I have (x3) 150W panels, and need 1600Wh a day. Suggestions for battery banks?

[Fractalcathedral]

Point taken, but the tradeoff seems to be that I don't have to pay rent, or can find ways to make it extremely minimal, don't have to plug into shore power, (which I'm concerned could have a fault and send huge currents back through to my system), and can park in places that are more secluded than your average cramped, $300 a month RV park, and still be able to work on digital art, watch movies, and play PS4 as I please.

I found a chart for D.O.D/ cycle lifetime earlier in my research, which looked like this:

* 50% = 200 cycles
* 40% = 500 cycles
* 30% = 1000 cycles
* 20% = 2000 cycles
* 10% = 4000 cycles

And I guess I took it for granted that this chart was applicable to AGM, (which I would be willing to pay for to avoid having to deal with the potential safety hazards of FLA, however manageable they may be with proper knowledge), but I think the article mentioned using a hydrometer, which I am unsure applies to AGM. How would this D.O.D chart look for AGM?

I ordered a 4th panel today, and I intend to put them into one 48v series, which eliminates the need for a combiner box. Does it also eliminate the need for a fuse or breaker between the solar panel and charge controller?

People mention 12v,24v, and 48v, but I don't often see 36v thrown in there. Is there any contraindication that should prevent me from going 48v panels > charge controller > 36v battery bank > 36v Inverter? Or any advantage to keeping it 24v?

Based on that chart, I was thinking 6 AGM 12v 155ah batteries, with two strings of (x3) in parallel. Gives me 11,160 Watt/hours total. 10,000 is a 20% depth of discharge after I adjusted my daily usage to be 2,000 W/h to compensate for 40% loss from module to freezer, so I could have a little buffer for multiple cloudy days.

Since the batteries themselves are 12v, what size would the wires have to be? Those rated for 12v? or can they be suited for the 36v, since that what each string of batteries will, in effect, combine to form? Once again, is there any links or books anyone can refer me which might provide any pertinent information about any of this?

[Sunking]

So AGM is better in areas of low solar isolation? Do they do better than FLA with charge rates below C/12?

Yes to both questions.

However in areas of low Solar Insolation like Gloomy Doomy Portland/Eugene where Sun Hours drop to less than 2 hours means you have to have a panel wattage that generates charge currents in excess of C/8, and FLA batteries cannot handle that kind of charge current where AGM can.

Example let's say you need 1 Kwh per day in two cities of Portland OR and Dallas TX. Both need the exact same battery capacity of 12 volts at 400 AH.

In Dallas the Dec/Jan Insolation of 3.75 Sun Hours only needs a 400 watt solar panel with a 35 amp MPPT controller which at max charge current = roughly 34 amps of a C/11 charge current which if good on a FLA battery.

Gloomy Doomy Portland and Eugene OR only gets 1.4 Sun Hours in Dec/Jan and will require a 1100 watt of solar panels using a very expensive Midnite Solar Classic charge controller generating 92 amps of charge current or C/4 charge rate and will require a AGM battery to handle that high current.

In Dallas it would cost you roughly $1800 to $2000 with $700 to $800 of that in batteries that last 4 to 5 years. The first 5 years would be roughly $1/Kwh which is a hard slap in the face when power cost less than 10-cents per Kwh in TX.

In Portland/Eugene it would cost you roughly $3500 to $3800 of that $1500 to $1600 in batteries that last 2 or 3 years. First 3 years brings your Kwh cost to $$2.10/Kwh which is a wicked slap in the face because you can buy it for less than 11-cents per Kwh from clean renewable hydro dam power in that area. There is nothing clean or green about battery systems. A huge waste of resources and very dirty.

[paulcheung]

If you willing to carry a small portable generator (1000 watts) and not afraid to use it, you can just use 2 Rolls S-550 batteries and wire them 12 volts, get a Xantrex Pro watts 1000 inverter and 600 watts panels. I have a similar system that consume about the same amount wattage, I have 675 watts panels and 450 AH 12 volt battery bank. I have to use generator for 2 hours to charge the battery bank any time I got a rainy day. The only problem might be the start current for the freezer, it the Pro watts 1000 can handle it then the rest is ok.

Also if you drive a lot, you can install an electronic Battery Isolator to charge the house battery with your alternator.

[Mike90250]

An AGM battery allows you to charge it faster then a FLA battery. So to compensate for low solar isolation you use more panel wattage and shove as much amps into that battery for the short time the sun is shining. Doing that with FLA will boil off the fluid.

or you can leap to the LFP batteries, which can take a hefty charge too, and cost some more $$

[SunEagle]

So AGM is better in areas of low solar isolation? Do they do better than FLA with charge rates below C/12?

An AGM battery allows you to charge it faster then a FLA battery. So to compensate for low solar isolation you use more panel wattage and shove as much amps into that battery for the short time the sun is shining. Doing that with FLA will boil off the fluid.

[LETitROLL]

It also forces you to use very expensive AGM batteries

So AGM is better in areas of low solar isolation? Do they do better than FLA with charge rates below C/12?

[Sunking]

Yeah, I am looking at looking at Eugene first, and then Portland if that doesn't work out.

You could not pick a worse location for solar. Well Seattle is as bad. It takes 4 watts to do what 1.5 watts will do anywhere else in the USA. It also forces you to use very expensive AGM batteries which cost twice as much and last half as long as Flooded Lead Acid. A battery system there will be 4 times higher than anywhere else.

[LETitROLL]

The prices on most panels now are a pretty good deal when you consider the amount of power they can generate over a 40 year lifespan, its the batteries that are the big loser from a financial standpoint, but you will do fine if you adjust for the weather and figure you have a little more on sunny days (and seasons), and less on short cloudy days, etc. Most people living off grid deal with that reality and conserve and adjust when needed. Solar has become much more affordable in the last few years, but the initial costs for a decent size system can still be a sizable investment.

[Fractalcathedral]

Going to need a big system to be completly off-grid in most parts of Washington in the winter. There are a few spots that get more sunshine, but the parts of washington I am used to are about in the 2 sun hours a day range in winter, and Cali in the good seasons closer to 5-6, so you will have to nail down where and when you really need it to work before you can really size the system correctly.

Yeah, I am looking at looking at Eugene first, and then Portland if that doesn't work out. Getting a feel for the city first and not dropping anchor until I know it's the place.

My sister lives in California and my Dad lives in Washington, so I'll be travelling between them. If I don't feel like cycling too deep into the batteries I can read or go outside. There's really no discouraging me at this point, I appreciate hearing the hard facts. I just don't want to be tied to shore power, nor do I want to be tied to a mortgage or throwing my money away on anything more than "I'll pay you 100 bucks to park here for a month" rent, nor polluting the environment. Solar for me is just a no-brainer.

[LETitROLL]

Could any of these safety concerns be remedied with thicker wires, fuses, breakers or installing a A/C Disconnect?

Any proper system regardless of the voltage should have the proper fuses, breakers, disconnect, etc. and when done correctly of course that greatly reduces any risk, but the risk is still naturally greater at higher amps.

[LETitROLL]

You mentioned early "the starting point of safety concerns". Could you elaborate on those?

Once you get above a certain amperage (60-90 amps roughly) the risk of bad connections, stressed components, inferior wiring, are all going to increase problems and the risk of fire, and things may be okay when new but can sneak up on you if not well maintained as those parts and connections age. At 24 volts (out of your battery bank) 50 amps you are looking at roughly 1000 watts total power, of course at 12v it will take 100 amps to get the same amount of total power (watts).

[LETitROLL]

Also remember when factoring in losses they are system wide (and worse at lower voltages), panels rarely produce their rated output, then you lose some of that lesser number getting to the controller, then more losses moving through that circuitry, then you try and put 400w in a battery and lose part of that to heat and more wires and connections, then an hour later to take it back out of the battery and lose more again, then most inexpensive inverters really rob you blind. In your application you would probably be closer to correct figuring a 30-40% ballpark loss clear through from panel to freezer. Not trying to discourage you, people do it, and you can make it work with cheap stuff or good stuff, but it does take a bigger system than most factor in for, and the cheap systems usually have more failures and repair bills, and more frequent battery replacement so it ends up being a case of pay me now or pay me later.

[Fractalcathedral]

The advantage of the 24v inverter is that it will draw only 1/2 the amps from the battery. The frige compressor will get the same from the inverter in any of the systems because they all eventually convert it to your 120v AC.

You mentioned early "the starting point of safety concerns". Could you elaborate on those? I am just curious, I am strongly leaning against 12v battery bank and towards 48v 4-module series with 24v battery bank. but I'm curious to learn the Why of any of this. Could any of these safety concerns be remedied with thicker wires, fuses, breakers or installing a A/C Disconnect?

A watt is a watt, so you are not really doubling your inverter capacity, but the higher voltage inverters are more efficient because it is less of a step up from 24v to 120v then from 12v to 120v, and also again only drawing 1/2 the amps from your battery so less problems with wires, connections, etc.

Thanks a lot man, I didn't know that. Does anyone has any book recommendations regarding the fine grain details of this stuff? It's pretty fascinating, to be sure, but I feel like all of my research is very fragmented, like that scene in Better Call Saul where Jimmy organizes the scrap of shredded documents.

[LETitROLL]

I'll be travelling between Washington, Oregon, and California, (3 to 5 peak sun hours a day), and it would be nice to be completely off-grid in Washington during Winter, if possible.

Going to need a big system to be completly off-grid in most parts of Washington in the winter. There are a few spots that get more sunshine, but the parts of washington I am used to are about in the 2 sun hours a day range in winter, and Cali in the good seasons closer to 5-6, so you will have to nail down where and when you really need it to work before you can really size the system correctly.

[LETitROLL]

Advantage = Safety of having 24v inverter delivering low-amperage surge to fridge compressor. Less likely to cause problems with early battery failure, inverter, or controller.
Advantage = Inverter wattage capability doubles to 1000w(?)

Downside= 36v for panel string is higher than Vmp of 22.5V. (Does this really matter, or will the MPPT controller convert that extra voltage to amperage?)

The advantage of the 24v inverter is that it will draw only 1/2 the amps from the battery. The frige compressor will get the same from the inverter in any of the systems because they all eventually convert it to your 120v AC.

A watt is a watt, so you are not really doubling your inverter capacity, but the higher voltage inverters are more efficient because it is less of a step up from 24v to 120v then from 12v to 120v, and also again only drawing 1/2 the amps from your battery so less problems with wires, connections, etc.


Yes, Mppt charge controllers will convert the overvoltage to amperage, to match whatever battery system you run.