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You aren't posting correct information, you are making assumptions that are unwarranted and therefor claim stuff that simply isn't true. Most things aren't true or false in an absolute way when it comes to complex systems, they are only true under specific conditions or when taking into account certain assumptions. Often it's easy to generalize and handwave away small details, because they don't matter for the end result we are going for. But you then can't say this is a fact and works in all cases, sometimes the details matter a lot.
When it comes to solar installations, those are very complex things. That's why you only find the resources you found, they are meant to convey a specific understanding of a complex system as it applies to the general audience. For example how many panels should I get, or how much money will I save on my energy bill if I get solar. If you go into the nitty gritty of solar installations it gets complex super fast and small details can matter a whole lot.
For example I have a micro-inverter system where each inverter doesn't take full advantage of the capabilities of my panels. However due to my location and the angle of my panels, the panels don't reach that peak capability for almost all of the year. Maybe in perfect conditions on a couple of days a year in the middle of the day, I go over the peak. I could change the angle, but that means more ballast is required for the bigger wind profile, which means I need a structural calculation done which costs money. So I opted to go for cheaper inverters, saving something like $300 on the whole installation, but that means I miss out on about $100 over the lifetime of the system in generated energy. Since that's a nett positive of $200, that's what I went with. I could have optimized a bit more to make use of the low-end of the solar output better if I went with a single inverter system instead of the micro-inverters, but that means a large device in a place that was inconvenient and the pricing calculation was tight.
The reason you aren't getting a straight answer is because it appears to be a XY problem situation (https://en.wikipedia.org/wiki/XY_problem). You are asking for something that doesn't really make a lot of sense to ask. So it's likely you are actually trying to figure out something else, have come to the conclusion this is the information you need and thus asked the question. However that conclusion probably wasn't correct, as the question doesn't make sense. So it would be really helpful if you ask the initial question you are trying to figure out and let people help with that instead.
When talking solar it would also really help if you state where about you are located on the planet and if you feel like sharing which country, as each country has very different ways of structuring the pricing of energy and that matters a lot when it comes to solar.
As posted below:
Just FYI I'mnot looking for a classic solar installation.
You all seems to base your answers on that, so obviously communication gets complicated.
I needed ballpark numbers for robotics and battery size calculations, napkin figures, to get somewhere to start off of.
I got my answer, as I edited in in the question.
Thanks BTW and sorry if you spent a lot of time trying to help me, I have definitely learned enough to set up solar panels at home on top of it all.
Alright, now we get to the real question, that's something we can help with.
How big is this robot going to be? Because to tell you the truth: solar panels kind of suck. If the angle isn't perfect and you don't have a lot of square meter, the output is terrible. That means putting them on mobile things is kind of hard. There usually isn't a lot of surface area available and almost always the angle to the sun is going to be terrible. And keep in mind they don't work in the shade. So inside won't work, in between buildings won't work, under some trees won't work, a bit of clouds and it won't work etc. So you need a big ass battery onboard to buffer energy, so the robot can charge up in the sun and then run on battery power the rest of the time. Then we get to weight, those regular 400Wp panels you were calculating with are regular roof panels. Those have a aluminum frame, plastic back and glass front. They are around 120x180 cm and pretty heavy. They are also sturdy but can break easily since they are made of glass. For mobile applications you need to look at RV panels. Those are usually flexible, rugged and much lighter. The spec you are looking for is Watt peak. That gives you the amount of watt the panel produces in perfect conditions. You can then calculate the losses you get in your situation because it won't be perfect. The batteries used in combination with solar are normally lithium iron phosphate. These can store huge amounts of energy and are very safe. Plus they last a long time and can do a lot of cycles. However they are very heavy and to get enough energy storage you need a big ass battery. They are also very expensive. For robots you are probably going to want lithium ion instead. These are cheaper, lighter and can still store a lot of energy. However they are very dangerous to work with and wear out faster. In a mobile application to prevent losses you also don't want an inverter that converts stuff from DC coming from the panels to AC. It's a lot better to stay at DC all the time, for example 24V. That way conversion losses are kept to a minimum. But you'd still want a good inverter with builtin battery charger, as the voltage coming out of solar panels fluctuates a lot. Just connecting them directly to batteries is a really bad idea. Solar panels also don't like it if you draw as much current as possible, that ruins their efficiency. Because of how they work, there is a sweet spot in the voltage and current. Be sure to get an inverter that takes this into account (keyword mppt).
Take a look at something like this panel:
https://www.amazon.com/Flexible-Monocrystalline-Semi-Flexible-Trailer-Surfaces/dp/B0BQ1Y8JMH
If you get three of these you can get something going. If you do it right you can get about 100W of energy under perfect sunny conditions with 3 of these panels combined. That isn't a lot of energy.
That's why you don't really see solar panels on anything mobile, it really kinda sucks. My advice for solar power robots: put a solar installation on the roof, put all of the energy generated over a year into the grid and simply charge the batteries for the robot from the grid. This way you can't just charge when there is sun and if there is sun and you don't need to charge the energy isn't wasted. And being on the roof they are sure to be at a better angle and without any obstructions. They can also be as big as the roof, which helps a lot. This is what we do with electric cars and it seems to be the most efficient we can get.
Thanks, this information is really useful!
Okay so here I go, this is where I am at the moment, I have this old robot idea based on the hitcher robot ("HitchBot" for the curious) and as I'm somewhat aware of my shortcomings I'm trying for a very simple start robot and build on top of the experience from that one.
So the first robot would be, and don't forget this is just napkin figures to get a first iteration, 40 cm long, 20cm wide (16x8"), and not too tall.
Inside would be, roughly, a raspberry, a camera, some 18650 batteries, two motors for moving (probably NEMA 8 stepper motors), electronics (controling the motors, charging the batteries) and a solar panel. I'll have a usb charge module for convenience too and some way to measure the solar panel charge (so the robot can angle itself as good as possible). Maybe a servo for the camera angle, maybe one for the solar panel.
Connected over wifi for starters, 4G in some distant future.
The 18650 could theoretically hold like 10Wh each, and one could drive the PI for some 10-20 hours (or weeks sleeping) or the motors, hopefully an hour or two.
Theses calculations are wrong ofc but hopefully not too off.
The robot would roam around in the summer time, in France, so lots of potential sun. Battery power to the rescue when stuck in the shadows.
Just extrapolating the numbers you just gave (3 x those 100w panels could give 100w in ideal conditions) gives 8 watt for a 20x40cm panel in ideal conditions.
So the robot would have to charge for 2 hour for a 1h of operation if losses are not more than some 35%. Not very good but somewhat usable. If it can charge in ideal conditions which is of course not the case.
So maybe 1h of operation a day?
If so, then I'd be quite happy for a first iteration.
Thoughts?
I know you don't want to hear it, but forget about the solar panels my man. It's not going to work and it isn't going to be worth it. You can charge the battery from the grid a thousand times for the cost of the solar panel. And that's excluding all the other extra components you'd need to include if you want solar charging. Plus all of the time you have to put into it.
But if you just want to do it for shits and giggles, just go look up a panel that fits your size and other specs. The watt peak is right there in the specs.
Ha ha yes this isn't meant to earn me anything more than blisters ^^
I'll try out some cheap panel to see if I can get anything rolling at all for starters.
If it doesn't work enough well, and I cant figure how to fold a bigger panel for example, I have a backup project which is a robo-boat, which could drift around in the ocean, but that comes with lots of other complications like is it legal, and salt water.
Cheers