State-of-charge control

This package actively controls the minimum state of charge (battery level) to adapt to load shedding and to reduce unnecessary cycling of the battery. It integrates with the EskomSePush API to get live information about load shedding in South Africa.

It currently only supports Sunsynk single-phase inverters (Deye inverters too, since they're the same thing underneath).

Compilation

1. Install Rust e.g. using these instructions.
2. Run cargo install socit to install the binary. Alternatively, check out the repository and run cargo build --release. This will compile the binary to target/release/socit.

If you want to cross-compile:

1. Install and set up cross e.g. using these instructions.
2. Run cross build --release --target=armv7-unknown-linux-gnueabihf (replace with your target architecture).
3. Find the binary in target/<arch>/release/target.

I found that running an arm-unknown-linux-gnueabi build on Raspberry Pi (model 1B) would produce incorrect results. Using arm-unknown-linux-gnueabihf (note the last two characters, for hard-float) gives correct results and is also a lot faster.

Configuration

Configuration is stored in a TOML file. There is an example in the repository, which you can copy and edit to provide your configuration. It contains detailed instructions on the available settings.

Execution

Run the binary (socit) and pass the configuration file as the only command-line parameter. It uses the env_logger crate for logging, so you can enable logging by (for example) setting the environment variable RUST_LOG=info.

Time synchronisation

You should ensure that the system running socit has its time zone correctly set and its clock synchronised e.g. with NTP. The inverter does not need to have time correctly set. Socit will compensate for an incorrect inverter time.

Algorithm

Periodically (at the time of writing, once per minute) it projects how the state of charge might change over the next 24 hours, assuming no grid input. During load-shedding, it uses pessimistic modelling (max_discharge_power and assumes no solar PV), while the rest of the time it uses optimistic assumptions (min_discharge_power and estimates solar PV assuming no cloud). It then determines a minimum state of charge that the system should have now to avoid falling below the minimum_soc later (if possible).

There are three SoC levels calculated. When above target_soc_high, no grid power is needed. Between target_soc_low and target_soc_high, grid power is used for the load, but the battery is not changed, while below target_soc_low, the battery is charged as well. Finally, the value alarm_soc has no internal effect, but in stored in the database can be used by external alerting tools: if the actual SoC is below alarm_soc, then there is a risk of falling below minimum_soc.

Trickle charge adjustment

As a separate feature, Socit can dynamically adjust your trickle charge setting to compensate for electro-magnetic interference (EMI) in the readings from your CT coil. Mine is particularly bad (errors are typically 200-300W and go up to 500W), causing significant export of power if not corrected for. My non-essentials (geyser and stove) draw either no power or a large amount of power (kW+), so any calculated non-essential power draw that's less than this is assumed to be CT coil error, and is compensated for by adjusting the trickle charge.

Note that this works for me because the EMI consistently causes the coil to over-read. If it under-reads, this solution will not work for you because the trickle charge cannot be set to negative values.

Changelog

0.3.0

• Add optional control over the trickle charge setting (see above).
• Change time handling: instead of setting the inverter's clock, just take the clock skew into account.
• Update dependencies.

0.2.1

• Refactor the robust modbus access into a separate crate (modbus-robust).

0.2.0

• Add alarm_soc
• Make the startup robust, so that if the modbus connection could not immediately be established, socit will keep running and repeatly retry.

0.1.1

Fix example configuration documentation to note that the connection to mbusd will be restarted if necessary.

0.1.0

First release.

License

This program is free software: you can redistribute it and/or modify it under the terms of the GNU General Public License as published by the Free Software Foundation, either version 3 of the License, or (at your option) any later version.

This program is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for more details.

You should have received a copy of the GNU General Public License along with this program. If not, see https://www.gnu.org/licenses/.