Solar Panel for Window

Do a search there is a lot of info on here about that.

However i dont know who told you 3 days because i go sometimes two weeks or more without any problems. Most only report problems after about two weeks or more. It really becomes a problem if a door is left ajar or something like an interior light is let on, ect.

 

A small solar panel is a fine idea to keep the 12 volt battery charged, but get one that is big enough, ~5 watts or so. The tiny little ones are not big enough to keep up with self discharge. Alternatively push the ready button for 10 minutes every 2 weeks or so. This had the added advantage of keeping the HV battery fully charged

 

First off, the battery on the Prius will NOT go dead in 3 days...that is, unless you have something wrong with your battery, or it's on it's last legs. There have been quite a few posts on this, regarding concerns people had about leaving their Prii at the airport for long (2-3 week) periods of time. The conclusion I got (from the posters who wrote in), this "myth has been busted". It seems like quite a few posters had left their cars out in the cold for up to 3 weeks, and upon their return, the car still started with no problems.

That said, and if it makes you feel any better, why not do what some of us have done, and buy (for about $30) a small jump-start/re-charger battery and keep it plugged in?

As far as the solar to re-charge, here is an article on the topic. Please note the second to last point under "conclusion" (important point):

http://autotechrepair.suite101.com/article.cfm/sunforce_12v_18w_solar_battery_maintainer

Summary -

Testing the Sunforce 50012 12V 1.8W Solar Charger​

The Sunforce 50012 Solar Charger will provide a trickle current at a sufficient voltage to maintain the charge on a lead-acid automobile battery. However, this unit may not not be able to charge a fully discharged battery.​

The Sunforce 1.8W solar charger will deliver peak performance under ideal conditions, which include

• Clear, sunny skies with no overcast
• Car window or windshield wiped clean
• Solar panel wiped clean of fingerprints or film
• Panel mounted so that it faces south and will receive direct sunlight for as much time as possible
• Panel oriented perpendicular to the sun (tilted or mounted to window or windscreen rather than laid flat on dash)

Under these conditions, at an ambient temperature of +8 °C, the panel delivered the rated 1.8W of power.

• 22.5 V @ 125 mA (no load)
• 20.4 V @ 85 mA running a 12V electric motor (1.7 W)
• 12.7 V @ 44.8 mA charging the lead-acid battery in an SUV (almost fully charged) (0.57 W)

The suction cups, intended to stick the charger to a window, did not always stay attached to either the glass or to the charger frame. If the solar panel is affixed to glass using the suction cups, it is best to ensure that the weight of the panel rests against the dashboard or the door panel. Under these conditions, the unit will remain in place.

Conclusions​

Based on the tests, and in comparison to the manufacturer's quoted features for both the 50012 and 50014, the following conclusions should be helpful to anyone looking to buy a Sunforce charger:

• The Sunforce 50012, because of its larger solar panel area, delivers a higher current than its smaller cousin, the 50014 Solar Power Sports Charger, making it more effective for maintaining charge on larger (higher CCA) batteries.
• Its lack of overcharge protection makes it unsuitable for smaller 12V batteries unless monitored; for that, the Power Sports Charger is preferred.
• The fact that the 50012 is not weatherproof may make it unsuitable for field charging (tractor, quad) in all but ideal conditions

 

Plugging into the cig. or accy outlet won't help anyway. They are turned off when the car is off. You'd have to wire them to the car or modify the outlets.

The panels above won't hurt the Prius battery. 100 mA full time is just fine. It would eventually deplete the battery of water, but it would take a year or two. The car itself will use up about 30 mA of that.

 

Codybigdog make a good point about charge controls.

Most tiny solar charges don't require a charge controller since the out put is so small. The car and the battery itself add a considerable draw over time. The self discharge of a lead acid battery in good shape might be 10-20% per month. The electronics add several hundred MA of draw 24/7 especially if you leave the smart key and security system on.

The best small solar panel I have seen for this kind of application is a 5 watt panel sold by Coleman. This is a fairly powerful panel to overcome self discharge, plus parasitic loads. Even though it is pretty big it doesn't require a charge controller because it's design voltage is only ~15.2 vdc rather than the ~17.5 in most Pv panels that are this size. By limiting the voltage to ~15.2 a lead acid battery virtually cannot over charge, especially if it has some parasitic load on it. I have had a number of these on tractor/stationary engine truck batteries for years and they work great.

You will have to wire them either directly to the battery with clips, or the jump port under the hood.

PS. The general rule in the PV solar world, is if the charge current capability of the PV is under 1% of battery ah capacity no charge controller is needed, as that is just about enough to keep the battery in float. So with the Prius battery being ~35 ah, that rule would be any solar panel that can put out ~ .35 amps into 12 volts. In fact it could probably be nearly double that, say .7 amps due to the parasitic loads.

 

I've just left mine set for over two weeks and it started fine. The traction battery was at the same level it was when I shut it down two weeks ago, and the 12 volt seemed just as viable.
Mindmachine,----- pray tell where did you get the mudguards??? I understand they have them in the UK, but how do you get your hands on them?? Do you know if they are "paintable"? Would like them to be the same color as my Barcelona Red IV. Thanks for any help.

 

There are two batteries in the prius. The main traction battery (shown on the mfd) and the much smaller 12v lead acid battery. Both are located in the rear of the vehicle.

The 12v battery is the one that has the risk of losing its charge if you leave the car sitting for several weeks at a time. You can extend this by disabling the smartkey feature (button under the steering wheel dash)

 

I use a Deltran BatteryTender Plus to keep the batteries charged while my cars are sitting.

It's a fairly smart charger that will maintain the charge without overcharging.