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xtopher avatar image
xtopher asked

Is this setup possible with solar and batteries

I'm wondering if the possible setup/config is possible, I'm doubtful and someone has asked me and I'm curious of the answer.


Say you have a solar array and battery. I want the battery to charge overnight on the cheap rate (7.5p/kWh) and power the house loads all the time. I want solar to export all generation as I get paid 15p/kWh for export. So regardless of the house load, I want solar to export, not satisfy house load or charge the battery. I want battery to match the house load and discharge during the day, even when there is solar.

I appreciate this is an odd setup but I have a tariff where import is 7.5p/kWh and export 15p/kWh.

I'm thinking most setups could not achieve this but MPII and cerbo, with the right monitoring could see the house load and add that to the solar output as 'export' which the house will take part of and the rest will go to the grid. I appreciate you're limited to the AC output of the MPII (say its a 5kVA and you have more solar than that, it will still send some DC to the batteries to charge which makes sense)


Can it be made to work?!

Multiplus-IIcerbo gxMPPT SmartSolar
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Alexandra avatar image
Alexandra answered ·
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xtopher avatar image xtopher commented ·
I did think about the D-ESS, but its not quite what we're after. It decides whether to export or import energy based on prices, it doesn't stop the battery being charged by solar AFAIK? Pretty similar outcome but not quite. Probably close enough most people would accept it.


I did try to set it up for my situation but for some reason it wanted to use battery power in the cheap rate rather than using grid alone. Also seemed to use predict it will use grid in the afternoon when battery and/or solar would mean its not needed. I need to have more of a play with it. Annoyingly it also doesnt do half hour slots which we have in the UK.

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Michelle Konzack avatar image
Michelle Konzack answered ·

You sayed:

overnight on the cheap rate (7.5p/kWh)

but what is your day rate for the power consumption at day time (or outside if the cheap overnight rate)?


I have already calculated this with some customers and it is definitively not rentable, even with the cheapest batteries you can get.

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xtopher avatar image xtopher commented ·
Its ~30p. I forget the exact number as I can run purely on off-peak/battery/solar so never get charged for peak rate.
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lifeingalicia avatar image
lifeingalicia answered ·

Hi probably - scheduled load over night (no battery usage).

During the day negative grid set - equivalent to solar production.

Need a piece of software (node red) or so to reset the grid set permanently.

But cost of Kw/h bat around 7cent plus Kw/h load 7.5 cent not much profit margin....

M

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xtopher avatar image xtopher commented ·
Agreed.


My thinking was with NodeRed you could monitor house load and set the export margin constantly to be house load + solar assuming the combination would be less than the inverter max AC output, any extra from solar would then just stay as DC and go to the house and/or batteries - better to generate and charge the batteries/power the house than derate solar for the sake of it.

I was just curious if it was possible in a default setup without NodeRed constantly tweaking it for us.

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