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Advancement and Development of Electricity and Technology
Building Integrated PV
Bypass diodes
Determining low temperature that caused the inverter to go over voltage
Another NABCEP PVIP Certificate in the mail!

Most Popular Posts

Feeder PV Connections 705.12(D)(2)(1)(b)
Crimping MC4 Connectors without the tool
Converting kWh to pounds of CO2
NEC 310.15(A)(2) Exception, 10% or 10 feet or less for sizing conductors
PV Temperature coeficcients in V/C, mV/C and %/C with conversion examples

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

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.

Exactly Predicting System Output and 690.10(A) Stand-Alone Inverters Required to Handle at Least the Largest Load


Q:

Hi Sean:
Two questions: First regards derating. It seems it is really important to get these parameters right. For example, if you have a lot of snow or dirt build-up, do you somehow try to guesstimate an anticipated average value over the course of the year? Are there more sophisticated tools for more accurately calculating a derating factor?
Also, you mentioned the NEC requires to size an off-grid for largest load. Wouldn't you want to size for the largest load of all combined devices that typically would be on at one time?

Referrals


Q:

Regarding system components, the lecture conceptually makes great sense. But, there are a ton of products out there and I am sure a lot of snake oil is being sold. More importantly, I think it is hard to make smart choices on components until one is competent with system design. Besides your great courses, what other resources would you recommend to get strong at system design?

A:

I just signed up to be an installer with a financing group today and they will only let installers use certain products that are bankable.

Low Temperature String Sizing, Portrait vs. Landscape, Sheathing Mounting and Temperatures


Q:

Hi Sean: I guess I have two questions: One is regarding construction and the other regarding string sizing. First you mentioned that shading of long edge is more desirable than shading of the short edge. Would this suggest that landscape mode is in fact preferable? Does a product like from QuickMount PV allow you to attach just to the sheathing versus the rafters?
My other questions is on string sizing. Should we be accounting for a derating factor when potential modules.

Rapid Shutdown Retrofits?


Q:

Hi Sean,
The new regulation for the 'rapid shutdown' function, was driven by first responders for their safety, do you think that they may request that the rapid shutdown be installed on existing large commercial systems?
Thanks

A:

Once something is built, inspected and permitted, the AHJ does not come back and make them change it. I am sure that they could request it.

Insurance companies and owners would probably be the driving force for something like this, seeing how they would like the firefighters to put out the fire, rather than watching it burn out of fear of shock.

705.32 Ground Fault Protection


Q:

Hello Sean,
About Question 33, if the building has less than 1000amp service, can we do the load side connection on subpanel?
Thanks!

A:

The answer is no, because the subpanel is on the supply side of the of the 1000A ground fault breaker.

In the NEC it says:
705.32 Ground Fault Protection: Where ground fault protection is used, the output of an interactive system shall be connected to the supply side of the ground fault protection.

Great reviews inspire me to work harder!


Survey Results

Submitted: 04/12/2016
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 was very informative and easy to understand. The discussion board is a very active and productive information resource. Tom and Sean were very helpful and prompt in their response and/or wise in their answer. Full of knowledge
How effective was the instructor's communication during the course?

NABCEP Exam Requirements and Cycles


Q:

Uh, did I miss something? I thought this course was until the end of this month. Or is this overlapping cycles? I was planning to take this class as part of the 58 hours I need to even qualify to take the NABCEP test this fall. I plan to return here to bone up after applying the lessons learned here on two more systems I'm planning to build to qualify also as the systems I built before my knee (and other body parts) crashed out in '12 don't qualify any more.

310.15(B)(3)(a) Derating and not counting the Equipment Grounding Conductor or When not to Count the Neutral

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

Q:

on question 52, looking at the derating part for the number of conductors in the conduit on table 310.15b3a we have two source circuits which is 4 conductors plus an equipment grounding conductor. The table shows 4 to 6 which at the end of the day the derating would be the same for 4 or 5 but you only consider 4. Could you explain why you don't count the 5th equipment ground conductor?? The footnote states the count shall not include conductors that that are connected to electrical components but cannot be simultaneously energized.

Wiring Colors


Q: (comment)

The black (A phase)/red (B phase)/blue (C Phase)/white (Grounded/Neutral) color coding is used for 120/240V or 120/208V systems. The color brown (A Phase)/orange (B Phase)/ yellow (C phase)/gray (Grounded/Neutral) color coding is used for 480/277V or 600V systems. Green, Bare or Green with yellow stripes is always ground for any electrical system. That is the difference in the colors. The occasional exception is in control wiring such as thermostat wiring.

Death by Falling-Be Safe!


Q:

My daughter had a friend who was a steel worker, fearless, could walk backwards on the steel. Well with him being him, he had his harness on but didn't tie off and he fell 20 feet to his death. On any elevated work space, the PFAS can't be stressed enough.

A:

Thanks for the story. It always hits home when someone has a real experience to share. Many people do just that and do not tie off. I had a guy in class who had a worker reach to tie off, slipped and died after lunch (wasn't a solar job).

MPPTs Stacked Series and Parallel with Shading


Q:

You said, "if the entire string is shaded with MPPT, then the PV source circuit would operate as if the entire string was in the shade.." ...
But then what of the other strings still in the sun?
Assuming for this example that there is some flat horizontal object (like a neighboring building) that causes the bottom landscape series string to experience a lower light level (not zero). So therefore the amperage of that bottom string would be less than the other (parrallel) horizontally strung series strings above the lowest shaded string.

Message for those of you here preparing to take the NABCEP PV Installation Professional Certification Exam, which is in 8-days!


Message for those of you here preparing to take the NABCEP PV Installation Professional Certification Exam, which is in 8-days!

Now is time to study hard. No procrastinating. Learn the material, but do not get overwhelmed with a concept that is difficult to understand. Remember that the exam is a numbers game. There are many very difficult questions and nobody gets all of the questions correct. Budget your study time wisely and plan to not study hard the night before.

8-days pre-exam strategy


8-days until the exam!

My advice is now is the time to study a lot. No procrastinating. Do not worry too much about obscure things that will probably not be on the exam. Do not spend too much time trying to understand the one thing that you do not understand. It is a numbers game and nobody ever gets all of the questions right.

Plan to be done cramming 2 days before the exam, when it is time to get rest and review. Remember that a good state of mind and a clear head will be the best thing that you can accomplish the night before.

PV Inter-Row Spacing Methods


Q:

Thanks Sean. Do you know which formula they would expect us to use? I've run across several in previous studies of varying accuracy levels:
Basic inter-row shading distance
(d) = 3H
H = height of module from back edge to surface

Better inter-row shading distance
(d) = H/tan AltA
H = height of module from back edge to surface
AltA = Altitude Angle on December 21st at 9:00 AM

Best inter-row shading distance:
(d) = [ (Sin TiltA) x M ] / tan AltA ] x cos AzAD

Converting kWh to pounds of CO2


Q:

Looking at the joint task analysis for non-financial benefit analysis it says to know how calculate CO2 avoidance, tons of coal saved, water saved, miles not driven, etc. Is that really something they would ask us how to calculate? Tons of assumptions go into each of those and several vary by geographic location. Any particular rules of thumb to remember for them or is it more likely they would give us all the inputs/assumptions and just ask us to calculate them based on lifetime kWh production of the system?

9 days until the NABCEP Exam Date! Advice


9 days until exam date!!

Now is the time to dive into the exam questions that we have here and to not procrastinate. The NABCEP PVIP Exam is famously difficult, which is why NABCEP Certificates are known as being the top of the field. Pass this exam and your salary will triple in 3 years, guaranteed! (It happened to me).

I recommend not getting overly concerned with anything obscure and especially not searching for answers on facebook.

Why we use cell temperature instead of ambient temperature when calculating the short PV string size


Q:

Sean,
On Question 51 can you explain why we use the high cell temperature over the high ambient temperature?
Thanks

A:

When we are determining voltage, what is important is how hot or cold the solar cell is, not how hot or cold it is outside. That is why airflow leads to better production. BIPV has less airflow than a rooftop, which has less airflow than a ground mount, which has less airflow than a pole mount.

John Wiles Solar Links

From HeatSpring.com PV Boot Camp Discussion Board

Q:

Dear Sean,
In assignment 2/36
Can't find the website you featured: (and RECOMMENDED WE READ ARTICLES FROM)
nmsu.edu /~td/Photovoltaics/Codes-Stds/C-S-Resources.html
New Mexico State University College of Engineering Codes & Standards
PV power systems and the 2005 national electrical code summarized practices

CLOSE AS I COULD FIND: https://ece.nmsu.edu/research/swtdi/codes/
QUESTION: WHERE DO I FIND THE PAGE YOU FEATURED FROM THERE?
QUESTION: WHICH PHONE APP?

PV Testing Equipment Recommendations


Q:

Sean,
We are currently needing to purchase a solar tester per customers request. do you know of any others line the Seaward Solar tester?
Thanks

A:

The Solmetric PV Analyzer is a favorite. Unless you are doing residential only, get the 1000V version.

http://www.solmetric.com/pva1000s.html

I also like the people at Solmetric, except for the fact when Vivint bought the company they took the SunEye off the market.

Thanks for the great Evaluations!


Submitted: 04/06/2016
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?:
Sean presents the materials in a fun enjoyable manner while keeping the material very informative and explanatory
How effective was the instructor's communication during the course?:
10/10
What would you change about the course?:
Nothing
If you enjoyed the course and are interested in providing a testimonial, please enter one here.

Why don't we all use the same version of the NEC?


Q:

in reply to the question of NEC 90.4,and the Montanna adoption of the NEC code,NEC is is specific in its wording and implication previous adoption of the NEC,so in their case yes they should go back to whichever was their last NEC book,although it would be outdated,setting themselves up open legal ramifications if things went wrong some where,yet if they had gone to the previous version before the current version ,their case and workmanship would be more in line with a logical approach.

When to clean PV

From HeatSpring.com PV Boot Camp Discussion Board

Q:

To keep modules operating at their peak efficiency, is there a recommended cleaning solution or is just plain old water the best thing to use? In SoCal I've seen many modules that are so dirty they could probably grow plants on them.

A:

I like using a window analogy. Many people never wash their windows but still get the sunshine.

If you have plants growing out of your PV, that would be shading and time to do something.

I would say that most residential PV systems are primarily cleaned by the rain.

Solar in Germany, the FIT, Hermann Scheer and his Solar Revolution


Q:

I'm currently traveling in Germany and am amazed at how much solar is in use here. Many of the installs look like they have been in use for well over 20 years. Lots of module mismatch in physical size. I have to wonder how well they perform. Some serious slope installs as well.

A:

If it wasn't For Hermann Scheer and the German solar feed-in-tariff, solar in the world would not be as mature as it is today.

http://www.hermannscheer.de/en/

Hermann was a German politician who promoted the policy of requiring the utility to pay 20 year contracts for a price that was a decent return of investment for the solar industry.

Monocrystalline vs. Polycrystalline Solar, which is better?


Q:

For the average consumer is there any advantage to installing a Mono versus a Poly module system?

A:

I would prefer the most efficient module and hopefully one that I could trust. That being said, usually mono is most efficient, but if you were to look at a 260W polycrystalline module made in 2017 vs. a 250W monocrystalline module made way back in early 2016, and the brand was the same, I would go with the poly. I think there are some out there who would disagree with me and 250 vs.

STC Voltage Higher than PTC, CEC and NOCT because ambient vs. cell temperature


Q:

Hi Sean,
I have just taken the test and question 25 seems to be off. Perhaps I require further clarification. Anyways, the question is:
Which test conditions have higher voltage?
a. STC, b. PTC, c. CEC, d. NOCT
According the the textbook STC (option 'a') is the correct answer and it explains that the reason is because the other test conditions have higher cell temperatures and therefore lower voltage.
Now, STC (option 'a') temperature is 25C, whilst the other are 20C.

Derating factors, accuracy and precision


Q:

Hi Sean,
This question follows a previous one on comparing the output in a 'irradiation rich' and 'rather hot' location (South Western US desert) versus an irradiation 'not as rich' but 'rather cold' location (South Western prairies in Canada).
I noted that when calculating the energy output of a system, irradiation and its derating (by a number of factors) is accounted. However, I can't see that temperature is taken into consideration for the calculus (it is not seen as any of the derating factors).

When does the PV bypass diode kick in with a partially shaded solar cell?


Q:

Can you go into more detail on what happens when a solar cell is partially shaded? At what point does the bypass diode trigger?

A:

That is a good tough question and there are many variables.

What it comes down to in an interactive (grid-tied) system, the inverter will MPPT the PV. If the array will be more efficient using the group of PV cells that include the partially shaded cell, then that bypass diode will not kick in, because the inverter will be working at the voltage that includes those cells.

PV Permitting and Finding Out What the AHJ Wants


Q:

Thanks for this answer. I have a follow-up about AHJ's in Massachusetts. It seems to be the most regulated of all the states. How do you check which AHJ is the right one and make sure of compliance in Massachusetts?

A:

The only real way to find out what the AHJ wants is to contact them.

1-Go down there
2-Give them a call
3-Check their website
4-Check www.solarpermit.org

Large solar installers have an advantage, because they keep a database and know which AHJs want what.

Solar PV Snow Removal... Is it worth the investment?

From HeatSpring.com PV Boot Camp Discussion Board

Q:

Would it ever be worth it to remove snow from a large solar field in New England? Or would the price of the snow removal be more than the energy lost?

A:

Probably not in California with the new $15/hr minimum wage. Even with $5/hr labor it would be difficult.
There are 100 names for snow in some cultures and I am sure there is an instance somewhere in the world where cleaning a module before the snow froze and stuck for a month would make good sense, but with those 99 other types of snow I think it is going to be cost effective to wait for it to slip off.

NABCEP Resource Guide Battery Question Explanation Hot and Cold Lead-Acid Battery Charging


Q:

Hi Sean,
NABCEP includes the following practice question in the NABCEP PV Installation Professionals Resource Guide:
  1. The battery bank for a backup utility-interactive PV System is located in a harsh environment with temp and humidity extremes. The system does not have a provision for temp compensation. What is the MOST LIKELY result on the battery state of charge?
c.) Overcharged in cold weather and undercharged in hot weather.
d.) Undercharged in cold weather and overcharged in hot weather.

690.8(B) Breaker Sizing


Q:

Hello
regarding question 6 explanation. I understand how you arrived at the 20 A breaker for the 100 A busbar. I am not familiar why you then took the 20 A breaker divided by 1.2 to arrive at 16 A.

A:

A breaker has to be sized based on 125% of the current of the device (and then round up). This comes from 690.9(B) of the NEC, which states:

"Overcurrent device ratings shall be not less than 125 percent of the maximum currents calculated in 690.

What to bring to the NABCEP PVIP exam


Q:

I understand we will be give a copy of the NEC by the examiners. So what materials specifically are we allowed to bring to the exam other than the FX 260?
I have the NEFPA70 2014 binder. Do I need to get a soft back or will the copies provided be our only source?
Thanks

A:

They will supply the calculator (it is recommended to get one to practice with) and they will supply an NEC Code Book, along with pencils and paper.

Bypass Diodes and Shading


Q:

Sean,
Why are all three bypass diodes affected by shading on the short edge of the module? What about the wiring/arrangement of the diodes causes them to be affected this way?
Also, what does MPPT stand for?
Thank you,

A:

MPPT stands for Maximum Power Point Tracking.
As we showed on the IV curve, there is a "sweet spot" where PV will work best with the optimal voltage and current combination for a given temperature and irradiance. With temperature and irradiance constantly changing, the MPPT will shift to optimize the PV production.

Easiest way to pass NABCEP PV Installation Professional Exam


Q:

Sean,
I have completed my OSHA 10 course and I am contemplating taking the OSAH 30 as it is recommended. What would you do if you were setting for the NABCEP PV Installer exam?

A:

I recommend taking as many courses as you can, including every OSHA class offered. If your only goal is to pass the NABCEP PVIP exam, and you have limited time, lots of studying, the 10-hour OSHA requirement, common sense and the advanced class here atHeatSpring.comwould get you through it with the least amount of effort, which is a heck of a lot of effort!

How often to equalize batteries (flooded lead-acid)


Q:

How often should batteries be equalized? I installed a few systems on a missionary compound in Haiti last year and we can initiate/schedule equalization of the batteries but have not done it just yet. All three systems are identical but the houses have different usage profiles, some loads have been modified since we left. They use big flooded lead-acid forklift batteries that the customer purchased. The customer has some one top off all of the batteries every month with distilled water.

Tesla Powerwalls in the cold


Q:

Are power wall battery systems affected by cold in northeastern areas or are they insulated in some way, since they will be on the outside of the structure and exposed to cold?

A:

Since batteries store energy chemically and chemical process slow down when it gets cold, there will be some loss in capacity.

Here is what Elon Musk says:

"Musk said that the batteries will have thermal management systems to allow them to power houses in hot and cold climates, too—the batteries have an operating temperature range of -20C (-4F) to 43C (110F).

Calgary Solar Energy


A:

Only after going over this chapter, I realized how significant is the temperature gradient / variation in the power / energy generation in PV.
In the last few weeks there has been a lot of talking in the province of Alberta - Canada about an upcoming 'solar boom' given the new provincial government commitment for phasing-out generation of electricity from coal (which accounts for about 55% of the electricity generation in Alberta) by means of replacing it with Solar and Wind.

A BIPV future?


Q:

It seems that even-though BIPV is more expensive than conventional silicon modules, in addition of presenting some disadvantages (lack of airflow being one) will likely become the preferred option sometime in the future. Would you agree on this assumption? 
I believe that alongside with energy storage, there is a lot of room for improvement on both, which is just a matter of time.

A:

My thoughts are that someday our grandchildren are going to say,

Shading, bypass diodes, portrait and landscape


Q:

Hi Sean,
The layout of an array, landscape vs portrait was to install as many modules as possible in the available space, maximizing the size of the system. From your discussion regarding the bypass diode, I note that if there were any shading issues, orientation of the module, when positioned in landscape will have the least affect on the functionality of the bypass diode and thus module output.
Thanks

A:

That is correct for typical crystalline PV assuming the normal shadow pattern with the shadow coming from the lower part of the module as with inter-row shading as opposed to a shadow coming from the side.

Estimating production for different tilt angles with PV Watts


Q:

For Solar Energy Fundamentals, do you have any good resources on energy optimization for different tilt angles and pitch? Often times I find myself constrained to a certain area or thinking ahead to a potential second phase for a client. Any good materials related to this topic would be appreciated.

A:

The simplest tool is PV Watts http://pvwatts.nrel.gov/
In the past when I have had consulting jobs for students setting up residential installation companies, I would make a table with the common roof tilts and annual production percentages as compared to optimal tilt and azimuth.

Battery inverter connected to battery vs. charge controller


Q:

In an off-grid system, do the batteries connect directly to the inverter? or do they need to pass by the charge controller before connecting to the inverter? (as suggested in the figure shown in the Chapter 1). Thanks!

A:

It can be either way. If the connection is made through the charge controller, which is usually the case, it is really just a pathway for the battery to be connected to the inverter on a typical system. Even when connecting to the battery through the charge controller, the conductors are sized based on the battery voltage and the inverter power.

NEC 310.15(A)(2) Exception, 10% or 10 feet or less for sizing conductors


Q:

I don't quite understand the Week 1, Assignments 2, Code-Compliant Conductor Sizing - Part 1 when you talk about the "10 feet or 10%" . I wonder if you can explain it more or give me an example.
Thanks!

A:

To put this in context, 310.14(A)(2) tells us:

When more than one ampacity applies to a given circuit length, the lowest value shall be used.

Then the NEC 310.15(A)(2) Exception states:

Where two different ampacities apply to adjacent portions of a circuit, the higher ampacity shall be permitted to be used beyond the point of transition, a distance equal to 10 feet or 10% of the circuit length figured at the higher ampacity, whichever is greater.

PV system installed prices as low as $1.50 to $1.00 per watt


Q:

Do you know the price break down of how utility projects are getting installed for $1.50/watt?

A:

It can be less than $1.50/Watt outside of the US with PV available for less than $0.50/Watt. I know people installing complete residential grid-tied systems in the Philippines for $1/W.

First Solar modules are often used in utility scale projects in the US and since they build their own projects and First Solar modules are not sold to the public, it might be that First Solar modules are less than $0.

MPPT is just for things connected to PV


Q:

Are MPP Tracking systems are features built-in in the Grid-Tied inverters? In Off-Grid systems are these features (MPPT's) in the charge controllers or in the inverters?

A:

MPPT is only built into equipment that is connected to PV.

All interactive (grid-tied) inverters have MPPT.
Many charge controllers have MPPT
All power optimizers have MPPT

What MPPT or MPP (same thing) does is control the parameters (voltage and current on the IV curve) so that the PV is working at the optimal voltage for maximum power production.

Grounded Conductors, White, Red and Black Wires


Q:

When it comes to color coding wires. Are white (or gray) wires / conductors grounded and neutral, or negative? This confuses me as I tend to relate white to negative, however in the text white appears to be neutral and grounded. If that is the case (white wires being neutral and grounded), what would be the color code for negative?
I am totally new to electrical design... sorry if the question sounds redundant? Thanks!

A:

That is a very good question.

North Facing Modules


Q:

I do not have any particular question on your second lecture. Super clear, and thank you.
One technology question: I heard a few years ago of researchers trying to create modules designed for the north side of a roof. I do not know if there is any developments in this area, but it seems like it could be an important development.
Frankly, using PV Watts (great NREL product showing that government can work), I discovered that my 15 degree north facing roof could produce energy cheaper than what I can buy it from in CT.

The Difference Between Voltage Drop and Voltage with Ohms Law and Voltage Drop Percentage Calculations


Q:

Hi Sean: I guess I am getting a little knotted up by this too. If we have a 100V system, I take it that this would be considered the "nominal" voltage of the system. However, if we have a 2A, 3Ohm wire in the system, wouldn't the voltage of the wire be calculated in determining the nominal voltage of the system?
Intuitively I understand why V drops (I think): As resistance increases, volts must drop. But, I am not sure how V in Ohms Law relates to V-system.

Lead-Acid Battery Ventillation and Debris under the PV


Q:

Hi Sean:
A couple of questions: If lead-acid batteries need to be adequately ventilated, how should this be done in super airtight structures? Can the batteries be placed outside the envelop? Is there an optimal temperature they should be stored at?
Also, what is the best way to keep debris from collecting under the modules. This seems like it could be a big problem.
Thanks

A:

In the NEC, it just says that battery banks need "sufficient ventilation" and does not give instructions.
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