The charge time principles (see charging page) are the same for solar except solar means it will charge if we have sun. That makes it free to recharge and the more solar you can have the better. You cannot have too much solar as any excess current from the solar gets sent off as wasted heat if you can’t use it all.
The amount that solar can charge the batteries is dependent on :
1. How many watt solar panels you have
2. What size amperage the regulator is.
3. Cabling used to connect it all together.
Solar can have some downfalls though.
1) lying panels not directly in sunlight such as on a roof, makes them only %70 efficient. Therefore 300w panels are in fact only capable of charging at 210 watts and
2) If it’s cloudy you’re limited as they won’t generate as much electricity.
3) The solar regulator is what controls how many of the panel’s amps goes back into the batteries. They come in different amp sizes but average around 15 to 30 amps sometimes up to 60 amps.
4) Sunlight hours is not daylight hours, the average sunlight hours in Mackay QLD is 5.8 hours. So having 300w panels that only work at %70 efficiency means, if we had 6 hours of usable sunlight they can deliver 105ah in 24hours.
If we use over 104 amp hours a day which is roughly 4 amps a hour then 120ah batteries will progressively get flatter every day. (note: our fridge uses 3.5amps per hour so 4 amps will easily become exceeded)
If the above explanation confuses you then the following is real-time, “yes I’ve experienced it” Data
600watts of solar on the roof
Redarc manager 3.0
The Redarc Manager has a built in 30amp solar regulator. This is twice as big when compared to the Jayco standard 15amp regulator.
3 X 120ah batteries totalling 360ah which equates to 180ah useable
1 x 120ah battery in the back of the Ute for consumption hungry appliances
By 7am in the morning when we get out of bed the Redarc Manager shows our battery levels at around the %87 mark. This means we have used roughly %13 of our 180ah since approximately 5pm the previous night. Keeping in mind that after 5pm is when the solar charging tends to die down. (QLD timezone).
To break that down further:
13% of 180ah is roughly 24ah
What used that 24ah in the 14hour period overnight is generally:
A couple of LED lights on until 10pm
12v TV on for 4 or so hours
218 Litre Waeco compressor fridge running
Occasional water pump usage
2 x Charging phones
2 x Laptop charging
The actual largest consumer in the above list is the Waeco fridge. It runs at about 3.5 – 4 amps during the day when it’s running (guessing 30 minutes in an hour). The 12v TV appears to draw 2amps when running and LED lights about 1amp each the rest in the list are negligible.
So over night when it’s not so hot the fridge runs very little. There’s generally not much else operating so overnight there is very little draw on the batteries.
How long for batteries to charge ?
At around 7am when the sun starts coming up our 600w of solar actually start to do their job, (all be it a small amount). Keeping in mind while writing this we are not being frugile with our electricity. By lunch time our batteries are usually back to %100 charged. So between 1pm ish and 5pm whatever we use in electricity generally doesn’t have a effect on our battery levels. This is because the solar during the peak hours of sun keeps up with what we consume.
As you may be able to tell, the setup we have is working out great for us and our habits. Although we do keep in mind leaving lights on etc. Un necessarily, we don’t get all paranoid about it for the meantime. This adds to the relaxing nature of full time caravaning.
Now you may think to yourself, 3 x batteries seem way too much if you’re only using %13 overnight. So I’ll just go with 2 x 120ah batteries or less. Well that’s fine for you but also keep in mind cloudy days, parking under shade, the solar covered in dust. The extra battery is a good re assurance.
We also have a 4th 120ah battery in the back of the ute. This is charged by a DC DC converter and recently also a solar panel on the roof of the ute. It basically runs our high consumption devices from a 2000w inverter such as our 1100w coffee machine. Because it’s all about priorities right ? 🙂