Some rough rules of thumb for a solar system are:

Peak Sun Hours by State

Sun Mecca (Arizona, Nevada, New Mexico): 6.91 peak sun hours/day.
Average US Numbers: 4.02 peak sun hours/day.

Outputs of typical 12V solar panels are:

100W panel: 5A
50W panel: 2.5A
20W panel: 1A

So for most of the US, rating a solar panel goes like this:

100W panel = 5A at peak sun * 4 peak sun hours/day = 20 amp/hours/day.

In reality, actual power sent to battery is going to be around 17.1 amp/hours with the following assumptions:

95% efficient charge controller
90% efficient battery charging

Comparing that 17.1 amp-hours a day to the best portable, lightweight genset....

The Honda EU2200i generator

This is a 1,800W genset -- it's expensive; $1,000 -- but, you get what you pay for in a lightweight, small, low fuel consumption AND quiet generator.

Weight: 46.3 Pounds
Size: 20.1" x 11.4" x 16.7"

Run Time (tank size is 0.95 gallons):
3.2 hrs @ rated load of 1,800W -- (0.296 gal/hr, 72 hrs = 21.3 gal)
8.1 hrs @ 1/4 load of 450W -- (0.117 gal/hr, 72 hrs = 8.42 gal)

Noise:
57 dBA @ rated load of 1,800W (Normal Speech level of Noise)
48 dBA @ 1/4 load of 450W (Private Office Level of Noise)

Doing some calculations for AC single phase wiring:

450W @ 120V @ 0.9 Power factor = 4.16A
1800W @ 120V @ 0.9 Power factor = 16.66A

Your typical 5 gallon fuel can refills the Honda five times (figure some losses in spillage); so that works out to the following amp/hours from that 5 gallon can:

480W = 4.16 amps @ 8 hours * 5 refills = 166.4 amp/hours
1800W = 16.66 amps @ 3 hours * 5 refills = 249.9 amp/hours

Average of 208~ amp-hours per can and a run time of 27.5 hours per can.

Time to replace the amp/hours from that 5 gallon can using the average of 208~ Ah:

100W Solar @ 17 Ah/day =  12.2 days
200W Solar @ 34 Ah/day = 6.1 days
400W Solar @ 68 Ah/day = 3~ days
600W Solar @ 102 Ah/day = 2~ days
800W Solar @ 136 Ah/day = 1.5~ days
1kW Solar @ 170 Ah/day = 1.22~ days (29.3~ hours)

Note that it takes a 1kW setup to get back power at a rate equivalent to that 5 gallon can's consumption (average run time of 27.5 hours per 5 gallon can for the Honda).

The size of that 1 kW array can be pretty compact -- I did some checking and it appears you can fit 10 x 100W panels in a 10 x 10 foot area if you lay them flat.

The biggest issue for high power solar is...cost.

That 1kW array would cost $1.3K at current pricing for the solar panels alone ($133 per 100W panel); figure another $100 for the charge controller and then about $700 in batteries to get the 400 Ah in batteries (remember max discharge of 50% for deep cycle?) needed to recover all that energy each day.

You're quickly into the hole for $2.1K and you still need to buy the wiring and the cable connectors for the whole system. :-|

I think the best thing to view solar as is as a supplement to a generator; so that you can save scarce fuel by not having to run your generator (or vehicles) to generate power to recharge batteries for lighting or personal electronics.

The 17~ amp-hours/day from a 100W panel is basically 17,000 milliamp-hours (mAh) -- enough to charge:

a iPad's 8,800 mAH battery about 1.8 times.
or
a phone's 3,000 mAH battery about 5.5 times
or
4 x 3-Ah batteries for deWalt/Ryobi cordless power tools

There are 12VDC Cigarette lighter chargers available for several major portable tool families:

DEWALT DCB119 12-Volt MAX and 20-Volt MAX Li-Ion Vehicle Battery Charger ($99 on Amazon)

Ryobi P131 One+ Portable Dual Chemistry Lithium Ion or NiCad Vehicle Charger (aka 18V) ($44.99 on Amazon)

With these, you can do a whole host of electrical items using the same battery:

Dewalt's 20V family is:

Drill
Impact Wrench
Impact Driver
Circular Saw
Jig Saw
Grinder
Reciprocating Saw (aka Sawzall)
7 1/4" Miter Saw
LED Handheld Light (500/250 lumens)
LED Cordless Spotlight (DCL043) (1000 lumens / 90 lumens / low power red)
LED Jobsite Light (7000 lumens)
Compact Worksite Radio (FM/AM, and 3.5mm aux jack)

Ryobi has a similar family of the usual tools.

Yes, some of these may be overpriced ($119 for the radio, $69 for the LED Handheld Light, $89 for the Cordless Spotlight), but there are some advantages to going this route:

1.) The tools (radios/lights) themselves are bigger, more rugged, and easily identifiable by the tool brand color (Yellow for DeWalt or Green for Ryobi)

2.) The Batteries are big, rugged, and easily identifiable -- while you might be able to get more amp-hours for your $$$ and lighter weight/size from Eneloop rechargable AA (etc) batteries, there's something to be said for big, bulky oversized batteries that you can easily find and put into a tool in low light.

A day after IRMA blew through.  84 hours without power.  Twin 30w Monos and a 14w Sunkingdom USB folder charging up a 22Ah mother battery and a USB power bank.



Testing the 12vdc system back in 2012.  Charging a mother battery and a li-ion charger.

Chris

Holy fuckin' thread revival.

This place has been pretty slow lately, so we need all of the help we can get.

Chris

I'm not complaining.

Every few years I am reminded of this thread

Some crude math for minimum "watt" rating for charging your USB devices.

Most USB devices charge at 2.1A @ 5V, or 10.5 watts.

To get that power at 12V, you need about 15W of continuous output.

(my calculations may be wrong/off)

If you see a "portable power" system advertized in stores (they're starting to show up now); consisting of a battery plus a small solar panel to charge it -- one of them is Nature Power's Emergency Solar Power System, pay CLOSE attention to the spec sheet.

The previously linked Nature Powers system is basically a 4,000 mAH battery paired with a solar panel.

If you look carefuly at the specs sheet, the maximum current for the 12V 2.5W panel is 166 mA at Pmax.

That means that uh, it would take 24 hours of continuous solar output to recharge the battery bank to 100% (and this assumes no recharging losses).

Gets worse. If we use the prior 4 hours average of peak solar a day, it would actually take six days to recharge the battery completely.

Meanwhile, your phone would drain that battery by the end of day #1.

So basically, 20W panels are the minimum size for "off grid" charging of personal electronics; as they generate 1,250 milliamps @ hour at peak solar. At 4 hours peak solar a day, that's 5,000 milliamps -- enough to charge a small battery bank completely, which you can then use to charge a phone.

You'd still have to ration daily personal electronics use; as a phone running full blast (actively browsing web, etc) sucks down about 800 milliamps/hour.

If you wanted to heavily browse the internet with your phone, you'd need a 50> Watt and above panel.

Oh, and if you're looking to make a portable system for camping, etc....

I highly suggest 50W as the maximum size of individual panels; it's a lot easier to fit a 50W panel into the back of car trunks and such than a 100W panel -- just buy two 50W panels and gang them up to equal that 100W panel.

Of course, if you have a huge SUV or pickup truck with long bed, this changes a bit.

https://www.engelcoolers.com/catalog/product/view/id/123/s/engel-mt45/category/32/

https://www.engelcoolers.com/pub/media/wysiwyg/pdfs/MT45F_Performance_chart.pdf

Basically:

25C (77F) Ambient Air Temp (Official)
Chill to 5C (41F): 0.54 Amp/Hrs
Chill to -5C (23F): 1.19 Amp/Hrs

29.4C (85F) Ambient Air Temp (Interpolated via curve expert)
Chill to 5C (41F): 0.804 Amp/Hrs
Chill to -5C (23F): 1.436 Amp/Hrs

35C (95F) Ambient Air Temp (official)
Chill to 5C (41F): 1.14 Amp/Hrs
Chill to -5C (23F): 1.75 Amp/Hrs

Looking around, it appears that Florida in the Summer (Worst case for a power outage) has this cycle around July 20:

15 hours around 85F (12.06 Ah to refrigerate / 21.54 Ah to freeze)
9 hours around 95F (10.26 Ah to refrigerate / 15.75 Ah to freeze)

Total:
22.32 Ah to Refrigerate/Day
37.29 Ah to Freeze/Day

So it appears that 3 x 100 W solar panels with a 100 Ah battery bank would be sufficient to run that Engel cooler near continuously for the worst case scenario -- keep something frozen in 95F temperatures in Florida.

Rough calculations for the Honda EU2200i gas generator is that a 5 gallon gas can (200 amp/hours per can) can run that refrigerator for 8.5 to 5.3 days (depending on refrigerate or freeze).

There's also this, but it's REALLY specialist:

http://www.hotspotenergy.com/solar-air-conditioner/

http://www.hotspotenergy.com/DC-air-conditioner/

Expensive, and seems to have only been around for ten years (since 2006).

or this

http://www.coolalaairconditioning.com/about/?1.html
https://www.kickstarter.com/projects/1056070297/the-coolest-solar-powered-portable-air-conditioner
http://www.coolalaairconditioning.com/content/?439.html

They claim 3500 BTU cooling for it, and a draw of 8 Ah when running.

It's currently vaporware, but it does show the trend of things; these things will become common in maybe ten more years -- this is the "proof of concept" breadboard.

1 kilowatt-hour = 3,413 BTU
1 Gallon Gasoline = 125,000 BTU = 36.62 kW-hr
5 Gallon can = 625,000 BTU = 183.12 kW-hr

So, for the Honda EU2200i:

Run Time (tank size is 0.95 gal.)
3.2 hrs @ rated load of 1,800W
8.1 hrs @ 1/4 load of 450W

5 gallons of gas gets you:

28.8 kW-hr (1800W load)
18.225 kW-hr (450W load)

So the Honda is basically 9.95% (450W) to 15.73% (1800W) efficient [12.84% average] at converting the maximum potential energy in a gallon of gasoline to electrical energy.

Gasoline has a specific energy of 46.4 MJ/kg. At the going rate of 12.84% efficiency for generators, that translates to 5.95 MJ/kg for electricty generation.

To put all this in scale:

Commercially Available Batteries
Lead Acid/NiCad: 0.14 MJ/kg
Alkaline: 0.4 MJ/kg
Li-Ion: 0.59 MJ/kg

Experimental Batteries (lab only)
Lithium-Nanowire: 2.54 MJ/kg
Lithium-Air: 6.12 MJ/kg

So it looks like we're maybe one generation or so away in battery technology reshaping a significant portion of the ICE infrastructure -- a lot of ICE engines require a significant amount of weight devoted to thermal management (fins, radiators, thicker than needed castings) that can go away with a battery.

That said, I personally don't think we will get up to 6~ MJ/kg and above densities, because the specific energy density of TNT is 4.61 MJ/kg, and there are safety issues there with shorting, etc.

Glad I found this thread.  Hopefully I can get a small rig set up.

I bought one of the newer Harbor Freight 100 watt thunderbolt solar kits.  I basically just want to run the included lights in my shed, and possibly have backup power for a HAM radio and/or my battery chargers for my cordless tools.  Maybe a 12 volt fan.  I do have a little 175 watt power inverter that I would like to try out.

After reading around various forums it gets a bit confusing with all of the new components on the market.  At least for me.

I don't know what battery to get for these purposes.  I am tempted to just buy 2 of the Harbor Freight thunderbolt AGM batteries at roughly $55 each after coupon.

Does anyone have any experience with a beginner project like this?  Can I accomplish my goals with this kit?

Thanks for the help.

@phurba
Thread revival due to Corona virus.

You know it's an old thread when there are warnings for people using 56K modems because the thread is pic heavy.

I'm doing some finishing touches on my cabin in AK this month, then it's going to be dormant until June.  

When I head up in June, I am installing power and some quasi-modern amenities.  Here's what I'm thinking.  I will only use it in the summers, for probably 2 months at a time.

Cabin is 24x14 with a small kitchen area and a bathroom w shower.  No appliances, plumbing or electrical of any kind yet aside from septic.

Power
Mostly 12v system, but will have a couple of 120v outlets in it for convenience.
Solar panels on the roof, 2-4 golf cart batteries.  Haven't sized it yet but I will post a link to a google sheet once I do if anyone wants to use it.

Main power usage will be:
- a small water pump to provide an intermittently pressurized water system for showers & faucets
- very occasionally the blower for a small RV furnace (or I may just go with a little buddy or even a kero heater, don't know yet) for the rare cold day
- 12v LED lighting fixtures
- a few USB outlets
- An inverter feeding the 120v outlets, which would be for a laptop, maybe some random kitchen appliance (hand mixer?  I don't know), running the charger for my cordless tools, etc.  Nothing major.  

I will augment the solar with a Honda 1800w generator for battery charging during high consumption/long periods of rainy days, running power tools on site (circular saw)

Aside from the battery bank and solar panels I will select a charge controller that can accommodate a genset, as well as an inverter for the 2 outlets.

Other
Even though diesel is widely used in AK for toyostoves, I am thinking propane since my usage will be summertime.
Propane fridge (could go with a kero fridge)
Small 2 burner LP cooktop in the kitchen, for those rainy AK days
RV 6gallon LP water heater or possibly tankless LP water heater for showers
I will bring a tote of water in for my water usage for now.  Septic exists on site.

I've sort of leaned heavily on the propane/RV appliance angle on this place, heater and little RV furnace seem cheap to buy, fridge seems like a no-brainer, but if I am missing something with this let me know.

Basically, I'll show up in the spring with my generator and system components, and my outside support needs will be to bring some gasoline in for the Honda and a couple of propane tanks (like twin 40s) which I would think would last the whole 2 months, since I will mostly be cooking outdoors.

If anyone knows of a generator even more quiet that the little Honda, I'm all ears.  I detest the sound of them, and I am going to make a 3 sided box to defect the noise away from me

I have a small creek on the property, I am going to calculate head and flow when I am up there and kick around the idea of a small hydro set up.  Even if it just trickle flows some power to the cabin, 24/7 adds up.

I can bring utility power to the site if I need to.  But the main reason for all of the above is to tinker and play, so I don't mind cobbling up some crappy (for instance) hydro setup and find out it provides a mouse fart worth of power to me from that creek, or whatever.  (I am not going to be in a dire situation if the system hiccups either - I'm a couple miles from a major highway.)  The area is heavily wooded so wind power is probably out of the question though.  I have no idea how the dimmer "arctic sun" will balance with long days to provide solar.  There is a strong chance the panels will be some way from the cabin to get clear sunlight (50 feet or so), so I am open to the idea of wiring for 24 or 48 volt.  It just seems that things get way more expensive stepping out of 12v.