Good question.

It is pretty hard to do just that without making this into a full fledged project of academic proportions... which happens to be something few of us will gain in doing.

However, it is possible to eyeball the benefits by using plain old inference and some calculations based on the trickle effect the solar panels provide to the 12V battery. Is this quantifiable? If anyone is willing to be methodical enough and include all variables then, yes, it is.

Now, a single panel setup is likely to keep the battery drain to a minimum especially if the onboard systems (car off) consume no more current than what the panel provides. In my case, the panels not only replace the power consumed by the onboard systems but also send the surplus to the battery in the form of a trickle charge that spans over 10 hours each day.

Anyway, if you plug a scangauge on your HCH-2, you will be able to tell when the IMA is charging the 12V system and how long those sessions last. These sessions will even occur when the vehicle is ON and in an Auto-stop. With a properly topped-off 12V system the IMA does appear to intervene less often and in smaller durations which by inference means that more of the NiMH SoC will be available for mostly propulsion duties.

Most of us have seen how easily the NiMH SoC is affected by the operation of accessories especially when autostopped and in a warm summer day. Right?
All this solar panel setup does, is reduce the rate of discharge of the 12V battery by supplementing a charge to it over a longer period of time that would otherwise have to come from the IMA's NiMH. In my case, this translates into lesser number of forced regens and hence better fuel economy.


Cheers;

MSantos