Can I use a grid-tie inverter on an Off-Grid System

rtribble

I currently have a very conventional off grid system (4 X TRacve 4855's)that supplies power to my house and barn. I also have a 240V line to my water/well pump over 2000 feet away. That location is a very good place to install a harris mini-hydro, producing say 2000 watts. The question is how to connect it to the main systems.
Plan A - Conventional - run wire using heavy gauge for ~~50V DC from hydro back to batteries 2000 feet (BAD IDEA)

or

Plan B - Creative - run a grid tie 2000 watt inverter connected to the main electrical circut near the end of the 2000 ft run. The question is will it all play well togther ?? the TRace Inverters creating most of the power, and the Grid-tie inverter staying in sync and adding power ?

stephendv

Re: Can I use a grid-tie inverter on an Off-Grid System

As luck would have it, someone has done _exactly_ what you're asking about: Connected a sunny boy GTI to their hydro and backfed their Trace SW4548e, see: http://lifeattheendoftheroad.wordpress.com/2012/05/15/commissioning-the-powerspout/

dmajwool

Re: Can I use a grid-tie inverter on an Off-Grid System

rtribble wrote: »

Plan B - Creative - run a grid tie 2000 watt inverter connected to the main electrical circut near the end of the 2000 ft run. The question is will it all play well togther ?? the TRace Inverters creating most of the power, and the Grid-tie inverter staying in sync and adding power ?

Hi. PlanB does sound very much in line with the SMA AC coupled range of products. The interesting point happens when batteries reach full charge and all loads are satisfied. What to do with the GTI at that point? It must be throttled in order not to overcharge and damage the batteries.

The SMA SunnyIsland grid controller and battery charge controller approaches this by signalling to the SunnyBoy to throttle. The signal is a rise in the grid frequency by up to a couple of Hz. Don't know if your TRace can do this or something similar in order to switch off your hydro turbine? The SunnyBoy must be setup in off-grid mode to enable the throttling response.

I have a SunnyIsland / SunnyBoy PV setup which works very well just as you are describing. The change in grid frequency is a clear invitation to switch on some opportunity loads :-)

Good luck with it!

David.

Eric L

Re: Can I use a grid-tie inverter on an Off-Grid System

If the Trace's won't alter the frequency to signal the GTI to throttle back (and I doubt they would), you could program one of the MX60 AUX functions to activate a diversion load, like water heating, to deal with the excess power.

rtribble

Re: Can I use a grid-tie inverter on an Off-Grid System

Thanks for the input. The AUX idea is good; I could have it turn on at 57V and use AC to heat water at 2000W. I have a 3000 gal. water tank next to my battery house. I could also pump more water into a storage tank for irrigation.

rtribble

Re: Can I use a grid-tie inverter on an Off-Grid System

so more questions....
1. does the Trace 4855 units charge batteries,if the output of the GTI inverter is greater than the load on the circuit.240
2. do i setup the GTI unit as 240V split phase
3. what if the load across the 120V circuits are not in balance ?
4. My Batteries seem to discharge and re-charge faster at 40 degrees than 80 degrees,is this normal ??
5. what voltage do i use for the AUX switch to charge batteries from the inverters ? Current setting for float is 57.6v

rtribble

Re: Can I use a grid-tie inverter on an Off-Grid System

My question is based on this comment I found in a link below

Fortunately the ‘off grid’ inverter that currently supplies our house, a Trace SW4548e is capable of ‘back feeding’ any surplus power into the battery bank. Trace don’t tell you this and if you have no means of regulating your batteries state of charge they will cook, but it is, in theory at least possible to connect a standard GTI (grid tie inverter) into your ‘AC bus’, use the power produced and then charge you batteries

rtribble

Re: Can I use a grid-tie inverter on an Off-Grid System

I wonder if anyone can answer the questions I posted sevarl days ago ??

BB.

Re: Can I use a grid-tie inverter on an Off-Grid System

I really don't know--But my first guess is:

rtribble wrote: »

so more questions....
1. does the Trace 4855 units charge batteries,if the output of the GTI inverter is greater than the load on the circuit.240

Probably (and confirmed in your second post). There is no charging control--So you have to make your own charge controller(s) to protect the battery bank.

You can use one or two shunt controllers and a load bank or two (same as wind turbine "charge control" setup). In theory, you should have two independent shunt charge controllers in case one fails.

You can use a voltage sense switch on the battery bank which opens a relay in the GT Inverter's AC output. That will turn of the GTI for at least 5 minutes--And will turn back on once the battery bank voltage falls below your set point (+5 minute delay for inverter to 'qualify' the AC is good again).

2. do i setup the GTI unit as 240V split phase

Most UL/NRTL Rated GT Inverters seem to be 240 VAC units (in the US). The newer models have to meet a new requirement that they also measure Line to Neutral voltages too--So, if the GTI is less than 5-8 years old or so, then yes, you will need to set it up as split phase (or use a transformer to provide a neutral output).

3. what if the load across the 120V circuits are not in balance ?

It will be the responsibility of the Off Grid Inverter to "balance" the 120 A/B current. As long as you do not exceed around 77% to 81% of the OGI's output rating (say 2,400 watt 120/240 VAC inverter, then 77% of that would be 1,848 watts on one L to N leg)--From what I have read about a couple "current" 120/240 split phase inverters.

In the case of the Trace 4855 inverter--I think that is a 120 VAC only output--So you will have to use a balancing transformer to "take care" of the 240 to 120 VAC conversion with the typical GTI inverter. Outback makes an auto-wound transformer that (I think) can be used for this (if it is large enough).

Autotransformer
For step-up, step-down and balancing applications.

FW-X240
Autotransformer 4 kVA 120/240VAC 60Hz with 25 Amp dual pole breaker for mounting inside of FW500 or FW1000 AC enclosures.

4. My Batteries seem to discharge and re-charge faster at 40 degrees than 80 degrees,is this normal ??

Batteries have "less capacity" at lower temperatures... But this could also be an issue of battery bank vs charge controller temperatures too...

A remote battery temperature sensor will increase charging voltage to a "cold" battery bank. If the charge controller is in a separate room from the battery bank, then the internal temperature sensor may not be controlling the battery voltage correctly (to the needs of the battery bank).

5. what voltage do i use for the AUX switch to charge batteries from the inverters ? Current setting for float is 57.6v

Do you have a second battery bank to charge? Is the switch temperature compensated?

Anyway, my guesses to the questions.

-Bill

rtribble

Re: Can I use a grid-tie inverter on an Off-Grid System

Many thanks, one consideration, I have two 4855's stacked to produce 240v ac, the questions about balance, is IF I use a GT inverter, do I just wire it into the L1 and L2 lines, and not need neutral. This is important because I have about 2000 ft. of wire from the GT inverter (working off a Harris Hydro @ 2000 w) to hook into my grid at the other end of the property. the question becomes do I use 10 gauge wire with L1, L2 ? or L1, L2, N ? do I need common ground wire ?? so do I buy 2,3, or 4 wires.

BB.

Re: Can I use a grid-tie inverter on an Off-Grid System

In the "olden days" (a few years ago), a 240 VAC GT inverter only needed L1 and L2 connections and no connection to Neutral.

However, the newer regulations now require a 240 VAC inverter to also monitor the L1 and L2 to Neutral voltage (120 VAC) and turn off the power if the neutral connection fails somewhere.

For a pure 240 VAC GT inverter, the neutral wire does not carry any current so that it can be a very small gauge wire (probably use 14 awg as minimum wire for pulling with the rest of the cables for strength) without problem (my home solar system was upgraded to a new style inverter and they just connected the neutral sense to safety/conduit ground--That may or may not work for your installation with the additional voltage drop of the long wire run and the whole issue of where to drive the safety ground rods).

-Bill

unclesun

Re: Can I use a grid-tie inverter on an Off-Grid System

Very good question, also common micro grid-tie inverter can be used at off grid ?

BB.

Re: Can I use a grid-tie inverter on an Off-Grid System

Yes, it is possible... However, you need a good quality sine wave inverter that can be back driven by energy from the GT inverters... Also, once the battery is charged, you need some way to turn off the GT inverter so the batteries don't get over charged (or put a dump load on the battery bank).

Or--there are a few off grid inverters out there now that vary the frequency of the AC grid and "knock" the GT inverter off line to stop them from supplying energy.

It can be a bit on the complex side to setup a system with GT and OG inverters.

What is it you want to do? Emergency backup power, off grid living, saving money, etc.?

You might want to answer those question in the other thread you started--That would keep everything together in one spot.

-Bill

unclesun

Re: Can I use a grid-tie inverter on an Off-Grid System

Thanks, I want one multi-purpose use portable PV system, camping, blackout emergency, grid living, assisting my wind generator (but not hooked up together for easy maintenance and monitoring). I may modify my current the golfcart solenoid relay type wind charging controller, to activate GT invertor when the batteies reach the trip point, and disconnect (open) the batteries. Because wind generator is very hard to use for camping by several certain reasons.

BB.

Re: Can I use a grid-tie inverter on an Off-Grid System

Then there is no reason (that I can see) to go through the trouble of using a GT micro inverter...

Use a standard PWM (cheaper, smaller system with, now more expensive "12 volt" panels) or MPPT solar charge controller (more expensive, larger systems, more complex controller and communications options, and can use both smaller and larger solar panels designed for GT inverter use--which tend to be less expensive on a $$$/Watt basis).

The only reason to use a pure GT Inverter is A) because you have a utility connection and want to save money, and it is a way to use your GT solar power system to recharge an Off Grid solar power system (inverter+batteries+possible more solar panels+solar charge controller) for emergency backup power (longer term outages--I would suggest more than 1-2 weeks at a time).

Shorter outages are usually more cost effective to use GT Solar + a backup genset + backup fuel supply(ies).

-Bil

unclesun

Re: Can I use a grid-tie inverter on an Off-Grid System

Great ! I will go for MPPT GT inverter.
I will post my portable PV project at Biginners cornor as different thread after made my initial design. I shall be very happy if you could pay your attention to my portable project.

BB.

Re: Can I use a grid-tie inverter on an Off-Grid System

You are very welcome.

By the way, pretty much all GT Inverters have an MPPT (maximum power point tracking) front end electronics. So, usually, when you see us typing about MPPT Solar Controllers--We are taking about MPPT Solar Charge Controllers for charging your battery bank.

So--I am still not quite sure if you are talking about grid tied inverter to "save money" on your utility bill--Or are talking about a MPPT Solar Charge Controller (and its PWM SCC cousin) + Off Grid inverter to supply power when the utility is down/or not present (cabin, camping, etc.).

And--Just to confuse the issue a bit more, there are "Hybrid" Inverters that can do both, GT and Off Grid. These are usually tied to a battery bank (plus solar panels+charge controller+backup gensets, etc.)...

For the most part, describe what loads you want to power, and the conditions you want to power them under (backup to utility power, camping, cabin, etc.).... After the loads and requirments are nailed down--then we can talk about hardware to optimally meet your needs.

Talking about hardware first can be very confusing... The solutions can very a lot, depending on loads and needs. Gets into a lot of confusing hand waving. Designing towards a goal, I believe, tends to be lest frustrating for everyone involved.

We are flexible--We have also help with designs based on Costs, having YYY Watts of solar panels, only can install two golf cart batteries, etc. Just need a target to aim at.

-Bill

unclesun

Re: Can I use a grid-tie inverter on an Off-Grid System

Thanks for details.
I am thinking below MPPT 20A solar charge controller (China) as per Youtube review because of detail indication; in addition, I want to add on overheat relay controller (diversion controller to avoid overheat of battery banks,not regulator).

westbranch

Re: Can I use a grid-tie inverter on an Off-Grid System

2 related threads here

http://forum.solar-electric.com/showthread.php?17511-Eco-Worthy-20a-MPPT-charge-controller-review&highlight=eco-worthy

http://forum.solar-electric.com/showthread.php?16450-Chineese-Eco-Worty-MPPT-Controller&highlight=eco-worthy

YMMV

unclesun

Re: Can I use a grid-tie inverter on an Off-Grid System

I saw the same Youtube video review.