question

granvillea avatar image
granvillea asked

MPPT to inverter without batteries

Hi everybody,

I'm currently searching for a way to power a load of 5A/230V with a few solar panel. According to my calculations, I should buy 4 solar panel of 360Wp, to power the 1150W needed. I want those solar panel to be connected to a MPPT and an inverter without any batteries between those two. The installation is completely PLC-controled and I want to power my load only when the sun shines. I will have a contactor to connect my load and my solar panel together.

Is it possible to connect my solar panels to an MPPT and in an inverter without batteries between ? I' do not have any acces to the electrical-grid.

Thanks for reading me,

Granville. A.


MPPT ControllersPhoenix Inverterbattery
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1 Answer
Alexandra avatar image
Alexandra answered ·

Hi @GranvilleA

It is possible but will not always be stable, it also depends on the loads you are running. Most inverters and mppts use the batteries as a reference for production and voltage stability. You are also assuming the solar panels will always out put the power you are looking for, in real world application this is not always the case.

Depending on the loads you would like to start up as well you would need some ability for surge draw, like a motor start up and would also need to wait until you are in peak production to run your proposed load, with plc I guess this is not an issue but it would shorten your day runtime.

The next consideration is that you are not using the equipment as recommended by manufacturer so most likely will be voiding warranty. That being said there are several threads on this community with similar thoughts as yours

https://community.victronenergy.com/questions/26030/mppt-without-battery.html

https://www.victronenergy.com/live/drafts:mppt_faq#q4can_the_output_of_the_mppt_be_used_as_a_power_supply_thus_without_batteries
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granvillea avatar image granvillea commented ·

Hi @Alexandra

Thank you very much, your indications are welcome and the threads you have given are useful.

In order to compensate for consumption peaks, and to have more stability in energy management, I would put a battery between the MPPT and the load. Would it be a problem to charge and discharge the battery at the same time? I imagine that the PV will fill my battery continuously and that at a certain voltage level I will be able to take energy from the battery to power my load. In this way the MPPT will use the battery as a voltage reference. I suppose I should size my battery to minimise the voltage drop caused by my load.

Is this a good solution?

Thank you for your help,

A.

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Alexandra avatar image Alexandra ♦ granvillea commented ·

Hi @GranvilleA

Yes the battery size would be important, so size it according to load, and the battery C rating as well.

The three factors we normally consider are how long the load would need to run for off the battery and what is its peak amperage draw.

In a victron ess system with inverters and mppts, if you have a good sized array the load basically does run off the solar and battery is idle. So it can be done.

As for the type of battery (agm, lead acid, lithium), consider the depth of discharge and the lifetime you expect from the system to make your choice. I guess money is also always a factor too. I am am a fan of lifepo4 as they don't mind the small charge discharge cycling many times a day and the cost per cycle is generally cheaper than other alternatives as well. They also don't mind too much occasionally not being charged up fully.

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