Can DC-coupled MPPT feed directly into power need of ACout, or only be used to charge batteries (no ESS)

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harro asked Apr 10, '22

Can DC-coupled MPPT feed directly into power need of ACout, or only be used to charge batteries (no ESS)

I have a solar panel (340W) with a Bluesolar MPPT (DC-coupled), BMV-700, Cerbo GX and Multiplus. The ACout of theMultiplus is attached to a separate network in the house which is only attached to this ACout (not mains feedback). The Multiplus can use the ACin or the inverter to provide power to this network.

Ideally, I would like to keep the batteries fully charged and prioritise the solar power to feed into that separate network (i.e. use solar power until the load exceeds the solar power and then complement with ACin or if that is useful to add power from the batteries) and only switch to the batteries/inverter during power failure.

For what I read on the Victron website, this could be (easily) achieved by installing an 'assistant' IF I would feed back into the net. However, I can not feed back into the net.

So my question is, how to achieve this situation (solar power complementing net power, having priority)?

I configured a set-up similar to described by Edphonse https://community.victronenergy.com/comments/54058/view.html using the virtual switch, but it feels like a sub-optimal configuration.

Currently I use the virtual switch to use the Multiplus as inverter until the battery voltage drops to 25V (then use ACin), or the load on the ACout exceeds 300W (and then the Multiplus also charges the batteries if needed until bulk is completed).

This sort of works but is clearly a 'hack' and power is lost by charging and inverting. Edphone also importantly notes that using this approach the batteries and Multiplus will wear quickly.

So effectively my question is whether I can use the solar power to feed into the ACout network without needing to discharge the batteries (I read in one of the posts that there is an option to keep the batteries at fully charged state, but then also the solar power input seems to be throttled back).

Or, perhaps the current set-up is still usable, but I would need to increase my solar power capacity (which is admittedly quite low) so that it would always exceed the normal load on the ACout. That is assuming that the solar power will be used for direct power and not only to charge the batteries.

Solar Panel virtual switch

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kevgermany ♦♦ commented · Apr 10, 2022 at 08:15 AM

To run off solar, the panels need to cope with your normal load. So increase in capacity is needed as you say.

Ignore AC in is probably the cleanest way. Inverter always on. Grid input will then be low and if you set a reasonable limit on the assistant, battery wear will be acceptable (depending on type, maybe 30-50% DOD). Some skillful tuning will assist. But if you want to minimise grid input, battery wear is the trade off, depending on PV capacity. And overnight use.

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Answer 1 · 2022-04-10T13:03:01Z

JohnC answered · Apr 10, 2022 at 01:03 PM

Hi @harro

To do this just set the target charge V in the mppt to very slightly higher than that of the Multi. Like just 0.1V should suffice, even less. So when solar comes on it will push the Multi's charge off.

With your batts always fully charged you may be using a flat Storage V anyway, so this becomes very easy.

I'd invoke DVCC in the Cerbo so that both units are seeing the same measured V.

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