My first solar off grid system

[Pieter Blackie]

What is the orientation of your panels?

also remember that a PWM controller will sacrifice efficiency. I have a PWM controller in one of my circuits and the best I can get is 78% with optimal all-year orientation of a 72cell house panel.

I think using 60cell panels would work well with a PWM controller in a 24v system as the working voltages of the panels are closer to the charge voltages of the battery and hypothetically less efficiency loss.

Hi Mate I am not to clued up when it comes to solar, currently running 2 of the below panels in series they are facing east at about 20% basically lying on the roof at the same angle as the roof?
Cheap 350w ebay panels I bought
max I currently get is about 7A

 

[pollenface]

If you have an Android phone you can download an app called Optimal Tilt for PV which can give you an ideal orientation and based on your location.

It is strange that those panels don't specify short circuit current or current at maximum power point, which most panels usually would. Maybe they are suss. I don't think they're true 350w as they're roughly the same size as my 250w panels (120×100cm).

I have a collection of cheap ebay panels but haven't scored a bad one yet. My oldest is about 11yrs and still going strong.

 

[wattmatters]

It is strange that those panels don't specify short circuit current or current at maximum power point, which most panels usually would.

I think they would be lucky to be 350W for both panels. 18V is pretty low max power voltage. I would expect 350W panels to be closer to 35V.

With a surface are of 0.9m² these would be about half of what is required to generate 350W in good solar conditions. They are more like 180W panels.

As a rule of thumb, a good solar panel can convert ~20% of the light hitting it to electrical energy (assuming a load is present). Less if it is hot or not such a good panel.

Under good insolation conditions (i.e. sun high in the sky, no cloud/shade) you can expect about 1000W/m² of light energy hitting the Earth's surface (and less if the sun is at a lower angle of inclination, and of course much less if it is cloudy).

So under good insolation conditions each 1m² of panel can generate up to ~200W of electrical energy. Less if the sky is not clear, there is shade, the panels are hot or the sun is not high in the sky and the panel surface is normal to the direction of light rays.

 

[solarguy101]

Nice work on your first project. I did my first one this year as well. Looks like you are somewhere in Australia or perhaps NZ (just going on the style of AC power outlets).


I think your primary problem is the batteries.

According to the specifications of those batteries, they are NOT designed to operate in series. 12V operation only.

Connecting them in parallel in a 12V system is fine but not in series to create a 24V, 36V or a 48V battery. Their BMSs are not designed for it (most likely a mosfet voltage rating issue).

To put 12V LiFePO4 batteries in series requires batteries with an internal BMS designed for operating in series (most are not). In general you are better to buy a dedicated 24V battery as it will be designed for it.

Unfortunately you are about to find out that LiFePO4 batteries designed for 24V operation are considerably more expensive than two of the Kogan specials you have.

To keep costs down you may want to consider building your own from 8x individual LiFePO4 cells with an 8s BMS. Just like Will does in his videos. Or buy a pre-built 24V battery from China via Alibaba / AliExpress but that comes with purchase risk as is often discussed on here.

Looking at your set up (you are way better at constructing things than me), it looks like you have a battery DC disconnect/isolator switch but no battery overcurrent protection (i.e. a fuse or DC overcurrent breaker). This leaves your system exposed to BMS protection only and that's a risk. I strongly advise adding overcurrent protection for your battery. Something like a suitably rated HRC fuse in a fuse holder although at these lower voltages an ANL fuse is probably as good.

How much did you pay for Rapid X 100Ah batteries ?
thank you

 

[solarguy101]

If you have an Android phone you can download an app called Optimal Tilt for PV which can give you an ideal orientation and based on your location.

It is strange that those panels don't specify short circuit current or current at maximum power point, which most panels usually would. Maybe they are suss. I don't think they're true 350w as they're roughly the same size as my 250w panels (120×100cm).

I have a collection of cheap ebay panels but haven't scored a bad one yet. My oldest is about 11yrs and still going strong.

can i ask how do you search for panels on ebay ?
I know how to search on ebay, but I am asking about the parameters

thanks

 

[wattmatters]

How much did you pay for Rapid X 100Ah batteries ?
thank you

You might be thinking of someone else. I don't have any of those batteries.

 

[Pieter Blackie]

How much did you pay for Rapid X 100Ah batteries ?
thank you

Bought them from Kogan and paid $279 each

 

[pollenface]

can i ask how do you search for panels on ebay ?
I know how to search on ebay, but I am asking about the parameters

thanks

If they don't show all the specs in the product description I don't touch them
here's an example
No VOC, No IMP, No ISC, Smaller, Lighter, More convenient - because they're not 350watters.

My old man got a folding panel for camping claiming to be 140w and smaller, more efficient - it turned out to be about 80w.

 

[solarguy101]

If they don't show all the specs in the product description I don't touch them
here's an example
No VOC, No IMP, No ISC, Smaller, Lighter, More convenient - because they're not 350watters.

My old man got a folding panel for camping claiming to be 140w and smaller, more efficient - it turned out to be about 80w.

thank you for sharing that about things to look for