Off-the-grid with grid-tie inverter?

[servant74]

I came here looking for information on Micro-Grid Tie inverters, but reading this entire thread has been educational.

I am currently renting, but am considering as we retire to a different area, putting in solar to at least cover the 'minimums' for lights and possibly a few other small loads. Basically doing lighting as DC LEDs, and a few other dc-only loads. But the wiring for DC loads needs to be larger wire to do it safely with low loss especially if it isn't 'near' the battery source. -- Basically choosing to reap the 'low hanging fruit'.

Could someone point me to use and information on micro-GTI's?

[Xringer]

There are a lot of (illegal in USA) small Chinese GTIs on Ebay.

Here's a link to a site you might find interesting.
Solar Beginners Corner

It's not too hard to set up a solar charged DC power supply for DC LED lighting.
But you only need a GTI if you need 120vac (or 240vac) for standard lighting etc loads.

Oh yeah, you don't need jumbo wire unless you plan on running a lot of amps.
Most panels don't put out a ton of current. A 200w panel might supply 5 or 6 amps..


The best legal micro GTI that I know about is the EnPhase 240vac units.
That's the one I would use (after doing all the code required stuff).
Amazon.com: Enphase: Patio, Lawn & Garden

[servant74]

Thanks XRinger....

I could see for big installs the microinverters could possibly even reduce the cost of a solar system, even non-gridtie, given the better power transmission efficiency of AC vs DC. (Reduce size of wire as voltage is raised, for the same power capability). But you are right, on small (like most home or small commercial) installs, it is better just to use bigger wire or re-locate the power equipment to optimize the power transfer. Converting the AC back to DC for battery storage adds yet another inefficiency in the system.

Thanks again for the quick reply.

[NeilBlanchard]

I may have missed it in this thread, or another thread, but this seems to be directly relevant:

http://physics.ucsd.edu/do-the-math/...t-solar-setup/

[buteman]

I know this is an old thread but I have become interested in finding if I could use my grid tie system if the grid fails.
I see one problem is caused when the panels are producing more power than you need.
Would it be possible to monitor the GTI voltage and switch in dump resistors so that they hold the voltage at a safe level?
I'm thinking you could use a few resistors and just switch more and more in progressively.
I think you could use a small SBC such as the Raspberry Pi to control things.

[Xringer]

What kind of system are you using? Some systems aren't easy to convert to off-grid.

I've seen some windpower dumping systems using hotwater tank heating elements. It makes more hot water when the wind is blowing too hard.

[buteman]

Thanks for the quick reply Xringer.
Not really studied it. It was installed before we bought the house. It's around 4 Kilo watt and appears to have 16 panels arranged as 2 banks of 8 with 192 volt per chain. That's about all I know. Electronics has been a hobby for 60+ years and computing since the mid 80's so I just thought I might be able to rig something up if the grid did fail. I haven't attempted to buy anything and see no point until/if I can get further information.

[Xringer]

It sounds like you have a standard system with one main GTI in a big box hanging on a wall somewhere. You should check the brand and model info. If it's a brand-name company that has a website, they might carry the hardware needed to switch back and forth between On and Off grid.

I'm not sure that it's a good idea to set up for off-grid without a battery bank. Since clouds tend to vary PV output a lot.
I've been watching this guy: https://www.youtube.com/channel/UCoj...q8kmJme-5dnN0Q
Trying to find something that might be a good back-up for my wife's CPAP Machine, that be re-charged by the grid and maybe by a PV panel.

I don't want to rely on my very old Lead Acid battery bank, or go out and crank up the gas generator when it's -4 degrees in the middle of a blizzard.

[buteman]

If the grid goes down for a long time I imagine it would be practical to wire the panels in parallel but then the current would obviously go up tremendously. In that case I guess it would be wise to split them into smaller groups to run the cables initially and then combine them somewhere near a charge controller to feed into a battery bank.

If the grid is down for a shorter time would it be practical to do the following:

Use a high power H Bridge wired to a transformer rather than a motor. If the bridge was driven to switch at say 60 Hz could that then be set up to produce a lower voltage output, rectified and fed to a charge controller?

[Xringer]

You might not be able to re-configure your panels and still have them work right with your current inverter.
Here in MA, it might be illegal to change anything on a PV installation.

Maybe your best bet would be to check out your panel information and see if you could replace your inverter and use your panels with a new Hybrid solar Inverter. https://www.amazon.com/MPP-SOLAR-Inv.../dp/B07C4M1GVK