newbie with some questions

gizzy2014 · April 2014

im new to solar energy and am working on a solar powered enclosed trailer for a school project.

i need opinions on what we have picked out to buy for it and need a CC recommendation

batteries: Extreme X2-power part number: SLI24AGMDP
these were recommended by batteries plus to us, if you have a better suggestion feel free to add it

panels: 3X
max watt: 255
max Vmp: 30.4
open circuit Voc: 37.5
max system V: 600
max power current: 6.36A

so basically right now i just need a CC recommendation from someone and im sure ill have more questions as we get alittle farther into our project

mike95490 · April 2014

Re: newbie with some questions

It would be helpful to know what the loads are going to be, that's the first step in a project. You don't want a Honda CRZ if you have to haul 3 kids and 2 bags of soccer balls daily.

Cariboocoot · April 2014

Re: newbie with some questions

Welcome to the forum.

Well I guess Batteries Plus is staffed by idiots because those are automotive AGM batteries, not deep cycles. So right away it's all gone wahoonie-shaped.

Now let's get back to what Mike said: how much power are you trying to supply? Without knowing that requirement you are in the 'wild guess school of design' with very little chance of success.

gizzy2014 · April 2014

Re: newbie with some questions

Cariboocoot wrote: »

Welcome to the forum.

Well I guess Batteries Plus is staffed by idiots because those are automotive AGM batteries, not deep cycles. So right away it's all gone wahoonie-shaped.

Now let's get back to what Mike said: how much power are you trying to supply? Without knowing that requirement you are in the 'wild guess school of design' with very little chance of success.

ok well thats good to know, he said they were a deep cycle on the phone

thought i would add this is a high school project, and this trailer is to haul our 2 competition cars to the track

Our loads would be power tools if we need them, and our teacher wants to have a stereo system in there he said 300-400 watts on the system he would like to put in there, we plan to have 3 LED light strips on the ceiling for our lighting, and possibly may add a tv on the wall for a ps3 for after the track closes and there isnt anything else to do after dark there.

Cariboocoot · April 2014

Re: newbie with some questions

gizzy2014 wrote: »

ok well thats good to know, he said they were a deep cycle on the phone

Yes and when they're trying to sell you stuff they'll say whatever you want to hear. Technically RV/Marine batteries are "deep cycle" but they aren't designed for RE use. About the only auto battery that will work is the Optima, and even then you have to get the right one.

thought i would add this is a high school project, and this trailer is to haul our 2 competition cars to the track

Our loads would be power tools if we need them, and our teacher wants to have a stereo system in there he said 300-400 watts on the system he would like to put in there, we plan to have 3 LED light strips on the ceiling for our lighting, and possibly may add a tv on the wall for a ps3 for after the track closes and there isnt anything else to do after dark there.

Well that's not going to work unless you've got a huge budget.
Power tools can draw quite a lot of power. 300-400 Watt stereo (presumably that's the RMS output rating) likewise - just look at that Watt number. A TV and PS3 can be a couple hundred more Watts. Only the LED lighting is really a low load.

And then you have to have the answer to the impossible question: for how long will these things be running? That's Watt hours and it is vital to sizing a battery bank.

For example if the TV set-up is 200 Watts and you watch a 2 hour movie that's 400 Watt hours right there. In terms of battery capacity (with conversion efficiency or inverter draw) that's about 34 Amp hours @ 12 Volts. For a set of GC2's (the default for off-grid systems because they are very economical in terms of Watt hours for the price) it would be 15% of the total capacity, or 30% of the maximum discharge. And that is one item on the list running for two hours. Now imagine that stereo taking twice as much power.

See what I mean?

BTW to recharge that set of GC2's you need about 385 Watts of panel, and that amount goes up in direct proportion to the amount of power you use too.

Small inverter-generators are your friend. Far more power capacity for far less investment.

BB. · April 2014

Re: newbie with some questions

Start with a Kill-a-Watt type meter... Until you measure your AC loads (average/peak watts, hours of use per day), you are just guessing. You can get a DC Current Clamp meter and/or DC AH/WH meter too.

A Battery Monitor (like the Trimetric is also very nice, but kind of pricy for a smaller battery bank).

Off Grid Solar power is expensive... Very roughly around $1-$2+ per kWH -- Or about 10x the cost of utility power. And it is even worse for part time usage of power (i.e., weekend/seasonal/random use is expensive because most of the collected solar energy is "lost" as the batteries can only store ~2 days of useful power--Vs 9+ months of full time off grid living). Plus the monthly maintenance (measuring specific gravity, filling with distilled water, checking connections, cell/battery voltages, etc.).

Golf Cart batteries are great for a "training battery bank"--However, they typically will only last 3-5 years before they need to be replaced.

If you are trying to do a solar project--Pick something small (like 2-4 golf cart batteries at most, and enough panels to support that), and get a Honda/Yamaha smallish inverter-generator (eu2000i, eu1000i, etc.).

Generators will last many years, if not a decade or more, if properly stored (drain fuel after use, etc.). And they only consume fuel when actually running (a 1,600 watt inverter-generator Honda eu2000i will run ~4-9+ hours on one gallon of gasoline).

-Bill

westend · April 2014

Re: newbie with some questions

All good advice above. What your goal seems to be is inline with what some install on an RV. Here is a link to some pictured solar installations.

As other's have posted, defined power usage is the key to a good installation. Here is a link to a downloadable power use calculator.

If part of the project is to keep everything to the lowest price and if you have available real estate for mounting, I would suggest using nominal 12V modules (you may have already made that decision), an inexpensive brand name PMW solar charge controller, and a pair of 6V GC2 batteries. Depending on your use, a smallish (300W-600W) sine wave inverter would be a good choice for running screens, game consoles, stereo 120V system, and charging small electronic devices. If part of the use is to run small power tools or an air compressor, a bigger inverter will be needed (1000W+).

FWIW, my LED/LCD 32" screen draws 33W at 120V, 120V stereo receiver draws 40W at 120V, dorm fridge draws 80W at 120V (with a 6 amp lock-rotor draw). A 235W 24V nominal module, a 15 amp MPPT controller, a 1000W sine inverter, and two battery banks totalling 300 AH powers everything.

Good luck with your project.

newbie with some questions

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