Battery Backup Design

[Sunking]

I stored 50 gals of gas in high-quality 5-gal metal Jerry cans in an outbuilding away from the house..

When off-grid you do not use gasoline. Use LPG or diesel as they can be stored for very long periods of time.

[bflavell]

When off-grid you do not use gasoline. Use LPG or diesel as they can be stored for very long periods of time.

Agreed those are better sources of fuel when it comes to storage, but I'm trying to be able to use the $2K gas generator I already have. I store my gas with Stabil and then rotate it periodically to use in my vehicles. I'll look into the fuel conversion kits that gmaninPA mentioned.

[bflavell]

Hi bflavell - Do you have space limitations for fuel storage, or limitations for proximity of fuel? Propane tanks can be buried if the specs for doing so are followed. 1000g of propane can go a long way. If you want to keep your existing generator, you could look into a tri-fuel conversion kit for your existing generator. A company called Motor Snorkel (dot com) makes them and they work pretty well. I have two of their kits for portable Generac generators and they're easily installed. That could allow you a long-term, stable, and bulk fuel storage, but to keep your existing generator.

Space limitations. The yard of my new house is 1/4 of the size of my old yard (had an acre). With the pool and patio areas, there's not a lot of places to store fuel outdoors. And trying not to make it an eyesore. I'd have room in the garage for a good size propane tank, I just don't really like the idea of that much fuel in an attached garage, and would need to see if there are any insurance ramifications.

On energy comparison, I believe a gallon of propane has equivalent energy as 0.74 gallons of gas. And a gallon of propane weighs 4.25 lbs, so 1000g is equivalent in energy to 0.4 gallons of gas. Am I getting that wrong? This comparison assumes that gas generators run at the same energy efficiency as propane generators, which I'm not sure is true.

[zed]

I'm designing a battery backup system and wanted to get your thoughts. I use about 15,000 kWh/year, but am taking additional steps to reduce that (e.g. more LEDs, new variable pool pump). I figure an 8kW to 9kW system will get me to around 12,000 kWh, which I think will end up covering my use once I reduce some more. Here is the proposed system:

27 x LG Neon 320W Panels
1 x Radian 8048a with GSLC Load Panel, Mate 3 and HUB 10.3
3 x Midnite Solar Classic 150
1 x Midnite Solar 12 CB Combiner Box
1 x Midnite Solar 3 CB Combiner Box
5 x Midnite Solar MOV Surge Protectors (3 DC for combiners, 1 DC for GSLC and 1 AC for GSLC)
16 x L16RE-B Batteries (two 48V strings in parallel)
1 x DIY Sealed/Vented Battery Box (w/ two 48V Zephyr fans)
Racking (still figuring this out, but likely Ironside)
Cables/connectors (PV, batteries, inverter, etc)

I'm wiring the panels in 9 strings of 3 each. The reason for the three CCs is that I have three different roof facings: S (9 panels), SW (6 panels) and East (12 panels). So I wanted one CC per roof facing. I'll run two CCs (S and E) from the 12x combiner and the third CC (SW) from the 3x combiner. This also requires me to add another PV breaker in the GSLC and swap out the 2-pole GFDI with a 4-pole GFDI.

I was going to use FM80s at first, but I need AFCI and using the Classic 150s seemed to be the most cost effective way since Outback still does not have a great solution yet. They are coming out with the new Flexware ICS Plus, which has AFCI and rapid shutdown, but I hear it will be around $2K. California has not adopted 2014 NEC yet, so I don't need to have rapid shutdown, but I still need to comply with AFCI under 690.11 of the 2011 NEC.

Thoughts (good and bad are welcome)? Anyone using anything similar?

Thanks.

That sounds like an overly complicated setup.

I am totally off grid, but if I had a grid i could connect to it and grid feed.

A very simplified setup that will do the job far better than what you propose is same amount of panels BUT use a Sunny Island 8.0h and two Sunny Boy 5000TL inverters.

Much more elegant and dare I say...reliable? And much more scaleable.

[gmanInPA]

The two generators i have will burn between .8 to 1 gph. IMO, propane burns about as efficiently - and a little more easily on the engine - than gas. The huge advantage of LPG is that it stores indefinitely. If you bury a tank - you don't have to go very far (20') from your structure. There's more to it than that, just trying to make the point you likely have a spot you could use. Not sure how you equated 1000 gallons to .4 gallons of gas. Were you treating 1000 g as grams? If so - I meant gallons. You can bury a 1000 gallon tank. Since propane expands, you'll never have 1000 gallons in there because it's filled with room for such expansion. I would never store anything beyond a bottle tank in a garage. Even those i store as far away from the house as possible.

[Djcoak]

Gman as a newbie I wanted to say thanks for your posts, your teaching me a lot. Not sure why the total grid tied crowd doesn't understand the back up scenario.

[gmanInPA]

Gman as a newbie I wanted to say thanks for your posts, your teaching me a lot. Not sure why the total grid tied crowd doesn't understand the back up scenario.

Well glad my own learning has helped someone else. There are a lot of very smart people here (i'm not including myself in that description :-0) and much that can be learned. You will find a very small amount of active users are hybrid/backup systems. While people have been cobbling together hybrid systems for a long time, they're relatively "new" (well, hybrid inverters anyway) compared to off-grid and grid-tied systems. You WILL receive a lot of encouragement and admonishment to NOT use batteries because it is the most expensive way to make electricity. It is the least economical among solar setups. Regardless, I personally think there will be a strong trend towards more hybrid systems as the days go by.

I don't think that the grid tie crowd doesn't understand the backup scenario - they just have different goals than a hybrid user. As the saying goes, "when you're a hammer, everything looks like a nail". There is no hardware arrangement that will work for everyone. There are valid and invalid reasons to choose any particular option. Many people start off with the idea that they're going to save money - and that is just not likely to happen with a battery-based system, and so you'll see a lot of comments to that affect.