blue-sails avatar image
blue-sails asked

What ground fault device?

Last year I made an off-grid installation with six solar panels from Victron of 305 watts each. The solar array is expandable to a maximum of seven solar panels.

Why is seven solar panels the maximum limit of this installation?

I am glad you asked.

The installation is limited by the DC ground fault device and DC breakers.

The minimum expected winter temperature allows for a maximum of seven solar panels. This maintains the maximum open circuit voltage just below 300 volts.

In this case the limiting factor were the DIN rail safety devices from Midnite - GFCI and breakers - which are limited to 300 volts DC.

Any suggestions for a din rail GFCI and breakers that allow more than 300 volts would be appreciated.

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Alexandra avatar image Alexandra ♦ commented ·

@Blue sails

The solar panels limit is usually based on the Mppt, so that question cannot be answered withiut knowing more about the install components and battery voltage etc.

Neither can the other one about the GFCI either.

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blue-sails avatar image blue-sails commented ·

Hi Alexandra,

The Victron solar panels have an open circuit voltage of 39.7-DC volts. This is roughly 238 VDC for six panels and about 278 VDC for seven panels. Winter conditions increase this to about 299 VDC. Obviously the panels are connected in series.

The currently installed Midnite GFCI and Midnite circuit breakers have a maximum DC voltage tolerance of 300 VDC.

MPPT and batteries are irrelevant in this installation since this is a PV direct application.

I would like to add five additional solar panels to this installation; however, I am limited by the Midnite components to 300 VDC.

I am aware of a (n expensive) GFCI device from Morningstar that will work with 600 VDC; however, I do not know of any din rail circuit breakers that will work with more than 300 VDC.

I hope this additional information will suffice.

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Alexandra avatar image Alexandra ♦ blue-sails commented ·

Again PV sizing has to do with the device handling the pv. So not irrelevant here at all.

You question cannot be answered here directly. What are the local regulations? Or the PV inverter recommended sizes.

Are you only in reasing string voltage? And how if your PV inverter in the cold cannot take a higher VOC?

If you add a second string then Short circuit amps increase. And then how would that work on your pv inverter (unless you have a separate tracker).

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blue-sails avatar image blue-sails Alexandra ♦ commented ·

Hi Alexandra,

Like I said before, “this is a PV direct application.”

Therefore, there is no inverter.

You are correct in that the voltage increases as more solar panels are added to the existing single string.

The current is maintained as low as possible by keeping the solar panels in a single string (one of the main reasons for choosing the Victron solar panels).

The GFPD and the circuit breakers are not required for this installation; however, experience has taught me to be careful with human beings which may be susceptible to high voltages.

The additional expense of these devices is mainly for convenience and safety.

In any case, I am only inquiring about general knowledge from someone that may have previously worked with a GFPD and din rail circuit breakers at more than 300 VDC.

Kind regards,

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Alexandra avatar image Alexandra ♦ blue-sails commented ·

So you have no PV inverter between the panels and the AC power side?

Explain how the DC power from the PV is changing to AC to power your loads?

Does that mean you are using micro converters/optimizers?

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blue-sails avatar image blue-sails Alexandra ♦ commented ·

Hi Alexandra,

In a DC direct application there is no conversion to AC.

Therefore, there are no solar chargers, no batteries, no inverters, no micro inverters, and no optimizers.

The corollary to this is that if done properly there may be lower electrical losses.

There is, also, less stuff to maintain or replace. So there is less stuff that can go wrong.

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blue-sails avatar image blue-sails blue-sails commented ·

There are several different uses for PV direct. Here are some that come to mind:

  1. Hot water
  2. Space conditioning (cooling or heating)
  3. Refrigeration (with batteries)
  4. Ventilation
  5. PAP devices (with batteries)
  6. Smartphone charging (with DC to DC conversion)

You might say that this is more of an Edison mental state compared to a Tesla mental state.

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Alexandra avatar image Alexandra ♦ blue-sails commented ·

In theory other than the heaters, none of the uses you listed for arguement sake, need mother protection you are proposing. But even then not really. Look up David Poz water heater elements to PV panels.

Config is eveything when it comes to sizing protections on systems. So all your theoretical answers have not helped you get help in any way. Or me to help you.

Simple volt amp ratings for that is all you really need. Since you wont share what exaclty you are running. I am sure you can work it out yourself.

P VIR relationships and all that.

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1 Answer
blue-sails avatar image
blue-sails answered ·

Hi Alexandra,

I am not sure what is a “mother protection.”

However, if I attempt to understand what you meant, ground fault protection is essential from my perspective.

In addition I believe that since 2008 the National Electrical Code requires grounding of all PV systems regardless of use.

I am currently using direct PV for both hot water, air conditioning, and space heating.

The devices that I use work both with direct and alternating current. Therefore, a GFCI is an important safety device for me. There is a GFCI on the DC side as well as on the AC side.

These devices for hot water and space conditioning save me money upfront by having the lowest initial installation cost possible.

They save operating expenses by working directly off solar energy during daylight hours, and if one day I decide to add a solar system that converts DC to AC it will be a much smaller system compared to a system that accounts for 24-hours of use for both hot water and space conditioning.

Hot water and space conditioning are the highest residential consumers of energy.

In practice, this means that I will need a smaller inverter, a smaller charge controller, and a smaller battery. This will save me mucha mola one day.

I hope this helps.

In the meantime, I found out that Midnite actually has a 600 VDC circuit breaker which when combined with Morningstar’s GFPD of 600 VDC provides me with the means to increase my direct PV system.

Hopefully, this will help someone else.

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Alexandra avatar image Alexandra ♦ commented ·

You already had a soution apparently, so really asked a rhetorical question then.

So you have 600v of dc going into a 230v AC heating element? How have you overcome the thermostat issue and various other issues that will come up when switching between two types of power sources?

And not arguing with safety. 600v DC is a dangerous amount of voltage. Just wondered how you expected to be helped online without explaining your application/config fully?

I have yet to be wowed by the efficiency of the direct DC application, when the panels can have more than one use going through an inverter. Initial cost being the only saving really. Each to their own in that respect however.

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blue-sails avatar image blue-sails Alexandra ♦ commented ·
Hi Alexandra,

That is not very nice.

However, I will only address the first part of your comment.

(I know what I have done in the past, and I know it works fine for me, and I certainly don’t feel that I need to provide any further information on it.)

Since I first posted my question here, I, also, presented the question to Morningstar.

They answered back just a while back today by email with both solutions.

Thus, I posted them to answer my original question.

Kind regards,

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Alexandra avatar image Alexandra ♦ blue-sails commented ·

"You know what you have done in the past," Just asking you what you had done out of interest to learn something here since some kind of conversion would be needed is somehow offensive? Noted.

All I said was my experience with direct DC was not postive, and clearly you are investing more so you have had a positive experience. Also apparently you are offended by that? Ok?

Morningstar have a 600v mppt so I would expect them to have their own solution there. Since 600V DC is pretty dangerous voltage to work with.

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