Small Off-Grid Setup Questions with Schematic

[Solarmonkeys]

Good Day All

Long time admirer of the Sun, first time capturer of energy.

I have purchased the components of a small off-grid system for my Mom's place up in the mountains.

Using what little I know about solar systems I have created the posted schematic.

I have three questions and completely submit myself to this group's superior knowledge in this area.

1. Overall setup suggestions? This system has not yet been setup so I will take any suggestions on wiring, parts, etc.

2. What breakers are required for this setup? Any suggestions for make and model would be appreciated.

3. Where should this system be grounded? I think it is from the solar panel to the ground but than I don't know if this should tie into the negative of the whole system.

Thanks in advance for anyone who takes the time to help out.

Solarmonkeys

[waynefromnscanada]

One suggestion would be to make sure that inverter is either turned off, or disconnected from the batteries whenever it's not in use. Just checked the specs and it draws .5 amps just to idle along waiting for some load to power. That's roughly 12 AH per 24 hour day and a substantial bite out of you're 100 watt panel's daily production..
One big question though - - what do you plan, expect, or dream about this system powering? Would really help if we knew the expected loads.

[icarus]

Once again, welcome to the forum,, there are some very sharp folks here.

A couple of quick comments, first, carts and horses, ready, fire aim!

Before yo or buy anything, define the loads that you wish to or expect to run off your system. All hardware choices stem frothy loads, to do ithe wise brings heartache. Next, size all the components to themselves so they "play well together, particularly PV band batteries.

Finally understand the two most basic rule SoC off grid solar. The first is, loads always grow with time,, so factor in some head room. Second people almost always over estimate the amount of power they can actually harvest,and finally they almost always underestimate the loads. Start right in the beginning, and you will have a much more successfull project.

Once again, welcome,

Tony

[waynefromnscanada]

Haha Methinks icarus was in a bit of a hurry with his "frothy loads"

[SolaRevolution]

I have purchased the components of a small off-grid system for my Mom's place up in the mountains.

You've got the "horse" lets see how big of a "cart" you can pull;

(Remember that Watts = amps x volts. Watts= Power, Watt/hours = Energy)


Assuming that your battery is full, you have a total rated battery capacity of 33 amp/hours (c-20) @ 12v = 420 Watt hours. This means that if you draw 1.65 amps (21 watts) from your battery for 20 hours you will draw 100% of the energy from it. Unfortunately a battery is a lot like a "horse" in that if you take 100% of the energy out, it will die. If you take it out for a hard run and use 80% of it's energy it will survive, just don't expect it to live long if you do this every day. Daily usage should be in the range of 50% or less. The less deeply you "cycle" the more total cycles you can expect to get out of it. So,

100% =33amp/hours @ 12v = 420 watt/hrs (Rated battery capacity)
80% =26ah @ 12v = 312 wh (Max Depth Of Discharge)
50% =16ah @ 12v = 196 wh (Max DOD for regular usage)
30% =10ah @ 12v = 120 wh (Best regular DOD for max battery life)

To get the full potential from a battery you can only draw the power so fast. The 33ah C-20 rating means that to get the maximum energy from your battery it can only deliver 1.65 amps (20 watts) constantly for 10 hrs = 50% DOD. If you draw more current the battery will not be able to deliver as much energy before the voltage falls too low. The maximum current draw on that battery should be no more than about 3.0 amps (36 watts) constantly for 5 hrs = 50% DOD. It can deliver brief surges of about 16 amps (+/- 200 watts).

As waynefromnscanada pointed out, your inverter has an idle current of 0.5 amps @ 12.6v = 6.3 watts. This is while the inverter is on even if no loads are connected. It is critical that you turn off your inverter while not in use. Some of these small inverters can draw a small amount current even while turned off so it is a good idea to have a switch/breaker in the inverter-to-battery connection to completely disconnect it while not in use.

So when you figgure out how much power your loads will draw you need to figgure in the efficiency (+/- 85%) and the idle current of the inverter. For example , one 13 watt compact fluorescent light will draw 13 watts / .85 = 15.3 watts + 6.3 watts idle current = 21.6 watts. It would take about 9 hrs to draw the batteries down to 50% DOD. The max recommended load for this battery would be about 2 CFLs and a cell phone charger (+/-5 watts) for about 5 hrs to a 50% DOD. Even a laptop will be on the large size for this battery.

As for charging,
Your solar panel is rated at 100 watts (18.5vpm X 5.42a = 100w ) Fed through the PWM charge controller it will operate at the battery voltage. So +/- 12.5v x 5.42a = 68 watts. This is a charge rate of about 16% of your battery capacity. Pretty good ratio. If your battery has been drawn down to 50% DOD (-16ah from 33 total) it should take around 3 "noon sun" hours to recharge. Actual time will be about 5-6 hrs because of sun angle, inefficiency and lower charge rate for the top 10% of the battery capacity.

While the sun is still shining and the batteries are full, your incomming solar power will be at the use-it or lose-it stage. This would be the time to use the radio/small tv, laptop charging, etc... Just be sure to keep an eye on the battery and understand that once the voltage falls to ≤12.5 you are starting to draw from the battery again.

1. Overall setup suggestions? This system has not yet been setup so I will take any suggestions on wiring, parts, etc.

2. What breakers are required for this setup? Any suggestions for make and model would be appreciated.

3. Where should this system be grounded? I think it is from the solar panel to the ground but than I don't know if this should tie into the negative of the whole system.

I suggest that such a small system should be kept as a portable system. If the cabin is to be left unattended for long periods of time you may want to take the battery home and put it on a battery tender type charger. Otherwise be sure you can disconnect the inverter and leave the PV and charge controller connected.

1. This is a very small system so keep everything close together. (Your 120vac output can go a couple of hundred feet if needed on extension cords.) Your PV and battery wiring should be as short as possible.

2. This can be kept as a portable system. Wiring this into an AC power distribution system is possible but it would be silly. Automotive type fuses for the PV would work fine. The inverter has onboard fuses so one of these: http://www.solar-electric.com/mr60ampdccib.html or even these:http://www.solar-electric.com/anhicupoco.html could work as a disconnect for the inverter/battery connection.

3. If this is to be permenantly kept in place, by all means ground the chassis and frames to a 8' ground rod. The DC negative should be connected too. This small inverter will probably die if you try to bond the AC neutral to ground.


-Alex Aragon

[icarus]

In a hurry yes! But in fact I am relying on the iPad for nearly everything, and I don't proof read week (when I do) and the iPad has this strange auto correct so if you are not paying attention it spells out all kinds of weird stuff that I didn't intend. I need to be better about proof reading.

Sorry to all for the on going confusion.

Tony

[mtdoc]

1. Overall setup suggestions? This system has not yet been setup so I will take any suggestions on wiring, parts, etc.

Based on your schematic, here are some possibilities:

I set up a similar small system and used a Midnite Baby Box as an inexpensive breaker box. Note - it is not weather proof or outdoor rated.

Your 10AWG wire size is fine between PV and CC, Battery and CC. You will need larger cable between the battery and inverter - how large depends on the distance between them.

2. What breakers are required for this setup? Any suggestions for make and model would be appreciated.

These Midnite solar breakers in the 10 amp flavor would work well between your panels and CC, battery and CC. They easily mount in the Midnite Baby Box mentioned above. The nice thing about using these it that they can safely be used as switches as well The largest size of these breakers available is 63 Amps which might be just a tad small for your inverter's peak surge output of 800W. As also recommended by SolarRevolution below -I think it would be better to use one of these breaker/switches (80 or 100 amp) between battery and inverter. Be sure the cable size you use here has an ampacity that exceeds the breaker size.

The one thing I would caution if using the Anderson connectors mentioned below to connect and disconnect the battery and inverter - is be sure to turn off the inverter before doing this. If connected or disconnected while live you will get some arcing of the DC current and the Anderson connectors will get pitted and damaged over time.

3. Where should this system be grounded? I think it is from the solar panel to the ground but than I don't know if this should tie into the negative of the whole system.

I think there are grounding experts here that can answer that question much better than me.


Good luck and have fun!

[SolaRevolution]

This small inverter will probably die if you try to bond the AC neutral to ground.

BTW, this inverter does not appear to be listed by any underwriter. It seems intended for portable or mobile applications.

-Alex

[westbranch]

Sorry to all for the on going confusion
Tony

No problem Tony we are gettign bedder at reeding vetween the lettters...

[Solarmonkeys]

Folks

I apologize for taking so long to reply to your comments. I was recently elected the only semi-competent mechanic in my family. I have spent the last couple of weeks replacing fuses, oiling windows, etc. Sort of the perfect storm of minor problems that needed fixing.

I need to say that this is without a doubt the most incredible forum I have ever had the pleasure of working with. Your replies were both timely and informative, a rarity, as my own delays are proof.

Wayne - Good idea to read the Inverter specs. I probably should have thought of that. Will keep it switched off at the unit or the breaker when not in use. This solar system was designed to serve two purposes. One, as a small backup / emergency power system due to the power at my Mom's place being notoriously unreliable. Second, as a solar starter system. My idea was to let the system grow (additional panels, additional batteries, etc.) as the load grew. The idea was to get my Mom working with Greener energy and slowly transition to full or significant partial solar power.

Icarus - Good advice on the loads ... hehe.

SolaRevelution - Really really good technical information, thank you. I want to take full advantage of the system while it is in full sun to help bring down her electric bill. 1. Will do. 2. This system is going to be static. The Bussman switch looks very capable. Unless you all totally recommend against it, I think I will try the 63A breaker for position 1, to get them all in the Baby Box. 3. Grounding advice taken. Please see updated schematic. You are right about the Inverter being more for portable applications. I see that now. I will utilize this a starter inverter and replace it as the system grows. I can use it later in a portable application.

mtdoc - Thanks for steering me in the direction of the MidNite breaker box and breakers. I am going to try the 63A breaker between the Solar Charge Controller and the Inverter, again, unless you folks seriously suggest otherwise. Please see schematic. My rational is that the 63A breaker should have a trip amps of about 67.5A, which if my calculations are right should be able to handle just above the Inverter's rated surge wattage. Caveat, my calculations are seldom correct, so I will take any advice before I purchase these breakers.

OK, so I am attaching the updated schematic. I will take any advice you folks have. I need to make one more round of purchases and then we are going to get to work building this thing. Very excited.

Thanks again.

SolarMonkeysGreen Mom Revised Setup (28 Jul 12).pdf