True solar build possible?

Hey everyone, I just got my first prius, a 2015 prius 2. As any amateur scientist might I immediately got the idea to add solar to it to increase gas mileage. Naturally I scoured the internet and found a big, fat, "no way, it's crazy, never gonna happen". Of course I decided to find out for myself. What I want to do is connect 3 120watt thin flexible solar panels, sourced on amazon, to a small(maybe 50-100ah) battery bank which would charge when the car was parked and the HV was full but would ultimately lead to a dc-dc converter that would charge(even if only a little bit at a time) the HV battery. I'm having trouble finding specs on what would be a safe converter for charging. Obviously this wouldn't put too much strain on the car because it would be charging so slow that the regular hybrid system would be doing it's business with just a slight boost. just 5-10 mpg would be a huge success. the panels are $159 on amazon right now. batteries about $150 for a 100ah 12v deep cycle. Research suggests 4 batteries in parallel for a total of 48v. What I need is someone with the specs needed to safely trickle charge the HV without interfering with the normal operation. I'm a little unclear on what safe amp, watt, and voltage levels would be ideal for a low impact charger. Obviously this weak charge system would need to use about 250-300 watts dc even though the max would be 360 watts because as we all know solar panels rarely charge at full. However the batter bank would add a buffer so as long as it took maybe an hour or two for the bank to drain with no sun the system should be able to last for a few hours of driving before you were running purely off solar.

If this is completely impossible my other ideas include connecting an oil pan heater to the added batteries to warm the car in winter, possibly tapping into and running some of the 12v system from the bank instead of the HV converter, and even powering the air conditioner from the bank. Any ideas and numbers on inverters or battery management systems(BMS) would be greatly appreciated.

I've read several guides on safe handling of the HV battery and am 100% confident that if I had the right information I could make this work. Even if I have to turn the car off to safely charge the batteries it would still be worth it to have a full battery every day when I got in the car. especially for under $1000

 

Thanks Maarten, this is good info. The idea is with a very simple system you would have a fully charged hybrid battery after about 4-6 hours in the morning sun. even if it only adds say 30% to the battery that is still free power and if i can make it operational while the car is running i could shave off a little bit and maybe break even in a year or two. I have already sourced a 100w 12v oil pan heater that goes up to 368 degrees which i will combine with a 12v 55ah battery, 120w solar panel, a smaller 50w solar panel, toggle switch, and thermal control switch to keep the engine at about 180 degrees. I'm still very interested in running as much of the 12v system as possible from the 12v battery bank. I feel like that could really save a lot because it would leave more power for the HV system and require less batteries and solar panels than a trickle charge of the HV. maybe two 120 watt panels would be enough to make a nice dent in the 12v usage. I'm also looking in to dc air conditioning possibilities. I'm thinking I can make my own and feed it into the vent but I have to take a closer look at the vent system as that might be too difficult. Alternatively I could try some kind of peltier air conditioner which is much lower power but doesn't cool very much. Would be good for medium hot days that were in the mid to low 80's perhaps. a DIY A/C would be ideal because I could find the sweet spot between power usage and max cooling. since I could always use the regular A/C to augment it I would still save gas on really hot days.

 

My current setup is a 50w solar panel(soon to be upgraded with an additional 120w panel as soon as I test everything when I get the heater in the mail) to a charge controller to a 12v 55ah battery to the second charge controller to the prius 12v battery to keep it topped off when the car is off and I want to listen to the radio. When the heater arrives I will have a switch connected to a temperature controller to turn it on till the car hits 190 then off till about 170. The whole temperature game will be an evolving process to see what the optimal temp is to keep it warm without wasting energy heating it too hot. The heater is 12v 100w. The setup will have 170 peak watts with probably 100-120 in good sun. It should last most of the night after the sun goes down. I have a little 150 watt subwoofer that fits under the driver's seat. That can also be powered by the system so thats a little savings. I'm going to experiment with splicing into individual 12v components and putting a switch that switched from internal power to the battery bank. If the computer isn't too picky and if I do one component at a time I can determine if it's everything or just certain parts. I would be able to flip a switch and turn as many of the 12v components(headlights, wipers, cig lighters, internal lights perhaps) as possible to the battery bank. Things that the car would maybe put up an error message but not affect car functioning then I could get more out of the HV battery because it won't be draining as much into the 12v system which would have a nice clean flow of 360 watts if I deck the car out with 3 panels.

This is the 50w panel I have on there now. It's fixed with gorilla tape. I orginally got some really strong screw tightened suction cups but when I taped the edges down for reduced drag I realized that a few loops of tape underneath and tape all around the edges looked nice and held the thing on really secure. I will put up pictures once I get more of the system set up and maybe a video for convenience.

Apparently I can't post a link but if you look on amazon for flexible solar panel you will see what I'm talking about. The technology is really coming far.

The 120w one's I want were 159 but they went up to 172 which is still only 3 dollars more than a 100w version

At the end of the day it makes sense to put solar panels on the car and use the power directly rather than store it with the battery acting more as a buffer. Since I do drive at night a good amount I want to make sure to have a good balance of battery storage. Just like with a home setup it's better to have only a small battery bank and to have a grid tie inverter so you don't have to worry about storing enough power for a whole night. This would function similarly in that you would run out of power after a while at night but during the day you would maintain most of the charge essentially bypassing the expensive batteries and using the solar more directly. If you went with a nice 50Ah Lifepo4 lithium battery you would have lower weight, higher storage capacity, and faster charging speed, as most of you know I'm sure. At the end of the day I want to make something that is for alternative energy enthusiasts that will technically pay for itself without a huge multi-thousand dollar up front cost. I guess it could be an awareness spreader. I mean if we all had a few solar panels on our roofs with just a grid tie inverter and the states would actually reward that with credits toward your electric bill we would drastically reduce our fossil fuel home electricity usage for a few hundred bucks per household.