Good Sam Club Open Roads Forum: Tech Issues: slightly different solar qx
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 > slightly different solar qx

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BFL13

Victoria, BC

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Joined: 02/15/2006

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Posted: 04/08/21 10:29am Link  |  Quote  |  Print  |  Notify Moderator

When I got into solar we were spending summers off-grid out in the open at a "seasonal" site we had. PWM and an "aimed" 130w panel got us the AH needed.

I did my solar mostly ground- mounted in a tilting/twirling contraption I made. jimindenver got me onto the low cost Eco-Worthy 20 amp MPPT with a 250ish watt panel as a combo. Worked great. I now have a Tracer MPPT with another panel on the TC's roof.

I was surprised I didn't get as many amps as I thought I would would with the MPPT, but I measured along the whole path and learned where the various losses were. Learned how to do that here mostly ISTR. Once I understood how it really works I was happy with the amps

We still go back there but not for such long stretches and don't have our own site, so now the panels are on the roof. Still get bags of AH per day, hardly ever need the gen in the good weather May to Oct.

Take solar for granted now, lost the urge to measure everything as when a newbie.


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red31

Dallas

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Joined: 08/04/2008

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Posted: 04/08/21 01:29pm Link  |  Quote  |  Print  |  Notify Moderator

FWC wrote:

red31 wrote:

controller eff of mppt is a real loss of power via heat sink, esp cheaper models!
mismatched or in low power conditions.


While I can't speak to some of the off brand/cheaper models of MPPT controllers, for the reputable ones (think Victron, Morningstar) the conversion efficiency is really pretty good. In the figure below, the orange line is a Morningstar MPPT controller, they don't say which controller the blue line is. In either case the power lost to heat is much lower than the power gained by MPPT and reduced wire losses.


Victron's whitepaper and the graph 7.2 Absolute performance as a function of temperature (~page 10) convinces me with my various small 100w systems that mppt was a waste of my time locally in the heat. Their little blue shaded area is actually wider than they suggest!

7.2 Absolute performance as a function of temperature
https://www.victronenergy.com/upload/doc........-solar-charge-controller-PWM-or-MPPT.pdf

graph assumes mppt has higher voltage to continue to 'buck'. [emoticon]

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