question

ralphd avatar image
ralphd asked

How to Prioritize Solar MPPT over Shore Power Multiplus II

I have installed a Multiplus II on my boat. I also have solar panels connected through two MPPTs, and a Smart Shunt connected to the house battery bank (5 - 12V AGM batteries). The system is connected to a Cerbo GX with a touch 50.

My question is this: Is there an easy way to prioritize solar power over shore power when the boat is connected to shore power?

I have seen many posts from a few years ago but there seems to be no clear answer. The ideal situation would be when the sun is shining the batteries remain at 100% SOC and the solar powers the boat. If the load exceeds the solar output, the Multiplus II would make up the difference using shore power.

I look forward to hearing back from the community.

Thank you,

Ralph

MPPT ControllersMultiplus-IIcerbo gxsolarshorepower
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4 Answers
JohnC avatar image
JohnC answered ·

Hi @RalphD

The mppts will have priority when their target V's (Absorb and Float) are reached, if you have the Multi's just slightly lower. 0.1V (even less) is usually enough, but best to invoke DVCC to ensure they're seeing the same V reading.

The difficulty here is when the mppts Float and Multi is still in Abs. Consider setting the Multi to a flat Float, no Abs cycle. It will still charge when on it's own, just slower.

And it's also possible to shut the Multi down at (say) a certain SOC point, so that the solar has something to do. Ask if you want to try this.

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ralphd avatar image
ralphd answered ·

Thank you @JohnC ,

I will try lowering the Multi's voltage and invoking DVCC. I do have a question about the DVCC. Presently I have a "Smart Battery Sense" mounted to the battery to monitor voltage and temperature for the MPPTs. I also have the thermocouple from the Multi and the wired voltage sense connected to the Multi. In DVCC mode, which voltage and temperature sensors are used?

One other question, each morning the MPPTs start a new cycle and go into Bulk followed by Absorb. Is there a way to prevent the daily bulk? I am concerned that the daily Bulk charge may reduce the battery life.

Thanks again,

Ralph

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JohnC avatar image JohnC ♦ commented ·
@RalphD

DVCC has 3 parts, select as required. SVS for V, and it picks the Smartshunt by preference. STS for Temp, and there you get a choice. But your SBS may not be compatible, and frankly, do you need it?

SCS can also pass across shunt Current to the mppts, and I find it great to terminate Absorb with the mppt's Tail function (provided it's below 10A). See the Cerbo manual for DVCC stuff in general.

The morning Bulk phase is just a passthrough stage on the way to Abs. Unavoidable. The only danger from it is too much charge current, and you can limit that anyway, either in the mppts or with DVCC too if you have multiple charge sources.

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looknow12 avatar image
looknow12 answered ·

I've been trying to figure that out too. Spent a lot of time researching and today tried for several hours. There are a few thoughts out there.

The one thought I finalized on but didn't work is to add a virtual assistant https://www.victronenergy.com/live/dc_coupling:prioritize_solar but I could not get it working. Using VECONFIG I set it up and then you select a policy. All but two are deprecated. I tried the two and I could not get any AC power, I received a Error 6 - Error in DDC Program.

Ideally, the solution, which might not exist in Victron's firmware, is to dynamically limit the AC Input based on the solar and based on the AC Demand.

I.E. If the AC demand is 2000 watts and we have 500 watts of solar, limit the AC Input to 1500 watts. If the Solar is 1500 watts and demand is less than that, switch to Inverter.

I don't think anything can be programmed to do this.

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stevenebraun avatar image
stevenebraun answered ·

I experienced the same problem with my motorhome. There was 1000W of PV on the roof, 400A of Lithium batteries, and a Magnum MS2012 inverter/charger. How to prioritize the PV over shorepower? Whatever source has the highest voltage wins. Even though the voltages on the MPPT were always higher than the charger, the big problem always occurs when solar drops off. The Magnum took charge and stayed that way until the charger was power cycled. Eventually solved the problem by installing a PLC and program. It constantly checked for adequate PV input and battery SOC. If the SOC was OK and enough solar, the PLC switched off the charger. The motorhome would run on battery/inverter until low SOC or inadquate solar. Worked well for years and rarely did the motorhome reach low SOC.

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