Downside to using residential solar panels (on top of a RTT)

[dreadlocks]

yeah but if you have lead chemistry batteries you always have a ton of overhead during the absorb.. even with 1.5C charging rate.. its gonna spend >80% of the time under .7C.. so you got 100% Overhead 80% of the time.. most people here dont have an additional 1.5C of daytime loads, for boondocking most of the day load is fridge.. you can kick fans and stuff on later after battery is done bulking up.. Who's got a daytime load requirements higher than 0.05C with a small single battery setup.. I have to fireup a crockpot to get above that for any considerable time, and thats only ~120W.. still wouldent need 0.3C to charge and run it at the same time.. 0.2C would be more than enough.

 

[john61ct]

If there are other loads running while battery charging, you might want all the solar can produce, even if the battery alone can't suck it all up.

That's true, as long as the uses for "free excess" solar output are actually productive.

Some get obsessed over engineering don't want to "waste" any PV output

Pre-heating HW is pretty useless for example, but running an Instant Pot, maybe

IMO better to go to LFP instead

 

[john61ct]

yeah but if you have lead chemistry batteries you always have a ton of overhead during the absorb.

Not sure what you mean by overhead here

No lead chemistry accepts anywhere near .5C for any length of time.

Most even relatively high-CAR get down to .3-4C very quickly, and even the best quality FLA might accept **maximum** .2C

And for the last 4-5hrs of the charge cycle, current will be dropping to just a few amps, no matter what kind of lead chemistry.

Only solution to capture more of the PV output is to add capacity, and doing so with a supplementary LFP pack is really the way to go.

 

[dreadlocks]

I mean if you hookup a .2C charger up to a FLA bank.. for the vast majority of the charge cycle your using under .1C.. so that gives you an overhead of .1C+ for running daytime loads, thats more than enough already for most boondockers..

We are saying the same thing, a bigger charger than .2C for a FLA wont really see any tangible benefits.. even with day time loads AND charging combined, I highly doubt many here would see more than .2C output, and if they did it would be fleeting..

IMO if you want to oversize your SC so you can run daytime loads while charging, its unlikely to see any real world returns with any lead chemistries, because even a high rate charger spends so much time a tiny fraction of full load you inherently have plenty of overhead for abundant daytime needs.

ProTip: If sun is shining, and battery is only soaking a tiny fraction of potential output.. crank down the temp on that fridge of yours, then change it back once the sun goes away.. now your fridge is a battery, storing excess solar energy.. and because night time temps are lower, it can be surprisingly efficient.

 

[john61ct]

OK, I think less confusing to call it "charging power" as opposed to "power for loads".

To me "overhead" implies energy lost to inefficiencies.

In general I do not agree with sizing your SC for the CAR of your current bank chemistry.

If the panels can put out say 100Ah per day in peak-peak conditions, and the average is 60Ah, then if going to a 100Ah SC costs twice as much as capturing 80Ah personally I'd save the money.

But I wouldn't go down to a 40Ah unit no matter what, just because that's all my current bank will accept.

Infrastructure should last decades, banks are consumables, and just adding a LFP powerpack should not mean any "permanent" infrastructure should need upgrading.

Fridge / freezer units using eutectic "holding plates" rather than thin evaporators are a great use for "free excess" solar production, some only need "charging" for a few hours per day, do not consume electricity for the other 20+ hours.

Also reverse osmosis (RO) desalinating watermakers, rather than super efficient but low gph units designed to run all day, go with a high-gph design, even though it uses high amps, get all your fresh water produced in just a few hours a couple times a week.

Of course, supplementary ICE power generation is needed to make up for sub-optimal insolation conditions, but having lots of solar available to reduce genset runtimes pays for the panels very quickly.

 

[dwh]

Well, personally, with a 12v fridge and a tendency to do things like running an inverter for charging batteries and running a laptop (and please guys, I don't give a crap if it's less efficient than doing it all with 12v adapters...been there done that and 12v adapters for laptops suck...the inverter is superior) I don't mind the few extra bucks for a charge controller big enough to handle everything my solar can dish out.

Plus I've got some battery tools and a 12v compressor. No telling when I'll want to power those up.

Better to have it and not need it.

 

[dreadlocks]

One can argue the same thing about lead batteries, they are inefficient and wasteful.. So Lithium is superior, hows your lithium setup? or are the inefficiencies and waste of lead more suited for your budget?

Theres more to life than scraping out efficiencies.. my inverter is 92% efficient, if my AC/DC PSU was 90% efficient.. were at 83% efficiency (your double inefficiency eh), for a 30W load thats a whopping 5W of power, nothing I'm loosing sleep over.. or worth $60-100 for a charger to gain back (with a per-device multiplier).. especially if the load is an intermittent load and I only need to charge a laptop on occasion and not all day, every day.. I could spend that money on more solar or better efficiency elsewhere.

 

[luthj]

Some computers do not have a good quality 12V adapter available (Apply devices often). The cigarette 12V style ports are a pain to use, especially for higher power devices (over 90W).

 

[dwh]

The inverter is not superior - it is inefficient and wasteful. You are transforming DC to AC using the inverter and then AC back to DC with your laptop plug - double inefficiency.

I'm fully aware of that. Inverter generators convert (not transform, that's AC to AC) AC to DC, then invert DC back to AC. In terms of watts produced per gallon of fuel, a syncronous generator is more efficient. Yet, depending on the situation, the inverter gen is a superior solution.

I stand by my statement.

But if you want to go that way that is fine with me - it's your call dude but the truth is the truth and an inverter is not superior.

For me it is. I've got 300w of solar and 400ah of battery, and a 12v fridge. I have two small netbooks, the smaller being an Acer that draws 9w running and 14w charging (according to acpid in Linux). I also have a 17" HP laptop beast that can draw well over 60w and requires a 90w power supply. And I pick up a few bucks here and there as a writer, so sometimes I'll sit there running that big HP all day.

Yet no matter what I do, even on a cloudy rainy day my battery bank is in float by noon.

Do I give a crap about a few watts wasted here and there? No. Do I give a crap about plugging something in and switching on the inverter and never having issues with overheated 12v plugs and power adapters? Yes.

Did you purchase the 12V DC adapter from your laptop manufacturer? I ordered this one for mine and have had zero issues.

Lenovo 65W USB-C DC Travel Adapter | 40AK0065WW

Shop & save on the Lenovo 65W USB-C DC Travel Adapter & hundreds of other popular PC, home, business & gaming accessories at Lenovo today ✔️ Free shipping

www.lenovo.com

I've got a pile of them, from the cheapest to the most expensive. Most have blown fuses and/or melted plugs. They work fine for my little Acer netbook, but for anything bigger they suck.


Efficiency can be important. Conserving every available watt can be important. But when you've got way too much solar and way too much battery, you don't have to give a crap.

And I don't.

 

[shade]

Since I already have mains chargers for all my battery operated appliances, I would rather spend that 50$-100$ (per DC charger...) on second rate Hookers.
Further, She may arrive with her own appliances needing a charge, I can accomodate. A few watts inefficiency be dammed.
As a legitimate ’ExPo Guy, Its a price happily I pay for convienience.

IMO, the best professional girlfriends still rely on mains power. Sadly, Milwaukee is still evaluation lithium battery powered prototypes for this industry. I understand the utility of a cordless PEX crimper, but I think plumbers have received enough attention.

 

[luthj]

Off grid fully digital compatible girlfriends are still expensive, and in the early-adopter stage. Hopefully they will go mainstream as the production secrets and industry knowledge percolate through the various channels. At one point the previous analog versions were widely available through most distribution channels. But sometime around 1950 there was a sharp decline in availability. No single factor could be identified for the decline, though some speculate vertical high volume hairstyles were to blame.

 

[shade]

Everything went downhill once we abandoned steam power.

 

[luthj]

Shade probably means direct drive steam devices. Industrial steam power makes the world go round.

 

[shade]

Enhance your calm.
Your jobs are safe.

I meant steampunk power, but maybe it's making a resurgence.

 

[dreadlocks]

I used to work next door overlooking a steam plant, most of downtown denver is heated by steam.. thats why the man hole covers are billowing it in the winter.