Mick,
In the first case you are selecting a resistor that matches the IV curve
peak power point at 1000 W/sq meter irradiance. You will indeed get 2000
watts of power into the resistor. For the second case, at 500 W/sq meter
irradiance, the PV module's IV curve has about the same peak power
voltage, but only half as much current. The resistance that would get
the maximum power changes from 29 ohms to 58 ohms. With a 29-ohm
resistor connected, the power into the resistor will be a little more
than half of the 1000 watts the PV module could deliver. The linear
current booster is designed to boost the current when the voltage (and
resistance) are less than optimum, so I think it would improve the power
transfer.
Kent Osterberg
Blue Mountain Solar, Inc.
www.bluemountainsolar.com
On 5/19/2012 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>
Voice: 970-731-4675
_______________________________________________
List sponsored by Home Power magazine
List Address: [email protected]
Options & settings:
http://lists.re-wrenches.org/options.cgi/re-wrenches-re-wrenches.org
List-Archive: http://lists.re-wrenches.org/pipermail/re-wrenches-re-wrenches.org
List rules & etiquette:
www.re-wrenches.org/etiquette.htm
Check out participant bios:
www.members.re-wrenches.org
