[RE-wrenches] NABCEP Exam was: PV excellent battery charger

Sun Mar 28 11:36:13 PDT 2010

Developing test questions is an on-going process as knowledge, understanding, and language evolve.

The PV industry started using 32 to 38 silicon single crystal solar cells in series to charge 12-volt batteries. At first, 33-cell modules were used without charge controllers for smaller PV systems by balancing the size of the PV array with the load and battery bank. Later, it was determined that 36-cell silicon single crystal and multicrystalline cell modules in combination with a charge controller provided reliable battery charging over a range of cell temperatures and also reduced the size of the battery bank that was previously used with unregulated systems. In the early 1980s, Arco Solar claimed that 30-cell single crystal so-called 'self-regulating' solar modules could be used for 12-volt battery charging without a charge controller. However, 30-cell modules did not provide adequate charging voltage for 12-volt batteries in hot and even in temperate climates. Still, PV is a excellent electric power source and a properly sized PV system using 33- to 36-silicon cell modules can charge 12-volt batteries well.

Joel Davidson
  ----- Original Message ----- 
  From: Bob-O Schultze 
  To: RE-wrenches 
  Sent: Sunday, March 28, 2010 9:18 AM
  Subject: [RE-wrenches] NABCEP Exam was: PV excellent battery charger

  Folks,
  While none of us obviously has access to the wording of the specific question itself, I can assure you that there are no "tricky" or non-sensical questions on ANY of the NABCEP exams. Our Subject Matter Experts (SMEs) who come up with the questions AND the answers aren't a bunch of nerds in a university somewhere, they are us; working wrenches like ourselves. All the questions and answered are submitted to a round table discussion of the SMEs to be accepted, modified to be made clearer, or thrown out. At the same time, they are reviewed by a professional testing expert for clarity, readability, and correct usage of the language. Of the four answer choices, there are almost always two which are dead wrong, one which could be arrived at if you didn't follow all the steps of the question or didn't exactly know the material, and the correct answer. If you think all that is easy to do, try it sometime.
  After the test is taken, the testing expert analyses the raw data and the SMEs review any items which seem questionable. For example, if most of the test takers INCLUDING those who did very well on the test otherwise missed a certain question, they take a hard look at it to see if there is ambiguity or if it can be interpreted differently from the way it was intended. It does happen that in spite of all the work put into developing the question, it is flawed in some way. When that happens, the question is discarded and all the test takers in that round get credit for it.
  As to putting together a study guide, that's even harder. Remember that it's a "Guide", not a book like the NEC wherein lie all the answers to the questions. The Entry Level test is not a snap by any means, but it is basic in nature to our field and there are no questions on it that an installer would have to face, IE, anything to do with the NEC. The Installer Certification test is difficult, as it should be. Unless you know our trade inside and out PLUS have done some study in the areas which you don't do at all or very often (we all have those), you will have difficulty in achieving a passing score. I know many good Wrenches who missed it at least the first time. Some of those just say, "Screw it, I don't need this shit". Others have challenged themselves to hit the books again and brush up on the areas they found out (from taking the test the first time) where they were weak and nailed it on the next round. Everyone I've ever talked to, including myself, has said that they are a better craftsperson for having taken and passed the test.
  Bob-O

  On Mar 27, 2010, at 8:02 PM, Darryl Thayer wrote:

        I have never seen the exam but I have been told several of the questions are nonsense.   Just like the study guide, and  from what I hear  there are  questions  of similar  nature on the installers exam.  Something is wrong with the test generation.  
        Darryl

        --- On Sat, 3/27/10, Warren Lauzon <windsun at wind-sun.com> wrote:

          From: Warren Lauzon <windsun at wind-sun.com>
          Subject: Re: [RE-wrenches] PV excellent battery charger
          To: "RE-wrenches" <re-wrenches at lists.re-wrenches.org>
          Date: Saturday, March 27, 2010, 10:55 AM

          To be honest, I don't think the question makes any sense. There are several "right" answers, but no good ones. I hope that is not the extent of the battery questions on that exam.

          ..................................................................................................
          Northern Arizona Wind & Sun - Electricity From The Sun Since 1979
          Solar Discussion Forum: http://www.wind-sun.com/ForumVB/
          ..................................................................................................
            ----- Original Message ----- 
            From: Drake Chamberlin 
            To: RE-wrenches 
            Sent: Saturday, March 27, 2010 9:28 AM
            Subject: Re: [RE-wrenches] PV excellent battery charger

            Hi Dave, 

            At 10:44 AM 3/26/2010, you wrote:

              Is the answer here (at least the one that NABCEP intends) just that the VMP of a "12V module" is higher than the voltage of a 12V battery? With the higher voltage it will charge the battery with its corresponding current based on the I-V curve. The objective reads "Explain why PV modules make excellent battery chargers based on their I-V characteristics

            This may be the answer they want.  The "Objectives" deals with the 5 key points on the IV curve, Vmp, Imp, Voc, Isc and Pmp.  >From a study of the curve, the obvious "excellent" load is one that takes power from Pmp, which direct battery charging doesn't do.  When I draw the curve, the Vmp of the module is above the resulting voltage on the curve.  

            What you say about the power loss not being released as heat in the batteries,  just not produced, makes sense to me.  I've never seen any real documentation about what happens to the power not gained in a non MPPT battery charging system. 

            We can definitely agree that "excellent battery charger" is an exaggeration. 

            Thanks,

            Drake 

            Drake Chamberlin
            Athens Electric
            OH License 44810
            CO License 3773
            NABCEP TM  Certified PV Installer 
            Office - 740-448-7328
            Mobile - 740-856-9648 

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