24v Solar help needed

[HazMan]

Hello Brains Trust,

I have been quiet of late, just working and enjoying the truck on long weekends this year.


We are heading off to Tasmania in a few weeks and I am wanting to install some solar panels to charge the 24v camper batteries. Previously all our trips have involved longer drives per day and the camper batteries have been charged sufficiently by driving, but because we will camp more and travel less in Tassie, I was thinking that it's about time for solar.

I have 2 x 150ah deep cycle batteries running a 24v setup in my camper and currently run a voltage sensing relay to charge them. Could someone please advise what would be a good and not too expensive solar set up.


Thanks,

Sean

P.S. I've been looking at the Redarc BCDC2420
https://www.redarc.com.au/in-vehicle-battery-charger-24v-20a

 

[gait]

I have Victron MPPT regulators. Just replaced framed solar panels with semi-flexible panels built from sunpower cells - roof 75 kg lighter. I imported direct from China but available (at higher cost) in Aus. Avoid the eBay semi-flexible unless you really know what they are.

Connect regulator to battery in parallel with whatever connection from vehicle battery you currently have. If there isn't an isolator in that connection add one. Parallel connection charges solar AND engine, DC-DC with MPPT chargers typically are solar OR engine.

How much solar depends on what appliances. Calculate a rough energy balance. Do you currently have SOC meter on batteries? If so read how much you use every day.

Is that 2 x 150Ah @ 12v in series or 2 x 150Ah @ 24v in parallel? Big difference.

While the sun is lower in the sky in Tassie there's more daylight hours at that time of year. Sort of compensates a bit.

 

[HazMan]

Thanks Gait,


I have 2 x 150ah 12v batteries wired in series to produce 24v.

I will have a look for those solar cells and that regulator.

Is it OK to have both the solar and engine charging the batteries at once?

Sorry for the dumb questions.

Sean

 

[gait]

yes, okay to have solar and engine charging at same time ......... once at absorption the volts will be the higher of the two sources, the other source reduces output.

from battery size its likely you may need 400 - 600 W of solar. Depends on energy use.

 

[HazMan]

Excellent, thanks for the advice.

I'll do some researching online tomorrow afternoon and see what the cost will be.

 

[HazMan]

Ok, more dumb questions....

There are many different Volt and Amp solar controllers, if I install 3 x 200w solar panels for 600w will this controller be OK or too big or too small?

Victron Energy BlueSolar 100/50 MPPT Solar Charge Controller 12V/24V

https://www.ebay.com.au/itm/Victron...034018&hash=item3f4d0b58d3:g:fy8AAOSwLvxbtBVP


Also, are these cells OK?

https://www.ebay.com.au/itm/SUNPOWE...332337927354?_trksid=p2385738.m4383.l4275.c10


Thanks,

Sean

 

[gait]

Solar Regulator is good. It will limit output current to 50 amps. Which at 24v is 1200 watts.

Read earlier post that said "Avoid the eBay semi-flexible unless you really know what they are."

The first thought on looking at the eBay link is the obvious conflict between heading and picture. They are not sunpower cells. Sunpower cells don't have stripes (conductors) across them.

Second thought is a look at the specs. The watts/m2 exceeds anything I have seen generally available. kg/m2 is at the low end.

They will probably work, I would be very surprised if they produced 200W, how long they will last is anyone's guess, some of the eBay panels warn against parallel or series connection these don't but also don't have spec for max system volts .....
there's probably a reason they are $0.65 / watt ..... If something seems too good to be true ...............

 

[SkiFreak]

As Gait has pointed out... the 100/50 Victron regulator would be fine, but unless you plan on expanding your solar capacity in the future, that model might be overkill for you planned installation.
A 100/30 or a 150/35 might be a better fit. BTW... the 150/35 is a really nice unit, and unlike most of the others, it is an all alloy enclosure.

 

[Neil]

Dont forget thatcas your in 24v the voltage output on the panels either in seiesxor parrallel is also critical. Your array needs to produce near 35 volts or above in whatever setup you have

 

[dwh]

A cell is the little black glass square. A bunch of cells strung together in a common housing is a module - also called a panel.

The flexible panels you linked to on eBay have a working voltage under load (Vmp - Voltage Max Power) of 17.8v (at 25C temp). The voltage will be somewhat less as they get hotter.

To fully charge a 24v battery bank you have to push it up to nearly 30v, and as Neil noted, you need some overhead above that. This is why modules in the "24v nominal" range (I.e., to charge a 24v battery) are built to have a Vmp of around 30v - 36v (depending on who made it).

Thus, those panels you linked to, having a Vmp of 18v, are in fact "12v nominal" panels.

Which is fine, but rigged in parallel, the "array" would operate at 18v, which is not enough. So they would have to be rigged in series. Those panels have a Voc (Voltage Open Circuit (no load)) of 20v, so three rigged in series would have a no load voltage of 60v, which is well below the 100v max of the Victron 100/30 (I myself have a 100/30 with a 300w/36v panel).

The max amperage those panels are rated to produce is 11.2a, so three of them could produce 33.6a at 18v (rigged in parallel). That would technically exceed the 30a max of the 100/30. However, again, the cells in the panels are glass and dark in color and facing the sun - they will almost always be hot and when hot they produce less. Even in perfect conditions, having a 30a limit would only shave off around 10%, and 99% of the time that wouldn't happen anyway.

But that's rigged in parallel. Three rigged in series would have an array Vmp of 53.4v.

Under perfect conditions 600w ÷ 53.4a = 11.2a coming into the Victron from the solar. Going out to the battery at a voltage of...let's say...27v then the math is 600w ÷ 27v = 22.2a which is well below the 30a limit of the 100/30.

So for those three panels into a "12v nominal" battery, the 100/30 is adequate, with possibly an occasional loss of a bit of charging power due to the 30a limit, but that wouldn't be a problem with a "24v nominal" battery.

 

[trackadda]

as for panels have a look on gumtree or e bay and see if there are any used 250 watt house panels for sale. Most upgrades will not use the pre existing panels so you can at times pick them up for around $70 to $100 each for 2 or 3 year old panels

 

[HazMan]

Thank's guys.

As you can see I have little idea about this but am learning... with your help.

I think the Victron 100/30 is the one for me and I will have to just find some quality panels. I like the semi-flexible ones for ease of fitting and weight saving (I'm under 4,500kg and need to keep that in mind)

Gait, would you mind sending me a link to where you imported yours from. In a private message is fine.


Ok, back to reading and learning....


Sean