21 and needing ALOT of help. First solar system ever.

JHart

Hi, my girlfriend and I have been renovating a 1950's aluminum spartan travel trailer that we bought off craigslist for a few months now. We want to keep it off grid and are, after ALOT of body work, paint scraping, ripping out and replacing, etc. about ready to put in the wiring. We want/need only enough capacity for 5 low wattage lights, one 90 watt per hour on demand propane shower, a blender which runs at 340 watts per hour (on for maybe 5 minutes a day max), and maybe an hour of lap top usage every once in a while. Everything else is fully propane. We are installing a water holding tank up top so everything is gravity fed.

We are both students, so we don't want to spend a whole lot on some super solar system that can power a flat screen and surround sound etc... We have only a few needs and want something solid that won't cost us an arm and a leg.

Also, since it is a shiny metal box, we would like to be able to park it in the shade, so we want the solar panels to be able to be set...i don't know, maybe 20 feet away from the trailer.

You now know about as much about my situation as I do. The preference again is to buy what can be replaced or upgraded later as cheap now and what can't be replaced later as quality now.

Please help me. I don't want to buy bits and pieces till I have the entire thing planned out in my head and frankly I have no idea where to start.

What solar panels should I buy, how many? How many batteries and what kind? what kind of inverter and do I really need an ac generator as part of my system? Any input would be greatly appreciated. Thank you so much for reading.

westbranch

Re: 21 and needing ALOT of help. First solar system ever.

Welcome, first thing that comes to mind is consider a small Honda gen set and a charger at this time if funds are sparse, Student? then later on when you can afford it.

Next you need to identify the loads and are any of them 120V vs 12, then attach a 'time' factor to cover how long they will run, so that we can figure out the number of Watthrs (V x Amps x time) you need to satisfy.

hth

Cariboocoot

Re: 21 and needing ALOT of help. First solar system ever.

Welcome to the forum.

What you need to do is look at it from the right direct: loads first. You have some idea what you need to power, but you'll have to get it a little more precise before you can make a stab at design.

For instance the "90 Watt per hour" for the propane shower unit. Is that water pump and/or electric controls for the burner? How long will you use it for?

It looks like the blender is your largest load at 340 Watts (not "Watts per hour"). Largest total loads are needed in order to size the inverter. You will probably be in the 1kW or less area.

But Watt hours is what determines the size of the battery bank. Use 340 Watts for 5 minutes and that's 28 Watt hours. Use 90 Watts for a 20 minute shower and that's 30 Watt hours. "Low Wattage" lights is a bit vague, and again the amount of time they are on for adds up. A 13 Watts CFL left on for three hours is 39 Watt hours, so the 'smallest' load can actually use the most power.

I think you will be wiring up for all 120 VAC stuff, no 12 VDC at all? Certainly not anything in the 240 VAC department. Just from the three examples above we see 97 Watt hours used, and you probably want a bit more than that. Space is also a consideration as batteries take up a fair amount. They are also heavy and in the case of FLA's need to be vented which limits your location.

Let's just look at a 'sample' system for 100 Watt hours (very, very small):

100 Watt hours AC is about 110 DC (inverter conversion efficiency) and you'd probably need about 5 Watts to run the inverter. Now we're at 115 Watt hours, might as well say 120 to make the math easy. On 12 Volts that's 10 Amp hours used, so for 25% DOD you'd need only 40 Amp hour 12 Volt battery. This can be done. Recharging isn't difficult because not a lot of power is needed to do that: about 70 Watts.

But (you knew there'd be a 'but' didn't you?) is it practical to go that small?
50 Amp hour AGM battery: http://www.solar-electric.com/unbamo45agms.html $91
600 Watt 12 Volt inverter: http://www.solar-electric.com/samlex-pure-sine-wave-inverter-pst-600-12.html $207
85 Watt solar panel: http://www.solar-electric.com/so85wa12voso.html $199
6 Amp PWM charge controller: http://www.solar-electric.com/mosupamoco6a.html $46
Plus wires and misc. hardware and you're under $700.

IF (and it's a big 'if') that is what you need.

Your desire to park in the shade and have the panels several feet away complicates things, as the lengthening of the wire run from the panel to the controller means greater power loss which must be overcome some way. This usually means higher panel Voltage and an MPPT controller to 'adjust' to the proper Voltage at the battery.

But the Watt hour requirement is all-important for getting things right. Which is where the generator comes in: in case you get it wrong or the sun doesn't shine you can still have power.

How are we doing so far?

BB.

Re: 21 and needing ALOT of help. First solar system ever.

One thing to remember is that the 'standard' solar panels are single weight (~1/8 inch) tempered glass. They are fragile, and if scratched or bumped hard, the tempered glass will shatter into a a 1,000 little cubes.

If you do not mount to the trailer, you must have a way of storing safely for the trip, and they need to be staked out so the wind does not blow them over. Also--Anything not nailed down is sometimes fair game--I would think about bolting them to the trailer--Probably less chance of damage.

Also, is this weekend boon-docking, or weeks/months at a time dry camping?

So far, your loads are pretty reasonable. A 300 Watt TSW 12 VDC inverter like this one, would be a good fit.

Interestingly, the modern LED Flat Screen TV does not use a lot of power these days.

-Bill

vtmaps

Re: 21 and needing ALOT of help. First solar system ever.

JHart wrote: »

one 90 watt per hour on demand propane shower, a blender which runs at 340 watts per hour (on for maybe 5 minutes a day max), and maybe an hour of lap top usage every once in a while.

Welcome to the forum,

As has been mentioned, you must know your loads before you design your power system (similarly, you must know know what your trailer weighs before you buy a truck to tow it).

In order to know your loads you must learn the language of loads. For example, "watts" is a rate. "watts per hour" is a rate of a rate. If your loads were 100 watts at noon, and then 175 watts at 1 PM, and then 250 watts at 2 PM, and then 325 watts at 3 PM, you would say that the power you are drawing is increasing at the rate of 75 watts per hour.

If your blender is drawing 340 watts, that is a RATE of energy use. If you multiply it by hours, you get the AMOUNT of energy that it has used. Thus if it is on for 2 hours it has used 680 wattHours of energy.

Both the rate and the amount of energy are important in designing a system. The amount of energy (watthours) you need will determine the size of the battery... a battery stores watthours of energy. The rate (watts) that you need to draw will determine the size of the inverter you need.

--vtMaps

bill von novak

Re: 21 and needing ALOT of help. First solar system ever.

FWIW we did something similar about 15 years ago. We converted a minivan and used a 12V 100AH AGM battery as the "house" battery to run lights, a thermoelectric cooler, a laptop, a satellite communications system, an audio system etc. Rather than deal with crystalline panels we got "raw" amorphous panels (no frames) and stored them under the mattress; they were only about 1/8" thick and were indestructible. This includes one hasty departure when I left them on the roof and drove off, and ended up dragging them 30 feet down a dirt road.

However in our case the majority of our power came from the car's alternator. We didn't stay in one place for longer than about a week, and were more often on the move than not.

JHart

Re: 21 and needing ALOT of help. First solar system ever.

Well first off, thank you so much for all the help guys. I can't tell you how much of a blessing this has been. Special thanks for being willing to dumb things down for me. Well, I'm going to try and address things in the order they were posted. You're doing great thus far .

Everything is 120v.

We probably will only use the show for exactly 20 minutes maximum a day. The power draw on it comes from everything you guess, temperature controls, pump, and ignition. So 30 watt hours.

The lights are 15 watt lights and I see us running 3 of them at MOST for 4 hours a day which puts us at 180 watt hours if I'm understanding this correctly.

Space for the batteries really isn't much of an issue; the trailer is 38' long and we put aside a good bit of space for them. On a related note, it tops out at 6,500 lbs and my girlfriends V10 can haul that fine from experience.

We are planning the months at a time kind of deal so thanks for the advice and whenever we move them we will do so very carefully, but those neigh on indestructible kind sound lovely.

So the general consensus here as far as i can tell is understand my load to the best of my abilities and then you guys can tell me more accurately what I need.

Here is my best attempt with all the help you guys have given me:

shower-30 watt hours

lights-180 watt hours

blender-28 watt hours

laptop-190 watt hours (if we watch a movie on it)

That puts us around 500 watt hours to have some margin. Am I understanding this correctly? So, if I am, what then would you all suggest item by item and is it feasible/cost efficient to create much larger battery bank than needed on a daily basis in case on multiple rainy days as opposed to getting a generator?

Again, I can't thank you all enough for you interest, your time, and your advice, especially considering how utterly frustrating my first post and maybe even this second post must be for all of you seasoned tech pros out there.

Thanks for reading.

westbranch

Re: 21 and needing ALOT of help. First solar system ever.

Well you can drop the CFL lights and go for LEDs. You should be able to cut that use to 1/4 to 1/2 depending on type of lighting you need, spot, flood, ambient. Lots of choices out there. Off hand start with 'Lights of America 'http://www.lightsofamerica.com/ for ideas and go from there.

I assume you mean 120V AC, that being so there will be a small inverter draw during its run rime, size dependant that needs to be accounted for..

hth

mike95490

Re: 21 and needing ALOT of help. First solar system ever.

My suggestions
A couple 12V 2W LED lights Attachment not found.
Very awesome gadgets, worth not using the inverter for
https://www.wiredco.com/10_LED_SMT_SMD_Warm_White_G4_Disc_LED_Module_12VAC_p/10ledwarmwhiteled.htm with their integral driver, they are good up to 30V

Dedicate a higher power inverter for the blender outlet, they generally have a universal motor, and run fine on a mod-sine inverter. (maybe it will run fine from the suresine)

Use a Morningstar SureSine 300w 600w surge inverter for your other loads, clean sine wave, low power inverter, with a remote off switch. It's surge capacity is not quite enough to start a fridge with.
http://www.solar-electric.com/mosu300wasiw.html

Plan a small genset to recharge with, or use the tow vehicle as a beefy charger. The 12V pin in the round RV trailer connector is only good to about 20 amps, then resistance drops too much voltage across it.

Have you verified the elevated domestic water tank has enough flow rate to enable the burner on the water heater ? Some have a pressure switch that needs 5psi to enable the burner (prevents dry run of heat coils).
(your holding tank is for the drain water, don't mix up domestic with holding)

Maybe a Sandwich Board style PV panel (ground mount) would work, use a couple water jugs as ballast & Anderson connectors for quick connects.

zoneblue

Re: 21 and needing ALOT of help. First solar system ever.

Thats where the shurflo type pumps really shine. 50W, for 10 minutes a day. Sweet as...

vtmaps

Re: 21 and needing ALOT of help. First solar system ever.

JHart wrote: »

That puts us around 500 watt hours to have some margin. Am I understanding this correctly?

I think you did not take into account the inverter load and inverter inefficiency in your calculations... but you did round up your load to 500 watthours which is reasonable.

The usual design criteria for a 'balanced' off grid system calls for a daily discharge of 25% of a batteries capacity. In your case that is a battery that stores 2000 watthours. A pair of golf cart batteries would be more than adequate and would be cheap.

JHart wrote: »

is it feasible/cost efficient to create much larger battery bank than needed on a daily basis in case on multiple rainy days as opposed to getting a generator?

That's a really good question. If you 'oversize' your battery bank, you may find that when the sun shines day after day your daily discharge is very shallow. That is NOT good for the health of your battery. The midnite Classic charge controller has a feature to prevent shallow discharges... it can be programmed to NOT charge the batteries on days where the battery starts out with a high SOC.

Another aspect of large battery banks is cost effectiveness. Suppose that your battery will get 1000 cycles at a daily discharge of 25% (=75% SOC). Now, suppose you double up the battery bank so that your daily discharge is only 12.5% and you expect to get 1800 cycles. What you've done is spend twice as much on your batteries and they won't last twice as long.

There may be very good reasons to 'double up' the battery bank. For example, if your daily load of 500 watthours was a 500 watt draw for 1 hour, you would need the doubled up battery because the RATE at which you are drawing the power (500 watts) could not be easily sustained by one pair of golf cart batteries.

A pair of golf cart batteries are usually about 220 amphours (220 amphours X 12 volts = 2640 watthours). That amphour rating is based on drawing the battery down to 0 over 20 hours. If you draw 132 watts for 20 hours that is 2640 watthours. Peukert's law says that the amphour rating of a battery decreases as the draw (watts) increases. If you were to draw 500 watts from a a pair of golf cart batteries, they would have much less than their 20 hour rating of 220 amphours.

Your 340 watt blender draws 340 watts, and only for 5 minutes a day, so a single pair of golf cart batteries will work well for you. The 28 watthours you calculated for the blender would really be a bit higher because 340 watts is higher than the 132 watts that the battery's capacity is based on.

Many off-grid folks design their systems around a single large load... for example a conventional deep well water pump. They supersize their entire system just to pump water. Sometimes they are much better off spending money to buy a 'solar friendly' water pump and then spending half as much on their power system. In your case the blender stands out. You would probably be very well served by the Morningstar 300 watt pure sine wave inverter... a marvel of good engineering. Unfortunately, your blender is a bit above its capacity... perhaps you could find a more efficient blender or a 12 volt blender as an alternative to 'supersizing' your inverter.

--vtMaps

Cariboocoot

Re: 21 and needing ALOT of help. First solar system ever.

Even with the conversion efficiency and inverter consumption 500 Watt hours should be fine (yes, I did the calculations based on 428 Watt hours listed use).

I agree with vtMaps: you've got the space go for the least expensive Watt hour storage. The GC2's at 220 Amp hours would be discharged about 18% from your usage. Maybe a tad more as you're bound to find things to run once you've got the power available. Everybody does.

In terms of panel normally we'd go with around 343 Watts on an MPPT for this. Your desire to have them detached from the trailer (and remember Bill's warnings about damage) means the MPPT will make things much easier. You're looking at a 30 Amp controller such as MidNite's Kid or Rogue 3048 or Morningstar's TriStar 30 MPPT. This will give you a great deal of flexibility for your panel choice as practically anything that meets the Watt requirements will work; the MPPT will take care of the Voltage difference and allow higher array Vmp to overcome the wiring distance between array and controller. You could have a little more panel (up to 468 Watts) or perhaps even a little less. More will probably be cheaper.