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anestis avatar image
anestis asked

What is the best size MPPT for my needs?

Greetings,

I am trying to design an off the grid solar system for a small and remote house and I am very new to solar power. After reading a lot of review and doing some research I’ve decided to use Victon BlueSolar MPPT for Charge Controllers and Victron MultiPlus for an Inverter.

My daily consumption is 6KWh. I will be using six LG400N3K-V6 panels. Because the panels in the array receive tree shade at different times in the day I have decided to separate them in three groups. Each group will have two panel connected in series and then to their MPPT charge controller. So I will use three MPPT charge controllers and the output of each charge controller will go through its own breaker in parallel to the battery.

The Panels have a Pmax of 400W, Vmpp of 37.2V and Voc of 45.2V . Also Isc is 11.16 A. For low Temp Voltage I added another 5V. So my Voc for low temp would be about 50V. For the two panels connected in series 100V.

I have not settled on the system’s battery yet but I am considering the BYD Premium LVS 8.0 . The Battery Nom Voltage is 51.2V but the Battery Absorption Voltage is 56.5V.

For the inverter I decided to use Victron MultiPlus 48/5000. It would give me flexibility for connecting an A/C source (Wind Turbine or Diesel Gen) to the system in the future.

My question is about what size charge controller is the correct size to use. Would the BlueSolar MPPT 100/20 be suitable for the job or should I go with the BlueSolar MPPT 150/35.

Any input and advice would be very helpful and much appreciated.

Best regards

Anestis

MPPT Controllers
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ejrossouw avatar image ejrossouw commented ·

I'd recommend https://www.victronenergy.com/mppt-calculator as it takes into account temperature etc.

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seb71 avatar image
seb71 answered ·

Do not use a 100/xx solar charger when you have string Voc=100V.

Get a 150/xx solar charger.


Also, better get SmartSolar MPPTs and not BlueSolar MPPTs. You can set them up with a phone (no extra hardware needed) and you can also use VE.Smart Network for better functionality (although for larger systems, a GX device - such as Cerbo GX - will give you much more).


Depending on how much Sun hours and clear skies you have, a 2400Wp PV array might be too small for your daily 6kWh needs, especially in winter and with the shading issues you mention.

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anestis avatar image anestis commented ·
Hi seb71,

Thank you for your answer. I do agree with you, the 100/xx would be right at my limit of max low temp Voc of 100V (for two panels). I am leaning towards the BlueSolar MPPT 150/35 but I am a little confused on deciding the correct Amp rating. Is 35 OK for my need?

Also the Sun hours are plenty where the system will be used and most of the year it is clear sunny days. But I do have some tree shading going on at some locations at certain times during the day but not much. Also the 6Kwh is on the very upper side that I'll be initially using. In reality it will be closer to 5Kwh and when my load requirements increase in the future I can always add another (two panel with Charge Controller) string to the system. What do you think about using the BYD Premium LVS 8.0 for battery in such a system? Any better choices?

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seb71 avatar image seb71 anestis commented ·
For each of your 800W PV arrays (2x400W PV modules), when used with a 48V (nominal) battery, you need a charger which can output about 15A. But the smallest 150V MPPT charger from Victron is 150/35 (you could connect a 2000W PV array to it). The upside is that it will run cooler with only 800W.
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