Solar panel for camping

Re: Solar panel for camping

Justniv wrote: »

You took the wind out of my sails
i've already bought the cells
my plan is to buy an inverter as well, and charge controller, like this one http://www.ebay.com/itm/Solar-Charge-Controller-Solar-Panel-Battery-Regulator-Safe-Protection-12V-24V-/171061139015?pt=LH_DefaultDomain_0&hash=item27d409d647

Sorry about that--We try to be conservative and have found few people have the skills (and the material/equipment) to build reliable solar panels. To give you an idea--This person did a nice job of documenting how to build a DIY panel similar to how a factory would:

http://fieldlines.com/board/index.ph...,144982.0.html
http://fieldlines.com/board/index.ph...,144995.0.html
http://fieldlines.com/board/index.ph...,145004.0.html

And, here is why larger arrays of DIY panels (and panels of dubious sourcing) is not a good idea:

Panel Fire Question

it doesn't need to be that precise, worst case I'll just calculate like each led bulb/speaker charger/phone charger gonna draw a bit more

Some of us are engineers here and have been accused of "over design" regarding off grid power systems (others here have learned the rules through the school of hard knocks). And to a degree that is true. For an off grid home or business, reliable power (with the least amount of maintenance) is usually a good design goal.

For something for camping where you go without lights for all 6 hours per day in cloudy weather, you just go to bed earlier.

i'm planing to use the system for 6 hrs max. (0.85+0.32)*6= 7.02Ah.
so by your advise i should buy a battery of 20Ah or more.

Backing up a moment... Size/weight of lead acid batteries can be a real drawback. Having a battery that will store 4x the daily energy is good for an off grid home/business where they will want 5-8 years or more life from their battery bank.

Hiking or even a "car trip", carrying around a smaller version of your car's battery may not be the best choice (short of going with very expensive Lithium Iron Phosphate batteries and there chargers).

A Lead Acid battery will last longer if it is not cycled too deeply. 50% maximum discharge is good for >1,000-2,000+ cycles or more. And discharging to 20% state of charge, you may only get 100-500 cycles out of it (i.e., the difference between 2-4x daily load vs 1.25*daily load).

And, if the battery will only last 2-4 years, plus you will only be using for ~28 cycles per year (2-4 weeks of camping), even 28 cycles to 20% state of charge will still last almost 4 years (check battery specifications, there are many different types of small batteries out there). So, a 4x larger battery may be overkill for the application.

Don't plan on taking the battery below ~20% state of charge (or dead), that will usually permanently kill the battery (or it will die in the next few weeks).

so if i'm using only twice a year it's not very smart buying this battery because it's gonna be rouin after ~3 years?

Yep--And you need to recharge the battery once every 1-3 months (depends on type of battery, flooded cell vs AGM/GEL for example). So it may die in long term storage (who remembers to plug in a battery every month or so).

Plus, if you leave the battery plugged in 24x7--It may die from over charging (many chargers do not do "float" well). My personal choice has been a cheap 1 amp battery charger and a lamp timer set to turn on ~1 hour per day--That is usually enough to keep the battery charged without over charging.

You could also set up the solar panel+charge controller+battery to recharge in storage (if you can get the panel into sun light)...

I'm sorry but i didn't understand the calculation and all the values.....

5.85 AH * 14.5 volts charging * 1/0.77 panel+controller derating * 1/6 hours sun = 18.4 Watt minimum suggested array

• Amp*Hours -- I think you have that fine
• 14.5 volts -- Battery bank charging voltage for a 12 volt battery bank (Power=Volts*Amps -- So the higher charging voltage of a lead acid battery needs more "wattage" from the solar array to fully recharge the battery bank).
• 0.77 -- That is, roughly, the derating factor for name plate Wattage (STC Standard Test Conditions) plus charge controller losses. I.e., a 100 watt panel will only output ~77Watts into the battery bank on a normal summer day (there are more details if you are interested, but this is "good enough" derating fudge factor for most installations). The less efficient the system, the larger solar panel needed.
• 6 hours of sun -- That is the rough amount of "noon time equivalent sun" that a solar panel will collect in North America on a sunny summer day (no clouds, no shade). We can looking actual hours of sun per day if you let us know where you will be camping and the season (i.e., perhaps 6+ hours in June/July, 4+ hours for nine months of the year, 2-3 hours of sun deep winter). The less sun you get, the larger solar panel you will need.

You multiply that all out per the formula, and we can estimate the smallest wattage solar panel you can use to meet your needs on a sunny day. Note that for your system, you will be looking for solar panels with Vmp (Voltage Maximum Power) in the range of ~17.5 to 18.6 volts). Too low of voltage, the battery won't properly recharge. To high of voltage, and the 0.77 derating number will get worse (i.e., a high voltage panels will have less energy available to recharge your battery bank).

• 7.02 AH loads * 14.5 volts charging * 1/0.77 panel+controller losses * 1/6 hours per day of sun during summer = 22 Watt minimum solar panel for summer use

Regarding your EBay charge controller--Don't know anything about it. It may work OK, or it may not last very long. Just don't know.