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gunnarh avatar image
gunnarh asked

Victron SmartSolar 100/15 absorption time with constant two-hour mid-day shadowing?

So I'm in the process of installing a small off-grid solar system at my cottage, three panels of 120W each, serially connected, feeding 12V lead-acid batteries (roughly 300 Ah). I live at 67 degrees north (basically at the arctic circle), so I need to really use all solar power I can to keep the batteries charged.

Note that the panels are over-dimensioned during summer time, but in late autumn/early winter I need every ray of sun I can catch. Obviously in mid-winter the sun is even below the horizon for some time, but we don't go there in Dec-Jan as it's just dark and cold, so no consumption, just hoping to keep the batteries alive.

Now, just south of my cottage there is a small high-rise dense forest (not owned by me) which will always cast a full shadow between 10am to 12 noon (but before and after that time it will be free sky). There is unfortunately no way I can install the panels on my property to avoid this daily shadow. Now, after reading the forum I'm a bit concerned about how the absorption charging will work, as it seems like it can only pause the absorption time for max one hour?

After the two hours of daily shadow, the batteries might still have a decent voltage due to the morning charge, so I think that the controller might sometimes (or every day?) restart with a very short absorption time? But believe me, at 67 degrees north the batteries will still need to continue with absorbtion most of the day. Also, the bulk of the possible daily sun-time for me happens 12 noon to sunset, so it's important that I can use that energy. Actually, based on experiences from friends with similar setups (but non-victron controllers), many not-so-sunny days their batteries do not even reach float those days.

I have still to decide what controller to buy, and from all other aspects I think the Victron 100/15 seems fine, but again, I'm a bit unsure how the absorption phase will work? I have read the on-line manual, and know that you can fiddle with max absorption time and tail current, but seems like it's not possible to extend the "pause time" to accommodate for my shadowing case in a good way...?

Follow-up question 1: How come that the max pause time is not simply user-settable? That would be a super-easy fix, or would there be any drawbacks with that?

Follow-up question 2: Will the daily shadowing impact the controller's sense of "daytime", i.e. will it correctly identify the sunrise and sunset, or is there a risk that it will start "sunrise" at 12 noon (especially later in the season when the sunrise is closer to the start of the shadowing)?


MPPT Controllers
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seb71 avatar image seb71 commented ·

In the morning more likely the charger will be in Bulk stage, not in Absorption stage.

I would be more concerned by the small PV array size for your conditions - 360W PV for an 12V 300Ah battery. You do not specify how much energy you want to use and when (day/night).

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If you don't have a shadow-free spot, at least can you install them South facing (or maybe rotated a few degrees West from geographic South, to account for that shadow) and at a high angle from horizontal (to better catch the winter Sun at your latitude)?

Or you have to install them on a building roof, for instance (with the roof orientation imposing the azimuth and elevation of your PV)?

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gunnarh avatar image gunnarh seb71 commented ·
The panels will be installed facing south, vertically on the rooftop of the building (to catch the low winter sun, as well as avoid them being snow-covered). We don't consume much when we are there, just charging some phones and tables, plus some LED lights during the autumn.


The reason for the relatively large battery (compared to the panels) is that I have some surveillance cameras (actually three remotely controlled old Android phones) running over the winter, and they will consume in total about 3Ah per day. Add the battery natural discharge, say 1 Ah per day, so roughly 4Ah per day. This is enough for roughly one month without any sun, if I allow discharge to 50%.


Sun is really sparse in Nov-Dec-Jan, so when it does show up I really need to collect all of it...
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kevgermany avatar image
kevgermany answered ·

I'm not sure what your concern is.

If the pause time is exceeded, the charge cycle will restart, so after the black out period, the controller will restart in bulk. Then switch to absorption once absorption voltage reached. If you're concerned about shorter absorption time after a same day restart, you can increase the absorption multiplier.

You don't know at the moment if the mid day blackout will trigger float from tail current or cut out from excessively long pause. Early float trigger is another concern, but you should be able to configure the charger to avoid this.

I think you're going to have to either experiment once you have all the equipment.

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gunnarh avatar image gunnarh commented ·
Yes, my main concern is that after the mid-day blackout the battery will still need a lot of charging, but it might have a voltage high enough (due to being charged two hours earlier) to make the absorption time short. Yes, I guess I need to experiment...
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