So...I'm Confused (what a concept) :)

t.ferguson

Hi All! I will preface this by saying I have no electrical knowledge or skills whatsoever, though I am willing and eager to begin learning. I am planning to live out of a van next summer and would like to rig it up with some solar power. All I need have working is a simple alarm clock, a laptop, a lamp and the occasional camera battery charger, ect. I have read a few articles, but have hit somewhat of a wall as to what my mind can comprehend. I suppose I am looking for general recommendations and advice on how to set this thing up in the simplest yet most efficient way possible. I would like to try and keep the whole thing under $1000.
Thank you for reading!

-Tess

BB.

Re: So...I'm Confused (what a concept)

Welcome to the forum Tess.

There are several ways you can proceed.

1) Use a Kill-a-Watt type meter (there are DC Amp*Hour / Watt*Hour meters too) to measure your AC power loads then design the system to support them.
2) Measure your roof top area and figure out how much in solar panels you can fit. Then size the battery bank to match the panel wattage.
3) Measure how much room you have for batteries, then design the system around the batteries.

An alarm clock--Probably a small travel alarm is your best bet--I don't recall any 12 VDC powered alarms, and AC clocks can be problematic with AC inverters (and wasteful of power).

You can get a couple of 12 VDC LED lamps, or use an AC powered LED Lamp. For battery/cell chargers--Again you can use a 12 VDC charger or a small AC inverter--Depends if having AC power is important to you or not (I like AC adapters a bit better over 12 VDC adapters--but if you have DC adapters already--they will usually work pretty well).

So--Recommend that your measure your loads first. This will set your expectations on how much power you can generate via solar/battery bank. If you use a smaller laptop and LED lighting--You could get away with 500 to 1,000 Watt*Hours per day (i.e., 40 watt computer * 10 hours = 400 Watt*Hours of load).

Also, knowing your power needs--Is 2 days of stored energy (with 50% maximum battery discharge) "Good Enough"? Will you be "dry camping" a lot--Or driving most days and/or working at places where you can plug in an extension cord?

Anyway, a "smallish" system that can provide 500 Watt*Hours per day during the summer (a minimum of 4 hours of "noon time equivalent" sun per day could look something like this.

First, 1-3 days of storage with 50% maximum discharge on the battery bank, 500 Watt*Hours of AC power. Pick 2 days:

• 500 WH * 1/12 volt battery * 1/0.85 inverter eff * 2 days of storage * 1/0.50 max batt discharge = 196 AH battery bank (20 Hour Rate)

The above would be 2x 220 AH @ 6 volt "golf cart" sized batteries (two large car batteries) for a 220 AH @ 12 volt battery bank

For recharging a battery, we recommend around 5% to 13% rate of charge. Starting with 10% rate of charge as a good "balanced" design:

• 196 AH * 14.5 volts charging * 1/0.77 panel+charger deratings * 0.10 rate of charge = 369 Watts of Solar Array

A 369 Watt solar array (say 3x 140 watt panels = 420 Watts as an example) would produce around:

• 420 Watts * 4 hours of sun * 0.52 over all system efficiency (AC Inverter system) = 874 Watt*Hours per day or more (average 6+ months of the year)

The above is just a "rule of thumb" based system design... Depending on what is important to you--We can "play with the numbers" to better meet your needs.

For example the above system is designed to reliably run a small cabin for 3-5 years for ~9 months of the year without needed a backup generator... That may be way overkill in terms of "conservative" design for your needs.

If you don't have the space for a pair of large batteries, you can use smaller batteries (less energy storage for bad weather/extra loads, and they may only last a couple of summers). Or if you don't have room on your roof top for that large of solar array--You can look at a small Honda eu1000i gasoline inverter generator. They are very quiet, small, and fuel efficient (run the genset a few hours every couple of days)... Etc.

When looking at your loads--Frequently the loads that run the longest time use the most power (i.e., a laptop computer running 12 hours a day can use more "energy" from the battery bank than using a microwave to heat your meals). For small system, picking loads that are very energy efficient (like a small laptop vs a large desktop computer) will be very important.

Will you be having help to install the system? RV shops can do the installs, but you are probably better off telling them what hardware (batteries, inverter, charge controller, solar panels, accessories) than letting them design the system themselves...

I understand the electrical math can be confusing--But is is really only a couple equations and if you follow the numbers--It does a very good job of helping you to design the system.

More or less it works out to Watts * Hours of use = energy needed to run your loads (in Watt*Hours or WH) (similar to Miles driven / Miles per Gallon = Gallons of gas used).

You may see talk of Amp*Hours--It is very similar to Watt*Hours == We just need to know the voltage to make the conversion:

• Watts = Amps * Voltage
• Watt*Hours = Amp*Hours * Voltage
• Watt*Hours = 3 amps * 10 hours * 12 volts = 30 AH * 12 volts = 360 Watt*Hours

-Bill

niel

Re: So...I'm Confused (what a concept)

welcome,
you have a modest request here and i don't see any problems running those items off of 12v except maybe the camera. you may be lucky if it takes aa rechargeables as there are some 12v chargers for them otherwise you may want to approach some places if there is a 12v car adapter available for the camera. in fact, many alarm clocks can use rechargeable aa batteries too and could last for quite some time between charges. you'd want a charger that facilitates an input voltage of 12v and there are some out there and shouldn't be more than $50-$60.

now i would suggest that you use a separate 12v battery for these items to insure you have enough power to start the van. these items won't have much of an overall large demand unless you do allot of shooting of the camera and use the laptop nearly constantly, but it would be difficult for me to guess at a capacity for you without knowing the draws of each item and the length of time during a typical 24hr period for the draws. i feel confident that a 100ah 12v battery would cover your needs, but a smaller one may also and you may need to determine that with the total ah you'll have in your daily loads. worst case is probably about $300 for an agm battery and i'm sure you can get one at a lower price depending on if agm, if name brand, at what capacity in ah, etc.

worst case charging requirements during sunny periods would be to deliver about 1/2 of the battery capacity over about 5hrs and at a 100ah battery this is 50ah give or take. over 5hrs means each hour requires a 10a charge so this is a 120w minimum for the pv and there are 140w and 145w pvs out there that could most likely meet your worst case needs. this will be just under $300.

for mounting this there are mounts available so you can put it on top of the van, but you could also have a ground mount remotely located from the van allowing the van to be in the shade while the pv is in the sun. in fact, you could probably make something to hold the pvs, but i won't go into details on it unless you opt this route.

to charge the batteries you could use a pwm controller of which there are many to choose from. the better ones will have a remote battery temperature sensor ability and i strongly recommend that sensor be bought if the controller of interest does not come with it. if you find you have enough cash you could even buy a small mppt controller, but this is not a necessity. you can look over some of the controllers here,
http://www.solar-electric.com/chco.html

once you have a better idea of the general course you'll take then specifics can be elaborated on along with wire, fusing, etc. so leave a small margin for miscellaneous stuff like this.

t.ferguson

Re: So...I'm Confused (what a concept)

Thanks guys! I appreciate it. I'm sure I'll have more questions later, but this is a great start.

Desert Rat

Re: So...I'm Confused (what a concept)

You can also wire the solar batteries to the van's charging system via a battery isolator so the batteries would be charged while driving. The isolator allows the solar batteries to charge, but keeps them otherwise separated from the van's electrical system.