titooon2014 wrote:Hey steveo,
Thank you for sharing about the ups, it is definitely a great idea !
May I suggest you have a look at Dr Angel thread about homemade 18650 battery pack ? For the future at least...
Are your batteries brand new ?
Lithium is now much better to use for solar, and considering you seem quite skilled you may want to go this way. It will take time but will be rewarding.
Much better because
- Better charging efficiency, a lot of losses with lead acid esp at high level of charge
- You can use 90% of the DOD without damaging the battery. If you want to keep a long life span on lead acid, a dod of 30% is recommended. So 3 times less capacity needed for lithium. That would be about
- Available easily through computer batteries - however lot of work involved as you ll see in the thread.
- much better lifespan for lithium
- Very quick charging possible from potential generator
At the end they are a better bang for your buck even if you have to buy them new.
Anyway back to your design.
Have you calculated your needs ? I suggest you keep that AGM bank at 30-40% depth of discharge max for getting at least a good 3 years (1000cycles) of lifespan if new, and hopefully 5. That would be 12V/283Ah or around 3.3kWh available. Make sure that s fine, because if you are used to a "normal" house this will be a problem.
On a Sunny Day with 2000W of panels you should be able to produce 10 kWh, so better use as much energy as possible during the day, for instance charge your EV.
Regarding your 30A MPPT I doubt it is 48V compatible. If not you have a problem, 30A means at the output, which in 24V would be 720W. Connecting 9 panels with a 24V battery will likely kill your mppt. See manual for max power @voltage.
By the way, Investing in solar is like buying your energy for the next many years so it can appear costly at first. I don't think you will easily beat grid-tied subsidized electricity prices, but it may cost you less overall on the long term because being off grid tend to make you much more aware and careful about your energy use...
I agree with you on the lithium batteries, I hope to one day do this with A123 Cells. I have some 8p12s modules that i can recycle to eventually build a full pack, however at this time i acquired this lead acid battery bank, it is still in good shape and they are the proper AGM Cycling battery from Trojan. I need to read into the spec sheets to see there details, i'll try to find that out shortly and report back. Will note to self 30% dod! ..
To bad i can't set the cutoff voltage via the UPS.. and i'm not sure how i can change the cutoff/modify to ups to do that... I also need to test the voltage the ups will shutdown at... I intend to keep the batteries juiced as much as possible. I will even consider charging the bank at night (off peak) for a couple hours if nessasary, i can do this by keeping the ups tied in with a simple timer.. I think its charger is only 250w per ups unit.. . but if i use 2 units tied into the 24v back -- we can get a 500w charge rate for say 4 - 6 hrs a night just to boost soc !.. then in the day time solar can take over and grab a couple of free kwh!
I haven't actually calculated my needs per say, some of this equipment i've acquired over the years and i hope to make something that will meet my needs. Even if i have to charge my ev at night and run my household during peak with the solar system, that is my main goal.
reg the solar controller.. not my preferred controller.. it was something i had kicking around and wanted to use.. It should charge 24v bank fine.. how much current it can take at a given battery voltage i don't know and have not investigated that far, i might be limited there. I know the solar controller can charge a 24v bank as 24v pannel input or 48v pannel input.
i agree with you here for sure:
"By the way, Investing in solar is like buying your energy for the next many years so it can appear costly at first. I don't think you will easily beat grid-tied subsidized electricity prices, but it may cost you less overall on the long term because being off grid tend to make you much more aware and careful about your energy use..."
I had a much more advance.. higher cost system which i purchased and resold just because it was just a monster of a system that i don't really think i needed.