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Bypass diodes
Determining low temperature that caused the inverter to go over voltage
Another NABCEP PVIP Certificate in the mail!
NABCEP PV Installation Professional Exam Results
NABCEP PV Installation Professional Exam Happy Camper!

Most Popular Posts

Feeder PV Connections 705.12(D)(2)(1)(b)
Converting kWh to pounds of CO2
Crimping MC4 Connectors without the tool
Bonding Neutral to Ground
NEC 310.15(A)(2) Exception, 10% or 10 feet or less for sizing conductors

Categories

Advanced PV Course
NABCEP PV Installation Professional Exam Prep Course
NABCEP PV Technical Sales Exam Study Group (which will evolve into a full course)
PV Boot Camp and NABCEP Entry Level Exam Prep Course
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HeatSpring PV Course Blog

Bypass diodes


Q:

I am trying to fully understand what is happening as it pertains to bypass diodes. When a single cell is shaded, the diode acts by decreasing the module voltage in exchange for preserving current. 
As an example, if the module current was 9.18A module Voc was 45.1 and one cell was shaded, then in theory the amperage would remain 9.18 and the approximate module voltage would decrease proportionally to 30.1 (one third/diode)? Or is the truth somewhere in the middle?

Determining low temperature that caused the inverter to go over voltage


Q:

Sean: Thanks for a great course. Two questions: I think I would like some additional training for the PV Installation Professional Certification Exam. Do you have any recommendations?
Also with the addition practice questions, I got really knotted up on questions 74 and 78. On question 78, when you state the temperature coefficient for the module, is this actually Voc x Temperature Coefficient Voc?
Again, thank you for two great classes. I look forward to meeting you in person someday, and perhaps attending hands-on training you might offer.

Another NABCEP PVIP Certificate in the mail!

Post NABCEP PV Installation Professional Exam Comment

Thanks for a really good prep class, Sean and Heatspring! I also got my certificate on the first try.

A:

That is excellent that you passed the NABCEP PVIP!! Glad to help!

Thanks for the feedback,

Sean White

Post NABCEP PV Installation Professional Exam Comment

NABCEP PV Installation Professional Exam Results

Post NABCEP PV Installation Professional Exam Comment

Dr. White, I received my certificate today! Thanks so much for the great course, I will definitely recommend it to others who are prepping for the exam.

A:

That's great! Congratulations!!

Post NABCEP PV Installation Professional Exam Comment

NABCEP PV Installation Professional Exam Happy Camper!

Post NABCEP PV Installation Professional Exam Comment

Hello Sean,
I passed the exam. I got the certification yesterday. I am so happy I passed it first time trying. Your class was a great help.
Thank you so much!

A:

Congratulations!!

Post NABCEP PV Installation Professional Exam Comment

Advanced PV Class Review


Submitted: 05/21/2016
Training: 40-Hour Advanced Solar PV Installer Training / Online / Anytime

How would you rate this course?
10/10
What did you like about the course?:
That it continuosly answers questions that I've had or I get in the workplace. I like that Sean uses a lot of examples and does not limit to the short explanation of an answer.
How effective was the instructor's communication during the course?:
Great.
What would you change about the course?

Passed the NABCEP PVIP Exam!!

From HeatSpring Advanced PV Course Discussion Board

Q:

I took the April exam for the first time and just found out I PASSED. After the completion of this course I felt really prepared and confident going into it . This course definitely covered enough information to pass the NABCEP exam and much more that I will be able to apply in my future career in solar. Sean White's book is the "Swiss army knife "of study material. Somewhat small but jammed packed with all sorts of useful information.

PV in hot locations, is it worth it to cool the PV?


Q:

Dr.,
I believe it's difficult in Oman to get the most output from PV. This is because the temperature is very high especially in summer where the temperature reaches more than 50 degrees.
My question: Is there any means or technologies that can be used to cool down the cells even in summer which will help to increase the maximum voltage??
Regards

A:

The most cost effective way to deal with the heat is to mount with air spaces between the PV and the structure if it is on a building or if it is a ground mount, there are already air spaces.

Functions of a charge controller besides preventing over and under-charging


Q:

Good Morning Dr,
To which extent we can consider the stand alone systems. I mean is there any maximum capacity for stand alone systems that we can't go further capacity.
The charge controller is very important device that will help to save the batteries longer. Is there any other function other than preventing the batteries over/under charging? And what are the protection schemes related to this device if any.
Thanks

A:

If a stand alone system is big enough, it can be more of a micro-grid and if a micro-grid is big enough it can approach being a utility.

Why PV does not perform at its rated power on a sunny day due to derating factors


Q:

Hi Dr.sean,
I used to be in project that works with PV but the drop is reaching 20% of the rated power. The type of PV (polycrystalline)
At which condition the PV will be more efficient regard the production of power.
suppose we have two PV panels at the same intensity of sun rays for example 1000 w/m2 but each PV have different ambient temp for example PV1 (25c) and PV2 (50c) now which one of these will produce more power?

A:

If polycrystalline PV has lost 20% of its rated power under Standard Test Conditions, then there would have to be a manufacturing defect.

2014 NEC 690.7 Maximum System Voltage 600V and 1000V Distinctions


Q:

Article 690 - Part II - 690.7(C): Maximum System Voltage. In your lecture you mentioned that the NEC distinguishes between 3 family dwellings (up to 1000V PV max system voltage), versus 1-2 family dwellings (up to 6000V PV max system voltage). Two questions: First, I proudly bought the book, but I do not see this distinction in 690.7. From what I read, it addresses 600V and 1000V. Second, it seems arbitrary to distinguish to maximum inverter size between 3 family dwellings vs.

Thanks for the great review!!


Thanks for making my day with the review!!!

Submitted: 05/16/2016
Training: Solar PV Installer Boot Camp + NABCEP Entry Level Exam Prep / Online / Anytime

How would you rate this course?
10/10
What did you like about the course?:
Instructor was available for questions even if question strayed from entry level content. Instructor is industry leader
How effective was the instructor's communication during the course?:
Excellent - his videos contained recent events

Temperature Coefficient of Vmp, where do we get it? Just use the temperature coefficient of power.


Q:

Sean
My question is about determining the minimum number of modules required to turn the inverter on. All modules I have reviewed have "temp coefficient for Voc" but none have "temp coefficient for Vmp"
Example from Canadian Solar module
Temperature Coefficient (Pmax) -0.43% / °C
Temperature Coefficient (Voc) -0.34 % / °C
Temperature Coefficient (Isc) 0.065 % / °C

Is Temperature Coefficient (Pmax) -0.43% / °C used when calculating minimum number of modules required?

The Enphase ac battery, an on-grid only battery perhaps?


Q:

Thanks Sean,
The Enphase AC battery could be a big thing but they don't seem to promoting it for grid-tied battery backup or off-grid.
What’s your primary energy goal?
  1. I want to minimize my energy bills.
    Storage method: Self-consumption
    Storage method: Time of use optimization
    Preferred storage solution: Enphase AC Battery
  2. I want energy independence.
    Storage method: Backup

PV Wire Sizing, Terminal Temperature Limits, 310.15(B)(2)(a), 310.15(B)(3)(a) and 310.15(B)(3)(c), 110.14(C), 110.14(C)(1)(a) and 110.14(C)(1)(b)


Q:

Dear Doc,
A little late question ,concerning article 310 and 110.14 (c),110.14(c)(1)(a) or (C)(1)(b)
When you talk about terminal ratings,I am aware of three areas in solar where wires terminate ,combiner box ,inverter and main panel ocpd.
Are we talking here about, adjustment and correction factors ,dealing with ocpd of the solar breaker in main panel or the equipment shutoff breaker ,I am assuming these articles are referring to the main panel termination or equipment shut off termination.

Planning on adding batteries to a grid-tied system in the future


Sean, a further question. In the video you made the point that batteries are still expensive but costs are coming down. There was also a description of a grid tied, AC coupled system. If you are designing or purchasing a residential or small commercial system that may not require batteries now (perhaps you have net metering), but may require batteries in the near future, say a few years time when battery costs come down and net metering is removed, what should you specify so that your system is able to incorporate batteries without having to make costly change out of equipment,

PV tilt angle and snow


Q:

What is the best angle to put solar panels at for removing snow loads while still gaining solar energy?

A:

There is no exact answer for snow, since sometimes snow will stick vertical and sometimes it will slip off at a 5 degree tilt. There are hundreds of different types of snow.

From my experience, I rarely see snow stick to PV for more than a day. It often melts, slips or blows off.

I do not often see installers and designers worry about snow.

Here is an array that was designed for deep snow in Truckee CA:

Keeping conductors cool, other ways besides th Code


Q:

If there are wires in a conduit on a roof, what is the best way to prevent them from over heating? Let's take out the variables of wire size & wire insulation, & focus on good techniques to prevent general overheating from good old Mother Nature.

A:

The Code will err on the safe side, so if you are following the Code, you probably will not have to deal with other types of cooling, however I have thought of this:

1. You can paint your conduit white to reflect sunlight

Good day for a good review!!


Submitted: 04/27/2016
Training: Solar PV Installer Boot Camp Training + NABCEP Entry Level Exam Prep / Online / Anytime

How would you rate this course?
10/10
What did you like about the course?:
SELF PACED, BUT SCHEDULED.
How effective was the instructor's communication during the course?:
INSTRUCTOR WAS VERY HELPFULL
What would you change about the course?:
NOTHING

Mocroinverters with off-grid/stand-alone PV systems

From HeatSpring.com PV Boot Camp Discussion Board

Q:

Sean,
Per the Week 4 video for off-grid setup
PV - DC disconnect - Charge Controller -Batteries - Off-grid inverter
Is using micro-inverter with off-grid possible?
With off grid systems there is nowhere for excess energy to go. Is this where diversion loads are utilized.
thanks

A:

I have heard rumors of an off-grid microinverter, but have never seen one, they are as common as unicorns. It would be difficult to connect to a battery.

That being said, Enphase (the biggest microinverter company) has plans for what they are calling an ac battery.

Battery/Inverter circuit wire sizing question


Q:

Sean,
Finally was able to watch the week 4 video, it made a lot of sense, but now I some questions

  1. Battery to off-grid inverter conductor wire size is based on ampacity designed using the lowest voltage because less voltage requires more current. The more current, the bigger the conductor.

Could you please provide example using this 2000W inverter with 12v battery string?
http://outbackpower.com/outback-products/inverters-chargers/item/fxr-renewable-series-120v-a-models

Nano Solar


Q:

Dear Dr,
Greetings from continental shelf of solar tech.
What is the role of nano materials technology in Solar panel manufacturing? One of my professor was doing research in the area of Nano materials for PV design When i studied. Could you please tell simply about the nano materials role in PV cells?
Regards

A:

There was a solar company called Nanasolar, but they are not around anymore:
http://www.greentechmedia.com/articles/read/Nanosolar-Thin-Film-Solar-Hype-Firm-Officially-Dead

PV Racking and Tracking Systems of Today


Q:

I read once that the base structure of PV panel is also one of the important system to improve efficiency. Could you please explain that how a system will improve efficiency due to base structure?. Also there are some base structures which are controlled by a motor (with a micro controller system) to focus sun automatically to increase the efficiency. If so, Is there any optimal design for base structure?

A:

In the industry we call it a racking system and if the system allows for better airflow, that will increase the cooling, which will increase the voltage, power, energy and income from the system.

Calculating Magnetic Declination-East is Least!


Q:

Sean,
Question about declination
If "solar declination" is discussed then this is angle between magnetic south and true south? If east of 0° (in US ~ Mississippi River) then you add the declination angle and if west of 0° , then you subtract the declination angle?
If "declination" is discussed then this is the opposite of solar declination (magnetic north compared to true north)? If east of 0° (in US ~ Mississippi River) then you subtract the declination angle and if west of 0° , then you add the declination angle?

NREL vs. NASA data, Solar Satelite Reports and Entertaining Solar Nevada Conspiracy Theories


Q:

Sean,
The grid sizing videos were very informative.
I like that your videos are very current - you mentioned Solar City leaving NV when the net-metering agreement was changed. The Chinese company ENN (Reid's son is involved) bailed on their $5B dollar solar plant back in 2013 because they couldn't sell the energy generated from their solar plant to utilities in Nevada. If ENN return's now, it would provide some credence that the net-metering change was political.

Feedback from the first NABCEP PV Technical Sales Online Group


Submitted: 04/23/2016
Training: NABCEP PV Technical Sales Exam Prep Discussion Group / Online / Anytime

How would you rate this course?
10/10
What did you like about the course?:
The pace for me was good, also questions with answers really helped. In the 5th week I got bombarded with work so was playing catch up.
How effective was the instructor's communication during the course?:
Very good, seems like my teammates asked the same things I was thinking.

Ac coupled systems, microinverters and ac coupled charge control


Q:

Sean,
The LG MonoX ACe 300W Module has been discontinued (possibly reason for price reduction?). It has been replaced by LG Mono X ACe 300W PerfectAC Module. I'm guessing the original wasn't just "perfect" enough? ;)
Can micro-inverters be used in ac-coupled systems?
For dc-coupled systems, are there battery charge controllers that accept 240v ac has input source?
Thanks,

A:

They are always improving on technology. I wonder what comes after perfect next year.

Ac modules and old Enphase inverters without trunk cables

From HeatSpring.com PV Boot Camp Discussion Board

Q:

Sean,
Thanks for the offer to assist in providing distributor referrals.
As a student are we able to access these discussions after the class has ended?
I appreciate the link to the LG manual. The LG connects their trunk cable to an AC junction box, then the customer can decide on means to get ac to the distribution panel.

A:

The first 2 generations of Enphase microinverters did not have a trunk cable. They came with enough chord attached to one inverter to attach to the next inverter.

Ac coupled vs. dc coupled PV systems


Q:

Sean,
Thanks for the links on ac-coupling. For off-grid, does the reduction of one inverter plus the self-restarting capability of dc-coupled systems make it a better choice than ac-coupled?
The ability to add battery backup to existing grid-tied system without drastically modifying grid-tied system's wiring is definitely a bonus but at $20,000 for 4kw battery backup (ameresco quote) I can see the reluctance to spend the $$.
Thanks,

A:

You have it right.

Inter-row Shading on the Tropic of Cancer


Q:

Wonderful presentatation. The height and distance in PV panel is discussed as 1:3, if i reduce this distance, How much energy loss will be there if there is no shading? If we install PV panel in roof top means there is less area, so, it is not possible to give long distance between the PVs. So, what is your advice?

A:

The height to distance shading ratio can be variable based on latitude, space available, the type of PV system and expectations.

For your location on the Tropic of Cancer 23.

Carbon footprint of ethanol and other fuels


Q:

I seem to recall Al Gore saying ethanol was something he regretted promoting.

A:

That is a good example of taking more diesel energy to grow the corn with farm equipment than the gas that you would save by burning ethanol in your car. Besides Al Gore, there are many others that thought corn ethanol was the fuel of the future (especially farmers in Iowa).

Another fuel that has a higher carbon footprint is the sticky Alberta tar sands or oil sands (in Alberta they don't like you using the term tar).

Wooden PV Racking Systems


Q:

Is the concern about wooden racks is bonding? If a metal rack is attached to a wooden rafter how is that different from a metal rack connected to wooden cross piece on ground mount?

A:

If something is not conductive, then you do not have to use bonding and grounding. There are some systems that have no exposed metal parts, so they do not require equipment grounding. I have heard rumors that more of these systems are being developed.

If you are using a wooden racking system and PV with aluminum frames, you will still have to make sure that all of the aluminum frames are bonded.

Ac coupling further explained with references


Q:

Sean, sorry about not making myself more clear. My comment was about in a post of yours #1 and #2. A battery inverter keeps an grid-tied inverter runnin day and night with the grid-tied inverter charger the batteries during the day.

A:

Got it, 1 and 2 right here:

"An ac-coupled system is different from a bimodal/multimodal system, but both types of systems can work together.
Also, an ac coupled system can work off-grid or with the grid and batteries.

Connections: ac module connections, PV distributor connections and PV financing connections


Q:

Sean, that just proves it ain't what you knowbut who you know.
How does the PV get to the main panel if no trunk cable required?

A:

Here it shows how the connections are made:
http://www.lg.com/us/commercial/MonoXACe/index.jsp
It works like a trunk cable, but goes from module to module and you don't have to mess with dc, which is the biggest reduction in what you have to do.
Since it is made by LG, which is a large corporation with most of it's business outside the solar industry, I would be a lot less concerned about them breaking 10 years from now and going bankrupt.

Post NABCEP PV Installation Professional Exam Comment

NABCEP PV Installation Professional Exam Prep Course Discussion Board from HeatSpring Course

Post exam comment:

Hi Sean,
I did it. I think I can pass. Thanks for your help. I am glad I got this training. It helped me a lot. I think it would have been impossible if i haven't taken this course.
Yesterday, during the exam, I don't think there was any thing related to rapid shutdown, or feeders and taps.
There was one question about sub panel connection.

One of the questions is on the Sample of Nabcep Exam from NABCEP study guide.

Ac PV Module Calculations


Q:

Just finished System Components video part 1 and the LG AC Module looks like a great product. I did find out they are going for $618 per module and with (12) modules per string the total cost is $7416.
Question - Does the $7400 sound comparable to (12) 305w modules using micro-inverters? Comparable to (12) 305w modules using a string inverter? I would think design/installation cost would be much lower.
Question - Is my calculation correct? 305W@ 240VAC = 1.

IV Curve Tester Alternative: The Infrared Camera

From HeatSpring.com PV Boot Camp Discussion Board

Q:

Is there any more sophisticated and faster ways of analyzing strings rather than an IV Curve tracer? This method seems time consuming since it involves disconnecting the system and evaluating each string. Are there any new methods of evaluating PV systems with new 'non contact' sensors?

A:

The IV curve is effective. They could make built in IV curve tracers for every string or even every module, but it is not cost effective yet.

Another way to check modules is with an infrared camera.

690.11 dc arc-fault protection brought to you by the 2011 NEC


Q:

Sean - so how do inverters handle those short fluctuations in current (irradiance)? Are there times when the inverters Arc Fault Protection mistake this short burst of current as an arc and shut down temporarily?

A:

Hi Chris,
690.11 Dc arc-fault protection first came out in the 2011 NEC and when states started adopting the NEC, nobody had figured out reliable dc arc-fault protection yet. There were many false trips on the original systems. Apparently this same thing happened with ac arc-fault protection when the Code required it.

Post NABCEP PV Technical Sales Exam


Comment:

Hey Sean, the exam went great! Youe prep course and material more than prepared me for the exam. I think you did a great job with us these last 6 weeks. There was not 1 question I was not able to handle.

Reply:

Thanks for the feedback!
Glad to be able to help!!
Sean

Battery Backup PV for a Fridge


Q:

Personally for me, solar with some sort of backup is a must - at the least just to keep refrigerator running.
Sean, in your opinion would your backup generator be LP or diesel??

A:

It depends on a lot of factors. If you already have gas coming to your house LP or natural gas makes it easy.
If you are running a generator a lot, then diesel is the way. If you are a hippie, then you can use biodiesel.

The SMA inverters that have backup without batteries are neat. They call it SPS secure power supply.

Irradiance over 1000W per square meter

From HeatSpring.com PV Boot Camp

Q:

Can someone go into further detail on the enhanced irradiance conditions that would cause a PV source circuit current to exceed the short circuit current? Is there some sort of magnification of irradiance under certain conditions? If so, has anyone been able to determine these conditions are happening with modern data acquisition systems?

A:

Usually irradiance is less than 1000W per square meter, but in certain places you can have irradiance over 1000W per square meter on a regular basis, such as in the high desert.

Backup Batteries vs. Backup Generators

From HeatSpring.com PV Boot Camp

Q:

I never realized how complex a battery system could be. Although it sounds like a really cool idea to have a battery backup system on your house for when the grid goes down, for the amount of time the grid is actually down it seems a lot more cost efficient to have a gas generator.

A:

And not that bad of an idea to take the day off from having electricity.

I lived in a cabin in Alaska without electricity. It was fun.

You can make an argument that a gas generator is often better for the environment than a lead-acid battery bank for a back-up system that is rarely used.

Minimizing parallel battery strings

From HeatSpring.com PV Boot Camp

Q:

Sean, can you expand on why paralleled strings of batteries will not charge/discharge uniformly?

A:

If you have multiple strings of batteries, the connections to the strings will have different resistance. This can be because of a longer conductor, a better or worse connection, etc. Nothing is perfect and one connection will have less resistance and that string of batteries will be used more than the other strings, which will cause that string to wear out first. The more strings, the more likely the problem.

Ground Mount Tilt Angle vs. Hold Depth

From HeatSpring.com PV Boot Camp

Q:

Using Ironridge's ground mount Design Assistant, an array tilt angle of 35° (close to local latitude of 38°) the minimum hole depth is 7.5' but with tilt angle of 15°, the hole depth is just 5'.
Is it cost effective to dig a deeper hole, using more concrete in able to use latitude as the tilt angle?
Thanks

A:

That is a question with many answers and some of them do not have to do with the cost of the concrete.
Many people tilt at an angle less than optimal, so that they have less inter-row shading and can fit more in a smaller space.

Landscape Mounting for Shade Mitigation with Bypass Diodes


Q:

It was very interesting to learn that shading on a landscape panel is more desirable than shading a portrait panel. Most of the residential installs that I have done the panels were portrait, I wonder if it would be better to have all panels put down in landscape so any shading would have less of an effect on production?

A:

It is best to just put the PV where there is no shading or at least very little.
You do not see people mounting landscape on residential rooftops so that shading will only kick in one bypass diode per module.

Direct PV Lighting System?


Q:

Does the comment on Page 6 "There are no direct-coupled lighting systems ...." only pertain to residential lights?
Wouldn't the 12v lights in some RVs be considered a direct-coupled lighting system?

A:

A direct coupled or direct PV system has no batteries or energy storage, so the reason that a lighting system does not make sense, is that the lights would only work when the sun is out. I'm sure it has been done, it is just not practical, unless you live in a cave and want to keep your circadian rhythms the same as those surface dwellers.

Another great Review!!! Thank you!


Submitted: 04/14/2016
Training: Solar PV Installer Boot Camp Training + NABCEP Entry Level Exam Prep / Online / Anytime

How would you rate this course?
10/10
What did you like about the course?:
The course is very explanatory and is detail on every solar topic. I have gain more knowledge and information to offer better service to my customers. It is my hope to invite Dr. White to Liberia to teach a course at one of our vocational schools after the country election.
How effective was the instructor's communication during the course?

Maximum Number of Strings on a Combiner Calculation


Q:

I am having trouble grasping an outside sourced practice question:
A 225 kW(DC) commercial system with a single 225 kW(AC) central inverter is being installed. The module specifications are:
Maximum power (Pmax): 200 W
Voltage at maximum power (Vmp): 28.9 V
Current at maximum power (Imp): 6.93 A
Open-circuit voltage (Voc): 36.2 V
Short-circuit current (Isc): 7.68 A
Maximum system voltage: 600 V
Maximum series fuse rating: 15 A

Attaching Solar to SIP Roofs and Capturing Heat Under PV Systems


Q:

There are two questions I have regarding structural. First, with some projects I know they are using SIPS for the roofing layer that could be with at least a 12" foam core. Is attaching to the exterior sheathing enough? If so, how should this be done? Is a good construction adhesive enough to hold the rails in place?
My second question is more esoteric. It seems there must be a way to harvest all that heat coming from the bottom of the panel.

690.47(C)(3) Combination dc Grounding Electrode Conductor/ac Equipment Grounding Conductor


Q:

Hi Sean: On the PV Electrical System Design Lecture I got a little confused by the discussion on inverters and grounding. If power leaves the inverter, how are you "combining" the DC GEC? The slide says DC GEC may be combined with AC EGC, but I couldn't follow why this works
Also, when you say the right size being a number 8, I take it you mean the AC EGC should be 8 awg?
Thanks!

A:

It used to be that we would be required by the building departments to have a separate grounding electrode conductor (GEC) often going to a separate ground rod (electrode) for our solar inverters.
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