Question on battery sizing

Solar Guppy

Re: Question on battery sizing

Interesting, I know for a fact you can't run full power ( 6kw ) on a 100ah battery bank, possibly the manual is taking into consideration the yet to be produced small units. Its is NOT AN OPTION for the orignal poster.

Also, at a discharge of 150aHr, that battery bank might run 30 minutes before it turns into a molten mess ...

System2

Re: Question on battery sizing

Interesting, I know for a fact you can't run full power ( 6kw ) on a 100ah battery bank, possibly the manual is taking into consideration the yet to be produced small units. Its is NOT AN OPTION for the orignal poster.

Also, at a discharge of 150aHr, that battery bank might run 30 minutes before it turns into a molten mess ...
__________________

The manual covers three different models up to and including the XW6048, I doubt that they put 100Ah for a unit that is not being produced yet

My post stated that he would be able to use that small battery for refrigeration, lighting, a fan or two and entertainment (TV, radio, etc.), NOT running the pool pump, air conditioning etc. He is being advisesd to spend around $10k on a battery that will probably see five days of use in the next ten years because he is grid connected. He stated he doesn't expect the grid to just one day be gone. A small battery with his array will zero out his bill plus he can have lights, TV and cold beer when the lights go out for a day every couple of years. But it's not my money.

Cheers,

Bad Apple

mike95490

Re: Question on battery sizing

Solar Guppy wrote: »

Interesting, I know for a fact you can't run full power ( 6kw ) on a 100ah battery bank,

Are you speaking of "full power" in grid tie mode, selling back, with PV behind it,
or in a
"grid failed" mode where you only run of batteries at night or on a cloudy day, with no grid ?

With a minimal bank, I would not expect to run a machine shop, but basic lights, HVAC and a fridge should manage, as long as you aren't pulling 6KW continuously.
I also don't understand how, in PV sell mode, why 60hz ripple would affect the panels, with the GT series, there are no batteries at all, and the PV's are just fine without batteries.

System2

Re: Question on battery sizing

Why not just get a bank with a string or two of the cheap ole Sams/Costco Golf cart batteries and put an auto waterer on them.
It really wont be using a lot of water just on float the majority of the time any way but it be fairly maintenance free and vent them out side?

For 220 Ah ( proly 100Ah for reliable use) it'll be 8, and 440 (with about 220 usable) for 16 for about $1000.


They have a 3 year prorated warranty.

Solar Guppy

Re: Question on battery sizing

mike90045 wrote: »

Are you speaking of "full power" in grid tie mode, selling back, with PV behind it,
or in a
"grid failed" mode where you only run of batteries at night or on a cloudy day, with no grid ?

With a minimal bank, I would not expect to run a machine shop, but basic lights, HVAC and a fridge should manage, as long as you aren't pulling 6KW continuously.
I also don't understand how, in PV sell mode, why 60hz ripple would affect the panels, with the GT series, there are no batteries at all, and the PV's are just fine without batteries.

The XW-6048's battery Current is 4X more than a High Voltage Gridtie inverter ( 48V vs 200V ) and the enegry storage of the HV GT inverters is almost 20X more as the capacitor energy storage is the square of the voltage.

The ripple imposed onto the batterys can be so high that the Charger Controller ability to regulate the PV array and do propper Mppt is compromised. This isn't some thing I'm pulling from thin air or something I "think" I know ... I've worked on this exact issue in the design phase of the project.

100ah will not work for a system if the inverter is running large loads which includes selling Gridtie. 200 ah might work for typical gridtie only mode but the aHr rate discharges on the batterys will quickly kill the batterys if your powering large loads off the battery and that is very likely, why else would one install a 6kW inverter otherwise?

12kW XW system is NOT something for the do-it-yourself crowd should be playing with anyways. This needs to be spec'ed, installed, permited and inspected system by professionals, its NOT a do-it-yourself task.

mike95490

Re: Question on battery sizing

Solar Guppy wrote: »

The XW-6048's battery Current is 4X more than a High Voltage Gridtie inverter ( 48V vs 200V ) and the enegry storage of the HV GT inverters is almost 20X more as the capacitor energy storage is the square of the voltage.

100ah will not work for a system if the inverter is running large loads which includes selling Gridtie. 200 ah might work for typical gridtie only mode but the aHr rate discharges on the batterys will quickly kill the batterys if your powering large loads off the battery and that is very likely, why else would one install a 6kW inverter otherwise?

Ouch !

What about the possibility of locating right next to the inverter, some of the series "Super Caps" for cars? They are several Farads each, and are designed to be abused with ripple. I'd be concerned with even a large battery pack, if there is that much AC, shaking the lead off the plates.

System2

Re: Question on battery sizing

Solar Guppy wrote: »

why else would one install a 6kW inverter otherwise?.

Well, I thought I needed at least 10kw of inverter with a 10kw PV array. I hope would be GT most of the time, selling back the excess, with a battery bank for outages. Initially, I wanted to just put in the GT system with the option of adding batteries later; I'm hearing that this is not an option.

Solar Guppy wrote: »

12kW XW system is NOT something for the do-it-yourself crowd should be playing with anyways. This needs to be spec'ed, installed, permited and inspected system by professionals, its NOT a do-it-yourself task.

The system will be professionally installed. You can only get the Connecticut rebates if an approved installers puts in the system. In CT, it's actually cheaper to have it installed than to do it yourself; with new equipment, anyway.

I'm very new to solar and I'm just looking for ideas here in this forum.

RCinFLA

Re: Question on battery sizing

Everyone's situation is different. I suggest you first analyse your electrical usage. Start with you electric bill and plot it for a year. Hopefully you kept your billing details. Find out where your KWH's are going in your home.

How often do you have outages? I live in Florida so my main objective is power during Hurricane outage. You don't have to worry about Hurricanes in Conn. but from the news I see winter ice storms causing outage for a day or two. This would be my motivation for battery backup. Do you have gas hot water heater, and gas stove? My killer is central air conditioner and is 50-60% of my 50 KWH's per day usage total in the summer. If you have gas then probably refridgerator is you dominate consumer. They run 1.5KWH/day to 4KWH /day depending on model, size, and age.

If you buy a battery based inverter grid-tie systems you can always put a smaller battery system and still accomplish the same objectives as battery-less grid-tie system and have some degree of backup capability for power outages.

If you put in a battery based system figure on putting a few hundred dollars a year in the piggy bank for battery replacements.

Bad Wolf

Re: Question on battery sizing

First time posting. I heard about this board over on hearth.com. Solar is something I’m just beginning to learn about, and this looks like a good place to do it!!

I thought I’d resurrect this thread because its something that I’ve been interested in for a long time. Back in 2007 I would have said RCinFLA was correct that CT doesn’t get hurricanes, but then in 2011 we had Irene (7 days without power) a freak snowstorm (4 days), Sandy in 2012 (4 days) and a blizzard in 2013 (dodged a bullet on that one)
I got thru them on generators, but if I had had solar panels it would have killed me to have that potential and not be able to use it.

I’m beginning to design my retirement home and I’d like to incorporate Solar into it in some form.
Has anyone done a model cost comparison between the three systems? I mean for the same house/load a grid tie system costs “X”, an off grid system costs “Y” and a hybrid with a moderate battery reserve costs “Z”. I’m just looking for an order of magnitude. If the difference between GT and a hybrid is $10K I’ll just get a generator. But if its only $2-3K I might suck it up and go for it. Two or three thousand over 10-20 really isn’t that much.

Thanks

Blackcherry04

Re: Question on battery sizing

The first thing I'd ask myself is, If I build a PV Solar system and I made a plan around them and they get compromised, what would I do then ?? Having $500 or $5000 worth of batteries won't go far if you cannot re-charge them. That scenario makes a Generator of some size a must. I left my GT out of my plan, but in a long term outage, I'd start cutting wires. The last time I had a outage of that magnitude there was 3 inches of Ice on the panels, If I could of even got on the roof to get to them they were unusable for two weeks. My choice would be a propane Inverter Generator, with enough fuel for 2 week run. I do have a stand alone Inverter with 4 GC-2 batteries that I can plug in to serve as a catcher for the generator, that way I can charge or run pass through loads, it will run my refrigerator all night and power some loads when the generator is off.

BB.

Re: Question on battery sizing

Welcome to the forum Bad Wolf,

Designing a cost effective solar power system really depends on learning about the loads you want to supply.

Usually, I suggest getting a Kill-a-Watt type meter (for plug-in 120 VAC 15 amp maximum loads), perhaps a whole house type monitoring system (like T.E.D.) and/or a Current Clamp DMM (to estimate power needs).

Take the above information, and then work on 1) conservation and 2) what is your minimum power needs for the off grid situation.

In general, for short term outages (say 2 weeks or less), a small genset + fuel supply is probably a better "investment". For longer term outages (2-4+ weeks), solar can be helpful--But is not really "cost effective" unless you are pulling power 9+ months from the system.

Off Grid solar power systems need new batteries every ~5-8 years, and new electronics (charge controllers, inverters, etc.) every ~10+ years (can last longer, but have cash on hand for repairs/replacements if needed).

A smaller genset only draws fuel when running and it does not require "that much" in the way of maintenance/costs (and replacement is still not that expensive).

To give you a rough idea--An off grid system running ~9+ months of the year, over 20 years amortization+maintenance costs, will run you (very roughly) ~$1-$2+ per kWH--Where utility power runs you around $0.10 to $0.20 per kWH and a genset (fuel costs) will be on the order of $1.00 per hour...

To give you an idea of what "classes of off grid power systems" you are looking at:

1kWH (1,000 WH) per day: Run lights, small fan, laptop computer, charge cell phone, shallow well pump/pressure pump for cabin/home.
3.3 kWH per day: Add a very efficient full size refrigerator, deep well pump, washing machine.
10 kWH per day: Almost normal electrical life (lots of conservation, some electric cooking, perhaps a bit of A/C).
30 kWH per day: Standard North American Home daily power usage (national average). Some electric heat/hot water/cooking.
100 kWH per day: Living in Texas, full A/C, Electric Heat/Cooking/Hot Water, etc...

If you install the system yourself--Something like $5,000-$10,000 per kWH per day up front capital costs. And for a "true" off grid system, most people will still need backup genset for ~3 months of the year (bad weather).

Again, these are very rough numbers for US based systems to give you some back of the envelope starting point for sizing your system... And there is always the "scaling factors" (larger systems can be more cost effective--but need some professional design/installation help, etc.).

I hope these numbers do not cause you "grief"--The are just very rough starting numbers to help you understand how conservation/new Energy Star appliances and simply turning off stuff not needed during outages can help keep costs "reasonable".

Sometimes, you can compromise... Use a "small off grid solar system" (~1 kWH per day) for 24x7 power (lights, radio, laptop, cell phone charger, water pumping from cistern) and use a genset for morning/evening cooking/clothes washing/pumping to cistern.

I have some 40 lb propane tanks and a propane stove for cooking and a multi-fuel camp stove that will run on unleaded gasoline (or diesel, etc.). Sort of look at a power emergency like camping--But I live in a moderate climate and our "big one" will probably be an earth quake (which, in California, has relatively localized effects--Rather than wiping out a hundred square miles of homes/business/infrastructure).

It is easy to buy larger systems/equipment--But there are costs too... Large battery banks that still need maintenance/replacement... A "small" Honda eu2000i (1,600 watt peak) may run 4-9+ hours on a gallon of fuel. An 8 kW genset may run on ~1/2 to 1 gallon of fuel per hour. All depends on your power needs.

I keep looking at Off Grid/Hybrid (both off grid and GT support when utility is running) power systems... But I don't need much power (no A/C, natural gas for heating/cooking/hot water)--So a Honda eu2000i and 20 gallons of fuel will last me 10+ days pretty easily (more if I siphon fuel from my car/pickup, use fuel stabilizer and recycle fuel to vehicles ~once per year). It just never made any sense for me to install an off grid solar power system. Beyond that, lack of city infrastructure (water, sewage, etc.) may become more of an issue and may need to evac/move. Plus a home knocked off its foundation with a 1/2 ton of batteries and a large solar array is not exactly portable.

Energy usage is a highly personal set of choices--What works well for me, may not work well for you.

-Bill

jcheil

Re: Question on battery sizing

And myself living in FL where we have hurricanes frequently and many tropical storms of 50+ mph winds, I would never rely on my solar after a storm because the chance of the panels being destroyed in a storm are pretty high. I have yet to have been so unlucky, but if I knew a Cat3+ storm was heading my way, I would likely dismount my panels and store them inside until the storm as passed. And even though i have a simple ground mount, it would be a lot of work.

In hurricane Andrew, a 24" diameter, 8 foot piece of telephone pole broke off and flew 100+' and impaled my car thru the roof, floorboards and about 2 feet into the ground under the car.

For disasters like that, a generator is the way to go.

solar_dave

Re: Question on battery sizing

jcheil wrote: »

In hurricane Andrew, a 24" diameter, 8 foot piece of telephone pole broke off and flew 100+' and impaled my car thru the roof, floorboards and about 2 feet into the ground under the car.

That had to be a sight to see! Pictures would be interesting for sure!

Hogan

Re: Question on battery sizing

Buying 48 solar panels but no budget for battery?

Would opt for fewer panels, and build a system that has some storage capacity, but maybe this is all about the rebate?

Don'tcha need some battery capacity to process a grid-sellback intertie? Charge controller should deliver current to a battery,
then inverter draws from battery; as I understand the process.

Rebate covers the inverter too? Charge controller? Might think about getting another meter and just directing all your output there.