I did not start programming, but I do have a few Arduino controllers. I like the MEGA2560 boards as they have more I/O including 3 hardware serial ports. I also bought a user interface board with a small LCD screen and a few buttons. And then I found this power meter on Amazon.
PEACEFAIR 100A Multi-Function Meter Voltage Current Power Factor Frequency Energy Tester for Multi-Functional Physical parameters(1Meter+ 1open Type CT+ 1USB to 485): Amazon.com: Tools & Home Improvement
www.amazon.com
This meter has RS-485, so you need a small interface converter for the Arduino serial port to read the data. This is bidirectional so it can also be used on the gird side to measure if you are consuming or exporting. It does read only one hot lead though. My microinverters connect only across the two hot legs at 240 volt, so it would work fine to just read the solar production. There are some split phase versions in a single unit, but they are quite a bit more expensive.
Thanks, I’ll look into these. I’ll want one per leg since I am controlling for zero export on each leg separately (~300 to 400W of 240V AC translates to ~150-200W per leg).
The charger I have is a basic E-Bike charger from Amazon. You can order them in several different voltage and current ratings to match your battery bank. The one I have wants to charge to the full 58.8 volts of my 14S Li NMC pack. If I order another for a project like this, I would go a little less on the voltage. The 16S LFP one is 58.4 volts.
I’m currently at 24V (8S LiFePO4) and debating going up to 48V (16S LiFePO4).
At 24V, a 5A charger will consume ~160W, slightly more than m
Mine has a small power switch on it, I was going to wire a relay to that instead of trying to turn on and off the actual power. It does not seem to have much draw when switched off.
I was thinking I’d use a relay, but you are right, that may be less efficient than just controlling a low-current control signal. If I decide I’m going to 48V and need new chargers, I’ll keep that in mind.
Since you have no issue exporting up to 3000 watts, you don't have to be super critical. If you measure your main breaker power, it would be easy to switch on a 600 watt charger when you are exporting more than 1,000 watts. Then the export should drop to 400 watts. Then turn on a second charger if export hits 800 watts. How much solar do you have? How much do you want to add?
I’ve got 4kW of panels powered through 3kW of Microinverters. I’m only consuming an average of 350W throughout the day to power my 5 fridges/freezers so a single 450W panel powered by one of NEP’s new 500W ‘Mactoinverters’ should be enough to directly power all daytime use rather than relying on the much-less-efficient GTIL inverters...
It’s hard to know what the detection limits are for overproduction - 105% or 3150kW seems like it should be safely under the radar, but being anywhere near 110% for more than very short bursts would make me nervous.
So I’m thinking of a very simple dump-load where I may cascade my fridges to assure only one is on at a time (per leg) and use the chargers as the dump load of last resort (the true dump load). When I get to ~3075 or 3100W, turn on the charger and keep it on until total export drops under 2925 or 2950W.
My largest 3 fridges all consume over 150W when running, so as long as I spread them out, one of them should pretty much always be running. The two smaller ones are only 100W each but depending on duty cycle, I should be able to absorb most all of the extra generated AC power by just controlling my fridges and the battery chargers will just be there to full any duty-cycle gaps.
I’m only thinking of adding enough new AC-coupled solar to cover daytime average consumption (~10% of my 3kW grid-tied array). And adding more DC coupled to charge the LiFePO4 battery (more below).
The main motivation for the one AC panel is that it is so much more efficient to power with a single panel through a Microinverter @ 95+% efficiency that to put all that energy into a battery and power those loads through the GTIL inverters @ 75% efficiency (ouch!).
Using one 450W panel with a Microinverter will get as much power out of it as if it were a 570W panel generating DC and covering most daytime consumption while the solar is producing.
I am still a bit torn myself. Over 99.9% of the time, I have a solid grid, so it is most efficient to just have the microinverters grid tied. But I want to use my battery bank to power the house during the peak rate time. But to do this now, my battery bank is being charged with AC power from my system. It could be grid or solar. I have it just set to run on time from 9 am to 3:55 pm. That is the cheapest rate time, and when my Solar is normally making plenty of power, so I am still exporting some at that time. But since I am using battery power, it would be more efficient if I charged the battery from DC coupled solar.
Yes, that’s what I’ve concluded. MPPT charge controllers are much more efficient at getting Amp-Hours into a battery compared to Microinverters + AC battery chargers. What is the efficiency of your AC charger?
So if I add 4 more panels, I can't decide if I want to just add to my microinverters, or use a charge controller, and have those 4 panels directly charge the battery.
I’ll have ~4kW of DC-coupled panels charging a 560Ah 24V battery (or a 280Ah 48V battery). That will allow me to self power through 6pm - 11pm and all the way ‘til the next morning using the 2 GTILs, covering all of my peak and overnight consumption.
The lone AC-coupled 450W panel should cover all of my daytime usage without relying on the inefficient GTILs, which should reserve most/all of my 3kW (4kW of panels) grid-tied power for credit towards charging an EV.
I am using about 6 KWHs during my 5 hour peak rate time of use window. So the 4 x 300 watt panels = 1,200 watts, so I just need a bit over 5 sun hours to top up the battery each day, and not need any grid or AC charging. Rather than have to change the mode on the Schneider to charge, I could have a microcontroller watch the solar charging, and if it is falling short, turn on my 600 watt charge to ensure I have a full battery. If I am only getting 1/3 sun due to clouds, the AC powered charger would still technically be running on solar as my existing system would still be producing 1,000 watts, instead of it's peak 3,840 watts.
I’ve done the math and trying to self-power through battery energy which had been put there charging at 80% efficiency is not worthwhile (assuming 80% charging efficiency and with my very inefficient GTIL inverters).
1kWh of AC worth ~$0.20 results in 800Wh getting stored into the battery and then 600Wh of power generated through the GTILs @ 75% efficiency and worth $0.24 @ peak rates of $0.40/kWh.
You could argue a 20% profit is not bad, but then you need to figure in the battery cost. I figure my battery costing me over $1500 should deliver at least 3000 cycles, meaning each cycle is worth $0.50. Even if I’m optimistic and assume I get twice that number of cycles, it’s worth as much as the electricity being generated and I’m better off just conserving my cycles.
With DC solar charging, a whole kWh goes in and is converted to 750Wh going out worth $0.30. Still swamped out by the value of each battery cycle, but if I get 6000 cycles, at least slightly worthwhile.
So on cloudy days or smoky days, I don’t plan to top-off my battery with grid power and may just limit discharge to peak hours until it’s drained...
My next car is likely to be a plug in hybrid or full electric. In either case, I will also add some charging time. On days I am home, it can charge while the sun is up, but on days I work in the field, I would then want to charge at night. So Cal Edison does offer EV owners a lower 17 cent per KWH overnight rate. That is cheaper than cycling my battery bank to supply the charging power. And as a side benefit, it will also make my solar worth more to me as the little power I do use will be cheaper, and the peak rate time I do run off battery becomes more expensive.
Check the fine print. Yes, nighttime rates are cheaper but peak rates are higher and over more days. And I’m pretty sure my utility told me that changing to an EV rate would mean losing my NEM1 grandfathering and being forced on NEM2.
So my plan is to charge at nighttime rates and just build up the credits over summer to cover our expected annual driving.
The poor inverter efficiency of the current-generation of GTIL inverters is the biggest weakness of my current plan, but I assume that will improve over time as new-generation products emerge...