Im building a Big UPS for the office (Off grid Solar System?). Final Check!

[Mike90250]

....maintenance. You will need the generator anyway for batteries. Bruce Roe

That's because if the batteries stay in a discharged state for very long, they sulfate and go bad.


regarding your inverter, what is the transfer time, from the grid going down, to the inverter taking over ? 3 or 5 mili-seconds ? It needs to be less than 10 mS, or your computers will reboot.

[bcroe]

- Consumption around 800wh during office hours (Computers and other equipment)

Do you mean 800 Watt Hours per working day, or maybe the maximum power is 800 Watts?

If you care about money, you will get a tiny (and quiet) inverter generator set, to run 6 times a
year. Anything involving batteries will involve a huge increase in cost and continuous
maintenance. You will need the generator anyway for batteries. Bruce Roe

[SunEagle]

Hello mrdavvv and welcome to Solar Panel Talk

Since you post had multiple web links it went to the unapproved folder. I have approved it for all members to now see. I am sure someone will get back to you on your proposed system.

[mrdavvv]

Hello!, im really glad i found this forum, i have been reading a lot on the subject on the last few months and i think this is probably one of the best sources of information around.

This time i would like to double check with the forum about my installation before i burn my building. I have been collecting parts along this year and i finally should have everything ready to assembly.

I really like to mess and research about stuff, but this year the work has been brutal, so i havent got a lot of time to check my data, its very likely that something about what you are about to read its very wrong.

I know it would be better that a profesional installed this, but i live in a developing country, the solar companies are not very knowleable about off grid systems, 95% of them only do grid tie systems with microinverters. I am even having a lot of trouble sourcing parts because of this reasons. At the end i trust more my hours of research, than what one of the intallers that i talked to could do. There is probably someone around that could make this locally, but i talked with around 5 installers and i realized they really werent capable enough. And this is very time consuming too, so i decided to install everything by myself (Except solar panels)

---

Project:
- Uninterrupted energy supply for my office. In our area we are prone to have power outage once every couple of months, for about 4 8 hours. For a home its not that bad, but in a office without energy all the work stops, and that could get very expensive / troublesome. Also im running essential systems, like the alarm and CCTV server, i would like them to never shutdown for security reasons (This is probably the main concern).

Notes:
- Im only feeding a section of the building (Main office), so the grid of this specific section would be indepent of the other areas.
- Energy demand is kind of low, only some computers and the 24/7 low energy Server + Cameras
- System isnt really "Off Grid", as we are going to still be attached to it. We will use Solar during day, and Grid energy during night. Batteries just as a backup for outages. Im not feeding any solar to the external Grid. Basically only grid input, not output.
- Im using solar as a backup energy for day hours and not oversize the battery bank. Our main goal isnt reducing energy costs, just have energy all the time.
- Consumption around 800wh during office hours (Computers and other equipment) Wich will be supplied by solar primary and maybe Grid if solar isnt available or the load its too big. In an vent of a power outage, it will run only by solar.
- 300Wh during at night (Server and Cameras). They will run by the grid normally, and battery bank during cuts. Basically the batteries would never be used unless we get an outage.
- I should run fine with a couple of panels, but im placing 4 in case we end with a multiple day power outage. In that case im considering 4 - 6 panels so the system would be able to charge batteries (Depleted during night) and feed the office at the same time. (Havent make good calculations about this, but a guesstimate its 4 -6 panels).

Specs:
- Chinese hybrid inverter LV2424 from MPP Solar. Hope i didnt screw myself by buying this, but Outback and simillar solutions are cost prohibitive for the budget. They seem to have some good reviews in the internet, so i took the risk: Data. I really liked the capabilities of the unit, you can program a lot of scenarios, like using solar as main supplier, or batteris, or solar + grid, etc.
- 4 x Trojan L16E-AC 370AH, conected in series for a total of 370AH @24V.
- 4 x 380W Solar panel (1520W). (Most likely)
- Propposed Diagram Link

---

Most of my doubts are related to the battery system, (Probably one of the hardest parts):

Battery Bank
- Night hours consumption around 300Wh, around 2000 - 2500Wh.
- Im not very worried about day hours, we have sunny days for about 320 - 340 days per year, and the likely of a cloudy / rainy day + power outage at the same time its not that high. Nevertheless the battery bank should be able to feed for 24hrs straight (According to my numbers). We can turn off no essential systems in case of a longer outage with multiple sunless days. I can also get an small generator for this scenario.
- Basically the battery bank would only work during night outages, and the eventuality of a day outage without sun.

Batteries:
- 4 x Trojan L16E-AC (370AH), conected in series. 370AH @24V = 8880W
- For longevity, we should only use 50% of the capacity, so we have 4400W available.

Conections:
- Inverter max output 2400W. Can manage peak output of 4800W.
- 4800 / 24 = 200A. The cables and conections should be able to hold 200A.
- Could find reliable cables, so im making my own.
- For the load, i can run smaller cables than AWG 1/0. But im using this size because i couldnt sorce smaller ring terminals, the 1/0 seem to be more common.
- At 24V im getting .5% lost for the aproximate 100Cm of cable, perfect!: https://www.calculator.net/voltage-drop-calculator.html
- Seems to hold 170A (Peak output) with 90c isolation: https://www.cerrowire.com/products/r...pacity-charts/

Cable:
- Im using this terminals, they sare tinned to avoid oxidation of copper, i will add some silicon lube/ grease and then encapsulate with the heatshrink tubing as i wasnt able to source tubing with internal glue: Link
- AWG 1/0 should be crimped with 5 - 16tn machine, so im using a 12Tn hidraulic crimper DROF DCH12: https://ibb.co/XDDGjB9
- Im using AWG 1/0 Solder cable, maybe even speaker cable. They are very soft and 100% copper. (Its ok to use this kind of cables for this application?. it supports 105c at 600V Link

Usage:
- As i mention, the batteris are planned only as backup. In that case they will be used around 4 - 6 times at year. Considering that they are not going to be used, what would be the expected lifetime?. Havent check lately, but i remember that with daily use the batteris could last around 5 years if you take care of them. So if you never used them and you take care, they can last 10 years for example?....... Maybe i can change plans and use baterries all the time during night, they will be depleted less than 25% so they would probably lost a long time aniways.

So i think that its all!, i dont have a lot of specific questions, its more of a Sanity check type of post. So do you think im missing something?, the numbers have some sense?, im doing something very wrong?

Thanks a lot!