Additionally:
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Some panels have varying temperature coefficients which means some panels may perform slightly better or slightly worse as the temperature climbs or dips below or above the standard test condition of 25C/77F.
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It’s important to note that while the panels can operate in extreme climates, your true bottleneck is your solar generator. Lifepo4 batteries simply won’t allow you to charge if they reach an internal temperature below 32F or above 104F. This means you pretty much are only running the panels when the conditions are right anyways.
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The standard test condition of the panel is specifically rated at 77F/25C and 1000 W/m² of solar “power”. However in the peak of summer, you can exceed 1000 W/m² during solar noon, which means a “rated” 350 panel may actually produce around 400 watts of solar, an increase of 12.5%.
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The maximum theoretical power a panel can be produced can be calculated by finding its Area×Irradiance×Cell Efficiency. Keep in mind it won’t actually convert 100% into “usable” energy to the generator itself. So take my Bluetti PV350 panel. It has an area of 2.172m². The cell efficiency is “up to” 23.4%. So I take 2.172 X 1000 X 0.234 and I get 508 watts. You won’t get 100%. Say my panel loses 5% from the hot sun. It loses another 15% from internal resistance/heat dissipation and another 3% from the wiring/, this would be a total loss of 23%. This means I’m getting around 77%. What’s 77% of 508 watts? 391 watts, which explains exactly why I’m getting 390 ish watts during the peak summer months at solar noon.
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The reason why you want to know the OCV of your panel and the effects that temperature plays on voltage when its colder/warmer is specifically if want to combine solar panels in series. The solar panels will operate at slightly less power while under a load (i.e. a solar panel connected to it), but this does not matter. What matters is the initial voltage surge when you first connect it.
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For smaller units like the Bluetti EB3A/EB70S with a low VDC (12-28V), I find that most optimal setup is to run two 200 watt panels in parallel. The reason why is since you are limited to 28V and 8.5A, you want to run in parallel to combine the amperage. If I’m not mistaken the EB3A won’t even start charging until it has reached atleast 18W of input, so if one panel is running at only 15W, you will see zero/“Low voltage” error. During overcast days the amperage is very low, so combining them is the most beneficial. Here’s a video I made showcasing this benefit on my EB70S: Running Two Solar Panels in Parallel on EB70S
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Assuming the operating voltage was 18.5V the amperage would have been around 1.08A, meaning that when I ran in parallel i am now getting 18.5V X 2.16A or 40W as indicated on the generator. The maximum watts I have ever seen on my EB70S was around 165 watts. In the video above, earlier in the day when the clouds were not as thick I was getting around 65 watts for each panel, which means since I was able to take advantage of the combined low ampearge, I was able to double my capacity to 130 watts, which is 78% of its max solar charging capacity on a CLOUDY day. To give you an example, say you have a solar panel flat mounted on the roof of your vehicle and its sunny out. No need to whip out an additional panel because your EB70S will be getting enough power likely. However, if its day where its overcast, or it may be a mix of sun and clouds, you could whip out a portable solar panel and tilt it toward the Sun. The amperage of the two panels will combine to increase your input, but in the event the sun ever does peak out, your tilted panel will take full advantage and you will max out the input on your EB70S, creating an optimal configuration. The MPPT controller will simply reject any amperage above 8.5A which is the most the EB70S will allow in. So if its sunny out and each panel is producing 6A, it won’t double to 12, it will see 8.5A and reject the remaining 3.5.