Solar Power 101

Advance Notice: On Thursday, March 4th, 2021, episode #96 of my show Merriwether's World! I'll be going over the basic equipment, their pros & cons, and the necessary math you need to figure out what size solar system you need. This won't be covering "whole house mega-arrays" but sub-1,000 Watt emergency & camping systems. You can join the presentation live at either:
www.youtube.com/user/drmerriwether
www.facebook.com/foragingtexas

Replays will be available afterwards at both locations and I'll add those video perma-links to this thread after the presentation is done.
-Blast

Great! I'll tune in with great interest....

Awesome! Be sure to say "hi'
-Blast

This is an introductory-level presentation covering basic info and calculations needed for solar panels, batteries, charge controllers, power inverters, and so-called "solar generators". Feel free to ask questions in the YT comments or here in this thread. Hope it helps!
Blast's Guide to Solar Power: https://youtu.be/1nwUJXDAv7c?t=6
-Blast

I look forward to your opinions on "minimalist solar' rigs - system that would sustain phones, a few lights and possibly a tablet or other small items indefinitely when far away from the grid.

What sort of price range?
-Blast

You know me, a veritable tightwad. Reasonably cheap, but I realize you will have to spend money to get decent stuff. I am ideally looking at something that will power a cell phone(s), some general lighting and possibly a few other small gadgets. Would be independently sustainable, hence solar. useful in power outages, post earthquake, and also for field projects where we might be camping.

I am pretty sure I already have some useful components, but I could see spending $100-$200 additional, maybe more if there are definite advantages, but I am always partial to the $2.98 special.

One thing that came out in our recent power outage is that Mrs. Hikermor and I have very different opinions about what constitutes adequate lighting.

One thing I have demonstrated over the years -when you swallow hard and spend what is necessary to get capable gear, you will be repaid many times over when the gear performs well. It's an investment, not an expenditure....

Do you already have any deep cycle batteries and if so, what are their Amp-hour ratings? That'll help decide what size panel(s) you should use.
-Blast

I have a couple of 5000 mAh power banks and a few lights with 2000mAh capabilities. I also have three Goal Zero mini lanterns, thee old style with replaceable batteries. Their total capacity is around 18000 mAh.

I have a couple of 5000 capacity power banks which have lost their ability to charge, or their ability to register their charge rate.

Can someone double check the following math?

Okay, so you want to charge about 34000mAh worth of batteries.
34000mAh = 34 Amps
Watts = Amps x Volts
34 Amps x 12 Volts = 408 Watts but you need to add at least 10% extra to make up for inefficiencies so lets say 450 Watts.

A 30 Watt solar panel exposed to 8 hours of sunlight:
30W x 8h = 240Watts
So it'd take almost 16 hours of sunlight for one 30Watt solar panel to charge everything you have all at the same time.

Increase to a 50Watt solar panel:
50W x 8h = 400Watts which is almost enough power in 8 hours to charge everything

If using a 100Watt panel:
100W x 8h = 800Watts so it's charged in around five hours.

My recommendation:
50 Watt solar panel: https://amzn.to/30qaoH4
Blocking diode to prevent electricity flowing back into panel: https://amzn.to/3bx6i6l
PWM charger controller to protect batteries from overcharging: https://amzn.to/3qywuBy
12VDC & USB outlet connected to charge controller: https://amzn.to/2OfJKhq

Personally, I'd add a single, 35Ah deep-cycle battery to the system, connect it to the 12VDC/USB outlets, and then charge the smaller stuff off it.
-Blast

Thank you very much. Good stuff....

34000 mAh is 34 Amp hours, not 34 Amps.

34 A * 12 V with inefficiencies is more like 350 W, not 450 W.

Where you have Watts * hours above, your resultant unit should be Wh.

I’d suggest both another panel and also a deep cycle battery (Lithium if you can afford the upfront cost — they have a far longer cycle life than AGM and other lead-acid battery types) for charging everything.

D'oh, thanks for the corrections! Trying to figure out how much extra "oompf" to include in a solar system is a weak point of mine...along with math.
-Blast

I’m pretty good on power storage — I can run my generator full time for at least a day, part time enough to keep my fridge cold for several days. Siphoning gas from our cars would extend that, and access to a gas station would of course be better still. My generator won’t run my AC, but it will run a bunch of fans.

Generally I’d expect to run a generator part time to charge things and chill down the fridge. I have plenty of rechargeable cells, primary cells, flashlights and radios — I’m glad Mrs. Magnet doesn’t know how much. If I used my two ham radio portable power setups to charge other things we’d be good for days of heavy device usage without the generator, more if we used some restraint.

Where I’m lacking is in solar capability. I have a couple of small powerbanks that can recharge via onboard solar, and one 15W portable panel.

A few random thoughts...

The number of solar energy watts theoretically hitting your solar panel is not the number of watts in 12 volt DC going to your battery storage. Expect system losses of more than 10%.

In the informal experiment I ran a few years back, the closest I got was ~70% of the number in a panel’s name. One of the 21 watt panels actually measured out at 14.3 watts — that’s at roughly solar noon on a nice sunny SOCAL day. Add some clouds and move the sun left or right of center and I would expect the numbers to drop off.

My only recommendation is to buy a bigger panel than you expect to need. Then test it before you need it to make sure you have all the wires/cables to make the system work.

I have a 100 watt panel and Renogy Wanderer Charge Controller. No affiliation. The smaller, portable units you might throw in your backpack to take hiking/camping came with built in controllers and USB output.

Great thread! I need to need to get a solar rig I can carry backpacking and as an emergency power source at home.

I am on the same quest. So far, it seems that a feasible, fairly light rig for overnights and short trips where you might want to perk up your phone and maybe a headlamp would involve a power bank and not a solar panel.

My favorite power bank for this niche usage is a Goal Zero micro Charge lantern which also functions as a flashlight, lantern (with two power settings) and a usb port for charging other items. Very limited capacity because the 'power bank" is an 18650 battery with a capacity of 2600 mAh....But probably OK for short trips.

You can get larger power banks and at some point it will make sense to throw in a solar panel. From what I have read, solar panels hung on your pack are not really all that effective.

Yeah, for short trips a power bank is likely the way to go. But I usually get a couple of week-long trips in each summer. Hopefully my recent shoulder injury will be healed enough to do it again this year. A buddy of mine and I have a spot where we will hike back along a string of mountain lakes camp at one of 'em about ten miles in. A light weight solar charger would be handy for topping off batteries for flashlights, GPS, etc.

I can see the value of a solar charger in a base camp, since you can choose a good location in the sun and let it trickle away all day. The pics you see of people hanging them off their backpacks are mostly marketing IMO; the panel will not be getting direct sunlight much of the time.

An additional note. The Goal Zero product I mentioned is listed as "out of stock" currently. Hopefully it will return, but who knows??

I kind of figured the way to go would be to set up the charger in a sunny spot in a clearing at camp. Stuff can charge all day as one goes about one's business.