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Solar Charger for Porsche Car Battery

Posted by in Ask Bill on Apr 14, 2020 . .

Customer question (received via email 5th April 2020):

Hi. I am thinking of getting an Optimate solar battery conditioner/charger for my Porsche Cayman (3.4 litre flat 6 engine) during the current period of driving restriction as I don't have power in my garage. I have a couple of questions:

1) What size charger would you recommend? I have an off street parking space where the car would be parked pretty much due East but I could potentially leave the panel outside the car facing south (I assume the panel is weatherproof) during the day. However I do not have anywhere I can fix the panel permanently so would not want to do this overnight as although it is on private land I would still be concerned about security.

2) How long (ball park figure - 1 day, 2 days, under a week, over a week) would the recommended charger take to bring the battery up to condition if it starts in a fairly good state and we get typical UK spring/summer weather, i.e. some direct sunshine but probably more cloud.

Many thanks


Willgen Reply (Email from Bill 7th April 2020): 

Hi Caroline,

Many thanks for getting in touch. In answer to your questions:

1. I would suggest a 20W Optimate solar charger for the situation you describe.  The solar panel is fully weatherproof and can be left permanently outside if required. Solar panel output will be considerably higher when outside in a South facing position than when East facing or behind glass.

2. The 20W Optimate will provide approximately 1.6Ah (amp hours) of power for every hour it is in full sunshine. In mid winter we have (believe it or not!) on average the equivalent of 1 hour of sunshine per day, in mid summer upto an average the equivalent of about 5 hours of sunshine per day. Early April (now) average would be approx. 3.5hrs per day. So, assuming panel is well positioned outdoors in an un-shaded, South facing position from now through to mid summer you can expect between 5.6Ah now (3.5hrs x 1.6A) to 8Ah mid summer (5hrs x 1.6A) charge per day. The battery in your Porsche is likely to be approximately 70Ah capacity so 5.6Ah is replacing 8% of battery capacity and 8Ah is replacing 11% of battery capacity per day which gives a good indication of it's ability to keep the battery topped up but bear in mind solar output will be lower if panel is not well positioned (eg behind glass/east facing) and there will be drains on the battery (alarm etc) hence why I recommend the 20W Optimate and not the smaller 10W.

Link to products of interest:

Optimate 20W Solar Charger:
Optimate 4.6m Extension Lead:
Optimate Suction Cups (attach panel to inside or outside of car window):

I do hope that this helps - please ask if you have more questions. We currently have all Optimate products in stock and ready for rapid despatch.

Kind regards


Last update: Apr 28, 2020
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