Beginner - 200 watt vacation cabin PV System

[darksidekilo6]

Solar power enthusiasts, I am a beginner and this will be my first system. I have a vacation cabin that I am installing a do-it-yourself security system in that I want to run off of solar power. The cabin is on top of a mountain with plenty of unobstructed views of the sun. I have consulted with a few solar power vendors and now I want to make sure that they are leading me in the right direction and not just helping me empty my wallet. I have spent the better part of a week going through a vast majority of the posts on this forum and I must say that my knowledge is leaps and bounds ahead of where it once was.

However, I still have a few knowledge gaps that need filling. I will begin with the details of the equipment I plan to put on the solar system and the computations that have gotten me to this point. I will then close with the system that I am looking at along with my questions. Please don't hesitate to answer questions dealing with part of my post if you lack the time to provide feedback on the entire system. My ultimate goal is to keep the total price of the system in the $600 range after the Federal Energy Tax Credit.

Here are the electronic components that the system will power. All items will be powered 24/7 by the solar panels and I would like to have one day of battery reserves.

Wireless router: 8 watts
Alarm system: 8 watts
Wireless internet dish: 3 watts

So, based on the research I have done so far and a quick math refresher these are the numbers I come up with. Bear in mind, I am Marine and the only math the Marine Corps cares about is One Shot = One Kill.

Total energy needs in one day (in Wh/day): 456 watts (8 + 8 + 3 = 19 x 24 = 456 watts)
Total energy needs in one day adjusted for inefficiency at a factor of 1.5 (in Wh/day): 684 watts (456 x 1.5 = 684 watts)
Maximum instantaneous load: 19 watts (8 + 8 + 3 = 19)

Estimated hours of sunlight a day: 5
Solar panel output required: 136.8 watts (684 watts / 5 hours = 136.8 watts)
Solar panel output adjusted for inefficiency at a factor of 1.3: 136.8 watts (136.8 watts x 1.3 = 177.84 watts) I am rounding up to 200 watts so that I have flexibility to run other small electronic devices (radio, phone charger, etc.)

Battery Ah requirement: 57 Ah (684 Wh/day divided by 12 = 57 Ah
Conservative Battery Ah to keep battery above 50% discharged = 114 Ah ( 57 Ah x 2 = 114 Ah)

These are the components I believe I need for the system with specs for those that I understand:

2 x 100 watt PV panels: Grape Solar GS-S-100-TS 100 Watt Monocrystalline Off-Grid PV Solar Panel. I chose this model solely based on buyer reviews on amazon.com and they fit within my price range.

Charge controller: I researched the difference between PWM and MPPT and I understand that MPPT is more efficient and more expensive and that it is better for longer wire runs as you don't experience significant voltage drops. I will be placing my panels on the roof of my two-story cabin and running the wires to the controller in the basement. I would say the total run will be about 30 - 40 feet. I have not been able to find anything that details what is considered a long run. Additionally, I am not sure what Amp rating I need for the controller. I read some where that to get this figure you take the panel output and divide it by the battery voltage. In my case one of the online solar power vendors recommended 2 x 6v golf cart batteries. So, if I take 200 watts divided by 6v that equals 33.3A. Does that mean I need a charge controller greater that 30A? Most come in 10A, 15A, and 30A. I'm guessing my math might be wrong here.

Inverter: Cobra CPI 480 400-Watt 12-Volt DC to 120-Volt AC Power Inverter with 5-Volt USB Output. Again I chose this model solely based on buyer reviews on amazon.com and the price point. Now I am not sure if the equipment I am plugging into the system is considered sensitive. Again I read some where that sine wave inverters are better for sensitive equipment. I also read about modified sine wave converters.

Batteries: Based on vendor recommendation, I am currently looking at 2 x 6v deep cycle golf cart batteries connected in series that give me 60Ah a piece for a total of 120Ah. I chose 60Ah because it was the closest round number that when doubled was at least 114 Ah. I likely need some more guidance here.

Finally, wires and fuzes. What gauge wire do I need between the panels and the controller and then between the controller and the inverter? I am assuming that I should put a fuze on the hot leads between the panel and the controller, and another fuze on the hot lead between the controller and the battery, and finally a inline circuit breaker on the hot lead between the battery and the inverter. Not sure what size fuzes and circuit breaker.

That's it unless there is something else I am missing. In closing I would like to thank all that help up front for leading me in the right direction and hopefully giving me the knowledge to get this small system up and running.

Sean

[Sunking]

Hey Leatherneck welcome to the forum. Former USN here.

OK first mistake you made is the battery. You want a minimum 5 day reserve, which in reality only gives you 2.5 cloudy day reserve, [5 x 456 watthours] / 12 volts = 227 AH @ 12 volts. A good pair of Trojan T-105RE fit the bill perfectly.

As for voltage drop or wire size between panel and controller is to be kept to 2% pr less at full current.

If you are going to use a MPPT controller, do not use a battery panel, use a single Grid Tied Panel rated at 200 watts, or whatever is needed. GTI panels cost half as much as battery panels. That is why MPPT is less expensive. With PWM you must use more expensive battery panels.

Only other caution is you used 5 Sun Hours. That may bite you in the butt Marine. For battery systems find th esolar insolation in your area and determine the shortest month which is usually December or January. Once you do that then recalculate. Also note the 1.5 adjustment factor is only for MPPT controller. If you use PWM the adjustment factor is 2. So if you were to use say December and it is 3 sun hours, and a PWM controller then [456 wh x 2] / 3 hours = 304 watts.

Oh you asked about current. With PWM Input Current = Output Current. In other words is the total panel current. For example 200 watt battery panel current = 11.1 amps.
For MPPT Output Current = Panel Wattage / Battery voltage. So 200 watts / 12 volts = 16.6 amps

[darksidekilo6]

Sunking, thank you for responding. You are a "prolific advise-giver". I won't hold your USN heritage against you if you don't hold my solar power ignorance against me. Feel free to pile on the sarcasm as I work my way through your response. Also understand that I am currently in Afghanistan so my responses may come at odd hours given the huge time difference. Figured I would get an early start on a post-deployment project during my downtime.

OK first mistake you made is the battery. You want a minimum 5 day reserve, which in reality only gives you 2.5 cloudy day reserve, [5 x 456 watthours] / 12 volts = 227 AH @ 12 volts. A good pair of Trojan T-105RE fit the bill perfectly.

My initial 1 day reserve was just a shot in the dark. So I will factor your 5 day reserve into my needs equation. Also I have included your battery recommendation into my system.

As for voltage drop or wire size between panel and controller is to be kept to 2% pr less at full current.

You lost me at 2% pr.

If you are going to use a MPPT controller, do not use a battery panel, use a single Grid Tied Panel rated at 200 watts, or whatever is needed. GTI panels cost half as much as battery panels. That is why MPPT is less expensive. With PWM you must use more expensive battery panels.

What do you mean by battery panel. Are you talking about the PV panels and if so, are you saying to use one panel @ 200 watts rather than 2 x 100 watt panels. I have done minimal research on a GTI system. If shore power goes out on a GTI system at lets say 0200 will I still have power? I want to be able to connect to my security system over the internet even if the power is out. We recently had a series of break-ins at some of the cabins and the perps cut the shore power before they made off with their loot. Since my ISP is through a long-range wireless service, in almost all cases, when the power on the mountain goes out if my wireless internet antenna had power, I would still be able to connect to the internet because the internet receiver is located about 15 miles away. The security system I am purchasing sends me text message alerts if any of the sensors are triggered and I can also remote in via an IP camera to case the joint out if I need to.

Only other caution is you used 5 Sun Hours. That may bite you in the butt Marine. For battery systems find th esolar insolation in your area and determine the shortest month which is usually December or January. Once you do that then recalculate. Also note the 1.5 adjustment factor is only for MPPT controller. If you use PWM the adjustment factor is 2. So if you were to use say December and it is 3 sun hours, and a PWM controller then [456 wh x 2] / 3 hours = 304 watts.

So I googled solar insolation and visited a couple of the sites to get a better idea of the sun hours for December in my area. The cabin is in Western, NC and the December sun hours is about 4 hours. So with that adjustment, using a MPPT controller, i would need 222 watts. Round up to 250 watts to be safe. With my small system which would you recommend, PWM or MPPt controller?

How about inverters and this whole sine wave mumbo jumbo. Do I need to consider that with the equipment I plan to put on the system?

Thanks,

Sean
"Sweepers, Sweepers man your brooms and give the ship a good sweep".

[Sunking]

I have no problem helping, even Leatherneck Grunt Jarheads, military personnel . Not entirely your fault you got in the wrong line. Reading is not a requirement for Leathernecks . FWIW I left the USN in 1979. OK let's take it one step at a time.

As for the battery a 5 day reserve is required for 2 reasons, and it is straight forward..

1. It maximizes battery life, and best economic trade-off is 5 days or 20% daily discharge. For example the T-105RE in theory @ 20% discharge will yield up to 3000 cycles. In reality 4 or 5 years. At 50% discharge less than 1000 cycles or 2 to 3 years in practice, and if 80% discharge less than a year.

2. YOu need to have reserve to CYA for cloudy days. You never want to discharge your battery more than 50%. So in practivce a 5 day reseve works out to 2.5 to 3 days reserve.

OK for voltage drop means power loss on the wiring between the panels and charge controller. Wire has resistance, and when current flows through wire it develops voltage and power losses. We want to minimize voltage and power losses to 2% or less if economically possible. The two ways to do this is:

1. Use as high of a voltage as possible on the panels. This is why MPPT is preferable. We can run as high as 150 volts on a 12 volt battery. With PWM anything above 16 volts is a waste. 2% of 150 is 3 volts. 2% of 16 volts is .3 volts. One hell of a difference.

2. Larger wire than required to meet minimum safety parameters. Larger wire has less resistance.

So to determine wire losses we need to know 3 things. The distance, operating voltage, and maximum operating current. It is a calculation from that point.

As for solar panels they come in two flavors. Those made for battery systems, and those made for grid tied systems. Battery panels are low voltage with a operating voltage of about 18 volts. They must be used when using a PWM controller. That means they contain 36 cells. A 100 watt panel spec is typically 18 volts at 5.5 amps. When used with a PWM controller delivers 5.5 amps @ 12 volts = 67 watts. But the two points about Battery panels you need to know is the cost roughly twice as much as Grid Tied Panels, and are low voltage, and thus low power usually up to about 140 watts max. They arr more expensive because demand is much lower.

Grid tied panels operate at higher voltages and thus higher power levels up to 300 watts. They will have more than 36 cells up to 70 I think. If using grid tied panels you must use a MPPT controller. However once you get to about 200 watts of panel power, even though the MPPT controller is much higher than a PWM controller, the total cost is lower. For example in your case with 450 daily usable watt hours and 4 Sun Hours with PWM requires:

225 watt panel
15 amp PWM Controller

For MPPT
170 watt panel
15 amp MPPT controller.

Go price that out and see which is less.

As for inverters. Is there a 12 volt option for the equipment? If so use it and eliminate the inverter. However with sensitive electronic equipment (especially radio) use a True Sive Wave inverter. Besides as small of a load as you have, you do not need a large inverter. If you use the T-105RE battery the largest they can support is up to 400 watts which is way more than your equipment demands. Even a 100 watt is overkill for your equipment.

In the end your 200 watt assessment is correct. I suggest:

200 watt GTI Panel with Voc of 70 volts or less
15 Amp Morningstar Sun Save MPPT Controller.
2 Trojan T-105 or T-105RE 6 volt 225 AH battery
Morningstar Sure Sine 300 Watt Inverter

[darksidekilo6]

Sunking, the only thing the Marine Corps required was a heartbeat and a trigger finger. It is getting late here in Afghanistan and its time for me to go hunting for some bad guys. So I will digest your latest post and be back up tomorrow. Thanks again. To be continued.....

[Island Man]

Listen to SunKing. He's good and takes the time to share his experience. I wish I had done what you are doing and researched first as I listened to salesmen with no knowledge. All I can advise is to get a bigger system than you think now as you will love the free energy even though it turns out to be expensive. You will want to run more things than you envisage now. BE SAFE IN AFGHANISTAN AND GOD PROTECT YOU

[Sunking]

Sunking, the only thing the Marine Corps required was a heartbeat and a trigger finger. It is getting late here in Afghanistan and its time for me to go hunting for some bad guys. So I will digest your latest post and be back up tomorrow. Thanks again. To be continued.....

Semper Fi. I salute you. Shoot a bad guy for me.

[SunEagle]

Semper Fi. I salute you. Shoot a bad guy for me.

Keep your head down and get back safely. I am proud to have you guys out there keeping me safe.

[russ]

Happy hunting!

[bahamasolarnoob]

Feel free to pile on the sarcasm as I work my way through your response.

I read Sunkings posts just for the comedy.

[FloridaSun]

I read Sunkings posts just for the comedy.

agreed, the comedy here is in newbies that come on with 'authority' without a clue to Dereck's knowledge base. Cracks me up how some try to disagree with him and FACT. You can tell they have not taken time to read stickies or past posts on this forum. Sunking along with Naptown, Inetdog and others give out much time and patience in responses... and let's not forget good ol' Russ, always there to delete spammers and inane links. I thank you all for making this one super place to learn.

[bahamasolarnoob]

agreed, the comedy here is in newbies that come on with 'authority' without a clue to Dereck's knowledge base. Cracks me up how some try to disagree with him and FACT.

Right, and ofcourse I read them for the intel. And I like to see if I got it right, what I was thinking, when I see a OP.
There is a pattern though with these off grid systems, and once you re-read the stickies a couple of times it will slowly starts to dawn. Anyway back to the thread.
And thanks for your service.

[SunEagle]

I read Sunkings posts just for the comedy.

He will keep you laughing. Good to learn from too.