Alternative Technology Assn Forums

1. 

   wlb
   Member

   Does anyone know of a simple and cheap way of comparing different array orientations?

   I have a fixed north-facing array, angled for winter sun. A second array is on the roof facing north, but since the roof has only a 7 degree pitch, it is almost facing straight up - i.e. summer orientation.

   It is off-grid. The arrays are on separate, but networked, MPPT controllers. So it's all about battery charging. Bring the batteries to float as early as possible, and then hold them there as late as possible.

   As an alternative to array tracking, I've been wondering about fixed east and west facing arrays, and other variations so I want to compare several orientations. I don't need to know anything in detail - just a comparison of light falling on each area at the same time.

   What I have in mind is to use several small cheap PV cells, place 2 of them with the same orientation as the existing arrays, and others in the other potential locations. If I then log voltage from each cell it will give me an idea of how the possible orientations compare with the existing ones.

   I've got a multi channel data logger I could use, but can anyone think of any other way of doing a comparison like this?

   Posted Sunday 9 Dec 2012 @ 9:53:36 am from IP #
2. 

   Russell Moore
   Member

   The PVWatts site maybe?

   Posted Sunday 9 Dec 2012 @ 11:28:36 am from IP #
3. 

   wlb
   Member

   Thanks Russell, but I want to be specific to my actual location and weather. If I can measure the light that strikes sensors orientated the same as my existing arrays and compare it with the light for alternative orientations, it will give me a comparison with the existing arrangement.
   It needs to be a hardware solution. Software can only make an educated guess.

   Just thought someone may have a simple clever method that I haven't thought of.

   I've never bothered to calculate or measure the power requirements of the house, and I've never paid a lot of attention to how much energy is harvested by the PVs. The only important thing in my situation is what time the batteries return to fully charged each day and how long they remain that way.

   The period between reaching float and remaining on float is that part of the cycle that I consider my free or disposable power.

   Posted Monday 10 Dec 2012 @ 3:44:31 am from IP #
4. 

   johnmath
   Member

   wlb said:It needs to be a hardware solution. Software can only make an educated guess.

   Actually, I think you have that proposition the wrong way around. Hardware will only give you data specific to the time of your test measurement, not long term averages - presumably you are not not using the data to move the arrays “live”. There is too much “noise” or variability in simple measurements - what you want is the theoretical best positions which are worked out with insolation/weather data collected over many years and calculated for your longitude. This is best done by software, because it’s tedious to do longhand.

   I did have a free iPhone application to do this, but I have taken it off my phone since I have optimised my array for annual yield and don’t plan to move the array again. I have seen software on the web too, e.g. http://www.velasolaris.com/vs2/index.php?article_id=10&clang=1

   Posted Monday 10 Dec 2012 @ 4:11:40 am from IP #
5. 

   TonyT
   Member

   NASA provides solar insolation kWh per sqm data:

   for any location (latitude and longitude),
   for any tilt angle and
   for any azimuth angle

   in the tables at
   http://eosweb.larc.nasa.gov/cgi-bin/sse/grid.cgi?email=tonyth2%40gmail.com&step=2&lat=-36&lon=138&num=319055&submit=Submit&p=grid_id&site
   lev=&veg=17&hgt=+100

   (Click on each "Parameter Definition")

   PVWatts is at
   http://rredc.nrel.gov/solar/calculators/PVWATTS/version1/

   Australian Bureau Of Meteorology data is available at

   http://www.bom.gov.au/climate/data/index.shtml

   then at

   http://www.bom.gov.au/jsp/ncc/cdio/weatherData/av?p_nccObsCode=203&p_display_type=dataFile&p_startYear=&p_c=&p_stn_num=086232

   Posted Monday 10 Dec 2012 @ 4:45:39 am from IP #
6. 

   wlb
   Member

   Thanks John and Tony,

   The weather data they work from isn't local enough. The weather here can vary significantly from places not all that far away at the same latitude. Plus there is the issue of trees at certain times of the year.

   I know from experience which days (from a weather perspective) will bring the batteries to float and at roughly what time of day. What I want to do is compare possible fixed array positions with the existing arrays on particular types of days in different seasons, just to find out if they are inferior, as good as, or better than the locations of the existing arrays. I do of course need to look at the entire day's input.

   Posted Monday 10 Dec 2012 @ 4:50:46 am from IP #
7. 

   Russell Moore
   Member

   To do want you want would take a minimum of six months of data recording, from say summer solstice to winter solstice at least. Of cause if you are prepared for all the work, that might put your mind at rest.

   Then you can compare your data with the sites others have listed, and see how it all compares.

   Posted Monday 10 Dec 2012 @ 6:46:55 am from IP #
8. 

   wlb
   Member

   I only need to do it on clear sunny days at several different times through the year - out of curiosity.

   And then for the info I need, on dull overcast days at several different times through the year.

   You're forgetting that all I need to do is a comparison with the an existing set up that I know very well. I'm looking for typical bad solar days at different times of the year, to see if the the alternative locations are equal to or better than what I'm using.

   Posted Tuesday 11 Dec 2012 @ 3:10:38 am from IP #
9. 

   dbindoff
   Member

   It may not be relevant for a while (since you look after your batteries very well) but have you looked at the PbC batteries, either Ultrabattery or Axion Power. These batteries operate indefinitely at partial state of charge, no float charging required. Hydro Tasmania is going to use ultrabattery (CSIRO is patent holder) for their King Island upgrade. There are many developments coming with these since cycle life is enormous also and very high charge/discharge capacity. Presently not really consumer available as far as I can tell but I expect that will change soon.
   (e.g. grid demand management, frequency correction, series hybrid trucks, electric locomotive, low cost hybrid cars, grid storage etc etc.)

   Posted Tuesday 11 Dec 2012 @ 3:34:33 am from IP #
10. 

    wlb
    Member

    Thanks. I didn't realize that they were also looking at them for power station use.

    The battery that I was really looking forward to was the Vanadium RedOx technology. I'd even gone as far as talking to V-Fuel about small off-grid versions. This was a few years ago and at the time they expected to have something available about 6 months hence. But it wasn't to be. They got well and truly screwed over thanks to the idiots who set up the licensing deals for the uni.

    Posted Tuesday 11 Dec 2012 @ 3:49:45 am from IP #

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