Solar panels?

[sbishop]

Hi folks...its been a few months since i posted anything but i'm still looking around! ;)

i'm getting ready to install a couple of small solar panels 15W each. they have been sitting in the box for 2 years now..so its time to get them on the roof. i've got a 1500w inverter and charge controller. Pick up 2 deep cycle 12V 110 AH batteries last night so i'm set to go. This setup is just for a small tv and maybe a few lights at the camp.

So my first question is what size wire should I run from the panels to the controller? it will be no further then 40ft. Is 12/2 wire over kill? the reason i ask is that i have some in hand.

Second question is how long will it run a tv and sattelite receiver? each take .6amp...so total of 1.2amps, is it correct to say that it will run 12amp at 12v? if the batteries are 110AH and i've got 2 would that mean i would get approx 18hrs?

At what point will my inverter stop working? at what voltage?

any guess on how long would it take to rechage the batterries?

Thanks for all the info.
Sbishop

[Ianab]

I'd run the heavier wire if you have it. Heavier gauge, less resistive loss. I suspect you will want to add more panels in the near future as 30w isn't a lot of power, maybe get 2 amps @ 12 volts? The 30w is best case. When the sun isn't overhead, or there is a bit of cloud it will be less.

Your run time maths is correct in a perfect world, but the inverter isn't 100% efficient. Might lose 10-20% of the power it converts. Takes you back to maybe 14 hour run time? Still useful of course. Inverter should cut out at maybe 11 volts? You don't want to suck the battery 100% flat as that tends to kill them.

Charge time? Pretty long. Batteries also aren't 100% efficient. You probably need to charge 130 a/h into them to get the 110 back out. Two amp charge? That's something like 65 hours of good sunshine, maybe twice that amount of daylight? It will get them charged, and keep them topped up, but you are probably only going to collect a couple of hours TV time per day.

To get them close to charged in a day would need more like 200-300w of panels? Hence the suggestion to run the heavier cable now.

For the lights I'd be looking to run 12v led lamps directly off the batteries. They are very efficient, and you don't waste any extra power in the inverter. Look at the RV and boat accessory places as they are becoming pretty standard in those markets

Ian

[sbishop]

So there no extra loss for using the larger wire?

our plan is too have enough for a few hrs in the evening for the kids to watch...and me too  ;D

Any suggestions on how to mount it on a 9/12 metal roof....attach it directly or have them propped up a bit?

i know 30w isn't much but its a start..maybe add a few more panels..but hopefully some day i can run a water wheel with a PMA from the river which is only 50ft away.

Thanks Ian

[Ianab]

Less loss with bigger wires. Think of it the same as a water pipe. If you use a larger dia, it restricts the flow less. A pipe that's too small makes back pressure and slows the flow. Same with electricity through a wire.

Angle of the panel? Ideally you want it 90 deg to the sun. On average this would be the same as your latitude. But if you wanted to be clever you could make an adjustable mount with summer and winter positions and get a few more watts.

What you have should work if it's a weekend camp. Build up enough charge during the week to give you a few hours power in the evening. Will power a couple of small LED lamps for quite a while. 10w of LED is a respectable sort of lamp.

Ian

[jdonovan]

So my first question is what size wire should I run from the panels to the controller? it will be no further then 40ft. Is 12/2 wire over kill? the reason i ask is that i have some in hand.

you can look up volt drop tables... most you find are for AC, when using them for DC double the drop the table shows.

Second question is how long will it run a tv and sattelite receiver? each take .6amp...so total of 1.2amps, is it correct to say that it will run 12amp at 12v? if the batteries are 110AH and i've got 2 would that mean i would get approx 18hrs?

Depends... generally batteries are rated at c/20 rate. That means full discharge over 20 hours. If you pull 2x the C/20 rate, you will not get 1/2 the run time, you get less as the battery has to work harder to supply the current, and more is lost to heat.

Most battery makers have discharge charts available and you can use it to approximate what your battery might do.

At what point will my inverter stop working? at what voltage?

RTFM.  Usually about 10.5 volts.

BUT you really really don't want to discharge them that low. A battery is good for X full discharges. But if you only discharge to 50% you may get 300% more life.

any guess on how long would it take to rechage the batterries?

Figure your panels will put out about 4-5 hours of 'equivalent' hours of charge on a sunny day. So 1 15Watt panel will put about 3-4 AH per day into the battery. You've got a loss of about 10-20% when charging, vs direct use from the panel.

Hopefully you're using a deep cycle/marine battery not a starting battery. A starting battery might only give you 50-100 discharge cycles before its done. A deep cycle might give you 10 times that.

[trapper]

what about dc tv.  My buddy has one in his cabin.  Inverter not needed.

[mad murdock]

what about dc tv.  My buddy has one in his cabin.  Inverter not needed.

good point. If you are running a limited circuit anyway, if you can stick with DC all the way, you will not take such a hit on efficiency.

[Ljohnsaw]

I plan on doing all 12v in my cabin.  The power company wanted $1,000 to just look and give me a proposal for power.  Their average installation was between $10k and $45k!!

So, I'm doing LED throughout, no microwave and propane stove/oven and water heater.  What else do you need?  There is no TV reception but I will probably have an RV TV with DVD/BluRay for the evening/bad weather days.

At the rate the solar panels are improving, by next year, I figure two large panels (3x5 or so) will put out 300w each.  I'll run a 24v system to the batteries (to lessen losses) and no more than 25' to any power outlet/light.

[mad murdock]

Lehman's even sells kerosene refrigerators if propane is not readily available. Amazing the things that are had these days to lessen ones need on electricity.

[John Mc]

At the rate the solar panels are improving, by next year, I figure two large panels (3x5 or so) will put out 300w each.

SunPower already makes 345 watt panels.  However, they're a lot more expensive per watt than the more commonly available 250 watt panels.

[maple flats]

What is the rating schedule on your panels? There should be a label showing Pmp (power, maximim power, in watts), Vmp (volts at max power), Imp, amps at max power, Isc, amps short circuit and Ptol, power variation panel to panel. I believe your 15 watt panels are going to be something like Pmp 15W, Vmp 15V, Imp 1amp, Isc 1.1A and Ptol maybe 0%/-5%. Am I right. If yes, you can figure 30 watts (connect in parallel) at 15V to calculate loss. At 40' if these numbers are correct you will lose2.6% with 16 ga, 1.63% with 14 ga, 1.02% with 12ga and .64% with 10 ga.
Regardless of whether my label guesses are correct, you can see the relationship as the wire ga gets larger. Bigger wire has less loss. These numbers are at 40' and they change as that number gets bigger or smaller. The main thing it to realize that at 30 watts you have very little you can afford to lose. The heaviest wire you can afford will net you the most usable power. The second thing is how you use it. If you are all DC you lose nothing in inverting to AC.
At best you will maybe be able to run an hour or 2, but only on days that had good sun. If you draw a battery down too low you ruin it. I would really suggest you try to get a bigger panel. Did you buy these thru Harbor Freight? You can do better. Go to a solar vender site and just look up their best price for several small size panels (I use a 50 watt just to charge my tractor batteries, both 12V, and I use a MPPT charge controller to regulate the charge and I only charge one at a time, I also have 6320 watts solar that sends excess power to the grid along with 1480 of those watts connected to a MPPT (maximim power point) charge controller to maintain a 48V battery bank for backup  but it normally sells excess to the grid., overcharging will ruin a battery too.grid. If you are small, you can connect directly and use no charge controller. If you get a bigger panel be careful to determine if it can overcharge the battery.
Be careful, if you just want to keep it simple, go with very basic system approach, everything you add will refine the system, but also starts making the price climb rapidly. (point in case, I first ordered 1 panel at 150 watts, 5 yrs later I had 6320 watts, grid connected and had spent over $32,000 US before tax credits and incentives that only happen if you are grid tied.)

[sbishop]

Sorry guys for not replying...my back gave out shortly after this post and i'm just getting around..feeling a lot better today.

Looks like i should get a few more bigger panels...again i'm just trying to recharge my batteries during the week while i'm not there....i plan on not running my batteries below 12.0V...every year i'll add a battery or two and make this a little bigger each year..thanks all that responded!

[jdonovan]

Looks like i should get a few more bigger panels...again i'm just trying to recharge my batteries during the week while i'm not there....i plan on not running my batteries below 12.0V...every year i'll add a battery or two and make this a little bigger each year..thanks all that responded!

mixed age batteries are not a good plan. The when the older battery starts to fail it can damage the whole bank of batteries.

[240b]

I own an off the grid house which I lived in full time for 6 years up until last year. My advice is figure out what you think you need and double it as far as capicity. Than install that much. It will only cost you more in the end trying to piece meal it.
(guess how I know).  Juice off the grid is the best thing going. If I was able I'd tap into it. But it was over 150k to run the service. The property was unique enough to bother building on..    Also I'd recommend a mix of wind and solar if the site is suitable..( the wind usually blows when the suns not out)

[beenthere]

240b
Where was that at?

[thecfarm]

Same price for power here too. About 25 years ago.  :  4-5 people went in on it and paid to put it in. Than 15 years later I had a home built here.

[240b]

VT, guy from co-op ball parked it for me.  Its about 3/4 mile thur woods to service, but they will only run new lines along the town ROW now. which makes it a most 5 miles to nearest pole.  Plus if I brought it in that way most likey a few new houses are going to pop up on the road. I am 3/4 mile past end of town row and the town road is a class 4 dead end.  Plowing snow stinks but its the price u pay.

[SwampDonkey]

I see no fairness in the first guy taking the hit to install power. The power company up here rebates the first guy for each additional transformer from others coming in. Which is a fair system I'd say.

[John Mc]

Power company here does the same thing. It's been almost 12 years since we put in the line, but if I remember correctly:   If someone taps on to the line you put in, you get a rebate based on home much of your line they used.  For example, if they tapped in 2/3 of the way down, and were the only other person on that line, they would pay 1/2 of the cost of that 2/3 of the line. 

There is a time limit, if I recall.  What sticks in my mind is 7 years, but I may be off on that.

Unfortunately, there is no such provision for roads.  The town would not open up the 400' of their right-of-way, to the point where our driveway splits off, so we got to do that one on our own (We also get to maintain it).  When someone else built and used about 375' of that road, we got nothing.

[240b]

Unfortunately, there is no such provision for roads.  The town would not open up the 400' of their right-of-way, to the point where our driveway splits off, so we got to do that one on our own (We also get to maintain it).  When someone else built and used about 375' of that road, we got nothing.
[/quote]

The joy of sharing a class 4 road. The section I share only gets fixed enough to be passable and the rest which I don't share is better than the town highway.  Yeah the power co-op will pro rate the cost if some one taps into it with seven years, but you still have to lay out the $$ to start with and I know of two people who are waiting out the seven year period to the day.

[maple flats]

When my brother and I built an office, workshop several hundred feet down a road from the grid power, we had to pay $5500 back is 1990. I think it was about 700' down the road. We got 1/3 back for each of the first 2 new homes to build, which followed 3-5 yrs later. There are now 4 others on that road. We never got more back than the 2/3 of the original.
That price is now much higher. Last year I had to pay a little over $28.00 per ft to run new lines to my sugarhouse for a 240' run. I got the 1st 100' free and had to pay $28.00+ per foot for the next 140'. I then ran another 230' underground to my sugarhouse, connected solar power to net meter into the grid. Even though I have carried a net flow toward the grid all but 1 month, I still have to pay a line delivery charge to the grid of $22.93 each month. It seems like they should be paying me, it is flowing towards them more than towards me. The utility just has total control, and charge for as much as the public service commission (PSC) allows. It seems like the PSC should not allow them to charge me to deliver power to them.

[John Mc]

That $22.93 is most likely what you are paying them to maintain the lines, read the meter, and handle the account administration for your account.

Here in VT, if you generate more than you use, the credit can be applied to the flat monthly charge, as well as to any future net electrical usage. Any crdit more than 12 months old basically becomes a gift from you to the utility.

[JSNH]

In New Hampshire the monthly fee is $11.50 if you use no electricity. Any surplus you build up a khw credit for the future. None can be applied to your monthly bill. I had 1500khw of surplus but used it up over the winter. I am back to overproducing and building up a credit again.

[maple flats]

I was at 1400 KWH credit about 2 days ago. In the months since I installed the system my only month that was not in the credit balance was last December. My system was activated on net metering Nov 26, 2012. Once we build our home there the tide will turn.

[mad murdock]

If you are running LED lights on 12V, you can purchase standard service 115VAC LED's and put in a Joule lamp (Oscillating Tesla Coil), that will effectively run in the instance linked, up to 12 LEDs, and pull only about 22-24 watts of power.  Very effective way to increase light without breaking the potential of your off grid system
https://www.youtube.com/watch?v=3C-WW9gd8SM

and the 2nd part of this how to
https://www.youtube.com/watch?v=GWq5uDdiQzE:
This guy has a lot of how to's that he has posted on youtube, and I have found his videos very instructional and realistic.  He admits right off that there is no such thing as something for nothing, so he is not claiming unreal results, IMO.