Distance of panels and batteries from house.

System · September 2007

Howdy,

I have read that it is advantageous to keep your Solar panels and batteries close to your house.
I am guessing that is because the connecting wires can get expensive if too long. Can someone elaborate on that please?
Also, what size connecting wires would be needed and what would be the absolute longest recommended?

Thanks,
kieta

icarus · September 2007

Re: Distance of panels and batteries from house.

The distance from the house for the panels and the batteries is largley a matter of where and how the loads are used.

Line loss is very much more dramatic as the voltage is lower. In other words, if you invert to 120vac or 240vac near the batteries, sending the higher voltage to the loads over longer distance with less line loss is viable.

On the other hand, sending 12vdc or 24vdc over any distance will result in huge line losses. ( I had a system that sent 12vdc 50 meters and there was a line loss of about 1/2volt with a 2 amp load. May not seem like much, but it is huge!)

So if you are going to use large dc loads in the building, keep the batteries close. If you are going to invert it really doesn't make much difference (within limits of course).

A final note. Remember to calculate line loss/wire sizing for all applications to be save, and have minimum line loss.

Good luck

Icarus

BB. · September 2007

Re: Distance of panels and batteries from house.

You can also change the "equation" a bit depending on how you choose your components...

For example, you can use an MPPT type solar charge controller to charge your batteries... You can get panel voltages over 100 VDC and since P=V*I, you can reduce the current and power losses (Ploss=(I^2)*R--1/2 the current, 1/4 the power loss in the same cable run)... So, you can install the panels in the sun, and the charge controller/battery bank next to the house.

If you are using Grid Tied inverters, the home sized, single phase output is typically 240 VAC, but the the inverters can take in 200-550+ VDC--so installing the GT inverter in the house instead of at the panel array is a very viable solution...

And, you can also choose 12 or 48 VDC battery banks... 48 VDC banks, 1/4 the current vs 12 VDC (and 1/16th the loss for the same cables).

And, lastly, like Icarus said, you can use an inverter/transformer to send the power even longer distances.

icarus · September 2007

Re: Distance of panels and batteries from house.

Reading my earlier reply I realize that I was not as clear as I might have been.

Send any current down a wire and you will have some loss at the other end. (Resistance) The trick is that the higher the voltage the lower the loss give the same circumstances. That's why your grid power comes down the road at very high voltage with comparitivly small wires, and then is transformed to 240vac for your service, coming into your house with fairly large wires.

So in a panel/ battery situation, what ever you do, you want to design for mimimum line loss. There is little sense having a large pv or battery capacity, but loose 30% over the distribution system. Before you build anything, find on this site the line loss calculator. Given the information there you can decide how you want to lay out your system.

Mangas · September 2007

Re: Distance of panels and batteries from house.

Array Field Panels 140 feet to Inverters/Batteries.

Solar Mechanical Inverters/Batteries via AC line 100 feet to house.

westbranch · September 2007

Re: Distance of panels and batteries from house.

Hi guys, some of the comments re panel output voltages here have got me thinking....uh oh...

I have a Mitsubishi 120 w 12 v 7 a panel in my system and am going to add panel #2 soon, still waiting on some combiners to arrive.

Hypothetically now, Am i right in thinking that, with all wire sizes staying the same, when I double up on the panels , staying in 12 v mode , I could double the distance from the panels to the Blue sky 2000E MPPT charge controller and get MORE input at hi noon due to the higher panel voltages generated at that time of day? This is not taking into account the low amperage developed at marginal incidence angles in the early morning...

Doesn't seem right to me, must be missing something, but I am no expert here (ask me about trees)

niel · September 2007

Re: Distance of panels and batteries from house.

actually paralleling another pv would impress double the current through the wires and cause double the voltage drop through the exact same wires used for the single pv. the only way to add that pv to the other without changing the wires is to send it as double the voltage to be converted down at a slight loss in the downconversion. the voltage drop would stay exactly the same due to the current and wire resistance being exactly the same. the % voltage drop will change because the voltage was doubled so percent wise it would be cut in half.

westbranch · September 2007

Re: Distance of panels and batteries from house.

thanks Niel, knew I missed something... higher voltage still needs larger wire, just less line loss/m

actually I plan on twinning the wires for panel 2, to be combined at the shutoff box, and then larger wire to the MPPT and from the MPPT to the battery. Maybe a bit more wire expense but easier/safer to install all the additional harware inside the cabin out of the elements.

Eric

Distance of panels and batteries from house.

Comments

Categories