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Advanced Photovoltaic Systems

AET 230-8204 Notes-Week 2


The highlight of this week is our Guest:

Tony Diaz of Century Roof & Solar 

You can learn more about Tony from his websites:

Tony is a C10 electrical contractor, a C46 solar contractor, C39 roofing contractor and probably a few more.


He just took the "hard NABCEP" PV installers exam & will tell us how it went and his path to taking the exam.


He will go over wire sizing and the NEC.


We should also get to see some photos of his project at the the California Academy of Sciences in San Francisco.

click the image for the museum website

Topics for this week:


Site Assessment/Surveys, Design & Proposal Software, Shading, Rebates, Taxes, Stimulus, Financial.


There are many different ways to asses a situation for PV.


As we should already know from out introductory PV classes, there is the Solar Pathfinder www.solarpathfinder.com and the Solmetric SunEye www.solmetric.com.

Benefits for the Solar Pathfinder:

  • Like a bicycle it is human powered.
  • You will not show up with dead batteries or an error message.
  • It takes no time to boot up.
  • You can take pictures of it and convert to digital.

Benefits for the Solmetric SunEye

  • High-tech reports.
  • It does all of the thinking for you.
  • It calculates for magnetic declination.
  • You can use it with a GPS and you won't have to enter the nearest city.
  • You can download the data into proposal generating software, such as OnGrid and Clean Power Finance.

Benefits of the compass, protractor, paperclip & sunchart method

  • The benefit to this method is that you have to really understand what you are doing. You will be correcting for magnetic declination & determining altitude angles for different bearings.
  • It is very inexpensive and there is a good chance you already have what you need at home.

Many times you will go to a roof and not need to take these measurements. When you are on a flat commercial roof in an industrial area, there is a good chance that the only objects that will make shade are on the roof, such as air conditioners. What I do is take an aerial image with me that shows the roof and the structures on it. Typically the resolution of the best online aerial images is 6 inches per pixel.


I have my favorite place to get images from, which costs


thousands of dollars per year. www.pictometry.com


They do not have everything, so I still use the others, which also are a great resource, such as:

People used to rent helicopters for views that you can now get for free.


Once I get on the roof with the images, I measure the height of the potential shading objects. I also draw on the image things I might not have seen, such as conduit and vents.


Ideally, we would get the building owners to work with us and move everything to the north side of the roof, where it will not cause a shading problem. I assume that as solar gets more mainstream that people will design buildings with all of the objects on the north side of the roof.


Many people use rules of thumb for how far away from a shading object you need to be. The closest you can get by any standard I have seen is 2:1 or twice as far away from the object as it is above the PV.


Once you start laying out the modules with a CAD program or with a pencil, you will get a better idea of how things will fit and at some point there will be a module that you will probably contemplate over. Should you place it there or not. One thing that will help you make your decision is how it fits with a series-string. If you add one more string, it might be overly shaded and if you left a string off, you might have more empty space than you wanted. In this case, you will probably err on the conservative side and leave some extra space on the roof.


You can also play with changing the amount of modules in a string, but on a large commercial roof, you will probably not sacrifice the voltage drop or increase in copper wire needed associated with the lower voltage you would get from a smaller string.


If you are using the pencil method, make sure you have a good eraser, because to make a good fit, you will be moving things around a lot.


Inter-row spacing exercise


Go to the second issue of Solarpro Magazine www.solarprofessional.com & read the article on calculating inter-row spacing.

Click on the image above to make a chart like this one below

We can also calculate the area under the module and get the north to south repeating distance of a row. The repeating distance is important, because it lets you know how many modules you can fit on the roof.

I like to do my layouts with simple rectangles.

Here is a link to my excel spreadsheet that calculates the repeating distances, so you can get a rectangle.

Another thing to keep in mind is that there is a space between the modules in a row, which varies depending upon the type of racking system you use. It could be an inch or more, so add that to the dimension of your rectangle.


It can get a lot more complicated than this.


What would you do if the modules were not facing due south?


What if you were above the arctic circle?


Many times, in my experience, designers end up using rules of thumb, such as a 3:1 or a 2:1 distance from shading objects. Rules of thumb are not very scientific, but the amount of money you might spend figuring out how to become a fraction of a percent more efficient could be better spent on adding another module for more than a fraction of a percent production.


Computer-Aided Design (CAD) Programs

There are CAD programs that can be used for this.


There is a SketchUp class coming up at the Pacific Energy Center that is about calculating shading.


SketchUp www.sketchup.com is a free 3D CAD program by Google.


If you want to develop a skill that will impress employers, learn AutoCAD. You can take classes at DVC, UCB Extension and from the makers of AutoCAD, www.autodesk.com


On tip is that since AutoCAD software is very expensive, don't do the 30 day free trial until the class starts. Wait until the last minute. You can download it once per computer. You can also purchase a student version that is more affordable for a student.


I have learned more about AutoCAD from a private tutor, than from a class. With a private tutor, I can tell them what I want to do & then they show me.


I have seen people do single line diagrams (SLD) of PV systems with Microsoft Word.


A co-worker of mine uses Microsoft Visio.


Here is a list of CAD software companies:

Rebates, Taxes, Stimulus & Financial


The portal website to the California Solar Initiative (CSI) is:

Once a month, the Pacific Energy Center (PEC) has a CSI class which you should attend. Having this knowledge will help you get a job.


The CSI paperwork is a bit complicated and there are many people in the industry that would like to put that paperwork on your desk.


It is not that bad, because there are friendly & helpful people on the other end processing the rebate paperwork who will help walk you through it. You will meet some of them at the CSI events at the PEC. It can be helpful to introduce yourself, so that they have a face to associate your phone calls with.


The rebates step down as more and more megawatts get used up.


You can see what level we are at right now at:

The reason that the rebate amount keeps falling is to give people an incentive to act now.


There are too many people afraid to sign contracts, because of all the hype you hear about solar getting cheaper.


Here are some of the reasons people give for waiting:


  • Nano-technology
  • Thin film
  • An article that cited $1/watt
  • 40% efficient module article
  • Stimulus package
  • Cap & trade
  • Carbon credits

It can be frustrating reading every new article about some technology that is going to revolutionize the industry in a year.


I think that a lot of this hype is from companies looking for venture capital funding.

Here are some reasons to get solar now:

(good to know for Solar Salespeople especially)


  • CSI rebate is dropping
  • Demand is low and supply is up
  • Approximately $3/watt all time low PV wholesale prices
  • Tax credits probably will not get better
  • If they wait, installers will be busy & prices will go up
  • If they wait a year, that is a year worth of PV production that they did not have. That is worth $$$.
  • How many pounds of greenhouse gasses are they putting in the atmosphere for each day of delay?

Here is where to go as soon as you know you are going to file for a CSI rebate:

When you submit an online reservation, it does not mean much. When you submit your application with "wet" signatures and a copy of a contract, then you will get a place in line for a particular rebate level.


If you are installing your own system, in place of a contract, you need proof that you have paid at least 10% down on the equipment. An invoice from a distributor will do.


You have to mail in the application and can not carry it to PG&E.


Towards the end of a rebate level, there is a rush of people trying to get a reservation.

If you are in a different utility district, this does not apply.


You can find out about different incentives for different areas at: www.dsireusa.org


Federal Tax Credits


The 3 letters that were most important to everyone in the PV industry last year were ITC, which stands for Investment Tax Credit.


The ITC was finally thrown into the Emergency Economic Stabilization Act of 2008 and extended for 8 years. This was very important. For the second half of last year, large commercial projects were put on hold, because if they were not completed & inter-connected to the grid by 12/31/2008, they had no assurances that they would be eligible for the 30% tax credit. On a megawatt project, that would amount to millions of dollars.


The 8 year extension of the ITC also removed the $2000 cap on residential PV projects. Now commercial and residential projects are eligible for a 30% tax credit, that may be carried forward, i.e., they can spread it out over the years until 2016.


At this point, like everyone else, I will tell you to talk to a tax professional to know for sure.


Note: Non-profit organizations & public institutions such as schools, who do not pay taxes can not benefit directly from a tax credit. One way around this is to have someone else own the PV system and this is called a Power Purchase Agreement (PPA).


A problem people are having now with the downturn of the economy is that they are not making money and therefore do not owe taxes. To counteract this problem, included in the American Recovery & Reinvestment Act of 2009 is a provision to turn the tax credit into a grant. This is for commercial projects and once the project is completed, a check for 30% of the project cost is supposed to be issued in 60 days.


This is all very new. To get the best information, look to the Solar Energy Industries Association at www.seia.org .


Taxes on Materials


You have to pay the sales tax rate of where the PV is shipped. If you are in Alameda County and install in Contra Costa County, the higher sales tax of Alameda County applies. If you have it shipped to Contra Costa County, then that sales tax rate could apply, however the extra paperwork associated makes that extra savings not worth the money saved.