----- Original Message ----- 
From: Lienesch, Gary W. (BP Solar) 
To: Cathy Colwell (E-mail) 
Sent: Tuesday, February 06, 2001 8:30 AM
Subject: Mainland High School Project


Hi Cathy,
    I can devote some time to this.  It might be good for you to channel the questions from your students.  

We would like to implement the application of solar photovoltaic cells onto/into the windows of municipal buildings in a hope to offset some of its electrical lighting demands. My group has been researching solar films and current window technologies.

You should also look into thin film technologies for this application.  Search our database for Millennia and PowerView.

We are hoping that someone in your company would take a few moments and answer some of our questions.

   (1) How many solar cells would it take to produce a 100 watt array?

This is not an easy question.  It doesn't reflect the way systems are designed.  Cells are put in series to produce the desired DC system voltage.  Power is achieved by putting in parallel these series strings.  An end user should think in terms of a module.  That's the basic building block for the end user.  Cells come in different sizes, efficiencies and technologies.  There is no standard cell that can be referenced to answer the question.

   (2) How should those cells be incorporated into the windows? sandwiched between the panes of double pane windows? As strips on the surface of the actual window?

What one should do is purchase a photovoltaic (PV) laminate.  That's a module without a frame.  Then have the builder put the laminate in an architectural framing system such as those made by Kawneer.  To build your own laminates requires an incredible startup expense.  Once you build prototypes you do environmental testing to see if they'll last 25 or 30 years.  Then you have to acquire several external certifications that are expensive.  The area you are investigating is BIPV (Building Integrated Photovoltaics).  Do research this in our database.  Thin film products work well in this application.  
   (3) What type of solar cells would be best?

It really depends on the application.  Anything can work.  Most everything has been tried.  Search for some examples to see what has been done.
   (4) How would the voltage be collected from the window?

Typically, the laminates are wired in series to produce up to 480 VDC and this is fed into a grid-tied inverter.  This is connected to the building's electrical supply to offset power consumed by the building.  Our parent company, bp, is building all new gas stations with PV canopies over the pumps to generate green power.

One thing you don't want to overlook is to first, make your electrical loads as efficient as possible.  Minimize the loads.  You can spend $10 on a compact fluorescent lamp and save yourself $100 you would otherwise spend to power an incandescent lamp with the same light output.  It's far cheaper to make your loads more efficient.  Then power what's left with PV.

-Gary-

The contest ends on February 28th when we have to open our website to the contest's judges. We are in need of a person with technical expertise to open a diaglogue with my students and help them with the final technical phase of the project.

I hope that you will consider helping my group reach a successful conclusion to their research efforts.

Sincerely,
Catharine H. Colwell