Step Up/ Down Transformer

[magnet creek]

Electrical question. I have a situation in our off-the-grid cabin where the distance between the 10kW Solar/Inverter/30KWh batteries and the load is rather long. The distance is over 1000ft and maybe even longer (2000ft) for a future extension. For a 50A line, his would mean really thick expensive copper wires 2 AWG or even thicker.
I was wondering if anybody here has experience with step-up and down transformers. The idea would be to transform up with a Pole mounted transformer (like you would find in you local utility distribution system) and step down close to the cabin, in the same way the utility companies do it.
I realize there are probably some code/ inspection issues to consider and that it may be cheaper to buy thick copper than to invest in transformers but I curious if this has been done succesfully in an off-the-grid application.

 

[Mjs]

If you're being inspected anything over 600 volt will probably require an EE to draw the plans. You could do a 240V step up to 480 volt and then down to 120/240 on the other end. Benefit being the inverter will only see 240 so no imbalance if using a HF inverter. Drawback is the expense of a 600 volt breaker or fused disconnect switch for the step up xfmr.

 

[n2aws]

I've never tried 1k feet. But you may want to include more detail.

ie, are you planning microinverters and converting the power to AC, and then moving that power the 1k feet?

Or are you planning on taking the DC voltage up to like.. 600V, and running that back to a centralized string inverter/charge controller?


I'd probably do the 600V dc, and then do some calculations to see if it's cheaper to run multiple 8awg strings back, or a single 1/0 or whatever the numbers end up being.

Keep in mind, if code compliance is a concern.. the NEC limits you to maximum DC voltage. Not sure about AC voltage.

 

[timselectric]

It will work. But you will have some efficiency losses.
I've done the 240>480>120/240 before.
But only because it was the only option.

 

[zanydroid]

How does the cost/trenching pain look if switch to aluminum instead of copper?

Can the inverter be moved to the load so that you can send 500VDC from the array?

 

[CoolWill]

A utility transformer is very inefficient and lossy. If you could just send the high voltage DC along some #2 aluminum, I think you would be better off.

 

[Shimmy]

It is going to be cheaper to just add separate systems for the remote loads. If you really want to do it anyway, at least consider making a microgrid at the remote locations so you limit the current on the main circuit.

My old rule of thumb is that at 480V the maximum economic distance was 800 feet with pipe and wire and 1,200 feet with busduct.

 

[DIYrich]

You could add an inverter and storage at the cabin. It could draw a constant low amperage load, and batteries at the cabin could supply the peaking needs. One 15 amp 240v line can supply 86kWh per day.

 

[magnet creek]

Thanks for the great ideas. Just to clarify the receiving remote cabins would all have their own solar and inverters. The distribution line is merely to provide additional charge in case the cabins run low. So a low amp solution is absolutely doable.
I did not consider a DC alternative at 500/600V, which seems interesting. Would an inverter take such a high voltage? I think my current Growatt tops at 145V?

 

[DIYrich]

I did not consider a DC alternative at 500/600V, which seems interesting. Would an inverter take such a high voltage? I think my current Growatt tops at 145V?

A lot of inverters, like the Sol-ark, go up to 500v. The internal high voltage DC bus is around 400v, to make it easier to invert to 240v AC.

 

[Shimmy]

Thanks for the great ideas. Just to clarify the receiving remote cabins would all have their own solar and inverters. The distribution line is merely to provide additional charge in case the cabins run low. So a low amp solution is absolutely doable.

Perfect. Don't worry about voltage drop then. Maybe go for #10 wire and try to limit current to about 3A. Just use grid-tie equipment at the remote locations.

 

[Vigo]

I agree, the easiest thing would be to just run a regular 240v circuit with cheap wire and then just limit the battery charge current setting of whatever is receiving that 240v.

 

[zanydroid]

Maybe decide on a circuit ampacity and then take whatever the cheapest wire is that can do the voltage drop. Maybe #6 or #8 aluminum since you need to land in a disconnect anyway so you save one set of dual rated splice.

 

[DIYrich]

Just be careful if all cabins are recharging at the same time.

 

[theoldwizard1]

I was wondering if anybody here has experience with step-up and down transformers.

No experience, but it would still be very expensive and you would require at least one custom transformer.

If the power requirements were about 15A so you could use 14AWG UF-B wire it MIGHT be cost effective. Having an inverter that you could adjust the output voltage UP 10% - 20% would be MANDATORY !