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Mohamed Mamdouh Elkadragy avatar image

Setup of a victron off-grid PV system without battery storage

For an off-grid system setup including PV and Genset, but doesn’t have any battery storage.

  1. How would the suitable Victron components be, Is possible to use the Quattro in that case, or any other Victron inverter?

  2. Can the Easysolar solution be used in that case without a battery connection?


The loads are mainly an AC pump and some lighting loads.

system design
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4 Answers
JohnC avatar image
JohnC answered ·

The pv charge controller will also need a battery V to reference (say a Bluesolar in the Easysolar box too). Or any-ole ac pv inverter (even hybrids) will need a reference point.

You won't need a big bank, and even weak/old batts might do. But consider intermittent clouds and the effect they might have on your 'load programme'. A Multiplus or an Easysolar can buffer you through such tough patches - how well they do it is dependent on the batt capacity.

And oh, your system seems quite simple, so a Quattro (2x ac inputs) shouldn't be needed.


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WKirby avatar image
WKirby answered ·

The inverter still needs a battery (even if it is a small bank). At the most basic level, the inverter logic circuits cannot operate without DC supply. It cannot run on AC only.
Another way to think about it is if the inverter cannot "think", then the transfer switch will be open which makes the inverter completely useless, it will not even pass through.

It will be like a car with no petrol.

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Please analize the attached setup. Is it feasable?

The MPPT water heater is DIY and worked fine during this summer connected directly to the PV panels, but a lot of energy is available when the overheat protection disconnects it at 85 degrees.

In this new setup the air conditioner has the priority and the MPPT water heater is the buffer that uses only the remaining available power. It is also the reference for the inverter.

No backup (battery) is needed. It must work only when sun is up in the sky.

The only problem could be when load is disconnected and water heater also is disconnected the PV open circuit voltage (two panels in series) could reach 80V. Could this voltage make any damage to the inverter?

The ripple can be filtered with condensators?

Please don't do this, the AC has a big startup peak, capacitors won't be enough.

Also you'll damage the inverter's capacitors due to the big ripple.

Francisc avatar image Francisc Daniël Boekel (Victron Energy Staff) ♦♦ ·

Understood. No battery - no inverter. Ok but...

I want to use a battery as small as possible. I think to my car with 1,9l diesel engine. A 65Ah battery handles a few starts a day for at least 5 years. I think the power needed to start a diesel engine is much higher than the startup peak of an AC with inverter technology. So, we must solve the ripple. Look at this setup.

The water heater can be set to work in a quasi-fixed voltage regime (no MPPT). This means a very sharp characteristic, it can pull 0-85 A depending on the voltage (28-28,8VDC, level and gain are both adjustable). It behaves like a hypothetical huge 28V/2500W Zenner diode and was tested at 30V, 60V and 240V with the PV panels in different configurations, even as a string with 8 connected in series.

The battery must be a starter (car) battery (2x12V) which can handle high current for short period of time, no deep cycle needed. It is all the time charged to a maximal level (just like in the car). I think it handles the ripple better then deep cycle type batteries due to low internal resistance.

What will be the minimal capacity of the battery?

Which charger do you recommend for this setup?

Please do not hesitate to make any other comments.

Thanks.

Porcini avatar image
Porcini answered ·

I don't understand how this should work without battery. You always need a buffer if you don't use a directly powered dc-pump.

As well a Multi doesn't work without battery.

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WKirby avatar image
WKirby answered ·

No, Quattro / MultiPlus needs to work with battery.
If you do not have a battery, then you don't need an inverter.

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The inverter is needed as an intermediate device between the PV and the AC loads. otherwise, how can the AC loads be fed, and the Genset starts when there is no PV?