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.