Balancing the system, automation, efficiency, etc...

CALLD
CALLD Solar Expert Posts: 230 ✭✭
in Off Grid Solar & Battery Systems #1
I'm about to perform the final (for now) upgrade on my system - the 2x140w modules are waiting for a buyer and will be replaced by 2x300w modules. Total installed capacity will be 1810w. Battery capacity will be 24v/260Ah AGM's + 24v/100Ah reserve. Permanent loads will be 3x120w refrigerators & home security system (60w). Average demand over a 24hr period is 16kw/h which is largely supported by grid-power at night. Solar kicks-in at dawn and is terminated 2 hours before sunset - a process which is currently performed manually. Adjustments to the loads and time-on are current all performed manually and are weather permitting. A recently added factor is rolling blackouts - largely unpredictable but usually only lasting for 2 hours at a time, twice daily. Battery capacity needs be able to cater for these outages at all times. Worst case scenario is an outage between 06:00-08:00 or 18:00-20:00 when demand on the system is 800-900watts average.
The loading varies due to the weather - hot humid weather and the refrigerators draw much more power than in cold dry weather. Worse is that hot humid weather is usually accompanied by lower production (clouds and hotter panel temperatures).

I need to automate the system as it's becoming really stressful to watch it 24/7.

I'm proposing a programmable relay be installed to enable switching to and from the grid dependant on battery voltage, all fine and certainly not too much rocket science - until you throw unpredictable 2 hour rolling blackouts into the mix....

Any ideas?
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  • unseenone
    unseenone Solar Expert Posts: 61 ✭
    #2
    Probably would be useful to understand the system architecture better. There is no reason your system should need any manual management if you are willing to spend the money for the right equipment.

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  • South Africa
    South Africa Solar Expert Posts: 295 ✭✭✭
    #3
    CALLD wrote: »
    I'm proposing a programmable relay be installed to enable switching to and from the grid dependant on battery voltage, all fine and certainly not too much rocket science - until you throw unpredictable 2 hour rolling blackouts into the mix....

    Any ideas?

    Yes, it is getting more and more common to use both (off-grid and utilities) in the most cost effective combination, automated.

    Victron / Outback has solutions for doing it for you, with a few extra parts, but it is quite expensive.

    What I did:
    Bought a Victron Battery monitor to check battery bank SOC. It also has a built in relay linked to the SOC.

    I then added a multiplug to my inverter:
    Outlet one powers devices that must be 24/7 on solar like lights and 2 small fridges.
    Outlet two has loads that are primarily on solar, switching to utilities depending on SOC, and then back to batteries if no utilities power.

    - If SOC is down to 95%, switch back to grid (need the spare in batteries for night loads and the 2/5 hours potential load shedding).
    - If SOC is 97%, switch back to solar.
    In the mornings, SOC is +-80% so takes a few hours to charge to 97%, then on solar the rest of the day.

    Now, the 2 sine waves from utilities and inverter will argue. So I have a 1 sec break and a 2nd hand old UPS (with AVR) to handle the 1 second break between the 2 different power sources.

    Cost: A lot less than Victron / Outback solutions. :-)

    5kVA Victron Multiplus II, 5.2kW array, 14kWh DIYLifepo4 bank, all grid-tied.


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  • unseenone
    unseenone Solar Expert Posts: 61 ✭
    #4
    I sent you a PM South Africa---
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