12 volt battery solar charger

What is the price difference between each model?

 

Your 12-Volt battery is something like 30 AH. So it will take 3000 mA (3 A) for 10 hours to charge. none of those solar panels will be able to CHARGE it. The biggest one probably will be Ok to MAINTAIN the current charge if you park the car for a long time, i.e. it will not discharge. Also, I would connect this panel via diode, just in case.


- Alex

 

Another way to look at it is this: What is the value of the energy produced by such a device?

An optimistic view is that you might get ~5 hrs of max power output per day on average. The biggest model at 72mA would then make about 4.32Wh of electricity per day.

Our electricity average in US costs ~11c/kWh, so the value of that energy would be about 0.0475c per day or 17.3c per year. This would be the case compared to running battery tender / float charger at home.

Looking at it another way, without a battery tender your ICE in the Prius may run a little bit extra to replace the energy from the HV battery used to replace that amount of energy into the 12V battery. A gallon of gasoline contains about 33kWh of energy, so assuming 30% net efficiency from the ICE, generator, and dc converter that would be about 10kWh worth of electricity per gallon. So that 4.32Wh would equate to about 0.0003927 gallons per day, or 0.143 gallons per year. At $3.50 per gallon, that's about 50c per year worth of fuel.

In either case it would be hard to justify the $80 purchase price. Small solar units like this are often very cost inefficient. Again using US numbers, the cost of installing larger scale solar on your house is now in the neighborhood of $3 per dc rated watt. This unit at 12V / 72mA would be 0.864 dc rate watts, so that's about $92.60 per dc rated watt.

Another thing to consider, particularly in a warm climate is will you waste more gas by parking in full sun and then having to cool the cabin with AC vs. parking in the shade? I imagine that's pretty likely.

Rob

 

Adding rooftop solar at home would be much more cost efficient, but historically you've have to do a pretty big system (at a pretty big upfront cost) to help spread out the overhead costs associated with having the panels installed and wired in to your home to make it cost effective. I hope we're going to start seeing a lot more options like the kit below, that take advantage of the availability of microinverters to enable small, relatively inexpensive plug and play solar.

Plug in Solar Panels|AC Solar Panels PlugandPlay

Note there are still some important issues being figured out in this area, and its probably not legal everywhere. This US kit gets around some of those issues by requiring a dedicated outlet/circut, and noting that you may still need to have your utility install a bidirectional meter. Both of which could add cost.

Going For Solar – DIY Small Scale Solar — Green Lifestyle Changes

I hope we'll continue to see advances in this area continuing to make small scale solar easier and cheaper.

 

None of these will do anything for you.. I have not measured the draw on a Prius C, but on my old 2001 Classic, I remember calculating that you needed a minimum of a 5 Watt panel for any charge to be put into the battery at all; anything smaller, and all you're doing is slightly offsetting the draw of the vehicle electronics (anti-theft system, etc that remains active, even when the vehicle is off).. If you can, find crystalline panels vs. amorphous panels: the crystalline panels are generally blue/black in color and you may see the crystalline structure of the silicon, vs. amorphous panels which are brownish in color and absolutely smooth.. The crystalline panels are more expensive, but more efficient as well, so for the same wattage, a crystalline panel will be much smaller than an amorphous panel.

On my classic, I had a 15 Watt crystalline panel (about 12x 10") in the back window with a charge controller (to prevent overcharge) connected to the 12V battery to keep it topped up (in Canada, I would have been getting several amps (not just milliamps) of charge current (after accounting for the electronics draw) during peak sunlight hours, which would be enough to keep the battery topped up), and I'd like to hook something similar up in the C2, but I'm still trying to figure out where to put the panel.. The rear window is out because due to the more vertical window surface and the presence of the spoiler, it is way too shaded and would not allow the cell to generate much current.. I'm currently thinking about the front dash: the surface of the cowl over the centre display- a good sized area that is not going to interfere with airbags, etc. Probably enough for a 10W crystalline panel, or maybe 15 or even 20W if I buy individual cells, and directly surface mount them on the dash and wire them up myself..

 

That sounds about right c4. Taking a quick look at cheap battery tender / float chargers they seem to be around 10-15W. You'd probably want to shoot for a similar amount of power in a solar float charger.

Something like this panel:


connected to something like this controller:


might be a workable solution for about $70, or this all in one version for $80:


Note that the size specs on Amazon seem to be wrong for the all in one 10W. The manufacturers site says its 26"x16" which might be a challenge. The higher efficiency stand alone panel says its 14"x11", somewhat more workable maybe.

 

You can see the crystal structure only in poly-crystalline units, not in mono-crystalline units.

A mono-crystalline device for 12V systems will generally have 32 to 36 discrete cells linked together by narrow foil strips, while an amorphous unit will usually have many strips that were all fabricated together, side by side, as a single part.

 

I can't see the links that you posted on Amazon, but the difference in size is likely because the larger one is an amorphous panel which is less efficient and you need a much larger size for the same output.. Amorphous panels are "thin film" technology that are made by depositing thin metallic and silicon films on glass or plastic (this is how they make the flexible panels)- very cheap, but again, much less efficient than crystalline panels which are made with individual slices of silicon with actual metal wires/foil strips on the surface, which are usually placed under glass for protection, but they can also be just laminated with plastic film in less expensive varieties..

My 15W crystalline panel consists of 6 discrete wafers of silicon mounted in a glass frame about 12x10"; the comparable amorphous panel would have been too big to fit into the car.. The crystalline panels also "age" better than the amorphous panels: they are spec'ed to maintain 80%+ output after 10-15 years, vs. amorphous panels which can be down to 50% of rated output after just a couple of years..

 

Exactly right c4.

 

Without knowing the details about the failed cars and drivers.......you should NOT jump to conclusions about why that happened and what will help prevent it.

HEAT is really hard on batteries; REALLY hard.

Making sure to park in the shade every day will probably do more for the battery's life than any tiny trickle charge you apply to it. And on models with the battery under the back seat, the temp inside the car with the windows rolled up can be 50 F or more higher than the outside temperature.
One of those little solar powered window fans might do more good than the chargers.

 

Let's understand what you are doing. Our shop is getting an electric car to handle daily gofer efforts and we are specifying a solar charger to do that effort, making it 'emission free'. For that you need solar panels, batteries, inverter, and charger for the vehicle.
In order to decide on a solar charging unit you need to find the expected consumption of power to recharge your intended battery, which should be a deep charge type battery. If you intend to recharge your Prius with a solar charger you can epect to comsume an average of 1200 to 1400 watts over 12 to 18 hours recharging. Thats 25 kilowatt hours of electricity available for recharging by 120vac inverters or 240v inverters. The better solar panels generate 100 watts max so you'd need about 20 solar panels getting exposure of 12 hours and 8 batteries in parallel to handle the recharge thru the inverters. A hybrid recharger, solar plus grid electricity to charge the batteries might be a good substitute. In a grid shutdown the solar unit can offer good substitue power for the household, beating a gas powered generator by a long shot.
All of this is based on a quick back of the envelope exam and assumes full solar panel utilization that continuosly 'aims'panels directly into the sun. My guess too is about a $10,000 investment. For us its a useful experiment but for the average electric car owner, maybe not
If you are looking at just powering the a/c my guess is you'll need couple of 100 watt solar panels to generate enough power to run the ac independent power source i.e. totaly separate from the car batteries. I'm not sure there's enough room as the 100 watt panels are roughly 2 feet by 4 feet each. The commercial units I see just lower the temp and not really cool the car; perhaps getting by on the a/c available from 100 watts of solar panels.

 

Yes, let's.
I'm pretty sure he was talking about hooking his panels up to the 12V aux. battery.
If so, pretty much none of what you said applies.

 

Actually, it does. Charging the auxillary battery is the case I thought he was intending and that charging is precisely the process he would need to do to charge that battery just as it would be to charge most vehicle batteries. It alsoapplies to the Li-n batteries as well.Energy needed is the same for either. The only difference is the time required to charge a battery to its capacity.
Powering a car cooler while parked is an alternate I thought he might be wanting. Its actually pretty popular in sunny climes. see some here efen. The point is, as several indicated, none of those solar panels have enough current to charge his battery. One of the higher rated ones say 25 A might be useful to maintain battery power ifthe car wasparkedfor a considerable period. Useful solar panels for charging a 50% charged battery is 200 watts. and have about 15 or 20 square feet of area. They are available for charging EV vehicles.