----- Original Message ----- From: Lienesch, Gary W. (BP Solar) To: 'Cathy Colwell' Sent: Wednesday, February 07, 2001 9:44 AM Subject: RE: Mainland High School Project (Round #2) Hi Cathy! -----Original Message----- From: Cathy Colwell [mailto:colwell@mindspring.com] Sent: Wednesday, February 07, 2001 6:14 AM To: Lienesch, Gary W. (BP Solar) Subject: Mainland High School Project (Round #2) You have been extremely thorough. My group meets this afternoon, Wednesday, February 7th at 3 PM, EST, and then again tomorrow afternoon. I will pass along these answers and we will research the directions you have indicated. These were some initial questions passed onto me after I told my group that you would be willing to try and help us. Which side of a building (N, S, E, W) would be best for building permanent solar cells into windows? [Gary Lienesch] In the northern hemisphere, the PV should face south. In the southern hemisphere, they should face north. How many hours of the day would the cells generate voltage (based on being in Daytona Beach, FL) [Gary Lienesch] You need to think in terms of current. It takes very little light to generate a voltage. The voltage is an intrinsic property of the way the PV is made. However, the current typically does the work and is in proportion to the irradiance (light intensity). For Daytona Beach, FL, the average daily insolation over a year is 4.65 ESH (Equivalent Sun Hours) That is the same as 4.65 hours of noon-time sun. How well you collect that energy is another matter. The tilt angle of your array is one factor. Would the windows still let in enough sunlight for general lighting purposes? [Gary Lienesch] Our PowerView soon-to-be-a-product is designed to do just that. The trade-off is that energy that passes thru the window is not used to make electricity. Crystalline modules could let a little light thru if the backing is translucent. Most of them are blue and don't let much light thru. Is there a minimum angle of incidence for the light rays? A minimum intensity? A maximum wavelength of light? [Gary Lienesch] Our design software takes care of that. But to answer your questions: Yes, yes and yes. ;-) Is there any general correlation with latitude? [Gary Lienesch] Yes, location and latitude both affect light collected. We use software that uses light measurements taken from many points on the earth. We select the nearest location where data has been taken when sizing a system. There are many variables - air mass above the array, cloudiness, dust and pollution, ambient temperature, wind and how the PV technology responds to some factors such as temperature - that come into play. I feel extraordinary lucky. Thank-you for your time and interest ... Cathy [Gary Lienesch] My pleasure. -Gary- ----- 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