Solar Tips and Tricks

[stewie110]

Hi All,

I am relatively new to Solar power while camping. So I thought that I would start a thread where people could offer some of the data, ideas, tips that they have from running their solar setup's in the bush.

The driver for this was the learning curve that I had despite reading significant volumes I found that the practicalities often differed from the manuals and real world use that I got. Possibly if the thread takes off it could become sticky.

I've have a cheap ebay 120watt folding solar panel that came with an MPPT regulator from a reputable brand for a few months. I have it hooked up to my trailer to keep the batteries charged and running the fridge which I generally use as a freezer set at -8c. The battery is a 120ah AGM. I have done two trips and wanted to share my experience.

First discovery was that not all MPPT regulators are created equal. I am sure that for many people that is a no brainer, however despite the unit coming from a reputable brand it seems to be pretty crap. How did I come to this opinion?

I bought two 120 watt folding panels from the same ebay seller both came with the same regulator, panels etc. I used mine to connect up to the trailer via the regulator and the other one my mate bought from me. He connected his up without the regulator going via a Redarc BMS. Over 10 nights camping in late November in central western NSW with perfect all day direct sunlight his batteries remained at a stable SoC with the same fridges. On my setup the MPPT regulator would stop charging until the batter dropped down to under 90% charge (as measured by the magic inside the regulator) and would then kick back into a charge cycle and fill up the batteries. The problem with this approach was that at the end of the day if the battery had not gotten down to under 90% after it's last charge/drain cycle it wouldn't kick back in and the battery would be pretty low the following morning. That left me with little confidence that if the weather was crappy I would have enough sun to bring the battery back up to full or close to full charge. It seemed like a daft design (but not being an electrical or battery expert It could be a deliberate battery health idea). Following on from this comparing with the BMS system in my mates setup during the day once the battery was charged the solar system could sustain his fridge directly with no battery use. Same fridge, same temperature, same solar the only difference was the regulator vs BMS.

I would be interested to know what people's experience is with MPPT regulators and if the above experience sounds about right?

Over the 10 nights camping my median Wh generation was ~450 with the highest day being 635wh which got the battery to 95% before dark with an external temperature of 35c.

According to the regulator the the 120watt folding panel generated 86w peak. Does that sound about right from other people's usage? That includes me moving the panels to be always in as direct sunlight as possible (possibly moved every 1 to 2 hrs during sunlight). I felt that it was pretty reasonable but I would be interested to understand other people's experience.

[PhilipA]

I have a GSL 10amp MPPT with 120W cheapo solar and 20 metres of 8 gauge cable with the MPPT near the battery and it charges even when the batteries are near full.
It will input about 6.5 to 7 amps even at 13.5 volts before it goes into float so about 87 to 94watts max.
I haven't checked total input over a day and I don't let my batteries get low so I don't know what the input would be if the batteries were low, but probably over 94 watts.
Regards Philip A

[DiscoMick]

I don't need an MPPT for my 80 watt folding panel to charge the 105 amp AGM in our camper trailer. Basically with sunshine after running the 40 litre Engel overnight it is recharged by mid to late morning and then keeps it charged while there is solar. All that's needed is a 10A regulator.

Sent from my SM-G900I using AULRO mobile app

[Blknight.aus]

. On my setup the MPPT regulator would stop charging until the batter dropped down to under 90% charge (as measured by the magic inside the regulator) and would then kick back into a charge cycle and fill up the batteries. The problem with this approach was that at the end of the day if the battery had not gotten down to under 90% after it's last charge/drain cycle it wouldn't kick back in and the battery would be pretty low the following morning. That left me with little confidence that if the weather was crappy I would have enough sun to bring the battery back up to full or close to full charge. It seemed like a daft design (but not being an electrical or battery expert It could be a deliberate battery health idea). Following on from this comparing with the BMS system in my mates setup during the day once the battery was charged the solar system could sustain his fridge directly with no battery use. Same fridge, same temperature, same solar the only difference was the regulator vs BMS.

There are 2 schools of thought (basic version) of how a MPPT regualtor should deal with battery charging.

1. charge the battery to max and then float it.
2. charge the battery and then let it discharge enough to allow bulk charging to be effective.

The latter generally is only on the kind of regulator that can provide a separate feed to the battery or the load so the solar power is put into the load first and then the remainder as well as providing load cutout Done well this can be more beneficial to the life of the battery in terms of how many years it will last but can leave you at a low state of charge if you get caught out with a cloudy day. (really good ones will let you have 14V on your load while the battery is slowly charging up from a lower voltage on the terminals. If you have one of these do all your aux battery charging for phones and the like during the day and turn the fridge way down cold while the suns pumping the power out)


the former usually relies on your low voltage cutout stuff to be handled by something not the regualtor. These just try to dump every ergatron they can or need to to keep the voltage stable at the battery float voltage. (with this setup use your batteries more at night or in the early morning for charging)

[Don 130]

From what I understand, some regulators which are supplied with ebay type panels, and which are labeled MPPT, are not actually true MPPT regulators.
Don.