Download EmbEddEd dEvELOpmENT

RESOURCES
APRS World, “Solar Insolation (Light Intensity),”
www.aprsworld.com/sensors/solarInsolation.
STMicroelectronics, “SPV1040: High-Efficiency Solar Battery Charger with Embedded MPPT,” 2011, www.st.com/
internet/com/TECHNICAL_RESOURCES/TECHNICAL_
LITERATURE/DATASHEET/CD00287506.pdf.
Tung, Y., Hu, A., and Nair, N., “Evaluation of Microcontroller-Based Maximum Power Point Tracking Methods
Using dSPACE Platform,” Australian University Power
Engineering Conference, 2006, http://itee.uq.edu.au/
~aupec/aupec06/htdocs/content/pdf/165.pdf.
Figure 6—Solar insolation is the measurement of the sun’s light intensity
falling upon the earth. As expected, this is less than the 1,000W/m2 used to
specify the potential output of a solar cell/panel. It will vary by latitude as well
as by time of year. This takes weather conditions into account. (Source: APRS
World)
expect to get 0.707 of the maximum on average. So, over 10 h,
that’s approximately 3,300 Wh/m2 (i.e., 10 h × 475 Wh/m2 ×
0.707) of illumination for the day. If you use Parallax’s 2.65-W
cell, you might see 3.3 h of capacity (i.e., 3,300 Wh/m2/1,000
W/m2) or 8.7 Wh (i.e., 2.65 W × 3.3 h) of energy over a one-day
period. And that’s under a clear sky!
So where does this get us? At my local electronics store, I
found a small 1.5” by 0.75” solar cell that is rated at 300 mA
at 0.55 V. That has a potential of 165 mW (i.e., 0.3 mA ×
0.55 V). On clear days, I might expect to gather 544 mW
(i.e., 165 mW × 3.3 h) of energy, which would be approximately 10 times the energy required for my remote device.
Even with poor efficiency, once my load capacitor (supercapacitor) was charged up to 5 V, I could draw off current to
trickle charge the batteries with a simple resistor. With a
potential of 5 V and load of 2.5 V (battery voltage), a 250-Ω
resistor would supply 10 mA for as long as I could keep the
supercapacitor charged. Even an hour of sunlight a day could
produce twice the daily requirements.
August 2012 – Issue 265
NATURE
74
Obviously, a good look at your locality’s solar data is a must
in order to be able to predict how insulation levels will affect the
current-generating potential for a specific installation. While
batteries may be sized to last a year, you may wish to extend
their effectiveness by adding some support to keep them
charged to extend their maximum lifetime. STMicroelectronics
offers a couple of evaluation boards you can use to get started
with a design (refer to Photo 1).
Energy harvesting from not just solar, but wind, water,
thermal, and other methods is being researched today.
Nature provides a plethora of possibilities. As stewards of our
natural resources, we need to use them wisely, lest we tip the
natural balance too far. There are some things we just can’t
live without. I
Jeff Bachiochi (pronounced BAH-key-AH-key) has been writing
for Circuit Cellar since 1988. His background includes product
design and manufacturing. You can reach him at jeff.bachiochi@
imaginethatnow.com or at www.imaginethatnow.com.
SOURCES
750-00042 2.65-W Solar cell
Parallax, Inc. | www.parallax.com
SPV1020 Boost converter and SPV1040 Solar battery
charger
STMicroelectronics | www.st.com
BQ2002 NiCd/NiMH Fast-charge management ICs
Texas Instruments, Inc. | www.ti.com
NEED-TO-KNOW INFO
Knowledge is power. In the computer applications
industry, informed engineers and programmers
don’t just survive, they thrive and excel. For more
need-to-know information about some of the topics
covered in this article, the Circuit Cellar editorial
staff recommends the following content:
—
Solar-Powering the Circuit Cellar (Part 1)
Preparing the Site
by Steve Ciarcia
Circuit Cellar 209, 2007
Have you considered installing a photovoltaic (PV)
system? This series of articles describes the entire
process, from site preparation to completion. Topics:
Photovoltaic, Solar
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Solar-Powering the Circuit Cellar (Part 2)
From the Ground Up
by Steve Ciarcia
Circuit Cellar 210, 2008
This article covers the massive task of preparing two
11’ schedule 80 poles (8” in diameter) to support two of
the three solar arrays. Topics: Photovoltaic, Solar Arrays
—
Solar-Powering the Circuit Cellar (Part 3)
Wiring & Electronics
by Steve Ciarcia
Circuit Cellar 211, 2008
Installing a major renewable energy source like a home
photovoltaic system is no small feat. This article describes
wiring and electronics. Topics: PV, Renewable Energy
—
Go to Circuit Cellar’s webshop to find these
articles and more: www.cc-webshop.com
CIRCUIT CELLAR® • www.circuitcellar.com