Design of Grid Tied Systew with Off-Grid Option?

[Shockah]

Which does not work since the station does not have a generator.....

Haha... truth.

I'd hope there are a few stations that have some sort of back-up.
If not, there will surely be a few looters willing to extract the gas from the in-ground tanks...
I know I have a 12 volt fuel pump that would work

I was managing a gas-station's service department in Dec '99,,, right before Y2K.
The station's owner purchased a large/expensive generator to back-up the pumps because he fell for the Y2K hype...

[FS2020]

Thank you inetdog and Shockah, this is the kind of constructive advice I was asking for.
In a grid down scenario, I would only need electricity for one computer, a couple cell phones, recharging flashlight batteries, and the pump for my rainwater harvest system. Then I would have water to drink, be able to flush toilets, and communicate. Forget the fridge and everything else. I have enough dried food and propane to boil water so we can eat for months.
I live in a passive solar house, so most of the heating is taken care of.
Frank

[inetdog]

Thank you inetdog and Shockah, this is the kind of constructive advice I was asking for.
In a grid down scenario, I would only need electricity for one computer, a couple cell phones, recharging flashlight batteries, and the pump for my rainwater harvest system. Then I would have water to drink, be able to flush toilets, and communicate. Forget the fridge and everything else. I have enough dried food and propane to boil water so we can eat for months.
I live in a passive solar house, so most of the heating is taken care of.
Frank

With that scale of power demand, you should definitely take a look at the TL-xxxx-US line of grid tie inverters from SMA. They include a built-in secure power supply which does not use any batteries for energy storage and gives you one isolated ~12A 120V circuit that is powered as long as the sun is shining on the panels.
If a cloud goes by and the available power is not enough to serve the load, it shuts off and then tries to start up again later.
Should work fine for laptop and cell phone charging during daylight hours. Then let those batteries or a small UPS carry you through the night.

Those models also include GFCI/AFCI protection on the DC side which should meet NEC 2104 requirements.

[Shockah]

Thank you inetdog and Shockah, this is the kind of constructive advice I was asking for.
In a grid down scenario, I would only need electricity for one computer, a couple cell phones, recharging flashlight batteries, and the pump for my rainwater harvest system. Then I would have water to drink, be able to flush toilets, and communicate. Forget the fridge and everything else. I have enough dried food and propane to boil water so we can eat for months.
I live in a passive solar house, so most of the heating is taken care of.
Frank

You'll need to determine the watt hours consumed by the "one computer, a couple cell phones, recharging flashlight batteries, and the pump for the rainwater harvest system."
Use this handy off-grid calculator to determine how much panel you'll need to dedicate and battery size.

For my "NATURAL DISASTER" plan, I would need about 3kwh per day... which means dedicating 6 panels and purchasing a 1250ah/12v battery pack, along with the CC and Inverter.
Quite an expensive survival kit... which is why I have only pondered it so far ...

[FS2020]

Thanks for the link to the calculator. Shouldn't be too hard to determine daily energy consumption of the limited appliances I want to power in a grid down situation.
I'm thinking around ten golf cart batteries, but I'll do the calc's to verify. I plan to install about 5kW of solar PV on my roof.
I understand basic electricity: Ohm's Law, Kirchoff's, keep my left hand in my pocket, but much beyond that I'm lost.
I'm a complete newbie at solar. Thanks for the advice!
Frank
Here's a photo of my double-shell passive solar house:
front_view_Nov18_2011_sm.jpg

[inetdog]

I'm thinking around ten golf cart batteries,

Caution: Whatever size (in watt hours) battery bank you end up with, keep two additional rules of thumb firmly in mind:

1. Keep the battery bank voltage high to minimize the need for large interconnecting wires. High amp DC can bite you indirectly even with one hand in your back pocket.
Just think about dropping a wrench across the battery terminals. That only takes one hand! Rule of thumb is that if you need more than a 500 watt inverter you should look at a 24 or even 48 volt system.

2. Try very hard to design for a single series string of batteries. For example, if you have a 48 volt system, use 8 six-volt batteries not 8 12 volt batteries in two parallel strings of 4 each.
If necessary, look at 12 four-volt or 24 two-volt batteries for a 48 volt system or 6 four-volt or 12 two-volt for a 24 volt system.
Forget about a 12 volt system if your shirt pocket estimate of your battery needs is close to correct.

[Sunking]

Sure a generator will suffice, until the gas tank empties... and I'm not a fan of standing in long lines at an overpriced pump.

Gas pump? What gas pump? A emergency generator does not run on gasoline. Try NG, LPG, or diesel.

[inetdog]

Gas pump? What gas pump? A emergency generator does not run on gasoline. Try NG, LPG, or diesel.

Good catch!

[Sunking]

I have enough dried food and propane to boil water so we can eat for months.

Then you have all the fuel you need to run a generator to charge a modest set of batteries beyond your needs. Ready to listen now?

Emergency generators do not use gasoline. They use NG, LPG, or diesel for large generators above 50 Kw. So no need to worry about neighbors stealing you gasoline or generator.

[Shockah]

Good catch!

Ditto...
but still, any of those also has to be purchased from a retailer once the tank needs replenishment.

( NG or LPG gas lines don't run through much of the islands... in fact just a very small percentage of Hawaii has gas plumbed in.)

[Sunking]

Ditto...
but still, any of those also has to be purchased from a retailer once the tank needs replenishment.

( NG or LPG gas lines don't run through much of the islands... in fact just a very small percentage of Hawaii has gas plumbed in.)

I can run my 12 Kw LPG genny for more than two weeks with a 500 gallon tank. Get a bigger tank than a 5 gallon BBQ tank.

[Shockah]

I can run my 12 Kw LPG genny for more than two weeks with a 500 gallon tank. .........

12Kw? Nice! You win...

[FS2020]

I can run my 12 Kw LPG genny for more than two weeks with a 500 gallon tank. Get a bigger tank than a 5 gallon BBQ tank.

How loud is your generator? How far away can neighbors hear you enjoying things they don't have, and that they need to survive
What happens when your hydrocarbon tank runs dry?

[DanS26]

Thank you inetdog and Shockah, this is the kind of constructive advice I was asking for.
In a grid down scenario, I would only need electricity for one computer, a couple cell phones, recharging flashlight batteries, and the pump for my rainwater harvest system. Then I would have water to drink, be able to flush toilets, and communicate. Forget the fridge and everything else. I have enough dried food and propane to boil water so we can eat for months.
I live in a passive solar house, so most of the heating is taken care of.
Frank

Frank,

Take a look at this product line from SMA.....it may provide the low amount of emergency power you need without going the battery route.

http://www.sma-america.com/en_US/products/grid-tied-inverters/sunny-boy/sunny-boy-3000tl-us-3800tl-us-4000tl-us-5000tl-us.html

It has drawbacks, but from your description of needs it may work for you. Daytime power only though. "Secure Power Supply" of 1500watts without the grid and without batteries.

[Sunking]

12Kw? Nice! You win...

It is a whole house genny. In summer when th ebig t-storms and twisters roll through and knock out power, I set back in my air conditioned house and watch everyone suffer in 100 degree heat without power. I cycle the generator with the HVAC only coming on when the HVAC switches on to conserve fuel. With Sun Tubes and bay windows provides all the light I need during the day.