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ttrainxl · 06-16-2023, 12:01 AM

Couple things. First, 250 watts at 14 volts is about 18 amps, as stated by someone else here. If your consumption is 13 amps, I’m not sure how you figure you’ll get five hours of range. Maybe adding the peak output of the panels and the reserve capacity of the battery? Second, you will never get peak output from your panels on a car. Driving in shade aside, a panel needs an absolutely perfect angle with the sun to get peak output. It just won’t happen without a sun tracker that physically angles the panels, which would cause major drag. I’d be very surprised if you ever get 10-12 amps.

On my off grid 33 foot sailboat that I live on for four to five months during the winter, I have three 100 watt panels, and while it’s enough to run the fridge and lights, I never get more than 10-12 amps from them, and I’m able to angle one of the panels. And two of them are new.

Also, a 74Ah battery is pretty darn small. My house batteries are group 31s that have a 190 amp reserve capacity. A group 24 is about the size of a small pickup truck battery and their reserve capacities are over 100 amps. And if you’re not using a Li-Ion battery, 50% discharge is a completely dead battery. So you don’t have 74 amps, you have 37 amps. A Li-Ion battery would significantly add to your range because you can discharge them to about 85-90%. For more range, add a couple more batteries.

Also, a solar array puts out amperage at any given time. When a cloud passes over, you’ll see amperage drop by 2/3 or 3/4 very often. It’s very difficult to estimate how many amp hours you’ll be putting into your battery bank. A general rule with boats is to figure your power consumption and build a system that puts out triple what you need. On my boat, on paper, one solar panel should be able to run my fridge, and one battery should keep up when it’s cloudy. In reality, three panels and 570 amps of battery power doesn’t keep up with the fridge when it’s been cloudy for four days, with the temp turned as low as it will go. And I’ve tested the duty cycle and it’s less than 50%. You’ll always have a 100% duty cycle in a car with the engine running.

I think this is a cool experiment and I wish you luck and hope I’m wrong, but I think you’ll get about 30 min of drive time in real world scenarios and have to wait all day to drive another 20 min. Unless it’s cloudy. Then you wait days on end if you can’t plug in.

Still, now I want to try it with my civic too! Haha.

06-16-2023, 12:01 AM	#10 (permalink)
ttrainxl EcoModding Lurker Join Date: Sep 2021 Location: Virginia Posts: 70 Thanks: 0 Thanked 10 Times in 9 Posts	Couple things. First, 250 watts at 14 volts is about 18 amps, as stated by someone else here. If your consumption is 13 amps, I’m not sure how you figure you’ll get five hours of range. Maybe adding the peak output of the panels and the reserve capacity of the battery? Second, you will never get peak output from your panels on a car. Driving in shade aside, a panel needs an absolutely perfect angle with the sun to get peak output. It just won’t happen without a sun tracker that physically angles the panels, which would cause major drag. I’d be very surprised if you ever get 10-12 amps. On my off grid 33 foot sailboat that I live on for four to five months during the winter, I have three 100 watt panels, and while it’s enough to run the fridge and lights, I never get more than 10-12 amps from them, and I’m able to angle one of the panels. And two of them are new. Also, a 74Ah battery is pretty darn small. My house batteries are group 31s that have a 190 amp reserve capacity. A group 24 is about the size of a small pickup truck battery and their reserve capacities are over 100 amps. And if you’re not using a Li-Ion battery, 50% discharge is a completely dead battery. So you don’t have 74 amps, you have 37 amps. A Li-Ion battery would significantly add to your range because you can discharge them to about 85-90%. For more range, add a couple more batteries. Also, a solar array puts out amperage at any given time. When a cloud passes over, you’ll see amperage drop by 2/3 or 3/4 very often. It’s very difficult to estimate how many amp hours you’ll be putting into your battery bank. A general rule with boats is to figure your power consumption and build a system that puts out triple what you need. On my boat, on paper, one solar panel should be able to run my fridge, and one battery should keep up when it’s cloudy. In reality, three panels and 570 amps of battery power doesn’t keep up with the fridge when it’s been cloudy for four days, with the temp turned as low as it will go. And I’ve tested the duty cycle and it’s less than 50%. You’ll always have a 100% duty cycle in a car with the engine running. I think this is a cool experiment and I wish you luck and hope I’m wrong, but I think you’ll get about 30 min of drive time in real world scenarios and have to wait all day to drive another 20 min. Unless it’s cloudy. Then you wait days on end if you can’t plug in. Still, now I want to try it with my civic too! Haha.