From 661af417a1005ca7120ead37e571651e1f5b7ab2 Mon Sep 17 00:00:00 2001
From: Michael Geers <michael@geers.tv>
Date: Fri, 17 Jul 2026 15:00:23 +0200
Subject: [PATCH] Tariffs: persist tariff values in 15min intervals (#31845)

---
 core/metrics/tariffs.go      | 42 +++++++++++++++++++++++++++
 core/metrics/tariffs_test.go | 55 ++++++++++++++++++++++++++++++++++++
 core/site.go                 |  1 +
 core/site_tariffs.go         | 32 +++++++++++++++++++++
 4 files changed, 130 insertions(+)
 create mode 100644 core/metrics/tariffs.go
 create mode 100644 core/metrics/tariffs_test.go

diff --git a/core/metrics/tariffs.go b/core/metrics/tariffs.go
new file mode 100644
index 000000000..66a04b2fb
--- /dev/null
+++ b/core/metrics/tariffs.go
@@ -0,0 +1,42 @@
+package metrics
+
+import (
+	"time"
+
+	"github.com/evcc-io/evcc/server/db"
+	"gorm.io/gorm"
+	"gorm.io/gorm/clause"
+)
+
+type tariffValue struct {
+	Timestamp   int64    `gorm:"column:ts;uniqueIndex"` // 15min boundary
+	Grid        *float64 `gorm:"column:grid"`
+	FeedIn      *float64 `gorm:"column:feedin"`
+	Co2         *float64 `gorm:"column:co2"`
+	Temperature *float64 `gorm:"column:temperature"`
+}
+
+func (tariffValue) TableName() string {
+	return "tariffs"
+}
+
+func init() {
+	db.Register(func(_ *gorm.DB) error {
+		return db.Instance.AutoMigrate(new(tariffValue))
+	})
+}
+
+// PersistTariffs stores the tariff values at the given 15min boundary, nil values omitted
+func PersistTariffs(ts time.Time, grid, feedin, co2, temperature *float64) error {
+	if grid == nil && feedin == nil && co2 == nil && temperature == nil {
+		return nil
+	}
+
+	return db.Instance.Clauses(clause.OnConflict{DoNothing: true}).Create(&tariffValue{
+		Timestamp:   ts.Unix(),
+		Grid:        grid,
+		FeedIn:      feedin,
+		Co2:         co2,
+		Temperature: temperature,
+	}).Error
+}
diff --git a/core/metrics/tariffs_test.go b/core/metrics/tariffs_test.go
new file mode 100644
index 000000000..03fb0953e
--- /dev/null
+++ b/core/metrics/tariffs_test.go
@@ -0,0 +1,55 @@
+package metrics
+
+import (
+	"testing"
+	"time"
+
+	"github.com/evcc-io/evcc/server/db"
+	"github.com/stretchr/testify/require"
+)
+
+func TestPersistTariffs(t *testing.T) {
+	require.NoError(t, db.NewInstance("sqlite", ":memory:"))
+	require.NoError(t, db.Instance.AutoMigrate(new(tariffValue)))
+
+	slot := time.Date(2026, 4, 15, 16, 15, 0, 0, time.UTC)
+	grid, co2 := 0.3, 250.0
+
+	// nil values omitted
+	require.NoError(t, PersistTariffs(slot, &grid, nil, &co2, nil))
+
+	var res tariffValue
+	require.NoError(t, db.Instance.First(&res).Error)
+	require.Equal(t, slot.Unix(), res.Timestamp)
+	require.InDelta(t, 0.3, *res.Grid, 0.001)
+	require.Nil(t, res.FeedIn)
+	require.InDelta(t, 250, *res.Co2, 0.001)
+	require.Nil(t, res.Temperature)
+
+	// duplicate slot ignored, first values kept
+	other := 0.4
+	require.NoError(t, PersistTariffs(slot, &other, nil, nil, nil))
+
+	var count int64
+	require.NoError(t, db.Instance.Model(new(tariffValue)).Count(&count).Error)
+	require.Equal(t, int64(1), count)
+
+	require.NoError(t, db.Instance.First(&res).Error)
+	require.InDelta(t, 0.3, *res.Grid, 0.001)
+
+	// all nil: no row
+	require.NoError(t, PersistTariffs(slot.Add(15*time.Minute), nil, nil, nil, nil))
+	require.NoError(t, db.Instance.Model(new(tariffValue)).Count(&count).Error)
+	require.Equal(t, int64(1), count)
+
+	// all values set: each column mapped independently
+	next := slot.Add(30 * time.Minute)
+	feedin, temp := 0.08, 21.5
+	require.NoError(t, PersistTariffs(next, &grid, &feedin, &co2, &temp))
+
+	require.NoError(t, db.Instance.Where("ts = ?", next.Unix()).First(&res).Error)
+	require.InDelta(t, 0.3, *res.Grid, 0.001)
+	require.InDelta(t, 0.08, *res.FeedIn, 0.001)
+	require.InDelta(t, 250, *res.Co2, 0.001)
+	require.InDelta(t, 21.5, *res.Temperature, 0.001)
+}
diff --git a/core/site.go b/core/site.go
index b60b6bac3..f03e24cfb 100644
--- a/core/site.go
+++ b/core/site.go
@@ -94,6 +94,7 @@ type Site struct {
 	stats       *Stats                   // Stats
 
 	collectors map[string]*metrics.Collector // keyed by meter ref
+	tariffSlot time.Time                     // last persisted tariff slot
 
 	// cached state
 	gridPower                float64                     // Grid power
diff --git a/core/site_tariffs.go b/core/site_tariffs.go
index aff0a3612..14c2bdb79 100644
--- a/core/site_tariffs.go
+++ b/core/site_tariffs.go
@@ -121,6 +121,38 @@ func (site *Site) publishTariffs(greenShareHome float64, greenShareLoadpoints fl
 	}
 
 	site.publish(keys.Forecast, util.NewSharder(keys.Forecast, fc))
+
+	site.persistTariffs()
+}
+
+// persistTariffs stores tariff values once per 15min boundary. Like the meter
+// collectors it is driven by the update loop, skipping the partial boot slot.
+func (site *Site) persistTariffs() {
+	slot := time.Now().Truncate(tariff.SlotDuration)
+
+	last := site.tariffSlot
+	site.tariffSlot = slot
+
+	// skip repeat ticks within the slot and the partial boot slot
+	if last.IsZero() || !slot.After(last) {
+		return
+	}
+
+	value := func(u api.TariffUsage) *float64 {
+		if r, err := tariff.At(site.GetTariff(u), slot); err == nil {
+			return &r.Value
+		}
+		return nil
+	}
+
+	if err := metrics.PersistTariffs(slot,
+		value(api.TariffUsageGrid),
+		value(api.TariffUsageFeedIn),
+		value(api.TariffUsageCo2),
+		value(api.TariffUsageTemperature),
+	); err != nil {
+		site.log.ERROR.Printf("persist tariffs: %v", err)
+	}
 }
 
 func (site *Site) solarDetails(solar api.Rates) solarDetails {