Inexpensive method for Grid Tie in to charge battery backup during a blackout

[jhop]

I have a thought that when it came down to a pinch and I might need emergency power, I could use my solar panels for to power essential items.
Does this seem possible without any other items?

My current system located in Tallahassee, FL is:
5.5kW grid tied solar power system consisting of 24x 230w Trina TSM-PA05 with max power of 30V at 7.66A
Xantrex GT 5.0: DC power from array when online reads 240V and up to 21A

Essential items to be run:
13W CFL light
22cu ft Refrigerator with Freezer 537 kW/yr
Laptop or other small electronic/charging of cell phone 100W

Can I repurpose existing items for an emergency? I.e. powered from car battery while charging them? I understand this will potentially wear down the battery, but we are speaking of emergencies.
I have two car batteries and also a hybrid 2006 Toyota Prius, any way to use this?

What size inverter should I purchase to power the refrigerator? It would seem that one rated for 1000 watts peak surge would be sufficient with 500 watts continuous. Is it possible to repurpose a backup UPS connected to the car battery for this function?

Is a charge controller required?

I can access the bare solar cell +/- wires from the Xantrex. What are the potentials for damaging my system by connecting wires to the system if I follow the following steps (and are all of these steps necessary) after a power failure occurs:

1. Flip dual circuit breakers to off position
2. Flip AC/DC switch to disconnect position
3. Wear rubberized boots and gloves
4. Connect alligator clips from battery terminals to the respective String 1 PV positive and negative terminals.
After 1 hour of charging, disconnect.

[Mike90250]

You will need a way to break a string apart. while you "can" charge a 12V battey from a 200V PV array directly, you will WASTE (not use) most of the power, the battery will limit the voltage ok, but you will draw a big fat 400V DC arc when you try to disconnect. You would need a 400V+ DC breaker to safely disconnect.

I would just get a MC connector tool for the cables, and when the fridge warms up, take some of the array apart, and with some pre-prepared MC connectors, re wire several panels to low voltage DC, and charge from that.
400VDC scares me, mostly because it's hard to stop the arc.

Throw a blanket or sheets over the panels to shut them off before starting any work

[solar_dave]

I would just get a small generator to carry you in emergencies.

[Sunking]

You are asking for a lot of trouble, possible setting your home on fire or electrocution. The systems are not designed to do what you want to do. To run your refrigerator that uses 1.5 Kwh per day requires a lot more batteries than a couple of car batteries you happen to have lying around. It will take at least a 900 AH battery bank at 12 volts, or about 600 pounds of batteries.

Buy you a generator. It will be a lot less expensive, and you can run a lot more than a light, laptop, and dorm refrigerator.

[jhop]

Thanks, this forum has been very helpful. Purchasing a $300 generator was next on my list if this wasn't an option. It seems like a waste to have the potential solar power locked up because of an outage. It sounds like I'd have to buy at least 6 more batteries, and then a suitable inverter and charge controller to make it work just for those infrequent emergency situations. Also, this information would be useful if I was stranded in my house with no hope to make it out for a week and I don't have a gas generator (or the fuel because of an extended blackout such as the one that occurred in the midwest that I was unfortunate enough to be stuck in) ...

Regarding the option to cover the solar array, that would be difficult as they are rooftop installed. Although 3 sets of strings come down grouped as 8 panels, even that might be difficult to control.

[Mike90250]

Yep, it sucks to have 4KW on the roof, and no power when the grid goes down and takes your PV offline.
There are, 400V - 48V DC- DC converters, but they are pricey, and you have to know how to work with really dangerous voltages and current. (dusk and dawn is when you have to make/break contacts, 400V @ 10 A will draw an arc like you won't believe. That's why they have special DC circuit breakers.) Battery charge control is run by Load diversion, if your batteries are full, turn on the electric heater, run the air conditioner. If you are going to feed 4Kw to the batteries, better have 4KW worth of inverter and loads on hand.
Generally, it's a mess.

[jhop]

I considered the DC-DC converter but thought it was cost prohibitive for my intended purpose. I would definitely have to run my loads, but running the central AC might be difficult without a higher powered inverter and then connecting it to my house as a whole house power source. It would be difficult to justify that expense, as a lower powered one could be justified for use while camping.

[CT YANKEE]

Using grid tie during power down

Hi
Newbie but:
Would this work in emergency?
1-OPEN MAIN AC LINE breaker
2-turn off all ac loads in house
3-plug small 100watt 12vdc/240vac SINE WAVE inverter into dryer outlet
4-turn on house load less than 100watt
5-restart grid tie inverter for house
6-turn on larger loads - NOT MAIN
5-smile
STOP STOP STOP STOP STOP STOP STOP
The Xantrex might be OK with this but the small sine wave inverter will probably blow up since not made to be a grid tie and see source AC on its output. Will engage brain longer before posting in future.
Dick
Dick

[jhop]

That would be a good idea provided that the small DC to AC inverter were able to replicate the sine wave to satisfy the Xantrex inverter. My assumption was that the Xantrex inverter would remain offline, but that I would have access to the wired solar panels to somehow fashion an emergency solution for power.

It would be interesting to have that small inverter powered from the same car battery that is being recharged from the solar panels.

I have read about possibly using a Honda gas engine to replicate the wave and being able to trick the inverter into believing that it was tied into a grid and therefore bring itself online. That solution might be alright, but then I might as well use that generator for its intended purpose, and I was trying to avoid having to spend more money for a very rare event.

[CT YANKEE]

Same would apply to any AC sine wave source - it had better be able to see 240vac from outside without damage!!
Dick