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MPPT | 7 comments (7 topical, editorial)
Re: MPPT (3.00 / 0) (#3)
by jimovonz (username at matata dot co dot nz) on Fri Jun 8th, 2007 at 04:26:52 PM MST
(User Info)

Flux is that inverter or converter losses you refer to? I presume you mean the efficiency of the MPPT controller itself (converter).

[ Parent ]


Re: MPPT (3.00 / 0) (#4)
by boB on Fri Jun 8th, 2007 at 07:56:21 PM MST
(User Info) http://bob.gudgel.org

>>Flux is that inverter or converter losses you refer to? I presume you mean the >>efficiency of the MPPT controller itself (converter).

I think he did mean converter and/or inverter losses.  Since MPPT can gain you from, like, 15% to sometimes over 30% relative to NOT using MPPT, even if the converter losses were say, 10%, you STILL win. (some)

boB


[ Parent ]



Re: MPPT (3.00 / 0) (#5)
by jimovonz (username at matata dot co dot nz) on Fri Jun 8th, 2007 at 08:16:14 PM MST
(User Info)

I don't think inverter losses are relevant. What Flux is saying is that in some situations you can get a net loss by having a MPPT controller connected. In a particularly hot environment the output voltage of the panel is low enough that the load presented by the battery is actually pretty close to the MPP. The less than 100% efficiency of the MPPT controller would make you worse off not better. The MPPT controller gives better results when the voltage differential between the panel and battery is greatest. As Flux points out, this is most likely to be on a cold clear winters day.

[ Parent ]


Re: MPPT (3.00 / 0) (#6)
by boB on Sat Jun 9th, 2007 at 12:16:59 AM MST
(User Info) http://bob.gudgel.org

Right.  This is true because when the PV modules are hot, the MPP voltage may be
at or below the battery voltage.  If below the battery voltage, a boost converter
rather than a buck converter might be in order.  Right AT the battery voltage,
a relay would be best since there is ~some~ voltage drop from either the MPPT
converter or even a PWM controllers MOS-FETs. (less than a 1 volt drop if done right)

If the PV array is wired for say the next higher nominal voltage than the
battery, the MPP Voltage will always be above the battery voltage.  However,
in this case, all else being equal, and not taking PV to controller wire
loss reduction into account, the controller will actually be less efficient
than if its input voltage (PV) was lower. (closer to the battery voltage but
higher than the battery voltage)

It's still typically better to wire the array for a higher voltage than
the battery voltage and use an MPPT controller.  This can help when the array is partially shaded too.

boB


[ Parent ]



Re: MPPT (3.00 / 0) (#7)
by Flux on Sat Jun 9th, 2007 at 12:35:36 AM MST
(User Info)

Sorry about that, I did mean converter as you all correctly deduced.

Mppt does ease the restrictions on the choice of panels. Things like using 3 panels for 24v become practical as long as the panels are the same current rating.

Flux

[ Parent ]



MPPT | 7 comments (7 topical, 0 editorial)

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