# Beginner - 200 watt vacation cabin PV System

Registered Users Posts: 4
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

• Solar Expert Posts: 3,738 ✭✭✭✭
Re: Beginner - 200 watt vacation cabin PV System
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.

Welcome to the forum. two 6 volt, 60 ah batteries in series is a 12 volt battery at 60 ah, not 120 ah. Most of the cheap golf cart batteries are a bit over 200 ah, so your plan to buy two GC batteries is OK, but you don't want 60 ah batteries. You will also need a bit more solar panel for a 200 ah battery bank.

You will not get 5 hours of good sun every day... do you have a generator and battery charger for backup?

--vtMaps
4 X 235watt Samsung, Midnite ePanel, Outback VFX3524 FM60 & mate, 4 Interstate L16, trimetric, Honda eu2000i
• Solar Expert Posts: 119 ✭✭
Re: Beginner - 200 watt vacation cabin PV System

Two things. The 200w of panel should be divided by the total system voltage ie 12v so it would be 16.6 amp. You need to figure in the amount of power the inverter itself is going to use. I dont know what the standby power draw is of this inverter is but it could be around 20w. If run all day your looking at another 480wh of power use. Both together gets you close to one kwh needed a day. You probably need to double your number of panels and get a 30amp controller.
Ned
• Banned Posts: 17,615 ✭✭
Re: Beginner - 200 watt vacation cabin PV System

I'm going to have to ask how you arrived at those power usage numbers to begin with. I have satellite Internet set ups with wireless routers and the power consumption is more like 40 Watts total, with the dish being the big user. Be very, very careful that you haven't underestimated your usage. Most people do.

Unless you can power your equipment from DC directly (usually you can't because off-the-shelf equipment tends not to be 12VDC and/or can't take the high Voltage of charging a solar power system) you would need an inverter and it too will have power consumption needs. My own system, if it were powered 24 hours a day with a small PSW inverter, would consume about 1.2 kW hours per day. This can be done quite easily, but let's double check the power usage first so there aren't any ugly surprises later.
• Registered Users Posts: 4
Re: Beginner - 200 watt vacation cabin PV System

vtMaps, thanks for the response
vtmaps wrote: »
Welcome to the forum. two 6 volt, 60 ah batteries in series is a 12 volt battery at 60 ah, not 120 ah. Most of the cheap golf cart batteries are a bit over 200 ah, so your plan to buy two GC batteries is OK, but you don't want 60 ah batteries.

After I sent the post I realized that I goofed up the Ah calculation. Duh, doubling the voltage does not double the amps. Thanks for the catch. I gonna run with 2 x 6v GC batteries at 200Ah
vtmaps wrote: »
You will also need a bit more solar panel for a 200 ah battery bank.

Ok, makes sense. So after some further reviews I think i'm going to give the DM Solar 2 x 145w panels a try or at least put them in my budget for now. Some of the other users on this forum recommend them and they have received good ratings on amazon.com.
vtmaps wrote: »
You will not get 5 hours of good sun every day... do you have a generator and battery charger for backup?

Googled solar insolation and found that in my area using the worst month, December, the solar hours per day stand at right around 4 hours. I do have a generator but only use it when I am at the cabin. When I am am not there I was hoping to just have the three items run off the solar power supplied to the batteries. I have adjusted my battery reserve capacity to 5 days instead of one.

Thanks,

Sean
• Registered Users Posts: 4
Re: Beginner - 200 watt vacation cabin PV System

Cariboocoot, thanks for responding.
I'm going to have to ask how you arrived at those power usage numbers to begin with. I have satellite Internet set ups with wireless routers and the power consumption is more like 40 Watts total, with the dish being the big user. Be very, very careful that you haven't underestimated your usage. Most people do.

So for each of the three items, I examined the DC brick on the power cord. Additionally, i hooked up one of those fancy watt meters you can pickup at one of the big name home improvement stores. Speaking specifically to the wireless interent dish, I also sent my ISP an email asking them to confirm the dish power requirements and they responded with "the receiver has very low power requirements, thus making it a great candidate for powering w/ renewable energy. The dish outside needs 3 watts/24 volts."

My basic design philosophy is to power my DIY security system off solar power when we are not there. So I would expect that, for the most part, the only power draw above normal on the three components would be if one of the alarm sensors has been triggered and the system sends me a text message to alert me. The rest of the time, everything should be sitting at normal operating wattage.

Am I on track?

Thanks,

Sean
• Banned Posts: 17,615 ✭✭
Re: Beginner - 200 watt vacation cabin PV System

Yup. You can't beat measuring power usage with a Kill-A-Watt meter under real conditions.

But this does mean you will need an inverter and that will consume power too. Fortunately you will not need a large inverter so power consumption will be minimal. I'm thinking Mornigstar 300 http://www.solar-electric.com/mosu300wasiw.html which only uses 450 mA (about 6 Watts) or for really inexpensive the Samlex 150 http://www.solar-electric.com/sa150wa12vos.html which uses about the same.

That roughly half an Amp will result in another 12 Amp hours per day. All together with the conversion efficiency factored in about 27 Watts DC * 24 hours = 650 Watt hours. A couple of GC2's should handle that no problem! It would be roughly 25% DOD, not including power supplied directly by panels during daylight.

You could probably get away with some quite minimalist charging too, if you allocate about 3 Amps for the loads. Rough calculations I get 15 Amps * 17.5 = 262 Watts so a couple of the 140 Watt panels (Imp about 7-8 Amps) and a 20 Amp PWM controller would do it.

Just beware that once you have this power on hand you tend to start thinking about running other things from it while you're there. Next thing you know you've bought 3kW of panel and a 48 Volt battery bank and a 4kW inverter and ...
Re: Beginner - 200 watt vacation cabin PV System

Sean,

Do you have some sort of Cell Phone Coverage there? There are various alarm systems that use cell phone text/digital messaging (or similar) for alarm systems. Should be pretty low power.

One of the difficulties with solar power--If you design for typical worst case, or the no-failure allowed worst case... Can your system shutdown for a few days of bad weather (or partial equipment failure) and still meet your overall goals?

The old Risk/Reward type thing. Lead acid batteries, for example, do not like to be taken to "dead". So, if a system is unattended, you should look at something that cuts of the battery voltage at somewhere around 11.5 to 12.0 volts when you are not there (and auto restarts when the full sun is available again).

One of the problems with remote cabins... The more you put in there (such as larger solar power system and an expensive alarm setup), the more you have to lose if somebody breaks in.

A small 40 watt panel is pretty easy to obscure from wandering eyes... 4x 140 Watt panels are much more "inviting".

Do you need "anywhere in the world" notification or would a small wireless alarm system that can transmit a few miles line of site to elsewhere be "good enough".

There are low power satellite comm. systems that are not too much money and use hardly any power. "Spot" is one that is intended for hikers/travelers, but I thing it is based on a larger commercial services--You may be able to hack a Spot personal comm device to get messages out, or research the commercial service (used for tracking shipments, etc.).

www.findmespot.com

-Bill
Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
• Registered Users Posts: 4
Re: Beginner - 200 watt vacation cabin PV System

Bill, thanks for responding.
BB. wrote: »
Do you have some sort of Cell Phone Coverage there? There are various alarm systems that use cell phone text/digital messaging (or similar) for alarm systems. Should be pretty low power.

So what I am going to be using for an alarm system is a new system from a startup company called scoutalarm. Essentially the system works through your internet router. You attach door, window, and motion sensors where you like, log in to the base station through a smartphone or the internet (no computer needed) and set your alert preferences and your done. If one of the sensors is tripped, the base station sends an alert to my smartphone app and then I decide what action to take. The base station does have a cellular card in it that gives me the option to have a company do the monitoring for about \$10 bucks a month but with all the new smartphones and other technology, why would I pay someone to do something that I could just as easily do my self. The whole system set me back \$260 and should be delivered some time in August. The only thing that needs power in the alarm system is the base station @ 8w. It also has an on board battery back-up that will last 12 hours.
BB. wrote: »
One of the difficulties with solar power--If you design for typical worst case, or the no-failure allowed worst case... Can your system shutdown for a few days of bad weather (or partial equipment failure) and still meet your overall goals?

What I am really trying to avoid is a burglar cutting the power to my cabin to essentially kill the alarm system before making of with my stuff. So with this system, if that happens I will at least get the first alert that one of the sensors was tripped. After that all bets are off. As for shutting down for a few days of bad weather (or partial equipment failure), I am ok with that and I will just hope that I don't get robbed during the down time.
BB. wrote: »
The old Risk/Reward type thing. Lead acid batteries, for example, do not like to be taken to "dead". So, if a system is unattended, you should look at something that cuts of the battery voltage at somewhere around 11.5 to 12.0 volts when you are not there (and auto restarts when the full sun is available again).

I did not think of that kind of component. Definitely would be handy and important. I will look in to it.
BB. wrote: »
One of the problems with remote cabins... The more you put in there (such as larger solar power system and an expensive alarm setup), the more you have to lose if somebody breaks in. A small 40 watt panel is pretty easy to obscure from wandering eyes... 4x 140 Watt panels are much more "inviting".

Fortunately for me the cabin is in a gated community so the break-ins we have had have been fools on foot climbing the mountain and stealing stuff that they can carry back down.
BB. wrote: »
Do you need "anywhere in the world" notification or would a small wireless alarm system that can transmit a few miles line of site to elsewhere be "good enough".

Funny you mention "anywhere in the world". I am in the Marine Corps and currently in Afghanistan. Does that count? But seriously, I do have friends on the mountain that could respond in my absence and this security system I purchased gives me the ability to have alerts sent to them as well so they can respond more quickly with "loaded shotguns".

I appreciate the help and additional critical thinking.

Sean