backchannel - contra alternator-only zealotry

I will push back on assertions made in this article that border on alternator-charging zealotry. The author is obviously clever, but weirdly partisan about a technical subject.

Full disclosure: I am a fan of alternator charging, and regularly encourage newbies to add that charging source to their rig. IMO a combination of solar + alternator is likely to work better and less expensively than either source alone.

general tone

Most solar installs are rationalizations… if that makes someone feel good, that’s fine, but it should be acknowledged as a fantasy that makes one feel good, and nothing else.

That sets the tone for the article. IMO this bias clouds the author’s judgement.

Solar imposes a scarcity mentality upon its users.

Does it? My experience is that a reasonable solar setup can lead to a sense of abundance.

It is not a fast-recharge power source.

Well, maybe not if one is using a “Zamp 200 watt portable solar panel kit” (MSRP $959, FFS).

My solar setup regularly produces more current than my alternator setup.

so one frets over how much power is being used and how long it will take to recharge the batteries (days for a nice-size battery).

On normal days my bank is back to ~100% SoC by 11am, and on overcast days by 2pm.

Solar is good for topping off and trickle charging and modest daily power needs

True, but it’s not limited to that. Again, mine fully recharges the bank daily with zero input from me. My average daily harvest is typically >1.75kWh, more than I need.

Solar is not as primary power source. It is a supplementary power source

For whom? Solar makes 90-95% of my power, depending on where I am. That sounds like a primary power source to me.

Solar panels are usually mounted in a way to significantly increase drag (on a Sprinter or van), thus reducing fuel economy day and night for every mile driven

This is highly dependant on MPH. I have noticed no decrease in my MPG but I drive 55-62mph most of the time.

Roof mounted solar panels with associated rack to protect the panels (mandatory) cause a loss of fuel economy via wind drag. This is generally not less than one mile per gallon, which is huge. Those losses in fuel economy apply for every mile driven,

Wait until you learn that some folks are idling to charge from alternator! Literally zero MPG!

Solar cannot charge a battery past 100%,

Nor should it. WTF?

so if the battery is near full, solar accomplishes nothing

… because… loads don’t exist?

if a good lithium battery is chosen and proper discharge and charge protocol is followed, this “topping up” idea is pointless and even a negative for most users, since lithium batteries should be cycled regularly, not left to sit at 100%.

Nothing about solar requires lithium to sit at 100%. Most SCC Li profiles don’t even have a quasti-float setpoint.

OTOH, solar can hold Pb at 100% SoC (mandatory, as you say) and alternator charging cannot.

The argument for solar vs alternator charging is absurd.


The solar panels and associated rack to protect them kills fuel mileage and driving range by up to 2 mpg—a huge net loss.

That is not my experience, as described above.

The primary alternator can charge a minimum of 2X to up to 20X faster,

That is not my experience, as described above.

Driving 30 minutes charging via the alternator is equivalent to solar for an entire day!

Is it? My average daily harvest this time of year is 2.25kWh. I have no doubt a bespoke secondary alt with external regulation could do that in a half hour (at 346A?) while driving. I doubt it could do it for the ~$500 my plebian solar setup cost.

Since my photography involves driving at least every few days, there is zero value to solar for charging,

Unfortunately for your argument, that is not a universal use case.

I would and do recommend that folks who drive regularly with Li banks to make the alternator the centerpiece of their power mix. And folks who are emplaced for longer periods and/or drive less consistently and/or have Pb battery banks to make solar the centerpiece. IMO this is the differnece between a pragmatic view and a dogmatic one.

Buying a van so as to scrimp and save on electricity is an absurdity

Again, your use case is not a univeral use case.

I assure you more vanfolk live on limited resources (money, electricity) than those with effectively no limits.

There is not enough roof area on a Sprinter van for a good daily charge unless one uses little power.

1000w on most eurovans is easy to fit. OP doesn’t give his power requirements unless I missed it.

my idea of a good camping spot involves shade,

Your use case is not a universal use case. <- seems to be a pattern here.

Some of us snowbird so we are always in mild conditions.

Solar only charges when the sun shines..

The alternator only charges when the engine is running. My idea of a good camping spot does not include generator or engine noise, but there’s no accounting for taste.

what if I want my 300 watt computer system to work on for 3-4 hours in the evening along with some microwaved popcorn?

  • 300w x 4 hours = 1,200Wh
  • Some quick googling suggests electric poppers run ~1200w for 5 minutes or less. 1,200W x 0.12 hours = 144Wh

So ~1,344Wh. My setup has this to spare 11 months of the year.

Sitting in an RV park? There is shore power

Cool. We won’t have to idle that $6000 Sprinter engine.

Sitting in the middle of nowhere for a week?

Usually for two at a stretch, but yes.

The money spent on solar is far better spent on a good high capacity battery i

Your use case…. nevermind

Get a 2nd alternator if you need air conditioning. Plan on idling because even two of the largest and best solar panels put out very little power versus what AC consumes.

Or snowbird to avoid air conditioning.

There are people who use solar or alternator to run A/C but both are out of my budget.

Solar power decreases substantially at my peak travel time (September through November). And in the hot summer, I want to park in the shade so when I come back to my van it’s not 110°F inside.

Your…. use…. case…… not……. <- I should make a macro for that

Late in the season, the sun peeks weakly into canyons only a few hours per day, and often there are clouds that greatly reduce solar output. Or snow or rain. So other power sources must be relied upon anyway.

Or one could size the solar setup to meet needs under the poorest conditions. Like I did, for cheap.

Furthermore, the engine must be idled for heat

Must it? My dog and I sleep on a heated mattress pad. And diesel heaters are all the rage.

The Lifeline/Concord lead acid battery technical document states: For repetitive deep cycling applications (deeper then 50% depth of discharge), chargers should have an output current of at least 0.2C (20 amps for a 100 Ah battery). If an output current is below this value, the cycle life of the battery may be negatively affected.

Absolutely true, and widely ignored; lead batteries do have minimum charging current requirements to stay healthy. This is one of the reasons I recommend alt+solar, as mentioned before. It is a non-issue with LiFePO4 since they have no minimum current requirements..

solar is good for those who leave their van parked for long periods.

Thank you for acknowledging that use case, albeit at the tail end of the article. I have done my best in various articles to say when alternator alone works, fine, when solar alone is fine, and the great majority of cases where a mix is preferable.

IMO it is important to discuss ideas fairly and with minimal bias. It’s the difference between helping people make informed decisions vs persuading them to adopt our opinions.

But it is very hard to justify on any other basis when a 2nd alternator is available.

And we regress to the mean after that moment of grace.

Quick! How many vanfolk have (or can easily add) solar vs how many have (or can easily add) a 2nd alternator?


I feel rather smug about having rejected solar, - source

ya think?