On 5/19/2012 5:47 PM, Larry Crutcher, Starlight Solar Power Systems wrote:
Good one, Mick. Here's the way I see it:
For question one, I say yes, other than the obvious wire and
connection losses, because you are operating the cell(s) at the peak
power point.
Since a PV solar cell is a constant current device and your 29 ohm
load did not change, reducing your Lab Light source to 500 W/m2 can
only affect the voltage and resulting power. This means your load
forces the voltage down to 120 volts resulting in 500 watts of power
dissipated. You have forced an IV curve shift of current AND voltage.
The LCB boosts current based on IV curve voltage. I don't think an LCB
can change anything in this scenario since you have forced the circuit
to operate at 120 volts and 4.15 amps.
Realizing that these LCB things run off the PV input because there is no
battery.... If an LCB outputs
maximum current into a fixed resistance, (and therefore maximum power),
kind of like an MPPT
charge controller does, then it ~should~ adjust its voltage "gear
ratio" to maximize the output
current and power.
At least I think the idea is correct, if the LCB was large enough and
high enough voltage operation
for your application. But then again, I may be missing something
here too.
boB
Keep in mind that I'm a solar dummy. My logic may be faulty.
Larry Crutcher
Starlight Solar Power Systems
(928) 342-9103
_www.starlightsolar.com <http://www.starlightsolar.com>_
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On May 19, 2012, at 12:35 PM, Mick Abraham wrote:
Hi, Wrenchies~
Kindly educate me regarding PV behavior when the load is a resistor.
Here's a hypothetical situation:
* Eight 250 watt PV modules (60 cells per module), all connected in
series for "peak" ratings of 240 volts DC & 8.3 amps
* Lab type cell temperature & illumination so that the eight would
truly pump 2,000 watts */into an ideal load/*
* A 240 volt AC heating element designed for 2,000 watt heat
dissipation at 240 volts AC...that's about 29 ohms resistance for the
heat element
* Connect the PV string to the heat element, with nothing in
between except a fused disconnect.
In the above situation, would the resistance of the heating element be
all that's needed to force the PV array to operate near the "peak"
wattage?
Would the heater actually get 2,000 watts to turn into heat?
+++++++++++++++++++++++++++
Now consider the same cell temperature but half the illumination.
That's similar voltage but half the amps at peak wattage. If this is
sent into the same 29 ohm
resistor--again with no intervening electronics, could we count on
1000 watts of heat?
If the answers come up "no", would the power throughput be helped by a
SolarConverters style MPPT pump controller (Linear Current Booster
kinda thing), assuming that one could be found to operate in the 240
volt range?
Thanks & Jolliness,
Mick Abraham, Proprietor
www.abrahamsolar.com <http://www.abrahamsolar.com/>
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