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MPPT - 55.8V array to 12V battery bank | 21 comments (21 topical, 0 editorial)

Re: MPPT - 55.8V array to 12V battery bank (3.00 / 0) (#10)
by Walt Er on Mon Aug 25th, 2008 at 08:36:21 AM MST
(User Info)

Thanks for all the great battery info. What I get from it is that I can size my battery to be at 20% SOC by the end of day 5, as long as this doesn't happen too frequently (couple dozen times per year).

By this statement, I see that you are assuming a 96.5% controller efficiency:

"Full sun with MPPT will give you around 193watts / 14volts = 13.7 amps Not as you calculated." (Also note that I changed to four 125W panels halfway through the post).

But what about the full sun part. The panels will only produce their peak power in full sun, perfect conditions, which is not all the time. I thought I had already factored in the rarity of perfect conditions by using only three hours of insolation, but should I knock down the rated panel wattage by some percent also?

Thanks - Walt

[ Parent ]

Re: MPPT - 55.8V array to 12V battery bank (3.00 / 0) (#11)
by scottsAI (user name at eml dot cc) on Mon Aug 25th, 2008 at 09:21:21 AM MST
(User Info)

Walt Er,

Welcome, hope it was help full.

Solar for a given location is rated in full sun hours.
I live in Michigan, which is rated at 4.5 full sun hours a day. AZ is 9.
The rating is based on average over the year and weather, fixed panels.
Look around, charts for this.

The reality we have daylight for 16 hr in summer, 8-9 hr in winter.

Morning sun is weak, yet solar panels generate power during this time charging the batteries, current starts out low, reaching near peak current by 11am, stays at peak for couple hours then declines.

Tracking helps by keeping the full sun reaching the panel, can add a couple hours of near peak power a day, further north the more helpful tracking and MPPT is. (and south of equator same thing). In Michigan tracking adds about 30% power collected a day, equal to power added by MPPT (based on many assumptions, standard panels being the first one).

When I do calculations I show all of it, reduces confusion of what I'm doing, helps other to learn by seeing the example!

Have fun,
Scott.

[ Parent ]

MPPT - 55.8V array to 12V battery bank | 21 comments (21 topical, 0 editorial)

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