SmartSolar with low PV voltage

DIY
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1

I am orienting to buy a SmartSolar with 48V output (vbat).

I have 1 solar panel (PV) that has the following specs:

  • Open circuit voltage: 48V
  • Max power voltage: 40V

According to datasheet for SmartSolar Charge Controller MPPT 150/35 with 48V output

1b) The PV voltage must exceed Vbat + 5 V for the controller to start.
Thereafter the minimum PV voltage is Vbat + 1 V

It means the minimum PV voltage should be 48V + 5V = 53V.

How can we resolve it? With a DC/DC converter on input or on output? Is there an alternative charger from Victron?

2

The easiest solution would be to have 2 panels in series.

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3

I know but I am limited with 1 panel on roof of a campervan.

4

Using a dc to dc boost wont work, and Victron dont make boost mppt’s.

Using a higher voltage panel, or lower voltage battery are your only choices.

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5

Remember that your mpp will be around 75-80% of Voc. You could find a smaller panel with the same Icc (I closed circuit) to put in series so you get a higher Voc. Also note that the smaller (and cheaper) 100/20 charger might be sufficient for your limited pv input. It can handle 1kw pv on a 48v system. Worth checking out.

6

I have experimented with this for my systems. You can use an Orion-Tr 48/48 converter power matched to the panel they go up to 380w to boost the voltage from the panel and output that into a 100/20 with a 60V output setting. Or you can setup a small 12v or 24v battery and charge from the solar then boost with an Orion-Tr 12/48 or 24/48 into a 100/20 MPPT. You can adjust the charge current in the 100/20, it will be quite low only a few amps 5-7 max with this setup. I am going to assume you have a 400w panel you only have voltages. The second option will work best but needs lots of parts.

7

Thanks for suggestions.

I want to apply a solar of 500Wp on roof of campervan.

There are also another options.

  1. That is a high-voltage PV panel that is only available for business, but not for homeowners. Like Sunpower Maxeon with Voc=70V. I need to find out.
  2. Buy a second panel and cover it partly under the first panel. Here 60% of the area will not get any sun energy (bypass diodes activated) and the remaining will have a certain voltage e.g. 15V. Total voltage will be > 53V.
    Am I understanding wrongly for option 2?
8 
Using a dc to dc boost wont work

Can you explain why it will not work?

The following can be an example.

9

The mppt is designed to draw the maximum amount of power available from a solar panel given the varying amount of sun (power) that is available.
Under low light (or varying light) the boost controller will not be able to give a steady voltage output.

Given you can fit 500w of panels on your roof, choose a 500w panel with a high enough Vmp to suit the mppt @ battery voltage.

Or 2 x 250w panels.
Or 3 x 170w panels.
Or 4 x 125w panels.

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10

Or you switch to a lower voltage battery system. Campers usually have 12/24v for this very reason.

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11

Why won’t a dc/dc boost work? Can it be made to work? What about the Victron BlueSolar PWM?

I am trying to charge a 48V LiPO4 battery with only 40VoC. I have a dc boost, but the mppt charger only yields 10W power. Is the problem coming from the boost voltage? Can it be stabilized?

12

The greater the difference between the PV voltage and cell voltage the more effective an MPPT charger becomes because it is less constrained in finding the maximum power point. Victron has a document on this on their website at MPPT or PWM

If your PV voltage is within 5V of the battery charging voltage then PWM charging is about as effective and much cheaper.

Your stated panel and battery voltage are not the best fit for each other. As others said already, two smaller panels in series for a higher input voltage or changing to 24V battery system will avoid some of the issues

13

Two smaller panels will fit in the place too.