I'm planning my off-grid system using (12) 340W panels, a Classic Lite 150 and either eight or sixteen Trojan T-105's. The batteries are 6v rated at 220AH for 20 hours and I was going to have to wire 8 in series to get 48 volts, obviously. I've searched all over the web, trying to determine how many batteries to use. I added up all my appliances and I get roughly 1.7kW. Also, I have a total of 16 panels so I can always add more and buy another or different charge controller. As near as I can figure, I need either 8 or 16 batteries.
These days I would give serious consideration to using lithium instead of lead acid.
Prices are decent and so much better performance and probably longevity too. Lead acid take regular maintenance or they don't last as long as they should. For best longevity cycle life you only want to take 20% out of them. So size your capacity according to that figure for lead acid. You can take more out of lithium so have smaller ah battery pack in comparison.
8 in series for 48v is better option instead of putting 2s2p ( two series of 8 - then parallel ) because it is difficult to keep the parallel ones in balance. That is a lot of battery cells to regularly check with hydrometer, water, equalize, etc.
Read up in lithium section of group. Also plenty of youtubers reviewing lithium cells these days. Will Prowse is one.
Larry
Don't know much about Lithium Ion. Do they make any 48v? I guess Battleborn is the goto co. for Lithium.
Hi sunbelt,
If you go to the following store (N AZ Wind & Sun), and type, ' Lithium ', in the Search Box you will see a number of Li batteries offered.
>> EDIT, to actually INCLUDE the Link referred to above:
https://www.solar-electric.com/
<<
Of course, there a number of other suppliers, as well. Wind Sun is a very reputable company (with which I have no association or interest), just a happy customer.
Is the system you are setting up, off-grid, Grid backup, RV, or ... ??
I looks like you used the Default temperatures on the Classic String SIzer. Do these temps reflect your actual highs and lows? This does matter, as the PVs that you have, are at the very limit of Voc and Vmp for a Classic 150 (IMO).
More later, Vic
Hi sunbelt..,
Just a few comments from scribbling on the back of the envelope.
A single string of GC Flooded Lead Acid (FLA) batteries would generally be limited to about 13% of the 20-hour Capacity (C), as max charge current. This is about 28 Amps. With your 12 PVs, you could expect almost twice that max charge current (with few other loads on the system).
As Larry mentioned, it is often best to try to avoid multiple parallel strings of batteries.
Also, the exact nature of your 1.7kWh loads might change the view in the needed battery capacity. Due to inefficiencies in battery charging, the Charge Controller (CC), and inverter, usually means that if all of the 1.7 kWh load comes from the battery, you will need to produce about twice that amount of energy as that load (when using FLA batteries).
There is also the consideration, for the number of days of little, to no sun that your site might encounter, which would normally increase the needed battery Capacity by a factor of two, or perhaps, three times the C needed for a single day (for two or three such days).
As you know, cooling and heating appliances demand a lot of energy, and often for extended periods of time. So being thoughtful about how much cooling and heating your environment will really need will serve you well.
It can also be a good idea to up-size your power system, somewhat to allow your loads to grow a bit, as it is often difficult to grow the system very much, at a later time.
FWIW, Vic
Yeah thanks vic, I'm off-grid in WY and it does get cold in the winter. I'm running off a generator now and I notice when I run the little space heater in the winter under my desk the generator really struggles.
If you have enough extra PV ( some used PV is really inexpensive these days too) and you want to run a space heater - you can just make a higher voltage series string of PV and then just run it directly into a resistance space heater ( baseboard without a fan is best ) . Then you don't need any controller, batteries , inverter . You would only need a thermostat to control either a relay or IGBT block that is rated to handle the higher DC voltage ( which would be something under 300v) If the resistance of the heater is a good match for your PV output then you will get a pretty good output from the panels. That is what I did with a bunch of used PV I got and I use it to heat water and also run into a space heater as needed.
Regarding your batteries - if you really want to stick with lead acid then you want to go with forklift type batteries instead of a bunch of golf cart type or L16's.
Larry
From this website:
https://pveducation.com/designing-an-off-grid-solar-electric-system/designing-an-off-grid-solar-electric-system-step-4-sizing-the-battery-bank/ (https://pveducation.com/designing-an-off-grid-solar-electric-system/designing-an-off-grid-solar-electric-system-step-4-sizing-the-battery-bank/)
I calculate the needed battery size using:
(Load AH/day) x (Days of Autonomy) / (Max DOD) / (Cold Temp Factor) = (AH Battery Bank Size Needed)
Load AH/day 35
Days of Auto 3
Max DOD 0.8
Cold Temp F. 0.8
Result: 164
So I would probably need a battery with about 200AH. Any recommendations for Lithium Ion?
If you wanted those lead acid batteries to last a long time you would change the depth of discharge from .8 to .2 . You won't get much lifespan out of batteries if you discharge them 80% compared to 20% .
Go to main Midnite Forum page and search lithium ( search doesn't work from other pages for some reason)
There were a lot of detailed lithium discussions in the past year .
Also the Will Prowse youtube page - he reviews a lot of lithium batteries
https://www.youtube.com/user/errolprowse
Larry