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and fuel cell varieties in addition to the very mature electro-
mechanical and photovoltaic stalwarts. Today’s consumer
is confronted with all these choices, in all manners of scale.
However, of the above technologies, photovoltaic (PV) or
solar power remains the dominate
technology within the personal
portable category.
PVs have a lot of features,
making them very attractive to
any front or back country trav-
eler. They are extremely depend-
able – there are no moving parts
to break, and they offer virtually
failsafe operation. PV technology
is robust, which is why NASA has been using it in space
since the 1950s. It is simple to operate; just plug-and-play.
PV is becoming more eco-friendly both pre- and post-man-
ufacturing. Recent advances in PV technology might soon
be ushering in new carbon-based cells, making them easier
and much cheaper to build. Finally, today’s PV offerings are
broadly available at retail.
Given there are so many choices in PV products, con-
sumers (and sales staffers) may wonder what makes them
fundamentally the same but different. To answer that, this
basic primer on PV function will attempt to clarify the
philosophical differences between technologies. This is fol-
lowed by a hypothetical trekking scenario for which seven
photovoltaic manufactures of outdoor power options were
asked to offer solutions.
The photovoltaic effect was first noted by a young French
physicist, Alexandre-Edmond Becquerel, in 1839. Yet it took
more than 120 years before efficiency breakthroughs helped
propel its commercialization (ie. 1960s). To efficiently gener-
ate electric current in materials exposed to sunlight, certain
physical properties of chemical compounds are required.
Silicon-based semiconductors, the foundation of most
microelectronic circuitry, are the principle materials used in
solar cells. Semiconductors are compounds whose tweakable
electrical conductivity dictates the extent and direction of the
positive to negative or negative to positive current flow. Lay-
ers of semiconducting material, or wafers, are constructed in
such a way as to create a positive and negative electrical field
on opposite sides of the wafer and are joined together to form
a circuit. When sunlight hits this semiconductor, electrons are
freed up and captured by aforementioned electrical fields,
inducing current flow or electricity (Figure 1).
The smallest PV units are called cells. They are ganged
together to make larger modules and even larger arrays,
powering structures such as the International Space Station or
a typical North American home (Figure 2).
Variations in chemistries, wafer design and overall con-
struction affect the efficiency or the ability to convert sunlight
to electrical current. Monocrystalline, polycrystalline and
amorphous silicon are the most common cell materials. In
general, monocrystalline is high-purity silicon with the great-
est efficiency. Continued advances in the less-expensive and
lower-efficiency polycrystalline technology are rapidly closing
the efficiency gap. Amorphous silicon, used exclusively in thin
film PV, has the lowest efficiency but, in many respects, the
greatest versatility. It is bendable, thin, cheaper to manufacture
and the most environmentally friendly. This brings up another
categorical difference: form factor.
When it comes to form factors, there are mainly two:
ridged monocrystalline and polycrystalline modules and
flexible thin film modules. The end user has to determine, of
the two forms, what works best for them. Typically, ridged
modules have slightly higher efficiencies but are heavier
and bulkier. Flexible modules can be integrated into tent
walls or backpack panels and rolled-up for easy storage.
Another key difference in design is how cells are inter-
nally connected. If cells are connected similar to links in a
chain, it is referred to as series or a series circuit. Conse-
quently, if one cell is damaged or fails,
just as if a link in a chain disappears,
the whole chain fails and no longer
works. Parallel or parallel circuit is
when the cells have some level of inter-
connectivity. If one cell is compromised,
the current has alternative paths it can
follow to continue the flow of electric-
ity. Parallel circuitry is slightly heavier
and internally more complicated,
thus more costly to build.
Finally, all power-generating modules require batteries to
store their generated charge. Unless there is no need for power
during periods of diminished light or nightfall, consider
recommending a storage cell. There also are integrated panel/
battery systems or component kits available from manufactur-
ers, optimized to best utilize their special features.
What follows are product submissions to supply power
for a hypothetical trip. The trip scenario is a party of two to
four people with two to four smartphones and one tablet or
action video camera. Battery storage capacity is shown in
milliampere-hour (mAh). For comparison, an iPhone 6 battery
is purported to be around 1800 mAh. A Samsung Galaxy S6
advertises 2550 mAh. Prices are MSRP.
Inside
Outdoor
|
Fall
2015
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