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Show the snail icon on low power charge slots in the plan #5353

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e5d70aa
Show the snail icon on low power charge slots in the plan (#5352)
Oct 2, 2026
4320572
Match the prediction engine's hybrid charge ceiling and floored PV wi…
Oct 2, 2026
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27 changes: 22 additions & 5 deletions apps/predbat/output.py
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Original file line number Diff line number Diff line change
Expand Up @@ -1076,19 +1076,31 @@ def get_charge_rate_kw(self, charge_window_n, minute_start, minute_relative_star
which stores a fixed reduced rate in the fractional part of export_limits_best, low power
charging (set_charge_low_power) throttles the rate dynamically minute-by-minute, so it has
to be recomputed the same way the prediction engine works it out (find_charge_rate()).

Returns (rate_kw, low_power): the rate achieved after the charge curve, and whether low power
charging asked for less than the maximum charge rate. The curve tapering a full rate charge
near the top of the battery is not low power - only the requested rate decides that.

The maximum is the one the prediction engine uses at the start of the slot: a hybrid inverter
whose DC charge rate is above its AC one can take the PV above the AC rate on top of it.
"""
window = self.charge_window_best[charge_window_n]
soc = self.predict_soc_best.get(minute_relative_start, self.soc_kw)
battery_rate_max_charge = self.battery_rate_max_charge
if self.inverter_hybrid and (self.battery_rate_max_charge_dc > battery_rate_max_charge):
pv_above = max((pv_forecast_minute_step.get(minute_relative_start, 0.0) / PREDICT_STEP) - battery_rate_max_charge, 0)
battery_rate_max_charge += min(self.battery_rate_max_charge_dc - battery_rate_max_charge, pv_above)
pv_window_kwh = 0.0
if self.set_charge_low_power:
window_end_rel = min(window["end"] - self.minutes_now, self.forecast_minutes)
# The window end is floored to a step boundary, as the prediction engine does
window_end_rel = min(max(((window["end"] - self.minutes_now) // PREDICT_STEP) * PREDICT_STEP, minute_relative_start), self.forecast_minutes)
pv_window_kwh = sum(pv_forecast_minute_step.get(m, 0.0) for m in range(minute_relative_start, window_end_rel, PREDICT_STEP))
Comment on lines +1095 to 1097
_, charge_rate_now_curve = find_charge_rate(
charge_rate_now, charge_rate_now_curve = find_charge_rate(
minute_start,
soc,
window,
self.charge_limit_best[charge_window_n],
self.battery_rate_max_charge,
battery_rate_max_charge,
self.soc_max,
self.battery_charge_power_curve,
self.set_charge_low_power,
Expand All @@ -1103,7 +1115,9 @@ def get_charge_rate_kw(self, charge_window_n, minute_start, minute_relative_star
low_power_pv_threshold_w=self.low_power_pv_threshold_w,
solar_full_rate=self.set_charge_low_power_solar_full_rate,
)
return dp2(charge_rate_now_curve * MINUTE_WATT / 1000.0)
# Compared in whole watts, find_charge_rate() steps the rate down in watts and converts back
low_power = dp0(charge_rate_now * MINUTE_WATT) < dp0(battery_rate_max_charge * MINUTE_WATT)
return dp2(charge_rate_now_curve * MINUTE_WATT / 1000.0), low_power

def publish_html_plan(self, pv_forecast_minute_step, pv_forecast_minute_step10, load_minutes_step, load_minutes_step10, end_record, publish=True, prediction=None, car_hold_minutes=None):
"""
Expand Down Expand Up @@ -1440,8 +1454,11 @@ def import_rate_color(rate):
state = "Chrg&nearr;"
state_color = "#3AEE85"
raw_state = "Chrg"
rate_kw = self.get_charge_rate_kw(charge_window_n, minute_start, minute_relative_start, pv_forecast_minute_step)
rate_kw, charge_low_power = self.get_charge_rate_kw(charge_window_n, minute_start, minute_relative_start, pv_forecast_minute_step)
reason_parts.append({"code": "charge_low_rate", "params": {"target_percent": limit_percent, "rate": rate_text_import, "rate_kw": "{:.2f}".format(rate_kw)}})
if charge_low_power:
# Snail symbol
state += "&#x1F40C;"
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if self.charge_window_best[charge_window_n]["start"] in self.manual_charge_times:
state += " &#8526;"
Expand Down
67 changes: 67 additions & 0 deletions apps/predbat/tests/test_plan_why_reason.py
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Original file line number Diff line number Diff line change
Expand Up @@ -400,6 +400,9 @@ def render(car_hold_minutes=None):
elif "Charging up to 80" not in _render(row, templates) or "{}kW".format(expected_charge_rate_kw) not in _render(row, templates):
print("ERROR: Chrg rendered text unexpected: {}".format(_render(row, templates)))
failed = True
elif "&#x1F40C;" in row["state_html"]:
print("ERROR: a full rate Chrg slot should not show the snail, got: {}".format(row["state_html"]))
failed = True

# --- Test 2: HoldChrg ---
print("Test HoldChrg reason")
Expand Down Expand Up @@ -451,6 +454,10 @@ def render(car_hold_minutes=None):
# dynamically via find_charge_rate() rather than a fixed fraction like export's snail encoding) ---
print("Test Chrg low power reason shows the throttled rate_kw, not the nameplate max")
low_power_window = [{"start": minutes_now, "end": minutes_now + 60, "average": 10.0}]
saved_predict_soc_best = my_predbat.predict_soc_best
saved_low_power_pv_threshold_w = my_predbat.low_power_pv_threshold_w
saved_inverter_hybrid = my_predbat.inverter_hybrid
saved_battery_rate_max_charge_dc = my_predbat.battery_rate_max_charge_dc
my_predbat.charge_window_best = low_power_window
my_predbat.charge_limit_best = [8.0] # small gap above the 7.9 current SoC - easily reached even throttled
my_predbat.predict_soc_best = _flat_soc(my_predbat, 7.9)
Expand All @@ -469,7 +476,67 @@ def render(car_hold_minutes=None):
elif "{:.2f}kW".format(rate_kw) not in _render(row, templates):
print("ERROR: Chrg low power rendered text missing the throttled rate: {}".format(_render(row, templates)))
failed = True
elif row["state_html"] != "Chrg&nearr;&#x1F40C;":
print("ERROR: Chrg low power state cell should show the snail like a slow export does (#5352), got: {}".format(row["state_html"]))
failed = True

# --- Test 4c: low power mode on but the target needs the full rate - not a slow charge, no snail ---
print("Test Chrg low power at the full rate shows no snail")
my_predbat.charge_limit_best = [10.0]
my_predbat.predict_soc_best = _flat_soc(my_predbat, 2.0) # too far from the target to throttle within the window
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_, raw_plan = render()
row = _get_row(raw_plan, minutes_now)
if row is None or _codes(row) != ["charge_low_rate"]:
print("ERROR: Chrg low power full rate reasons unexpected: {}".format(row and _codes(row)))
failed = True
elif "&#x1F40C;" in row["state_html"]:
print("ERROR: Chrg low power at the full rate should not show the snail, got: {}".format(row["state_html"]))
failed = True

# --- Test 4d: PV that only arrives after the window's last whole step must not abandon low power,
# the prediction engine floors the window end to a step boundary and so never counts it ---
print("Test Chrg low power ignores PV past the floored window end")
my_predbat.charge_window_best = [{"start": minutes_now, "end": minutes_now + 62, "average": 10.0}]
my_predbat.charge_limit_best = [8.0]
my_predbat.predict_soc_best = _flat_soc(my_predbat, 7.9)
my_predbat.low_power_pv_threshold_w = 100
pv_step[60] = 0.25 # 3kW for the step starting at the floored window end
_, raw_plan = render()
row = _get_row(raw_plan, minutes_now)
if row is None or _codes(row) != ["charge_low_rate"]:
print("ERROR: Chrg low power floored window reasons unexpected: {}".format(row and _codes(row)))
failed = True
elif "&#x1F40C;" not in row["state_html"]:
print("ERROR: Chrg low power should stay throttled when the only PV is past the floored window end, got: {}".format(row["state_html"]))
failed = True
pv_step[60] = 0
my_predbat.low_power_pv_threshold_w = saved_low_power_pv_threshold_w
my_predbat.set_charge_low_power = False

# --- Test 4e: hybrid inverter with a DC charge rate above the AC one charges through bright PV at
# the combined rate, as the prediction engine does - that is the maximum, so no snail ---
print("Test Chrg on a hybrid inverter in bright PV shows the combined AC+DC rate")
my_predbat.charge_window_best = low_power_window
my_predbat.charge_limit_best = [10.0]
my_predbat.predict_soc_best = _flat_soc(my_predbat, 2.0)
my_predbat.inverter_hybrid = True
my_predbat.battery_rate_max_charge_dc = my_predbat.battery_rate_max_charge * 2
pv_step[0] = my_predbat.battery_rate_max_charge * 3 * 5 # PV at three times the AC charge rate
_, raw_plan = render()
row = _get_row(raw_plan, minutes_now)
if row is None or _codes(row) != ["charge_low_rate"]:
print("ERROR: hybrid Chrg reasons unexpected: {}".format(row and _codes(row)))
failed = True
elif row["reasons"][0]["params"]["rate_kw"] != "{:.2f}".format(max_rate_kw * 2):
print("ERROR: hybrid Chrg rate_kw should be the combined {}kW, got {}".format(max_rate_kw * 2, row["reasons"][0]["params"]["rate_kw"]))
failed = True
elif "&#x1F40C;" in row["state_html"]:
print("ERROR: hybrid Chrg at the combined rate should not show the snail, got: {}".format(row["state_html"]))
failed = True
pv_step[0] = 0
my_predbat.inverter_hybrid = saved_inverter_hybrid
my_predbat.battery_rate_max_charge_dc = saved_battery_rate_max_charge_dc
my_predbat.predict_soc_best = saved_predict_soc_best
my_predbat.charge_window_best = window
my_predbat.charge_limit_best = [8.0]

Expand Down
4 changes: 3 additions & 1 deletion docs/predbat-plan-card.md
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Expand Up @@ -111,7 +111,9 @@ charging and discharging activity - if Predbat plans this, the state will show a

- **Limit %** - Alongside any battery activity (charging, discharging, etc) there will be a SoC limit. This limit is what the SoC is planned to be at the end of the slot.
e.g. 'Charge&nearr; 70%' is charge to 70% SoC, and 'Exp&searr; 4%' is force exporting the battery to the 4% reserve level.<BR>
If Predbat is planning a slow charge or slow export then the limit will be preceded by a snail symbol (&#x1F40C;) and will be shown as 'limit.tens_of_percentage_rate_reduction'. e.g.: 16.3 means limit of 16% and charge/discharge at 70% of normal rate.
If Predbat is planning a slow charge or slow export then the State will be followed by a snail symbol (&#x1F40C;).<BR>
For a slow export, with plan debug enabled, the limit will also be shown as 'limit.tens_of_percentage_rate_reduction'. e.g.: 16.3 means limit of 16% and discharge at 70% of normal rate.<BR>
For a slow charge ([low power charging mode](customisation.md#inverter-control-options)) the rate is worked out as the slot runs, so the planned rate is shown in the slot's description instead.

- **PV kWh** - The predicted solar forecast for the half-hour slot, estimated from the [Solcast Forecast](apps-yaml.md#solcast-solar-forecast).<BR>
If the PV forecast is above 0.2kWh for the slot it will be coloured Melon Red with a little sun symbol, above 0.1kWh it will be Yellow with a sun symbol,
Expand Down
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