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HeatSpring PV Course Blog

Blog

PV tilt angle and snow

Posted on 27 April, 2016 at 14:07 Comments comments (0)

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:


They are using a 35 degree tilt.

I have seen zero tilt in Canada. When there is snow on it, it will not work well, but when there is snow on it, it is that dark time of the year.

Thanks,
Sean White


Keeping conductors cool, other ways besides th Code

Posted on 27 April, 2016 at 13:59 Comments comments (0)

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
2. You can keep wiring in the shade
3. You can put your conduit where there is good airflow.
4. You can put the conduit over a cooler roof, such as a white roof or a living roof.
5. You can keep your white roof clean and reflective.

The Code calls for accounting for greater than 3 current carrying conductors in conduit, wires in sunlight over a roof and high ambient temperatures.

We can find these Code variables in 310.15(B)(2)(a), 310.15(B)(3)(a) and 310.15(B)(3)(c).

Thanks,
Sean White


Good day for a good review!!

Posted on 27 April, 2016 at 13:48 Comments comments (0)

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

Posted on 27 April, 2016 at 13:01 Comments comments (0)
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. It will be a battery inverter that is connected to the ac side of a microinverter system.

https://enphase.com/en-us/products-and-services/storage/our-system

There are also other ways to connect any grid-tied/interactive inverters, including microinverters to ac coupled networks.

An ac coupled system will use a battery inverter to make a micro-grid that you can connect microinverters to. This is expensive.

Here is an example of an ac coupled system with microinverters:
http://www2.enphase.com/global/files/Enphase_Application-Note_AC-Coupled-Battery-Based-Systems.pdf

With off-grid systems, diversion loads are a good way to make use of the array's potential when the grid is down, however you still have to have the ability to turn the PV off if the diversion load breaks by Code according to 690.72(B)(1)

Thanks!

Sean White

Battery/Inverter circuit wire sizing question

Posted on 27 April, 2016 at 0:56 Comments comments (0)

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
Thanks

A:

First of all, I would like to let students know, that the information here will definitely not be on the NABCEP Entry Level exam. This is a question that is way beyond the scope of an entry level PV class, in fact, I heard that there were no wire sizing questions on the last NABCEP PV Installation professional exam. This is probably because wire sizing has many rules that are not clear and top experts in the field have disagreements on exactly how to do wire sizing.

Wire sizing is the most difficult part of my advanced PV class. There are many different factors that we have to take into consideration at the same time, such as number of conductors in conduit, is the conduit in sunlight on a rooftop, what is the ASHRAE 2% high ambient temperature, what is the temperature rating of the conductor, what is the temperature rating of the terminals and what is the rating of the overcurrent protection device.

Let me just give you an overview explanation of how an average electrician might approach this calculation.

If the battery is 12V nominal, then lets say that we are turning off the inverter when the battery voltage gets down to 11.8V. Let's also say that the inverter efficiency is 95%.

To determine the current on the battery to inverter circuit.

2000W output / .95 = 2105W inverter input

2105W / 11.8V = 178A
(that is a lot of current and higher voltage would be better)

Then we have to go to the 301.15(B) tables in the NEC

Let's say that we just have a single conductor that is in free air not in sunlight and not in conduit at an ambient temperature not over 30C to make it simple.

Table 310.15(B)(17)
See link for screenshot:

Table shows that if we used a 90C rated copper conductor, then we can carry 190A on a 2AWG conductor. We will still have to check the terminal temperature column here and let's say that we are using 75C rated terminals. In this case, a 1AWG 75C rated wire/terminal can carry 195A. We will choose a 1AWG conductor at this stage.

Note: we would still use the 90C rated column when derating for conditions of use if we had the conductor in a hot place or had 4 or more current carrying conductors in a conduit or a raceway.

We then will check our overcurrent protection device size by multiplying maximum circuit current as described in 690.8(A)(4) here

by 125% and rounding up to the next common overcurrent protection device.

178A x 1.25 = 223A

round up to 225A overcurrent protection device

Here are the common overcurrent protection device sizes:



Will a 225A overcurrent protection device protect a 1AWG conductor that is rated for 195A in the 75C column (terminals)?

We will then round up the 195A conductor to a theoretical overcurrent protection device of 200A and this check shows us that a 195A can be protected by a 200A overcurrent protection device, but not a 225A overcurrent protection device.

We then go back to table 310.15(B)(17) and try the next larger size of wire, which is a 1/0 AWG wire rated for 230A.

Then we can round up 230A to 250A theoretical overcurrent protection device and this checks out, because a 1/0 AWG wire can be protected by a 250A overcurrent protection device. Therefore a 225A overcurrent protection device will protect better.

In this case we can use a 1/0 AWG wire!

If the wire was going any distance, we would also want to check for voltage drop, just for efficiency.

Also, if there were other derating factors that we mentioned above, we would have to take the other factors into consideration. When we derate for heat, such as ambient temperatures, 4 or more current carrying conductors in conduit or sunlight on a rooftop, we would use the 90C column and we will not have to apply the extra 125% of current.

I highly recommend that you take the advanced PV course if you want to learn more about wire sizing!


Thanks,
Sean White


Nano Solar

Posted on 24 April, 2016 at 15:46 Comments comments (0)

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
There are many intelligent researchers looking for a solar technology of the future that will revolutionize solar and bring down the costs. It would be great if this will happen, but so far we have not dramatically changed our technology since the first silicon PV was available in 1954.
Since then, there have been a constant supply of investors claiming that they have the new product and in about 2 years, it will be available in mass to the public. So far, nothing has happened, but it would be great if it did.
As for the nano materials, we hear talk of graphene solar cells, but I have learned to believe it when I see it.
All of that being said, I do support research in new materials, I just will not expect a breakthrough unless I see it going up on a roof for a decade. Research is noble and nobody would have invented PV without it.
Thanks,
Sean White

PV Racking and Tracking Systems of Today

Posted on 24 April, 2016 at 15:44 Comments comments (93)

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. This increase is not huge, but it is noticeable and often a few percent increase depending on the amount of cooling.

Trackers are racking systems that will have the PV face the sun as the sun moves through the sky. When PV was 10x more expensive 10 years ago, tracking systems made more sense, because we were able to extract 20 or 30% more energy with the tracking system. Now with PV so much less expensive, it often makes more sense to buy extra PV instead of an expensive tracking system, which moves 365 days per year, flexes cables, is effected by wind and has many moving parts that require replacement and maintenance. Often if you see a tracker today, it will be a broken tracker. One of the great things about PV is that is often has no moving parts and requires very little maintenance. Trackers add big maintenance costs over the lifetime of the system.

All of that being said, the main kind of tracker that we see today is a horizontal single axis tracker. These trackers can support hundreds of kW of PV with a single motor. The will face the sun in the east in the morning, go flat at solar noon and face the west in the afternoon. The maintenance and space required per MW are better for these kind of trackers.

Concentrating PV requires a 2-axis tracker, but concentrating PV is extremely rare. It is just a better investment to use the mass produced products that we use today, which are mostly 60 and 72 cell PV modules that are about 1m wide and 1.7m or 2m in length.

In this fast growing industry, there are many exciting ideas and  when you look back 5 or 10 years, most of the exciting ideas have gone bankrupt. This is much as it was in the computer industry in the 1990s. Most of the companies went bankrupt, but still computers turned out to be the future. Wish I had a time machine and could tell myself which companies made it!

With PV, what is the standard for PV systems today that banks will invest in is the standard system, usually with no tracker, but sometimes on large ground mounted systems a horizontal axis tracker. For buildings trackers are very unusual.

Thanks,
Sean White

Calculating Magnetic Declination-East is Least!

Posted on 24 April, 2016 at 0:11 Comments comments (0)

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?
thanks,

A:

If you are converting from magnetic azimuth to true azimuth, you will add to your magnetic azimuth in the west (about west of the Mississippi) and you will subtract from magnetic declination on the east coast.

One way people remember this is by saying east is least (you subtract in the east).

If you were going from true to magnetic, you will do the opposite.

Another way of looking at it is you will rotate clockwise to make the correction on the east coast and you rotate counter clockwise on the west coast to make the correction.

If you sit there and think about it, you can contemplate how the magnetic north pole is over the middle of Canada.

Most of the time, you do not have to worry about magnetic declination, because all of our GPS, satellite and maps are already at true azimuth. If you use a magnetic compass, you will have to correct for magnetic declination.

If you fly an airplane, then you will have to get really good at converting back and forth from magnetic and true azimuth. Runway numbers are based on magnetic azimuth.

Thanks,
Sean White


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

Posted on 23 April, 2016 at 21:53 Comments comments (114)

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.
There is a slight difference in the annual average between the NREL and NASA websites for a given GPS location. What would be the cause?
The Optimum Angle on the NASA site would make using the Wattsun Seasonal Adjustable Rack easy to set. Per the Wattsun website, the east-west axis would have a solar yield gain of 20%
For another course I have used rooforders.com to get a detailed presentation of a roof ($20-$25). I was able to import the dxf file into Sketchup. You weren't joking that there is a learning curve with Sketchup!!!!!

A:

I heard some talk on a GTM Podcast about some kind of Senator Reid, Cliven Bundy, China/BLM/Tortoise/Solar/Cattle conspiracy and meant to look it up.

It sounds like you already know what is going on and here is what I figure is a fact based source (Politifact):

http://www.politifact.com/punditfact/statements/2014/apr/24/blog-posting/did-sen-harry-reid-drive-standoff-bundy-ranch-pers/

I found another source that was obviously political that had communist China photos of Reid merged with solar modules, proving that solar is a communist plot to take over America. Hahaha. I am glad those people keep me entertained. I like a good conspiracy theory, and probably some of them are true.

To get to your question about data from NREL and NASA, NREL gets a lot of its data from land and NASA extrapolates from space. Whatever data you use, it is going to be off somewhat, so best is to compare data to real results on a completed job and them use those figures to further detail your figures. Remember, we are working with a lot of inexact variables, weather, atmosphere, temperature, dust, pollen, bird droppings, shadows, morning dew, clouds, wind, degradation, resistance, etc., so the best we can do is a good guess and the more experienced we are, the better we are at guessing. NREL is really experienced with solar, so I would pick NREL data first, but NREL data is not everywhere, but NASA has data for all of Earth and even Mars. I am trying to model Oman right now and it is not as easy as NREL country.

I like that RoofOrders.com report! I just downloaded the sample solar report and might just have to use them sometimes. I just signed up to do financing through a company I have been teaching for for years and they have their own way of doing reports that I am learning with a range finder. Amazing how fast the industry has adapted after the Solmetric Suneye was taken off the market.

I can tell you are a good study!

Thanks,
Sean White

Ac coupled systems, microinverters and ac coupled charge control

Posted on 20 April, 2016 at 18:46 Comments comments (1)

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. They probably work fine together.

Any grid-tied (interactive) inverter will work in an ac coupled system. The interactive inverter will not know the difference from the real grid and the ac coupled grid made by the battery inverter.

In order to control overcharge from the interactive inverter, the battery inverter can make the inverter turn off by slightly changing the frequency and making the interactive inverter anti-island (turn off).

There are other ways of controlling charge, such as when you have products that were designed to go together they can communicate.

Another way of controlling charge is a diversion load, which will turn on when the battery is charged and there is extra sunlight. A common diversion load is a heating element in a hot water heater. The NEC does not allow us to rely upon the diversion load, so we will need another way to control the overcharge.

Thanks,
Sean