Is My 2025 Solar Charger Malfunctioning?

This sounds like questions you should be asking the dealership or Toyota help line.

I'm averaging around 4.0 Kwh/mile in a gen4, don't know what your larger, heavier gen5 is doing. Toyota is always optimistic on it's display; but when you manually average everything out, you can see the actual vs Toyota's reporting. You'll need to do some math, rather than rely on instrument cluster projections to get the true story.

 

is 10 kwh the available energy, or the total battery?
are the charged miles and % on the same screen?

 

I've got a '24 with the solar roof and have made similar observations. It’s definitely elusive, and no doubt the miles gained metric is just a user-friendly estimate.

Toyota likely only knows precisely how much electrical energy the solar panel collects, but can only infer how many miles that might translate to. Hopefully it's based on some calculated personal driving history. But who knows and over what time period might it be averaged?

Given that the solar panel only charges the EV battery when the car is off, and while driving it helps power 12V accessories (which indirectly improves EV range), you can only wonder how does Toyota tally and report this data on the display and elsewhere as miles. Perhaps the Toyota marketing department was involved?

 

You can get a cheap short-term subscription to the official repair manual and you'd be reading the exact same things the service tech would be.

 

Sorry, I can’t answer your question about the largest solar charge increase by percentage. When I took delivery, the MID display by default showed "EV Energy Remaining" as a percentage, but after discovering I could change it to "EV Distance Remaining" in miles, I preferred that. So, I only focus on EV mile range when driving and only check the battery percentage when I begin and end wall charging.

How do I know my solar roof is working? Well, on a particularly sunny day at solar noon last month in my part of the world, I did happen to check and saw it deliver the full 185 peak watts that it’s capable of generating.

And after soaking in that sun, it's all up to the math and software processing that Toyota does with that solar energy and how they choose to feed that energy back into the vehicle and interpret and display it in all their various ways—including showing the remaining battery percentage or the mileage, in my case.

How about going back to your all-time solar stats? Take the total distance of solar miles driven and divide it by the total kWh. In my case: 128.9 miles / 28.8 kWh = 4.47 mi/kWh. That’s a number I can relate to as representative of my EV range overall.

However, if I take a short outing today as an example, the solar data says it generated 0.118 kWh of energy, which Toyota then says delivered 0.4 miles. Well, that calculates to 3.39 miles/kWh. That’s way below my actual driving efficiency (even the MID display showed the trip today at 4.1 miles/kWh, in the blazing heat with A/C running and two seats ventilating at the max).

So, there are all sorts of ways to drive yourself mad with these things, which are hidden behind Toyota’s math, software, and averaging—stuff I’ll never get to see the code for. Who knows, maybe their daily solar numbers aren't accurate?

Like, did you notice that in the past week or so, the Toyota app now shows battery percentage in a 0-100 range, whereas it was always showing it in a 32-100 range? Toyota made that change on their backend. Why? Perhaps it was wrong and now it's right (or vice versa). I understand and can live with the presentation of that percentage either way. But no need to digress talking about that any further.

Keep us posted as to your own findings.

 

Well, if the panel is only generating 185W and your burning 4.5Kwh per mile - I wouldn't expect much movement - if any on a 10+Kwh battery. Considering you'll need to generate peak output for an hour, just to get 185 whr, multiply that by 10 hours to get a single 1.8 Kwh. Assuming full output for the entire 10 hours, which wouldn't happen unless your above the arctic circle during summer months.

I don't know what your expectations are - but the math tells the story....

PS: a third of your traction pack is reserved for hybrid operations, so the ICE will kick on when you reach that level.

 

you can get warranty service at any dealer. i have to warn you though, unless they offer to look at it for free, they are going to charge you and tell you there's nothing wrong.

 

You may be able to get solar data (possibly even for free) that can guide your expectations.

You could also get a solar recorder that simply measures how much light is available at any given time and records a plot over time. Then plug in the math and you'd have a kinda-sorta guess as to how much power the built in panel is generating.

Not sure it's really worth it though, because (as LRO relates above) we really don't know how Toyota is accounting for charging losses, or how it even calculates what % to show on the meter or if they are even accurate.

What are the solar stats the car is reporting? It sounds like there isn't much point paying attention to the battery state-of-charge yet, so what data is available from the solar charger?

 

Okay, that makes it sound like the panel and charger are working as expected, but the overall state-of-charge reporting system is not quite right, much as LRO described from their experience in post #11.

I'm not sure I'd even expect to find a troubleshooting procedure for that within the repair manual, because that's an embedded software function.

Apart from that, Toyota (and many other automakers) have been criticized over the accuracy of their reporting of battery charge, whether it's the direction the needle points, the amount represented as a percentage or as range remaining. I don't know what to tell you there other than it looks like a hard problem since everyone's screwing it up.

Personally, I'm satisfied to think that "ingredients may not add up to 100%" because of rounding and smoothing errors, and that's even assuming they're doing the underlying math correctly. But then our car doesn't plug in and never displays its charge as miles or percentages: a fractional gauge is all we have in ours, and that isn't very interesting to monitor so we've disabled that in favor of a large clock and fuel gauge in the settings. We just let the magic happen.

 

I guess I'm confused. Are you, or are you not getting a bonus of 2ish miles per sunny day out of it?

From the back-of-envelope math I'm doing, "about 2 miles a day" would line up with my expectations for a PV system with a max output of 185 watts in a car that gives about 4.5 miles per kWh.

From my point of view, the problem isn't in the energy being captured, it's entirely in the way the accounting is being resolved into a percentage of state of charge and reported to you.

It's like you go to a farm stand and buy an apple for $.80. You hand the cashier a $5 bill, and they hand you four one dollar bills and two dimes and say "Here's $3.62 in change." They've given you the correct change, but they've reported it incorrectly. That's... inconvenient and unprofessional, but it's not cheating you. The bad report just makes it sound that way.

This is not to suggest that bad reports are not a problem, but it really sounds like the important part (free solar miles!) is working correctly- something to be happy about overall.

I'm sure there will eventually be other posters on the topic, hopefully you won't have to wait too long before you get more info.