Quote:
Originally Posted by ttrainxl
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.
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That is great information, thank you for taking the time to share!
I came up with my 5 hour range estimate by adding the power consumption just from the engine's essential electronics (~8 amps) to the power consumption of turning on my LED low beams (~3 amps) and the radio on a medium volume (~2 amps) for a total of 13 amps since that's a typical load for me while driving at night. According to Odyssey's data sheet, I'm looking at a maximum of 5 hours of battery life with a load of 12.7 amps, but for battery longevity and reliability reasons, I'm not going to be draining the battery anywhere near fully. Of course whatever solar power I get, using the alternator for regenerative braking, and not having to use lighting during the day will also add to my range. Anyways, range really isn't much of a problem for me since I almost never travel that far and I can always use the alternator if I do take a long trip.
You are absolutely correct about the non ideal performance of the solar panel on a car. It's rated at 50 watts and I have seen up to 44 watts out of it in ideal sunlight, but it definitely doesn't run at full output all the time. In my driveway, I'm lucky to get 25-30 watts from it a lot of the day thanks to all the trees around me. Even a tiny bit of the panel being shaded has a drastic effect on its performance.
In addition to eventually adding about 200 watts of flexible solar panels to the roof, I'd also like to try a lithium ion battery at some point. By replacing my lead acid battery with a 190Ah lithium battery, I could more than double my capacity and save about 15 pounds at the same time. I'd likely get a somewhat smaller battery though for more weight savings and a significantly lower cost since I don't need such a large capacity for my uses, especially since I could safely use more of its capacity than a lead acid battery.