APPLICATION
relationship between the variables in the power
balance:
Power consumption = (instrument loads x time) +
(system losses x time)
Power available = (power input x time) – (system
losses x time)
Efficiency
Clearly, the greater the operating efficiency of a
Issue I 2010
system, the lower the overall power requirements
will be. In designing residential PV power systems,
it is generally accepted that every $1 spent on
energy efficiency measures results in $3 that will
not have to be spent on additional power
producing equipment (i.e., a larger PV array,
battery bank, etc.). Equivalent documentation does
-pv-management.com not seem to exist for this relationship in PV-
powered research projects, but it is probably safe
.solar
to assume that the ratio is equal to or greater than
www
Graphical depiction of or chassis becomes the grounding point to which that expressed above.
the terms Azymuth and all of the negative conductors are referenced.
30
Altitude. Although not as good a system as a true earth Here are a few things to consider:
ground, it does ensure that over current devices
will operate as designed. 1.DC-Only Systems
-Most electronic equipment actually operates on
Power Consumption (Load) DC power, despite the fact that most of the
In a well-designed PV system, there should be a commercially available equipment is designed to
relative balance of power. In other words, there plug in to AC power sources. In essence, AC
should be enough power input to equal (and travels long distances better than DC. In a typical
slightly exceed) the amount of power going out to research project, however, distances are typically
instrumentation and other loads. rather small, and DC may provide a more efficient
power supply.
In some instances, this will need to be calculated
on an annual, rather than a daily or weekly, basis. 2.Logic Circuits
A PV array or battery bank will ultimately lead to -The use of a programmable logic circuit, or PLC,
failure if it is too small, whereas the penalty for too allows for much greater control of the system. For
large a system is excessive cost, weight, and instance, does every instrument need to be on all
difficulty of deployment. Essentially, a researcher the time for sampling, or could some be quiescent
Complete 12 volt DC should always plan on oversizing the system to for the majority of the time, waking up to take a
solar system, with a PV ensure reliability. sample once an hour? The power reduction can be
array charge controller dramatic when this approach is taken.
and battery A couple of simple formulas help to define the
3.Thermal Strategies
All electrical equipment performs best within a
certain temperature regime, and typically this is
not–40º C. (PV panels are the exception: The
colder it gets, the more efficiently they work.)
Efforts made to control the internal temperature
environment can yield great rewards. Controlling
the environment of any type of enclosure, be it a
battery box or a home, relies on just three things:
1. A thermal energy source
2. Insulation to prevent the heat from escaping
3. Thermal mass to moderate temperature swings
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