineering is excited to announce the addition of Bill Chaney. PPS specializes in value engineered designs, risk mitigating construction services, and cutting edge O&M solutions; all of which will leverage Bill’s extensive solar experience in matching contractors with the services they need to maximize their profit and reduce risk.

Bill Chaney brings seven years of solar experience after leading a mid-sized regional engineering firm as the COO.  He started that solar division and grew it to the largest on the East coast. Bill said “It’s amazing how the Pure Power team leverages engineering, construction, and O&M experience to drive down the installed cost for contractors and developers. Pure Power’s value-engineering techniques are way ahead of the curve and give contractors the edge they need in today’s competitive market. The future of solar is centered around reducing installed costs, and no one is doing more to further this cause than Pure Power. I’m excited to be a part of this forward thinking initiative.”

Richard Ivins P.E., the president of Pure Power Engineering, said “We are in the business of helping contractors build solar projects faster and easier. Bill will use his extensive experience to ensure our clients are provided with whatever services they need to maximize their profit.”

Reach out to Bill today and congratulate him at (201)687-9975 x104 or bchaney@purepowerengineering.com

Pure Power Commissions 3.4 MW Carport System

Pure Power Engineering have successfully performed system start up and commissioning of the photovoltaic installation at the County College of Morris. The system is comprised of 3,442.29 kW of photovoltaic modules installed on thirty three carports/canopies and one roof mount. The distribution of the power is established through localized equipment pads in each of the five parking lots back feeding a newly installed transformer network that interconnects with a 15 kV medium voltage gear. Data acquisition is accomplished through three independent DAS networks monitoring twenty inverters and six weather stations. The complicated distribution structure and project size created unique challenges for efficient and safe commissioning of the system.

Through a custom developed commissioning procedure, Pure Power Engineering was able to successfully coordinate four commissioning teams to simultaneously work on the system. This multi-faceted approach to the system commissioning allowed for maximized production over a minimized timeframe. During commissioning, Pure Power Engineering used refined safety practices and procedures to minimize risk of worker injury or system failure. The combined efforts of pre-commissioning planning and training allowed for the system to be commissioned in record time. Pure Power Engineering looks to utilize this knowledge base in the future where projects require a quick and efficient system commissioning.

Brad Bowery’s East Coast SREC Markets Presentation

SRECtradeLogo

On the evening of February 6th, as part of the PV America East Trade Show and Conference, a select group of solar developers, financiers, equipment manufacturers, and installers gathered to hear a presentation on the state of the East Coast SREC Markets by Brad Bowery, CEO of SREC Trade Inc. The event was organized and hosted by Pure Power Engineering, Inc. as part of their core philosophy of adding value for their customers wherever possible. Rick Ivins, President of Pure Power Engineering explains. “Our specialty is designing systems and then project managing their construction in such way that we increase the profitability of our clients’ projects. We wanted to approach the problem from a different angle and help them with their profitability by providing information from the financial side of the equation. Brad did a great job of doing just that.” The presentation focused on the challenging New Jersey SREC market, as well as the current trends in Massachusetts, and Maryland. Attendees of the presentation were very interested in the message. Rick Peters, President of Solar Energy Services Inc. of Millersville MD commented “It was very insightful to hear Brad speak about the regional SREC markets. It was particularly valuable to hear his perspective on MDV-SEIA’s approach in helping to maintain a stable SREC market in Maryland.”

Now is the Time of Year For Solar Maintenance

Solar arrays are valuable revenue generating assets that require a certain amount of maintenance.  How much exactly depends on what type of installation we are talking about (ground mount vs. roof mount), the size of the installation (obviously larger systems require more than small systems), the system’s age (older systems require more), and numerous smaller factors such as the tilt of the panels (flatter systems require more maintenance) and the quality of the original installation itself (better installs should lead to less maintenance).

With all of these factors influencing the amount of maintenance a system requires how is the system owner to know what is appropriate for their system? The easiest way to answer that is by asking what your risk tolerance is. If you are the type of person who gets their oil changed every 1500 miles, and never misses a checkup at the dealer, then you should definitely have your solar array looked at more than once a year. If you tend to push the envelope when it comes to changing your oil or painting your house, then maybe an annual checkup is enough. All systems, no matter what their size, tilt, mounting method, etc. should have an annual check up performed by a qualified technician.

The best time to perform maintenance is actually in the late fall / early winter. Daily generation rates are at an annual low at this point on the calendar and shutting the array down for a day or two if necessary will not amount to significant lost revenue. In fact sometimes it is three times cheaper in terms of lost revenue to maintain a system in December than in the peak generation months of April or May.

Some other points to consider about solar maintenance:

  • Snow removal from atop a solar array is not necessary from an electricity generation standpoint.  The snow will absolutely melt within a few days and the amount of electricity you are missing out on does not justify the cost of removing the snow.
  • Snow removal may be necessary however if the system is roof mounted and if the roof cannot handle the combined weight of the snow and the array.  This condition is next to impossible to find on a pitched roof that utilizes a penetrated racking.  Flat roofs with ballasted systems are the most likely to face these sorts of issues.  In New Jersey roofs with ballasted systems must be capable of carrying the weight of the array plus the prescribed snow load (The snow load starts at 20 pounds per square foot in the shore areas and southern part of the state, and increases up to 30 pounds per square foot in Warren and Sussex counties in the northwest).
  • Snow removal should only be performed under the supervision of a qualified solar technician.  A considerable amount of damage can be done using shovels and other tools around a solar array.  You may be risking your installation and manufacturer’s warranty if you do not have the proper supervision.
  • A little maintenance can go a long way – small issues have a disproportional effect on array performance.  A loose connection here, and a few dirty panels there can really reduce your production.  The only way to reduce these effects is through regular maintenance.