Features for the Perfect Monitoring Software for a Residential System

[svetz]

If a station is using the same panel for irradiation checking and for powering components, how does that work? Is the power draw perfectly constant, so as not to affect panel voltage?

Good question...might check some of the DIY weather stations and see what they do...if you find out let us know!

 

[WoodsieLord]

If a station is using the same panel for irradiation checking and for powering components, how does that work? Is the power draw perfectly constant, so as not to affect panel voltage?

If the same panel is used to power the reading equipment and to perform the test iteself I would switch a greater load temporarily. I can't imagine any other way... Or, at least, that's the way I will try to implement my future home-brew sensor

 

[Fred S]

Sounds good - switch to a different, constant resistive load for the test.

 

[svetz]

Now that the batteries are installed and we have ways of getting the battery information (see this post and a few below it) we know how to tell if on or off grid and the battery information. So, time to start addressing these bullets from the OP:

• The state of the battery
• Duration of battery at current consumption
• Time until the Battery is recharged

Going on/off grid should be an alert. In addition to an alert, it should trigger a set of home automations/actions to reduce power consumption, but that project's not ready yet so we'll have to just leave a hook and cycle back to it later.

The expected recharge/duration is based on the rate at which power is exchanged, number of remaining life-cycles, temperature, inefficiencies, and the peukert's law. The system is LiFePO4 so those effects are minimized, might it be possible to ignore them? Time to review WoodsieLord's and other threads to see how theory differs from reality.

Update: LiFePO4 graphs! https://www.batteryspace.com/prod-specs/9055.pdf

 

[svetz]

Enphase doesn't publish data on their batteries. But, from this data, the first graph shows peukert's law doesn't seem to important for LiFePO4, that is the difference between 1C and .1C is a few minutes:


From the second graph, temperature would have a bigger effect... assuming temperature ever changed that much here. The third graph was just sorta interesting, hadn't seen anything before about hypermiling batteries.

For the elements of interest:

• The state of the battery - Start by trusting the Envoy's fuel gauge as the alternative is to count all the watts in and out and we don't know how to get that data yet.
• Duration of battery at current consumption: SoC * capacity / (current_discharge_rate - solar_power_est)
• Time until the Battery is recharged (100 - SoC) * capacity / (solar_power_est - current_discharge_rate)

Calculating the estimate of the solar power will be tricky. I wonder how hard it would be to factor in the upcoming weather? From data we know the watts to expect from irradiance and the irradiance to expect at the time of day. The only thing not known is how to get future irradiance. I wonder if there are trends that can be used from the weather station, they do try to predict a few hours out. Fortunately none of these have to be too accurate.

 

[svetz]

More Resources!

• ianganderton posted about a NASA API to get all sorts of local data.
• upnorthandpersonal posted about another site, PVGIS.
• The New Mexico State University has an excel spreadsheet for some data: https://aces.nmsu.edu/pubs/_circulars/CR674/welcome.html

 

[svetz]

Finally got around to updating the code to add the battery information to the log... very boring... just tacks data onto the end of the meter.log file for now (some day it'll be used to trigger automation).

OnGrid=TRUE SoC=90% Charging: 92 watts Remaining: 14:36​

I didn't bother updating/posting the code as it doesn't sound like anyone's using it. See post #17 in the enphase blog for the API information.

 

[svetz]

Given some of the oddity of the events I found that I would have liked to known the voltage and frequency of the system.

First thought was a power meter like KillAWatt, but as Alton would say they're uni-taskers. While I didn't see any that had remote monitoring I did see smart plugs that had remote monitoring and as a multi-tasker that seemed more useful as I could replace a smart plug in use now. While I've seen some smart plugs with voltage displayed on the app (example), didn't see anything with frequency. But I'll probably start recommending these over kill-A-Watt meters now.

Then it occurred to me I'd seen the Envoy report frequency data. So, something to add this weekend.... http://envoy.local/ivp/meters/readings and simplified response:

[
    {
        "voltage": 245.237,
        "current": 31.879,
        "freq": 60.000,
...