Author Topic: A few semi SAPS questions  (Read 850 times)

0 Members and 1 Guest are viewing this topic.

petect

  • Jr. Member
  • **
  • Posts: 53
A few semi SAPS questions
« on: October 06, 2017, 09:13:51 AM »
Hi All

I have a few questions about bringing pv into the house and connecting to the house electrical system. I intend to do this “by the book” and have it inspected , As I don’t want any problems with the insurance company.

Here’s the situation: Semi-stand alone system. Ground mount rack . Wiring from the panels to the house entrance to be trenched and in pvc conduit 18+” deep.
The Questions:   What types of wire can I use ? Can I use thhn, or am I restricted to wire rated for burial? The length of the run will be about 75’, and I would like to keep my options open when looking for possible bargains.

The house will remain on the grid with a few circuits powered by pv. I plan on using a manual transfer switch ( double pole,  on-off-on ) to allow me to connect these circuits to the grid during long periods of darkness. A small battery bank will probably be necessary to keep the lights on so I don’t have to switch over every night.

Should the transfer switch go before the inverter (dc side) or after (ac side)?
Are the transfer switches used for emergency generators acceptable for doing this?

Many more questions to come later – I have to start somewhere.
Thanks in advance
 Pete

SparWeb

  • SuperHero Member
  • ******
  • Posts: 3338
  • Country: ca
    • Wind Turbine Project Field Notes
Re: A few semi SAPS questions
« Reply #1 on: October 06, 2017, 12:54:47 PM »
A few other things for you to consider.
First, a sub-panel for your PV powered loads.  Actually, you would be talking about an Inverter-powered sub-panel, that "can" be tied to the grid-powered panel, however there are implications.  How you do this can be expensive.
A overly simple approach is that the inverter, powered by PV and batteries, can only power the sub-panel and there is no interconnection between sub-panel and grid panel.
This is too simple because you would want to have: a) chance to power the sub-panel from the grid sometimes, and b) chance to power the grid panel from the inverter sometimes.
The transfer switch can be as simple as you state, but to pass inspection it must both switch the power supply of the grid panel to the inverter AND IT MUST DISCONNECT the grid panel from the grid.
You don't know when the power company will restore power to your house.

Second, the inverter you use will determine the options you have.  You won't want a battery-less grid-tie inverter so I won't bother listing its limitations that will hamper your plans.
An Outback or a Xantrex inverter however, can to sync up between grid and inverter output from batteries in one go.  This allows the inverter to act like the transfer switch, and choose to power your backed-up loads from either the grid or the inverter-battery-PV system.  They will also recharge your batteries on those dark days when the PV doesn't do it.
No one believes the theory except the one who developed it.  Everyone believes the experiment except the one who ran it.

System spec: 135w BP multicrystalline panels, regulated by Xantrex C40, DIY 8ft diameter wind turbine, regulated by Tri-Star TS60, 800AH x 24V AGM Battery, Xantrex SW4024

petect

  • Jr. Member
  • **
  • Posts: 53
Re: A few semi SAPS questions
« Reply #2 on: October 06, 2017, 05:51:37 PM »
Hi Sparweb
Thanks for your reply. The plan is to be able to have maybe 6 of the house circuits capable of being powered by either pv & batteries, OR be connected to the grid through the main breaker box. That’s where the manual transfer switch comes in. Being double pole , with ON (pv), OFF, ON (mains) positions, I could switch those circuits from pv to mains without back feeding into the mains. I would use one of the transfer switches that are made to be used with emergency generators to prevent the safety issue you mentioned.

http://www.homedepot.com/p/Reliance-Controls-50-Amp-10-Circuit-Manual-Transfer-Switch-A510C/206503336

Thanks
Pete

SparWeb

  • SuperHero Member
  • ******
  • Posts: 3338
  • Country: ca
    • Wind Turbine Project Field Notes
Re: A few semi SAPS questions
« Reply #3 on: October 07, 2017, 10:05:47 PM »
Yes, that works too.  Using a manual switch, the circuits are shut off before they are re-energized on the other supply, and then switched back only when you choose to do so.
This does tie you to the house at specific times, otherwise the transfer you need won't occur.  Either the batteries don't get used, or they get overused if you miss a switch-over.
That may be fine.  Also consider if the switches in the transfer are designed to be operated daily, or if they're intended to be used occasionally.  Circuit breakers are NOT designed to be switched manually over an over again and have a short life if used that way.  Whether a manual transfer switch has the same reliability limitation, I don't actually know.

The reason I brought up the inverters is because they free you from this responsibility.
http://www.xantrex.com/documents/Discontinued-Products/SW2512MC-SW4024MC2UserGuide.pdf
http://www.outbackpower.com/downloads/documents/Make_the_Power/FXR_A/fxr_operator.pdf

In the Xantrex, go to page 89 of the PDF (81 on the page) and read about Utility Backup Mode.  In the Outback, go to page 19 and read about the Mini Grid Mode.
Built-in transfer switch.  Automatic.  You choose the point of transfer.  Set and forget it.
Pick any inverter designed for use in RE systems and you should find a system that works this way.  I just happen to be most familiar with these two.
BTW: The Xantrex has 2 AC inputs so you can connect both the Grid and a standby generator.  And it will start the genny for you.

I also suggest you draw up a system schematic (like the ones in the Xantrex manuals) to see your system with a manual transfer switch.  It will not be any simpler than relying on the inverter to transfer for you.

There's nothing wrong with manually managing your power system, but it's not as much fun after a few years.
In case you're still considering the transfer switch, like the one you linked, ONLY works on AC.
You will want to keep your inverter connected to the batteries at all times (but have a big fat disconnect switch just in case) so that things like the internal clock and user settings don't get wiped.
No one believes the theory except the one who developed it.  Everyone believes the experiment except the one who ran it.

System spec: 135w BP multicrystalline panels, regulated by Xantrex C40, DIY 8ft diameter wind turbine, regulated by Tri-Star TS60, 800AH x 24V AGM Battery, Xantrex SW4024

petect

  • Jr. Member
  • **
  • Posts: 53
Re: A few semi SAPS questions
« Reply #4 on: October 08, 2017, 11:17:15 AM »
SparWeb
Thanks again for your reply. The inverter manuals make for some very interesting reading. I didn't realize that they were so capable. Of course that level of sophistication comes with a price. I'll have to keep looking and possibly start smaller and add on later. Of course I'm sure that the eventual cost of doing that would be a lot higher than starting out with what would be my ultimate system. Just more proof that what they say about free lunches is true.
Thanks again
Pete

Mary B

  • Hero Member
  • *****
  • Posts: 796
Re: A few semi SAPS questions
« Reply #5 on: October 08, 2017, 05:23:42 PM »
I use these to switch an outlet for the fridge http://www.ebay.com/itm/Go-Power-TS-30-Transfer-Switch-30-AMP-for-Wind-Solar-Moblie-RV-Applications-/253176458309?epid=2254359306&hash=item3af27e2c45:g:9uoAAOSwmolZyrFQ you coul feed the inverter in, and a sub panel feed in then have a sub panel with the inverter oads.

petect

  • Jr. Member
  • **
  • Posts: 53
Re: A few semi SAPS questions
« Reply #6 on: October 09, 2017, 08:08:04 AM »
Hi Mary
Thanks for your reply. The transfer switch that you mentioned seems like it could be very useful.
Could you (or anyone else) comment on what wire options I have for burial in pvc conduit that will MEET CODE requirements? I will have a run of about 75’, pv modules to the house.  I will probably have to start with 1500 watts, if / when $$ allows I would like to increase to about 3000 watts. The more wire options I have, the more I might be able to shop around and possibly save a few bucks. 

Thanks again
Pete

Mary B

  • Hero Member
  • *****
  • Posts: 796
Re: A few semi SAPS questions
« Reply #7 on: October 09, 2017, 05:15:59 PM »
THHN specs http://www.southwire.com/support/THHNGuideSpecifications.htm yes it can be buried in conduit...

petect

  • Jr. Member
  • **
  • Posts: 53
Re: A few semi SAPS questions
« Reply #8 on: October 10, 2017, 06:43:48 AM »
Thanks Mary !