Good day, I am fairly new to this forum. Journey with a simple 12V battery and Mecer inverter a couple of years and when I damaged the lead acid battery, it was time to start building something a bit bigger.

 

Currently my setup is as follows:-

4 x 445W Canadian Solar panels

KODAK Solar Off-Grid Inverter King with UPS 5kW 48V

REVOV Lithium R100 5.1kWh 51.2V 2nd Life Battery

Raspberry Pi with Solar-assistant

Home Assistant, various IOT devices, including a few switched to automatically disconnect things such as the tumble dryer when load shedding kicks in.

 

My panels are on the eastern side of the roof and what I would really like to do is add a few on the western side for the late afternoon sun. Long term, I plan to upgrade to an inverter with at least 2 MPPT trackers, but was wondering whether an automated DC transfer switch or dual input, single output MPPT tracker could be used in the interim. Or any other smart suggestions would be welcome too:-)

 

Regards,

Heine

Heine, switching high power DC is not so easy.  I would not recommend an electro-magnetic relay due to DC arcing.  Did you maybe see a post someone did about 2 weeks ago where he was using a total of 4 solid state relays?  He included a wiring diagram.  I think he had exactly your problem.

Solid state relays are plentiful for AC applications.  DC SSRelays are not that common and they become expensive.  The problem is that for DC the switching voltage is limited.  So he used two DC relays in series.  I am not so sure if that is a good thing.  You need to switch at EXACTLY the same time.  And there is no zero-crossing point you can wait for, like in AC.

At the end of the day, it might be best to invest in a separate MPPT battery charger that you can sell at a later stage again, rather than buying a lot of solid-state relays and other hardware that will not exactly be cheap.  You are less likely to sell second hand relays and other bits and pieces for a decent price.  However, a MPPT will not be cheap.

If you do decide to use an electro-mechanical relay you will need to put a snubber across the contacts to try and limit the arcing.  A snubber is a capacitor and a resistor connected in series.   Obviously the relay contacts will need to be rate for the voltage and current you intend switching and allow a large safety margin.

Let's see what other people have to say.

I think that sort off confirms what I have been suspecting. Buy the larger inverter and sell the old one. Thanks.

Have you run it through an online solar calculator what the difference in generation would be if you simply increase the number of panels on the East side?

Obviously that will give you still a skewed profile towards production in the morning, but maybe there's enough production overall, and maybe it's an option to divert the money for a new inverter towards an extra battery?

Not saying it's the right answer, just a random thought on another option to consider.

Thank you GreenFields, just adding panels on the east side is also something I have considered, it is just that the 455's are now discontinued so part of the thinking was to add 605W x 2 on the other side.

8 minutes ago, heine said:

Thank you GreenFields, just adding panels on the east side is also something I have considered, it is just that the 455's are now discontinued so part of the thinking was to add 605W x 2 on the other side.

Makes sense, but just double-check your plans for 2 x 605W panels against the MPPT specs on the inverter.  Your Voltage may well be too low on that string to start up the MPPT if it's the typical high-voltage input type.

1 hour ago, heine said:

I think that sort off confirms what I have been suspecting. Buy the larger inverter and sell the old one. Thanks.

@GreenFields

Gave good inputs to take note of. 

The easy way is to supply the maximum current MPPT can handle as well as the maximum MPPT Voltage. 

Also how are your 4 panels connected series/parallel on the eastern side. 

If you can have the panels on the western side to the same or close to the Western side you can just parallel the 2 sides if the MPPT can accept it. 

It is also very easy to add  R1500 external MPPT of say 30A and you can then use this 54Vx30A=1620W to directly charge the battery. Ensure this MPPT can take the voltage based on how you are going to connect the new panels. Some of us have increased the lower voltage Axpert PV input this way. 

Edited April 6, 20231 yr by Scorp007

@Scorp007  Where do you buy your R 1500 MPPTs?  For R 1500 you can't even buy a decent 12V 8A lead acid battery charger.

I know that Victron is top end stuff, but they seem to go up in stages of current and in stages of voltages.  I am sure that many of Victron's MPPTs and other equipment such as inverters are of a common design and often will use the same PCB with just slightly beefier MOSFETS to take higher current / voltage.  Then charge R1500 more, just because it can handle 10A more, yet basically is the same.

I have seen other manufacturers follow similar trends, albeit at lower prices than the Blue boxes.

If you consider the above, you really do realize what you mentioned earlier in a different post.  Axpert inverters are excellent value for money, considering all the stuff crammed into those boxes.

26 minutes ago, Modina said:

@Scorp007  Where do you buy your R 1500 MPPTs?  For R 1500 you can't even buy a decent 12V 8A lead acid battery charger.

I know that Victron is top end stuff, but they seem to go up in stages of current and in stages of voltages.  I am sure that many of Victron's MPPTs and other equipment such as inverters are of a common design and often will use the same PCB with just slightly beefier MOSFETS to take higher current / voltage.  Then charge R1500 more, just because it can handle 10A more, yet basically is the same.

I have seen other manufacturers follow similar trends, albeit at lower prices than the Blue boxes.

If you consider the above, you really do realize what you mentioned earlier in a different post.  Axpert inverters are excellent value for money, considering all the stuff crammed into those boxes.

I bought my 20A Epever from Thesunpays @ R1300. Every possible setting for any battery including lithium via PC cable. Communica also have some great MPPTs from time to time. 

This at Itnerfricashop. Prices are changing all the time. 

 

Just compare:

Victron 100V/30A 12/24V solar controller R4000

EPEVER/Tracer 150V/50A 12/24/36/48V R4000

My choice the 2nd product anytime. 

12 hours ago, Scorp007 said:

Just compare:

Victron 100V/30A 12/24V solar controller R4000

EPEVER/Tracer 150V/50A 12/24/36/48V R4000

My choice the 2nd product anytime. 

A big plus is you can scale the Epever MPPTs by using them in parallel after one puts the same settings on each one. 

Hi Heine,

I second Scorp007's proposal to just put an array panels on the Western side to a total of similar Volts of the Eastern array and parallel to your single MPPT.

Just confirm midday Amps will not exceed max allowed. Cost of separate charger and/or switchgear is better invested in more panels.

Thank you everybody for the input. I learned quite a bit. I really liked the EPEVER suggestion @Scorp007 made. 

I think however I will start with adding a few more panels on the east side as @GreenFields suggested and wonder whether anybody has tried mixing and matching different brands. As I mentioned, I have four Canadian Solar 455's and Seraphim 460W panels may be a close match I thought. Any thoughts?

25 minutes ago, heine said:

Thank you everybody for the input. I learned quite a bit. I really liked the EPEVER suggestion @Scorp007 made. 

I think however I will start with adding a few more panels on the east side as @GreenFields suggested and wonder whether anybody has tried mixing and matching different brands. As I mentioned, I have four Canadian Solar 455's and Seraphim 460W panels may be a close match I thought. Any thoughts?

I have 5 different makes bought at different times. 4 makes in series so they will perform as good as the worst one. I could never see any lower PV per panel from the start when I only used 2 of the same make. 

No problem adding the new panels even as a different make. 

46 minutes ago, heine said:

Thank you everybody for the input. I learned quite a bit. I really liked the EPEVER suggestion @Scorp007 made. 

I think however I will start with adding a few more panels on the east side as @GreenFields suggested and wonder whether anybody has tried mixing and matching different brands. As I mentioned, I have four Canadian Solar 455's and Seraphim 460W panels may be a close match I thought. Any thoughts?

Double-check the Voltage and current parameters between the two panels. As long as Imp and Vmp are very close, you should be fine and it should be hardly noticeable. Problem would be if one of the panels produces max power at a significantly lower current, because then it will restrict the current through the entire string.

3 minutes ago, GreenFields said:

Double-check the Voltage and current parameters between the two panels. As long as Imp and Vmp are very close, you should be fine and it should be hardly noticeable. Problem would be if one of the panels produces max power at a significantly lower current, because then it will restrict the current through the entire string.

If the east is one string and the west string is in parallel into the same MPPT one can ignore the current. Each string will produce what it can. One will just keep each string the same panels or closely matched. 

Voltage for the 2 makes need to be seen but even if they are different by a volt or even 2 is not that bad at all. 

Short update... I sourced 2 x 545W panels which should be on their way shortly and just purchased an EPEVER 30A MPPT as per @Scorp007's suggestion. I will feedback some more once it installed.