Ask Lemmy

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.