Some of the interesting aspects of a parallel hybrid vs series are redundancy and operator control, the ability, even the requirement of what motive system should be used as the primary for that particular environment - the user's decision based on the specific criteria of the machine, the usage and their preference.
This can of course be supplemented with software, alleviating the driver's work load... but this presents a difficulty with the entire series/parallel debate and that's the sheer diversity of applications as well as variations of "hybrid", not just series/parallel but the size/type of motors, fuel types, capacity & discharge rate of the electrics and of course, intended use - sporty runabout vs long range commuter vs in-town grocery getter vs work hauler, etc., etc., etc.
As I read this thread I become more convinced that it's less about the tool then what job you're asking of it - and that's a nearly impossible question answerable only by an interested and educated consumer/builder.
My hybrid experiment isn't nearly as refined or well engineered as these commercial offerings, nor is it even a remotely practical choice for the "average" transportation needs. I built it within a fairly narrow field of perimeters, constraints both legal and personal as well as fiscal...
...I built a small, comparatively lightweight parallel hybrid for comfortable long distance trips in mixed terrain and variable driving environments that was as close to full compliance to the legal requirements of a motorized bicycle/moped as possible, as those requirements are far more restrictive than non-commercial automotive they imposed some challenges inapplicable to the debate in general.
Yet for my usage I find the parallel hybrid to be superior in all ways save one, operator complacency - I have to make almost constant decisions, choosing how much and where, why and when. Is it a short hop over to the store? Block to block slow traffic? Is there an outside source of "free" power (solar, hydro, communal charging station, etc.) Electric only then, I'm not even going to fire up the beast. Then there's the other end of the extreme - Is it a distance trip, exceeding the maximum electric range? Steep hills? Cargo? Aggressive fast traffic? Interestingly, in all of those situations I use both motive systems - ICE for the raw power & range with the electric supplementing it to reduce consumption/provide additional preformance.
There's almost no conditions in which I'd use ICE alone, but there is one that comes to mind and that's a systems failure, of one of my drives is inoperable for whatever reason - depleted/malfunctioning battery bank or electric motor or conversely, an ICE failure, mechanical or just OOG.
Don't laugh, it's happened lol
Thing is I wouldn't expect the "average" consumer to know about, understand or given those - want to deal with all the added complexity of choice. For most the tool is just that, a tool and no more & the want is to just turn the key and go. Remembering & finding a place to plug in a pure electric is a complaint I've heard with some frequency and that's pretty much all a pure electric ever asks of you. In the rare instance I let someone try my hybrid it's in electric only mode, I start to explain the dual throttles and gear ranging and their eyes glaze over and they start to back away slowly with a stammered "nevermind" - for these folks a series hybrid is a nearly perfect choice, usage couldn't be simpler & with their AAA card handy & warranty at the ready redundancy is irrelevant.
Is one better than the other? For you or me yes - for everyone in general? No, I think one can only pick out specific instances in which an aspect is superior much like the car vs truck debate which is again, specific usage, the wants & needs.
I do believe hybrids are a stopgap measure yet until electrics can sort out their reserve capacity & recharge rate hybrids (preferably alternative/multifuel) are one I hope to see with a greater level of acceptance - but their one massive drawback regardless of type is complexity, series or parallel you've dual motive systems at least with potential mechanical, electrical and electronic (software) failures compounded with every system, the level of driver & mechanic education required beginning to exceed reasonable expectations with the addition of every system.
Jus' some thoughts *shrug* I gotta admit as I read through this thread I can't help but wish I'd found this forum before I built my hybrid... I'm not sure I'd have done anything differently, but I'd have better understood what I was going to do before I went and did it anyway lol
Interestingly, waaaaay back in the "daydream" stage I really wanted to build an AWD diesel electric series hybrid, I ended up with a single drive four stroke gasoline/alcohol parallel hybrid due to both technology & fiscal limitations... but I'm pretty sure I'd have been just as happy either way, if for completely different reasons
