Introduction: Until recently
installing electricity generating solar cells (photovoltaic panels) on
a house was one of the last things on my list of ways to make our home
less energy consuming and more sustainabile. The cost was high
and the return on investment low. There were and are many other
less expensive ways to reduce a home's net energy use and carbon
dioxide production. That said, in the spring of 2010 there are a
number of circumstances that encourage one to consider
photovoltaics. To begin, the US federal government provides a 30%
tax credit for alternative energy sources including PV. Second,
the relatively slow economy has allowed the production of PV panels to
catch up with the demand. The highly subsidized German market is
no longer absorbing as large a portion of the panels produced as it has
been. The price of panels has been dropping. More on this
below. Third, interest rates on invested money are low
making investment in photovoltaic panels more attractive.
The Installation: Dick Stumpner
(Building Services, rstumpner@aol.com, 812-825-3484) and Ted Mendoza
(Gengee, ted.mendoza@gengee.com, 812-325-4477) installed a system of 18
panels on our house. Dick designed the PV system and did a solar
site analysis using the SolarPathfinder Assistant Version 4.1.6.0
(http://www.solarpathfinder.com). Ted designed the software
readout system that includes a number of sensors for current, voltage,
solar intensity, temperature, and relative humidity. Data from
these sensors are recorded by a HOBO (Onset) data logging system and
are available on line (see below).
Ted Mendoza & Dick Stumpner
Dick Stumpner w/
inverter
The Parameters: The photovoltaic
array contains 18 Sanyo (HIP-205NKHA1) 205 Watt panels, arranged in two
serial strings of 9 each. Each panel has a maximum voltage of
40.7 volts and maimum current of 5.05 Amps. The array is fixed at 45
degrees to the vertical and faces 16 degrees west of south. The
inverter is a Xantrex Technology, Inc. GT5.0-NA-240/208 (240V).
Initial
steps in installation
Final Panel Array
The Data: A number of types of data
are being recorded, starting with the direct current and voltage
generated by the 9-panel strings. In addition, a solar
pyranometer records the insolation in watts*m-2. Also, the
temperature and relative humidity are being recorded in two positions
near the panels. Plots of these quantities with time are
available on the internet and may be reached at the following site:https://www.hobolink.com/p/61f4eecea80fc72d9b573157ac4ddec6.
To
display
these data, click on benHOBO. The most
useful plots at the moment are the solar intensity, temperature, and
relative humidity plots. I am working on understanding the
current plot and generating a voltage plot from the panels.
Analysis: At this moment we are in
the beginning stages of understanding the collected data. The
temperatures and relative humidities are measured in a shaded container
off the end of the roof near the position of the solar cells
themselves. The insolation (sun's intensity in watts per square
meter) is measured using a pyronometer with sensitivity principally in
the visible portion of the sun's spectrum. A maximum value on a
sunny day is about 1000 Watts per square meter. The DC current
produced by each PV cell in full sun is approximately 5 Amps. Two
parallel strings produce a maximum current of ~10 Amps. Each cell
produces a maximum voltage of 40.7 volts. Each of the series
strings of 9 cells produces a maximum of 366 Volts. The total current
is available in these data sets and I am in the process of adding the
total voltage. When completed, you will be able to calculate the total
power produces by this array. The theoretical maximum for these
205W Sanyo panels will be 18 x 205 = 3,690 Watts.
