how to divert excess PV energy when Solar Controller is in float mode

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daniel1957 asked Feb 12, '21

how to divert excess PV energy when Solar Controller is in float mode

I have a 48v stand alone energy system comprising 2200 AH gel batteries charged by 2 PV arrays of 5kw each.

The Victron management system comprises a 10kw Quattro, 2 x 250/100 MPPT controllers, BMV712 and Venus.

On average the batteries go 100% SOC each morning at about 10:00 and by 12:00 (midday) they are on float with PV largely not utilised.

I wish to utilise the excess energy into water heating whenever the MPPT controllers have the batteries on float.

It seems to me that the system SOC is not a good, effective nor efficient way of tripping this point.

Water heating by 230v AC is a far better method of energy collection than solar hot water collectors however the Victron management system appears to not cate for this most basic requirement!

Years ago when I operated a 10kw wind turbine, I built a voltage regulator in the DC turbine output that would divert raw DC output (prior to the battery charging regulator) from the alternator into a water heater. I had it set up so I could adjust it from 58 - 62 v. It worked brilliantly and helped to keep an even load on the turbine thus saving it feathering the blades in strong winds.

Surely the Victron MPPT controllers should have something similar with suitable hysteresis parameters triggered by the float condition?

Hot Water Diversion

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Elimac answered · Feb 13, 2021 at 12:43 AM

If your MPPT chargers have relay output, you can use it to change state based on charge state. Check with Victron connect, option relay -> relay mode: float or storage state.

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Answer 1 · 2021-02-13T02:22:31Z

JohnC answered · Feb 13, 2021 at 02:22 AM

Hi @Daniel1957

I agree that ac heating is the way to go for you, and Victron actually caters for it very well. But rather than the mppts, look to your Quattro: https://www.victronenergy.com/live/assistants:start

The difficulty 'bleeding' ac is that it's either on or off, and if you have a massive heating element then you can get hysteresis on your batts. Your challenge will be to deal with that, and frequent switching might best be done with an external SSR driven from (say) K1 relay in the Quattro. Else you could even use ACOUT2.

I'm not the person to preach how to use Assistants, but I use one to bring in a secondary battery charger when the primary bank is under full charge. I already have the ssr, all I need now is more pv and an ac hot water unit, and I'll be there too.. :)

What you're after is akin to auto starting a generator, but in reverse, And that could be done too. But you've plenty options to try, and a great existing setup to kick you off.

To do this properly is somewhat of a holy-grail for offgridders, and we'd love to hear how you go with it..

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Answer 2 · 2021-02-19T06:40:35Z

daniel1957 answered · Feb 19, 2021 at 06:40 AM

yes thank you.

both my Victron 250/100 MPPT solar controllers have relay functions.

I have found on page 18 of the manual that I can programme the relay to trip on float charge state which is exactly what I need to dump PV energy when it is not being utilised anyway.

On page 19 it mentions that the "minimum closed time can be programmed to a minimum time as well.

This therefore will do everything that I need.

Now I need to set up a WiFi smart control system as my battery room is located 100 metres from my house where the hot water energy dump through 230vAC will occur.

I have found "Shelley UNI" WiFfi smart modules selling for $25 each.

this is getting very interesting!

We just need to wait for decent low cost battery storage......but that may not occur in my lifetime!

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