Off grid shed power.

[Whk60]

I'm new to this and would like some suggestions on how many 100w panel for our needs. We bought a 14x 28 shed. Half for my shop and half for Mema. Going to use small power tools and a computer, LED low voltage lights and a small fridge. During the summer the shed will be utilized about 4 or 5 days a week at 6 to 8 hrs. In winter maybe two or three days at 2 or 3 hrs most. Heat is not an issue during the cold months. I had thought to use a 12v system with 4-100w panels a 60 Amp MPPT controller, and two Lead Acid, deep cycle marine batteries at 115 AH. Any suggestions on whether it should be larger. My main concern is running the refrigerator.

 

[45North]

I'm new to this and would like some suggestions on how many 100w panel for our needs. We bought a 14x 28 shed. Half for my shop and half for Mema. Going to use small power tools and a computer, LED low voltage lights and a small fridge. During the summer the shed will be utilized about 4 or 5 days a week at 6 to 8 hrs. In winter maybe two or three days at 2 or 3 hrs most. Heat is not an issue during the cold months. I had thought to use a 12v system with 4-100w panels a 60 Amp MPPT controller, and two Lead Acid, deep cycle marine batteries at 115 AH. Any suggestions on whether it should be larger. My main concern is running the refrigerator.

What's the power requirement of your frig?
You can get it either from the sticker or else measure it with a kill a watt type meter.

 

[Whk60]

What's the power requirement of your frig?
You can get it either from the sticker or else measure it with a kill a watt type meter.

About 40 to 45 KWH

 

[chrisski]

It’s good if you can plug the fridge into a kilowatt meter And get the daily usage. I just looked at a super efficient RV fridge run off 24 volts that uses no more than 1.5 kWh per day on sunny days, and supposedly 800 watt hours on a cold day. The guy had upgraded from a 6 kwh per day fridge. The watts and time used for power tools will make a big difference also.

I have Milwaukee 18 volt tools I charge. With the super effivient fridge I have, and not using table saws but the 18 volt tools, I could probably run that with the 1000 watts of panels, 2 kw inverter, and 4 golf cart batteries I have for my RV.

Throw in something unexpected like a big fan or a table saw, and what I mentioned certainly will not be enough. Even a friend leaving a laptop plugged in all day depletes quite a bit of energy. My son gaming all night could cost me 1.2 kWh of power from leaving the hanger plugged in. Also, to account for one cloudy day, I’d want to up my golf cart batteries to 2 batteries. After the energy audit, there’s places like PV watts you can go and figure out how many panels you need. Also, a good sized table saw may draw more starting juice than my 2 kw inverter will produce.

Whatever you put together solar wise would be much cheaper just to run a line from the house to the shed.

 

[Supervstech]

45Kw a year? A month? A DAY?

 

[solarbot]

I just looked at a super efficient RV fridge run off 24 volts that uses no more than 1.5 kWh per day on sunny days, and supposedly 800 watt hours on a cold day.

So, I've got two 100 watt panels and the sun doesn't rise very high in the sky these days, nor stay there very long. I measured it yesterday morning at 1.5 amps, 16 volts, nice and sunny, sun up about ten degrees. So 12 hours times 1.5 amps times 16 equals 288 watt hours. Double that and it still won't run your fridge. If OP lives at the latitude I do then eight 100 watt panels would be a bare starting point.

 

[chrisski]

So, I've got two 100 watt panels and the sun doesn't rise very high in the sky these days, nor stay there very long. I measured it yesterday morning at 1.5 amps, 16 volts, nice and sunny, sun up about ten degrees.

Is this tilted at the sun? I notice my flat panels could produce that little, but my tilted panels perform much better.

Either way, the OP at some point needs to chec PV watts. I am in Sunny Arizona, the worlds best place for solar. He probably is not in an area as good as I am.

 

[solarbot]

Is this tilted at the sun? I notice my flat panels could produce that little, but my tilted panels perform much better.

Right, it's flat, because it's on a boat on a mooring block. No way to predict the incoming azimuth. I do envy you your ideal conditions, but even so I get the following:

* run my bilge pump
* run my (very bright) anchor light
* run my weather station
* keep my batteries topped up
* charge my phone, headlamp, gopro
* run power tools for a short time every week or so

 

[Whk60]

About 40 to 45 KWH

It’s good if you can plug the fridge into a kilowatt meter And get the daily usage. I just looked at a super efficient RV fridge run off 24 volts that uses no more than 1.5 kWh per day on sunny days, and supposedly 800 watt hours on a cold day. The guy had upgraded from a 6 kwh per day fridge. The watts and time used for power tools will make a big difference also.

I have Milwaukee 18 volt tools I charge. With the super effivient fridge I have, and not using table saws but the 18 volt tools, I could probably run that with the 1000 watts of panels, 2 kw inverter, and 4 golf cart batteries I have for my RV.

Throw in something unexpected like a big fan or a table saw, and what I mentioned certainly will not be enough. Even a friend leaving a laptop plugged in all day depletes quite a bit of energy. My son gaming all night could cost me 1.2 kWh of power from leaving the hanger plugged in. Also, to account for one cloudy day, I’d want to up my golf cart batteries to 2 batteries. After the energy audit, there’s places like PV watts you can go and figure out how many panels you need. Also, a good sized table saw may draw more starting juice than my 2 kw inverter will produce.

Whatever you put together solar wise would be much cheaper just to run a line from the house to the shed.

Thanks I really appreciate the input. I will consider the 1000w panels, and inverter. Thanks again

 

[chrisski]

Thanks I really appreciate the input. I will consider the 1000w panels, and inverter. Thanks again

The 1000 watts of panels is something to start thinking about. That will work for me where I am at in sunny AZ, the best place in the world for solar. Up farther north, you may need less.

After you figure out your kwh of usage, you can go to sites like PV watts to see the hours of sun available in the worst part of the year you have. Farther up north in the winter with bad weather, your available sunshine hours may be as low as 1, which would mean you would need a lot more than. I find this link a very good example of why being located in Seattle and designing a system is a whole lot different because of poor weather and short days from where I live in AZ where there is ideal conditions.

 

[Whk60]

Not here. This is Michigan, snow and clouds everywhere, most of the winter. Will only use fridge during late spring and summer months, when sun is shinning and pool is de-iced.