Transmitting solar power a short distance

[adamarthurryan]

Hi, I'm currently building and living in a tiny off-grid cabin. I use a small amount of electricity for charging battery-powered tools and running a few corded tools like a grinder and circular saw.

My battery is a 48V 20Ah lifepo4 in a waterproof case (I use it to power my electric boat motor as well) and I have a 1500W inverter to generate 120V AC.

For charging I have 2@ 100W panels and a Renology Rover Boost solar charger.

The thing is that my cabin is in the woods and doesn't have a lot of solar potential. The roof is heavily shaded. So my solar panels are in a clearing about 300 feet away, with the inverter in a little trailer. I carry my battery there in the morning and let it charge for the afternoon while I'm out or whatever. So far I'm getting plenty of power for my daily needs. I charge up every other day or so.

But, the colder weather is coming and I'm aware that I won't be able to charge my battery at ambient temperatures in the winter.

One thought I had is to somehow transmit the power from my solar array back to the cabin. But how to do that? Obviously at 12V DC or whatever I'd need a huge cable. So I thought I could have an inverter with the solar array and just run a ~400 ft 12/3 exterior extension cord back to the cabin. But then how do I charge my battery? I'm not sure what I would do at that point...

Would I rectify the 120V from the solar panels back to 20V or whatever and feed it into the Rover Boost to charge my battery? And at the same time have my 48V -> 120V inverter hooked up to the battery to power my house loads?

Is that a thing at all? Or is there a whole other approach I should consider? Eg. getting some sort of heater for my battery and continuing to charge it in the field?

Thanks for your thoughts!

 

[Shimmy]

Easiest solution is to live with the voltage drop and just over-panel. Run the panels in series to boost voltage and select a SCC that can handle the Voc.

 

[Zwy]

Hi, I'm currently building and living in a tiny off-grid cabin. I use a small amount of electricity for charging battery-powered tools and running a few corded tools like a grinder and circular saw.

My battery is a 48V 20Ah lifepo4 in a waterproof case (I use it to power my electric boat motor as well) and I have a 1500W inverter to generate 120V AC.

For charging I have 2@ 100W panels and a Renology Rover Boost solar charger.

The thing is that my cabin is in the woods and doesn't have a lot of solar potential. The roof is heavily shaded. So my solar panels are in a clearing about 300 feet away, with the inverter in a little trailer. I carry my battery there in the morning and let it charge for the afternoon while I'm out or whatever. So far I'm getting plenty of power for my daily needs. I charge up every other day or so.

But, the colder weather is coming and I'm aware that I won't be able to charge my battery at ambient temperatures in the winter.

One thought I had is to somehow transmit the power from my solar array back to the cabin. But how to do that? Obviously at 12V DC or whatever I'd need a huge cable. So I thought I could have an inverter with the solar array and just run a ~400 ft 12/3 exterior extension cord back to the cabin. But then how do I charge my battery? I'm not sure what I would do at that point...

Would I rectify the 120V from the solar panels back to 20V or whatever and feed it into the Rover Boost to charge my battery? And at the same time have my 48V -> 120V inverter hooked up to the battery to power my house loads?

Is that a thing at all? Or is there a whole other approach I should consider? Eg. getting some sort of heater for my battery and continuing to charge it in the field?

Thanks for your thoughts!

Might be just easier to purchase some higher voltage panels, put them in series and just run some 10AWG wire from panels to your house. Or purchase a few more of the 100W panels and put them all in series and use 10AWG. Going 4S with the 100W panels put VOC at around 100V, but you will probably need a different charge controller.

I run 530W panels that have a VOC at 49.5V in 8S to my house 420 feet away. I can still pull full wattage from the panels on a good day.

 

[MichaelK]

For my own system I'm wiring four large residential panels in series for 120VDC. I'm running the wiring ~125' to my controller. If you can walk around and find any spot whatsoever with 150' or so, you could easily make it work with a 200V controller like the Midnight200. Use this voltage drop calculator to figure out what you'll get. As Shimmy mentions, the voltage drop may be acceptable as long as you keep the voltage a healthy level above 72V or so for an MPPT charging a 48V battery. Play with the calculator to see what you can make work.

https://www.calculator.net/voltage-drop-calculator.html

 

[adamarthurryan]

Oh, that makes sense to run the panels in series. I guess if I had a couple more panels I could get it up to 80 or so volts and then maybe it would be in range of making sense with a 12/2 cable...

 

[adamarthurryan]

Okay, thanks for the replies! That all makes a lot of sense. Definitely seems like wiring the panels in series with maybe 4S or something is the way to go. And yeah, a new charger.

 

[Crowz]

Mine are on 150ft 10ga wires but I'm running 300volts and higher so the amps are very low and work great.
High voltage makes having the array far away feasible for sure.

 

[MichaelK]

Oh, that makes sense to run the panels in series. I guess if I had a couple more panels I could get it up to 80 or so volts and then maybe it would be in range of making sense with a 12/2 cable...

Please look up the voltage maximum for your particular controller. Remember to include cold temperature compensation for your winter lows. At -40degrees, the correction factor is 1.25X. So, a panel string that's 120VDC at room temperature will be 150VDC during your winter low if it drops down to -40.

 

[adamarthurryan]

Please look up the voltage maximum for your particular controller. Remember to include cold temperature compensation for your winter lows. At -40degrees, the correction factor is 1.25X. So, a panel string that's 120VDC at room temperature will be 150VDC during your winter low if it drops down to -40.

Oh, I didn't know that about the increased voltage at low temperatures. And yes, I'll need a new controller, mine only handles 1s configurations.