From 381573b0eb956f4afbd312e80250daeafe21e646 Mon Sep 17 00:00:00 2001
From: andig <andi@evcc.io>
Date: Fri, 12 Dec 2025 18:29:31 +0100
Subject: [PATCH] HEMS: add "smartgrid" session logging (#25907)

---
 assets/js/components/Config/HemsModal.vue     |  74 ++++++++-
 assets/js/components/Config/YamlModal.vue     |   9 +-
 .../components/Config/defaultYaml/hems.yaml   |   2 +-
 assets/js/views/Config.vue                    |   4 +-
 cmd/setup.go                                  |  23 ---
 cmd/setup_circuits_test.go                    |   2 +-
 core/metrics/db.go                            |   9 +-
 core/session/db.go                            |  14 +-
 core/session/format_test.go                   |  17 --
 core/session/session.go                       | 120 +-------------
 core/site_optimizer_test.go                   |   4 +-
 core/site_test.go                             |   2 +-
 hems/eebus/eebus.go                           |  36 +++++
 hems/relay/relay.go                           |  59 ++++++-
 hems/smartgrid/smartgrid.go                   |  32 ++++
 hems/smartgrid/types.go                       |  34 ++++
 i18n/de.json                                  |  13 +-
 i18n/en.json                                  |  13 +-
 server/db/cache/cache.go                      |   6 +-
 server/db/db.go                               |  21 ++-
 server/db/registry.go                         |  14 ++
 server/db/settings/setting.go                 |  14 +-
 server/http.go                                |   1 +
 server/http_gridsessions_handler.go           |  44 ++++++
 server/mcp/openapi.json                       | 130 +++++++++++++---
 server/mcp/openapi.md                         |  22 +++
 server/openapi.yaml                           |  60 +++++++
 tests/hems-yaml.evcc.yaml                     |  11 ++
 tests/hems.spec.ts                            |  43 +++++
 tests/hems.sql                                |  14 ++
 util/config/config.go                         |   9 +-
 util/csv/writer.go                            | 147 ++++++++++++++++++
 util/csv/writer_test.go                       | 127 +++++++++++++++
 33 files changed, 915 insertions(+), 215 deletions(-)
 delete mode 100644 core/session/format_test.go
 create mode 100644 hems/smartgrid/smartgrid.go
 create mode 100644 hems/smartgrid/types.go
 create mode 100644 server/db/registry.go
 create mode 100644 server/http_gridsessions_handler.go
 create mode 100644 tests/hems-yaml.evcc.yaml
 create mode 100644 tests/hems.sql
 create mode 100644 util/csv/writer.go
 create mode 100644 util/csv/writer_test.go

diff --git a/assets/js/components/Config/HemsModal.vue b/assets/js/components/Config/HemsModal.vue
index d5f4b26cc..cd293ef25 100644
--- a/assets/js/components/Config/HemsModal.vue
+++ b/assets/js/components/Config/HemsModal.vue
@@ -7,21 +7,91 @@
 		:defaultYaml="defaultYaml"
 		endpoint="/config/hems"
 		removeKey="hems"
+		:noYamlEditor="fromYaml"
+		:disableSave="fromYaml"
 		data-testid="hems-modal"
 		@changed="$emit('changed')"
-	/>
+		@open="loadSessions"
+	>
+		<template #afterDescription>
+			<div
+				v-if="sessionCount"
+				class="alert alert-info my-4 d-flex justify-content-between align-items-start flex-wrap gap-2"
+				role="alert"
+				data-testid="grid-sessions"
+			>
+				<div>
+					<span>{{ $t("config.hems.eventsRecorded", { count: sessionCount }) }}</span>
+					<span class="ms-2">{{
+						$t("config.hems.lastEvent", { timeAgo: formatLastEvent(lastEvent.created) })
+					}}</span>
+				</div>
+				<a :href="csvLink" download class="alert-link text-nowrap">
+					{{ $t("config.hems.downloadCsv") }}
+				</a>
+			</div>
+			<p v-if="fromYaml" class="text-muted">
+				{{ $t("config.hems.yamlConfigured") }}
+			</p>
+		</template>
+	</YamlModal>
 </template>
 
 <script>
 import YamlModal from "./YamlModal.vue";
 import defaultYaml from "./defaultYaml/hems.yaml?raw";
+import api from "../../api";
+import formatter from "../../mixins/formatter";
 
 export default {
 	name: "HemsModal",
 	components: { YamlModal },
+	mixins: [formatter],
+	props: {
+		fromYaml: Boolean,
+	},
 	emits: ["changed"],
 	data() {
-		return { defaultYaml: defaultYaml.trim() };
+		return {
+			defaultYaml: defaultYaml.trim(),
+			sessions: [],
+		};
+	},
+	computed: {
+		sessionCount() {
+			return this.sessions.length;
+		},
+		lastEvent() {
+			if (!this.sessions.length) {
+				return null;
+			}
+			return this.sessions[0];
+		},
+		csvLink() {
+			const params = new URLSearchParams({
+				format: "csv",
+				lang: this.$i18n?.locale,
+			});
+			return `./api/gridsessions?${params.toString()}`;
+		},
+	},
+	methods: {
+		async loadSessions() {
+			try {
+				const response = await api.get("gridsessions");
+				this.sessions = response.data || [];
+			} catch (e) {
+				// Silently fail if no sessions available
+				this.sessions = [];
+				console.error(e);
+			}
+		},
+		formatLastEvent(created) {
+			const now = new Date();
+			const eventDate = new Date(created);
+			const diffMs = now - eventDate;
+			return this.fmtTimeAgo(-diffMs);
+		},
 	},
 };
 </script>
diff --git a/assets/js/components/Config/YamlModal.vue b/assets/js/components/Config/YamlModal.vue
index 42e620ac4..3459f09a3 100644
--- a/assets/js/components/Config/YamlModal.vue
+++ b/assets/js/components/Config/YamlModal.vue
@@ -6,9 +6,10 @@
 				{{ $t("config.general.docsLink") }}
 			</a>
 		</p>
+		<slot name="afterDescription" />
 		<p v-if="error" class="text-danger" data-testid="error">{{ error }}</p>
 		<form ref="form" class="container mx-0 px-0">
-			<div class="editor-container">
+			<div v-if="!noYamlEditor" class="editor-container">
 				<YamlEditorContainer
 					v-model="yaml"
 					:errorLine="errorLine"
@@ -27,6 +28,7 @@
 					{{ $t("config.general.cancel") }}
 				</button>
 				<button
+					v-if="!disableSave"
 					type="submit"
 					class="btn btn-primary"
 					:disabled="saving || nothingChanged"
@@ -62,8 +64,10 @@ export default {
 		defaultYaml: String,
 		removeKey: String,
 		size: { type: String, default: "xl" },
+		noYamlEditor: Boolean,
+		disableSave: Boolean,
 	},
-	emits: ["changed"],
+	emits: ["changed", "open"],
 	data() {
 		return {
 			saving: false,
@@ -93,6 +97,7 @@ export default {
 		async open() {
 			this.reset();
 			this.modalVisible = true;
+			this.$emit("open");
 			await this.load();
 		},
 		close() {
diff --git a/assets/js/components/Config/defaultYaml/hems.yaml b/assets/js/components/Config/defaultYaml/hems.yaml
index 0cdd128a9..88d65e8a2 100644
--- a/assets/js/components/Config/defaultYaml/hems.yaml
+++ b/assets/js/components/Config/defaultYaml/hems.yaml
@@ -1,4 +1,4 @@
-## external control via binary in put
+## external control via digital signal
 
 #type: relay
 #maxPower: 4200 # limit loadpoints to 4.2 kW total
diff --git a/assets/js/views/Config.vue b/assets/js/views/Config.vue
index 9f837a470..45710ba83 100644
--- a/assets/js/views/Config.vue
+++ b/assets/js/views/Config.vue
@@ -288,7 +288,7 @@
 						</DeviceCard>
 						<DeviceCard
 							:title="$t('config.hems.title')"
-							:editable="!hems?.fromYaml"
+							editable
 							:error="hasClassError('hems')"
 							data-testid="hems"
 							@edit="openModal('hemsModal')"
@@ -368,7 +368,7 @@
 				<MqttModal @changed="loadDirty" />
 				<NetworkModal @changed="loadDirty" />
 				<ControlModal @changed="loadDirty" />
-				<HemsModal @changed="yamlChanged" />
+				<HemsModal :fromYaml="hems?.fromYaml" @changed="yamlChanged" />
 				<ShmModal @changed="loadDirty" />
 				<MessagingModal @changed="yamlChanged" />
 				<TariffsModal @changed="yamlChanged" />
diff --git a/cmd/setup.go b/cmd/setup.go
index f01ef90a1..898996f83 100644
--- a/cmd/setup.go
+++ b/cmd/setup.go
@@ -22,8 +22,6 @@ import (
 	"github.com/evcc-io/evcc/core/circuit"
 	"github.com/evcc-io/evcc/core/keys"
 	"github.com/evcc-io/evcc/core/loadpoint"
-	"github.com/evcc-io/evcc/core/metrics"
-	"github.com/evcc-io/evcc/core/session"
 	coresettings "github.com/evcc-io/evcc/core/settings"
 	"github.com/evcc-io/evcc/hems"
 	hemsapi "github.com/evcc-io/evcc/hems/hems"
@@ -35,7 +33,6 @@ import (
 	"github.com/evcc-io/evcc/push"
 	"github.com/evcc-io/evcc/server"
 	"github.com/evcc-io/evcc/server/db"
-	"github.com/evcc-io/evcc/server/db/cache"
 	"github.com/evcc-io/evcc/server/db/settings"
 	"github.com/evcc-io/evcc/server/eebus"
 	"github.com/evcc-io/evcc/server/modbus"
@@ -578,26 +575,6 @@ func configureDatabase(conf globalconfig.DB) error {
 		return err
 	}
 
-	if err := session.Init(); err != nil {
-		return err
-	}
-
-	if err := metrics.Init(); err != nil {
-		return err
-	}
-
-	if err := settings.Init(); err != nil {
-		return err
-	}
-
-	if err := cache.Init(); err != nil {
-		return err
-	}
-
-	if err := config.Init(); err != nil {
-		return err
-	}
-
 	persistSettings := func() {
 		if err := settings.Persist(); err != nil {
 			log.ERROR.Println("cannot save settings:", err)
diff --git a/cmd/setup_circuits_test.go b/cmd/setup_circuits_test.go
index 518987f24..05365bd72 100644
--- a/cmd/setup_circuits_test.go
+++ b/cmd/setup_circuits_test.go
@@ -23,7 +23,7 @@ type circuitsTestSuite struct {
 
 func (suite *circuitsTestSuite) SetupSuite() {
 	_ = db.NewInstance("sqlite", ":memory:")
-	config.Init()
+	config.SetupSchema()
 }
 
 func (suite *circuitsTestSuite) SetupTest() {
diff --git a/core/metrics/db.go b/core/metrics/db.go
index 8f3b3956d..c5c1aeef9 100644
--- a/core/metrics/db.go
+++ b/core/metrics/db.go
@@ -15,7 +15,14 @@ type meter struct {
 
 var ErrIncomplete = errors.New("meter profile incomplete")
 
-func Init() error {
+func init() {
+	db.Register(func() error {
+		return SetupSchema()
+	})
+}
+
+// SetupSchema is used for testing
+func SetupSchema() error {
 	return db.Instance.AutoMigrate(new(meter))
 }
 
diff --git a/core/session/db.go b/core/session/db.go
index 0765ebeca..fc7da5c6c 100644
--- a/core/session/db.go
+++ b/core/session/db.go
@@ -17,12 +17,14 @@ var (
 	sessions Sessions
 )
 
-func Init() error {
-	err := db.Instance.AutoMigrate(new(Session))
-	if err == nil {
-		err = db.Instance.Find(&sessions).Error
-	}
-	return err
+func init() {
+	db.Register(func() error {
+		if err := db.Instance.AutoMigrate(new(Session)); err != nil {
+			return err
+		}
+
+		return db.Instance.Find(&sessions).Error
+	})
 }
 
 // NewStore creates a session store
diff --git a/core/session/format_test.go b/core/session/format_test.go
deleted file mode 100644
index 8a5fca527..000000000
--- a/core/session/format_test.go
+++ /dev/null
@@ -1,17 +0,0 @@
-package session
-
-import (
-	"testing"
-
-	"github.com/stretchr/testify/assert"
-	"golang.org/x/text/language"
-	"golang.org/x/text/message"
-)
-
-func TestFormatValue(t *testing.T) {
-	mp := message.NewPrinter(language.Make("en"))
-
-	f := 1.2345
-	assert.Equal(t, "1.234", formatValue(mp, f, 3))
-	assert.Equal(t, "1.234", formatValue(mp, &f, 3))
-}
diff --git a/core/session/session.go b/core/session/session.go
index cba27ef4a..540bfea96 100644
--- a/core/session/session.go
+++ b/core/session/session.go
@@ -2,20 +2,11 @@ package session
 
 import (
 	"context"
-	"encoding/csv"
-	"fmt"
 	"io"
-	"reflect"
-	"strings"
 	"time"
 
 	"github.com/evcc-io/evcc/api"
-	"github.com/evcc-io/evcc/util/locale"
-	"github.com/fatih/structs"
-	"github.com/nicksnyder/go-i18n/v2/i18n"
-	"golang.org/x/text/language"
-	"golang.org/x/text/message"
-	"golang.org/x/text/number"
+	csvutil "github.com/evcc-io/evcc/util/csv"
 )
 
 // Session is a single charging session
@@ -42,112 +33,9 @@ type Sessions []Session
 
 var _ api.CsvWriter = (*Sessions)(nil)
 
-func (t *Sessions) writeHeader(ctx context.Context, ww *csv.Writer) error {
-	localizer := locale.Localizer
-	if val := ctx.Value(locale.Locale).(string); val != "" {
-		localizer = i18n.NewLocalizer(locale.Bundle, val, locale.Language)
-	}
-
-	var row []string
-	for _, f := range structs.Fields(Session{}) {
-		csv := f.Tag("csv")
-		if csv == "-" {
-			continue
-		}
-
-		caption, err := localizer.Localize(&locale.Config{
-			MessageID: "sessions.csv." + strings.ToLower(f.Name()),
-		})
-		if err != nil {
-			if csv != "" {
-				caption = csv
-			} else {
-				caption = f.Name()
-			}
-		}
-
-		row = append(row, caption)
-	}
-
-	return ww.Write(row)
-}
-
-func formatValue(mp *message.Printer, value any, digits int) string {
-	if rv := reflect.ValueOf(value); rv.Kind() == reflect.Pointer && rv.IsNil() {
-		return ""
-	}
-
-	switch v := value.(type) {
-	case float64:
-		return mp.Sprint(number.Decimal(v, number.NoSeparator(), number.MaxFractionDigits(digits)))
-	case *float64:
-		return mp.Sprint(number.Decimal(*v, number.NoSeparator(), number.MaxFractionDigits(digits)))
-	case time.Time:
-		if v.IsZero() {
-			return ""
-		}
-		return v.Local().Format("2006-01-02 15:04:05")
-	default:
-		return fmt.Sprintf("%v", value)
-	}
-}
-
-func (t *Sessions) writeRow(ww *csv.Writer, mp *message.Printer, r Session) error {
-	var row []string
-	for _, f := range structs.Fields(r) {
-		if f.Tag("csv") == "-" {
-			continue
-		}
-
-		digits := 3
-		if format := f.Tag("format"); format == "int" {
-			digits = 0
-		}
-
-		val := formatValue(mp, f.Value(), digits)
-
-		row = append(row, val)
-	}
-
-	return ww.Write(row)
-}
-
 // WriteCsv implements the api.CsvWriter interface
 func (t *Sessions) WriteCsv(ctx context.Context, w io.Writer) error {
-	if _, err := w.Write([]byte{0xEF, 0xBB, 0xBF}); err != nil {
-		return err
-	}
-
-	// get context language
-	lang := locale.Language
-	if language, ok := ctx.Value(locale.Locale).(string); ok && language != "" {
-		lang = language
-	}
-
-	tag, err := language.Parse(lang)
-	if err != nil {
-		return err
-	}
-
-	ww := csv.NewWriter(w)
-
-	// set separator according to locale
-	if b, _ := tag.Base(); b.String() == language.German.String() {
-		ww.Comma = ';'
-	}
-
-	if err := t.writeHeader(ctx, ww); err != nil {
-		return err
-	}
-
-	mp := message.NewPrinter(tag)
-	for _, r := range *t {
-		if err := t.writeRow(ww, mp, r); err != nil {
-			return err
-		}
-	}
-
-	ww.Flush()
-
-	return ww.Error()
+	return csvutil.WriteStructSlice(ctx, w, t, csvutil.Config{
+		I18nPrefix: "sessions.csv",
+	})
 }
diff --git a/core/site_optimizer_test.go b/core/site_optimizer_test.go
index f9f0aabe8..2739b7157 100644
--- a/core/site_optimizer_test.go
+++ b/core/site_optimizer_test.go
@@ -19,7 +19,7 @@ func TestSqliteTimestamp(t *testing.T) {
 	clock.Add(time.Hour)
 
 	require.NoError(t, db.NewInstance("sqlite", ":memory:"))
-	require.NoError(t, metrics.Init())
+	require.NoError(t, metrics.SetupSchema())
 
 	metrics.Persist(clock.Now(), 0)
 
@@ -56,7 +56,7 @@ func TestUpdateHouseholdProfile(t *testing.T) {
 	clock.Set(now.With(clock.Now()).BeginningOfDay())
 
 	require.NoError(t, db.NewInstance("sqlite", ":memory:"))
-	metrics.Init()
+	require.NoError(t, metrics.SetupSchema())
 
 	// 2 days of data
 	// day 1:   0 ...  95
diff --git a/core/site_test.go b/core/site_test.go
index 1a14e6f95..301ecf0b4 100644
--- a/core/site_test.go
+++ b/core/site_test.go
@@ -166,7 +166,7 @@ func TestUpdateHomeConsumption(t *testing.T) {
 	clock := clock.NewMock()
 
 	require.NoError(t, db.NewInstance("sqlite", ":memory:"))
-	metrics.Init()
+	require.NoError(t, metrics.SetupSchema())
 
 	s := &Site{
 		log:             util.NewLogger("foo"),
diff --git a/hems/eebus/eebus.go b/hems/eebus/eebus.go
index c6f9cc5bd..fdcd550dd 100644
--- a/hems/eebus/eebus.go
+++ b/hems/eebus/eebus.go
@@ -11,9 +11,11 @@ import (
 	"github.com/evcc-io/evcc/core/circuit"
 	"github.com/evcc-io/evcc/core/site"
 	"github.com/evcc-io/evcc/hems/shared"
+	"github.com/evcc-io/evcc/hems/smartgrid"
 	"github.com/evcc-io/evcc/plugin"
 	"github.com/evcc-io/evcc/server/eebus"
 	"github.com/evcc-io/evcc/util"
+	"github.com/samber/lo"
 )
 
 type EEBus struct {
@@ -28,6 +30,7 @@ type EEBus struct {
 	root        api.Circuit
 	passthrough func(bool) error
 
+	smartgridID   uint
 	status        status
 	statusUpdated time.Time
 
@@ -246,6 +249,39 @@ func (c *EEBus) setStatusAndLimit(status status, limit float64) {
 	c.statusUpdated = time.Now()
 
 	c.setLimit(limit)
+
+	if err := c.updateSession(limit); err != nil {
+		c.log.ERROR.Printf("smartgrid session: %v", err)
+	}
+}
+
+// TODO keep in sync across HEMS implementations
+func (c *EEBus) updateSession(limit float64) error {
+	// start session
+	if limit > 0 && c.smartgridID == 0 {
+		var power *float64
+		if p := c.root.GetChargePower(); p > 0 {
+			power = lo.ToPtr(p)
+		}
+
+		sid, err := smartgrid.StartManage(smartgrid.Dim, power, limit)
+		if err != nil {
+			return err
+		}
+
+		c.smartgridID = sid
+	}
+
+	// stop session
+	if limit == 0 && c.smartgridID != 0 {
+		if err := smartgrid.StopManage(c.smartgridID); err != nil {
+			return err
+		}
+
+		c.smartgridID = 0
+	}
+
+	return nil
 }
 
 func (c *EEBus) setLimit(limit float64) {
diff --git a/hems/relay/relay.go b/hems/relay/relay.go
index 936b8979b..435ab4b5c 100644
--- a/hems/relay/relay.go
+++ b/hems/relay/relay.go
@@ -10,8 +10,10 @@ import (
 	"github.com/evcc-io/evcc/core/circuit"
 	"github.com/evcc-io/evcc/core/site"
 	"github.com/evcc-io/evcc/hems/shared"
+	"github.com/evcc-io/evcc/hems/smartgrid"
 	"github.com/evcc-io/evcc/plugin"
 	"github.com/evcc-io/evcc/util"
+	"github.com/samber/lo"
 )
 
 type Relay struct {
@@ -19,6 +21,8 @@ type Relay struct {
 
 	root        api.Circuit
 	passthrough func(bool) error
+
+	smartgridID uint
 	limit       func() (bool, error)
 	maxPower    float64
 	interval    time.Duration
@@ -98,21 +102,62 @@ func (c *Relay) Run() {
 }
 
 func (c *Relay) run() error {
-	limit, err := c.limit()
+	limited, err := c.limit()
 	if err != nil {
 		return err
 	}
 
-	var power float64
-	if limit {
-		power = c.maxPower
+	var limit float64
+	if limited {
+		limit = c.maxPower
 	}
 
-	c.root.Dim(limit)
-	c.root.SetMaxPower(power)
+	if err := c.setLimited(limit); err != nil {
+		return err
+	}
+
+	if err := c.updateSession(limit); err != nil {
+		return fmt.Errorf("smartgrid session: %v", err)
+	}
+
+	return nil
+}
+
+// TODO keep in sync across HEMS implementations
+func (c *Relay) updateSession(limit float64) error {
+	// start session
+	if limit > 0 && c.smartgridID == 0 {
+		var power *float64
+		if p := c.root.GetChargePower(); p > 0 {
+			power = lo.ToPtr(p)
+		}
+
+		sid, err := smartgrid.StartManage(smartgrid.Dim, power, limit)
+		if err != nil {
+			return err
+		}
+
+		c.smartgridID = sid
+	}
+
+	// stop session
+	if limit == 0 && c.smartgridID != 0 {
+		if err := smartgrid.StopManage(c.smartgridID); err != nil {
+			return err
+		}
+
+		c.smartgridID = 0
+	}
+
+	return nil
+}
+
+func (c *Relay) setLimited(limit float64) error {
+	c.root.Dim(limit > 0)
+	c.root.SetMaxPower(limit)
 
 	if c.passthrough != nil {
-		if err := c.passthrough(limit); err != nil {
+		if err := c.passthrough(limit > 0); err != nil {
 			return fmt.Errorf("passthrough failed: %w", err)
 		}
 	}
diff --git a/hems/smartgrid/smartgrid.go b/hems/smartgrid/smartgrid.go
new file mode 100644
index 000000000..c2c650228
--- /dev/null
+++ b/hems/smartgrid/smartgrid.go
@@ -0,0 +1,32 @@
+package smartgrid
+
+import (
+	"time"
+
+	"github.com/evcc-io/evcc/server/db"
+)
+
+func init() {
+	db.Register(func() error {
+		return db.Instance.AutoMigrate(new(GridSession))
+	})
+}
+
+func StartManage(typ Type, grid *float64, limit float64) (uint, error) {
+	gs := GridSession{
+		Created:    time.Now(),
+		Type:       typ,
+		GridPower:  grid,
+		LimitPower: limit,
+	}
+	tx := db.Instance.Save(&gs)
+	return gs.ID, tx.Error
+}
+
+func StopManage(id uint) error {
+	return db.Instance.Where(&GridSession{
+		ID: id,
+	}).Updates(&GridSession{
+		Finished: time.Now(),
+	}).Error
+}
diff --git a/hems/smartgrid/types.go b/hems/smartgrid/types.go
new file mode 100644
index 000000000..b042bfc53
--- /dev/null
+++ b/hems/smartgrid/types.go
@@ -0,0 +1,34 @@
+package smartgrid
+
+import (
+	"context"
+	"io"
+	"time"
+
+	csvutil "github.com/evcc-io/evcc/util/csv"
+)
+
+type GridSession struct {
+	ID         uint      `json:"id" csv:"-" gorm:"primarykey"`
+	Created    time.Time `json:"created,omitzero"`
+	Finished   time.Time `json:"finished,omitzero"`
+	Type       Type      `json:"type"`
+	GridPower  *float64  `json:"grid,omitempty"`
+	LimitPower float64   `json:"limit"`
+}
+
+type Type string
+
+const (
+	Dim     Type = "consumption"
+	Curtail Type = "feedin"
+)
+
+type GridSessions []GridSession
+
+// WriteCsv implements the api.CsvWriter interface
+func (t *GridSessions) WriteCsv(ctx context.Context, w io.Writer) error {
+	return csvutil.WriteStructSlice(ctx, w, t, csvutil.Config{
+		I18nPrefix: "config.hems.csv",
+	})
+}
diff --git a/i18n/de.json b/i18n/de.json
index a25b3307f..bde27cc73 100644
--- a/i18n/de.json
+++ b/i18n/de.json
@@ -220,8 +220,19 @@
       "titleEdit": "Netzzähler bearbeiten"
     },
     "hems": {
+      "csv": {
+        "created": "Startzeit",
+        "finished": "Endzeit",
+        "gridpower": "Netzbezug (kW)",
+        "limitpower": "Limit (kW)",
+        "type": "Typ"
+      },
       "description": "Leistungsbegrenzung durch externe Systeme (bspw. Steuerboxen, § 14a EnWG). Setzt Lastmanagementkonfiguration voraus.",
-      "title": "HEMS"
+      "downloadCsv": "CSV herunterladen",
+      "eventsRecorded": "{count} Netzbegrenzungen gespeichert.",
+      "lastEvent": "Zuletzt {timeAgo}.",
+      "title": "HEMS",
+      "yamlConfigured": "Hinweis: Konfiguriert über evcc.yaml. Entferne den Eintrag aus der Datei, um die Bearbeitung hier zu aktivieren."
     },
     "icon": {
       "change": "ändern",
diff --git a/i18n/en.json b/i18n/en.json
index 8fe00e2b6..dbf47bcee 100644
--- a/i18n/en.json
+++ b/i18n/en.json
@@ -220,8 +220,19 @@
       "titleEdit": "Edit Grid Meter"
     },
     "hems": {
+      "csv": {
+        "created": "Created",
+        "finished": "Finished",
+        "gridpower": "Grid Power (kW)",
+        "limitpower": "Limit (kW)",
+        "type": "Type"
+      },
       "description": "Power limitation by external systems (e.g. EnWG 14a controllers). Requires load management configuration.",
-      "title": "HEMS"
+      "downloadCsv": "Download CSV",
+      "eventsRecorded": "Recorded {count} grid limitation events.",
+      "lastEvent": "Most recent {timeAgo}.",
+      "title": "HEMS",
+      "yamlConfigured": "Note: Configured via evcc.yaml. Remove the entry from the file to enable editing here."
     },
     "icon": {
       "change": "change",
diff --git a/server/db/cache/cache.go b/server/db/cache/cache.go
index 5c7980613..d971c0b2d 100644
--- a/server/db/cache/cache.go
+++ b/server/db/cache/cache.go
@@ -17,8 +17,10 @@ type Cache struct {
 	Value string `json:"value"`
 }
 
-func Init() error {
-	return db.Instance.AutoMigrate(new(Cache))
+func init() {
+	db.Register(func() error {
+		return db.Instance.AutoMigrate(new(Cache))
+	})
 }
 
 func Put(key string, value any) error {
diff --git a/server/db/db.go b/server/db/db.go
index c5217e256..8df101419 100644
--- a/server/db/db.go
+++ b/server/db/db.go
@@ -50,9 +50,24 @@ func New(driver, dsn string) (*gorm.DB, error) {
 	})
 }
 
-func NewInstance(driver, dsn string) (err error) {
-	Instance, err = New(strings.ToLower(driver), dsn)
-	return
+func NewInstance(driver, dsn string) error {
+	inst, err := New(strings.ToLower(driver), dsn)
+	if err != nil {
+		return err
+	}
+
+	Instance = inst
+
+	mu.Lock()
+	defer mu.Unlock()
+
+	for _, f := range registry {
+		if err := f(); err != nil {
+			return err
+		}
+	}
+
+	return nil
 }
 
 func Close() error {
diff --git a/server/db/registry.go b/server/db/registry.go
new file mode 100644
index 000000000..ae98bdcd2
--- /dev/null
+++ b/server/db/registry.go
@@ -0,0 +1,14 @@
+package db
+
+import "sync"
+
+var (
+	mu       sync.Mutex
+	registry []func() error
+)
+
+func Register(fun func() error) {
+	mu.Lock()
+	defer mu.Unlock()
+	registry = append(registry, fun)
+}
diff --git a/server/db/settings/setting.go b/server/db/settings/setting.go
index 56ce1299b..14f193075 100644
--- a/server/db/settings/setting.go
+++ b/server/db/settings/setting.go
@@ -33,12 +33,14 @@ var (
 	settings []setting
 )
 
-func Init() error {
-	err := db.Instance.AutoMigrate(new(setting))
-	if err == nil {
-		err = db.Instance.Find(&settings).Error
-	}
-	return err
+func init() {
+	db.Register(func() error {
+		if err := db.Instance.AutoMigrate(new(setting)); err != nil {
+			return err
+		}
+
+		return db.Instance.Find(&settings).Error
+	})
 }
 
 func Persist() error {
diff --git a/server/http.go b/server/http.go
index 0f0e2a727..7aa0b8bf6 100644
--- a/server/http.go
+++ b/server/http.go
@@ -158,6 +158,7 @@ func (s *HTTPd) RegisterSiteHandlers(site site.API, valueChan chan<- util.Param)
 		"sessions":                {"GET", "/sessions", sessionHandler},
 		"updatesession":           {"PUT", "/session/{id:[0-9]+}", updateSessionHandler},
 		"deletesession":           {"DELETE", "/session/{id:[0-9]+}", deleteSessionHandler},
+		"gridsessions":            {"GET", "/gridsessions", gridSessionsHandler},
 		"telemetry2":              {"POST", "/settings/telemetry/{value:[01truefalse]+}", boolHandler(telemetry.Enable, telemetry.Enabled)},
 	}
 
diff --git a/server/http_gridsessions_handler.go b/server/http_gridsessions_handler.go
new file mode 100644
index 000000000..31b3dfab9
--- /dev/null
+++ b/server/http_gridsessions_handler.go
@@ -0,0 +1,44 @@
+package server
+
+import (
+	"context"
+	"errors"
+	"net/http"
+
+	"github.com/evcc-io/evcc/hems/smartgrid"
+	"github.com/evcc-io/evcc/server/db"
+	"github.com/evcc-io/evcc/util/locale"
+	"golang.org/x/text/language"
+)
+
+// gridSessionsHandler returns the list of grid sessions
+func gridSessionsHandler(w http.ResponseWriter, r *http.Request) {
+	if db.Instance == nil {
+		jsonError(w, http.StatusBadRequest, errors.New("database offline"))
+		return
+	}
+
+	var res smartgrid.GridSessions
+
+	if txn := db.Instance.Order("created DESC").Find(&res); txn.Error != nil {
+		jsonError(w, http.StatusInternalServerError, txn.Error)
+		return
+	}
+
+	if r.URL.Query().Get("format") == "csv" {
+		lang := r.URL.Query().Get("lang")
+		if lang == "" {
+			// get request language
+			lang = r.Header.Get("Accept-Language")
+			if tags, _, err := language.ParseAcceptLanguage(lang); err == nil && len(tags) > 0 {
+				lang = tags[0].String()
+			}
+		}
+
+		ctx := context.WithValue(context.Background(), locale.Locale, lang)
+		csvResult(ctx, w, &res, "gridsessions")
+		return
+	}
+
+	jsonWrite(w, res)
+}
diff --git a/server/mcp/openapi.json b/server/mcp/openapi.json
index 76a6d2ba9..937c2281b 100644
--- a/server/mcp/openapi.json
+++ b/server/mcp/openapi.json
@@ -378,18 +378,10 @@
         "description": "Charging sessions",
         "items": {
           "properties": {
-            "chargeDuration": {
-              "description": "Duration of active charging",
-              "type": "number"
-            },
             "chargedEnergy": {
               "description": "Charged energy in kWh",
               "type": "number"
             },
-            "co2PerKWh": {
-              "description": "Average CO₂ emissions per kWh",
-              "type": "number"
-            },
             "created": {
               "$ref": "#/components/schemas/Timestamp"
             },
@@ -417,18 +409,6 @@
               "nullable": true,
               "type": "number"
             },
-            "price": {
-              "description": "Total price of the session",
-              "type": "number"
-            },
-            "pricePerKWh": {
-              "description": "Average price per kWh",
-              "type": "number"
-            },
-            "solarPercentage": {
-              "description": "Solar percentage of the session",
-              "type": "number"
-            },
             "vehicle": {
               "$ref": "#/components/schemas/VehicleName"
             }
@@ -454,6 +434,60 @@
         "minimum": 0,
         "type": "number"
       },
+      "GridSessions": {
+        "description": "Grid limitation sessions",
+        "items": {
+          "properties": {
+            "chargeDuration": {
+              "description": "Duration of active charging",
+              "type": "number"
+            },
+            "co2PerKWh": {
+              "description": "Average CO₂ emissions per kWh",
+              "type": "number"
+            },
+            "created": {
+              "$ref": "#/components/schemas/Timestamp"
+            },
+            "finished": {
+              "$ref": "#/components/schemas/Timestamp"
+            },
+            "gridPower": {
+              "description": "Grid power in watts",
+              "type": "number"
+            },
+            "id": {
+              "$ref": "#/components/schemas/Id"
+            },
+            "limitPower": {
+              "description": "Limitation power in watts",
+              "type": "number"
+            },
+            "price": {
+              "description": "Total price of the session",
+              "type": "number"
+            },
+            "pricePerKWh": {
+              "description": "Average price per kWh",
+              "type": "number"
+            },
+            "solarPercentage": {
+              "description": "Solar percentage of the session",
+              "type": "number"
+            },
+            "type": {
+              "description": "Type of grid limitation event",
+              "enum": [
+                "consumption",
+                "feedin"
+              ],
+              "type": "string"
+            }
+          },
+          "type": "object"
+        },
+        "type": "array"
+      },
       "HourMinuteTime": {
         "description": "Time in `HH:MM` format",
         "example": "12:30",
@@ -991,6 +1025,62 @@
         ]
       }
     },
+    "/gridsessions": {
+      "get": {
+        "description": "Returns a list of HEMS grid limitation events.",
+        "operationId": "getGridSessions",
+        "parameters": [
+          {
+            "description": "Response format (default json)",
+            "in": "query",
+            "name": "format",
+            "schema": {
+              "enum": [
+                "csv"
+              ],
+              "type": "string"
+            }
+          },
+          {
+            "description": "Language (defaults to accept header)",
+            "in": "query",
+            "name": "lang",
+            "schema": {
+              "example": "de",
+              "type": "string"
+            }
+          }
+        ],
+        "responses": {
+          "200": {
+            "content": {
+              "application/json": {
+                "schema": {
+                  "properties": {
+                    "result": {
+                      "$ref": "#/components/schemas/GridSessions"
+                    }
+                  },
+                  "type": "object"
+                }
+              },
+              "text/csv": {
+                "schema": {
+                  "description": "Download csv-file",
+                  "format": "binary",
+                  "type": "string"
+                }
+              }
+            },
+            "description": "Success"
+          }
+        },
+        "summary": "Grid limitation sessions",
+        "tags": [
+          "sessions"
+        ]
+      }
+    },
     "/health": {
       "get": {
         "description": "Returns 200 if the evcc loop runs as expected.",
diff --git a/server/mcp/openapi.md b/server/mcp/openapi.md
index 802589785..8200af16a 100644
--- a/server/mcp/openapi.md
+++ b/server/mcp/openapi.md
@@ -858,6 +858,28 @@ call deleteSession {
 }
 ```
 
+## getGridSessions
+
+Returns a list of HEMS grid limitation events.
+
+**Tags:** sessions
+
+**Arguments:**
+
+| Name | Type | Description |
+|------|------|-------------|
+| format | string | Response format (default json) |
+| lang | string | Language (defaults to accept header) |
+
+**Example call:**
+
+```json
+call getGridSessions {
+  "format": "example",
+  "lang": "example"
+}
+```
+
 ## getSessions
 
 Returns a list of charging sessions.
diff --git a/server/openapi.yaml b/server/openapi.yaml
index a594be65f..80765b72e 100644
--- a/server/openapi.yaml
+++ b/server/openapi.yaml
@@ -702,6 +702,42 @@ paths:
       responses:
         "200":
           $ref: "#/components/responses/NullResult"
+  /gridsessions:
+    get:
+      operationId: getGridSessions
+      summary: Grid limitation sessions
+      description: "Returns a list of HEMS grid limitation events."
+      tags:
+        - sessions
+      parameters:
+        - name: format
+          in: query
+          description: Response format (default json)
+          schema:
+            type: string
+            enum:
+              - csv
+        - name: lang
+          in: query
+          description: Language (defaults to accept header)
+          schema:
+            type: string
+            example: de
+      responses:
+        "200":
+          description: Success
+          content:
+            application/json:
+              schema:
+                type: object
+                properties:
+                  result:
+                    $ref: "#/components/schemas/GridSessions"
+            text/csv:
+              schema:
+                description: Download csv-file
+                type: string
+                format: binary
   /sessions:
     get:
       operationId: getSessions
@@ -1107,6 +1143,30 @@ components:
           chargedEnergy:
             type: number
             description: Charged energy in kWh
+    GridSessions:
+      description: Grid limitation sessions
+      type: array
+      items:
+        type: object
+        properties:
+          id:
+            $ref: "#/components/schemas/Id"
+          created:
+            $ref: "#/components/schemas/Timestamp"
+          finished:
+            $ref: "#/components/schemas/Timestamp"
+          type:
+            type: string
+            enum:
+              - consumption
+              - feedin
+            description: Type of grid limitation event
+          gridPower:
+            type: number
+            description: Grid power in watts
+          limitPower:
+            type: number
+            description: Limitation power in watts
           chargeDuration:
             type: number
             description: Duration of active charging
diff --git a/tests/hems-yaml.evcc.yaml b/tests/hems-yaml.evcc.yaml
new file mode 100644
index 000000000..46e72a657
--- /dev/null
+++ b/tests/hems-yaml.evcc.yaml
@@ -0,0 +1,11 @@
+interval: 0.1s
+
+hems:
+  type: relay
+  maxPower: 4200
+  limit:
+    source: const
+    value: true
+
+circuits:
+  - name: main
diff --git a/tests/hems.spec.ts b/tests/hems.spec.ts
index 35818f900..ae24f0613 100644
--- a/tests/hems.spec.ts
+++ b/tests/hems.spec.ts
@@ -29,6 +29,49 @@ test.afterEach(async () => {
 const CONFIG = "fast.evcc.yaml";
 
 test.describe("HEMS", () => {
+  test("grid sessions", async ({ page }) => {
+    await start(CONFIG, "hems.sql");
+    await page.goto("/#/config");
+    await enableExperimental(page);
+
+    await page.getByTestId("hems").getByRole("button", { name: "edit" }).click();
+    const hemsModal = page.getByTestId("hems-modal");
+    await expectModalVisible(hemsModal);
+
+    await expect(hemsModal.getByTestId("grid-sessions")).toBeVisible();
+    await expect(hemsModal).toContainText("Recorded 3 grid limitation events");
+    await expect(hemsModal).toContainText("Most recent");
+
+    const csvLink = hemsModal.getByRole("link", { name: "Download CSV" });
+    await expect(csvLink).toHaveAttribute("href", /\.\/api\/gridsessions\?format=csv&lang=en/);
+
+    await expect(hemsModal.getByTestId("yaml-editor")).toBeVisible();
+    await expect(hemsModal.getByRole("button", { name: "Save" })).toBeVisible();
+    await expect(hemsModal).not.toContainText("Configured via evcc.yaml");
+
+    await hemsModal.getByRole("button", { name: "Cancel" }).click();
+    await expectModalHidden(hemsModal);
+  });
+
+  test("modal yaml-configured", async ({ page }) => {
+    await start("hems-yaml.evcc.yaml");
+    await page.goto("/#/config");
+    await enableExperimental(page);
+
+    await page.getByTestId("hems").getByRole("button", { name: "edit" }).click();
+    const hemsModal = page.getByTestId("hems-modal");
+    await expectModalVisible(hemsModal);
+
+    await expect(hemsModal.getByTestId("grid-sessions")).not.toBeVisible();
+    await expect(hemsModal).toContainText("Configured via evcc.yaml");
+    await expect(hemsModal.getByTestId("yaml-editor")).not.toBeVisible();
+    await expect(hemsModal.getByRole("button", { name: "Save" })).not.toBeVisible();
+    await expect(hemsModal.getByRole("button", { name: "Cancel" })).toBeVisible();
+
+    await hemsModal.getByRole("button", { name: "Cancel" }).click();
+    await expectModalHidden(hemsModal);
+  });
+
   test("configure loadmanagement and hems via UI, verify logic", async ({ page }) => {
     await start(CONFIG);
 
diff --git a/tests/hems.sql b/tests/hems.sql
new file mode 100644
index 000000000..eb6f466ea
--- /dev/null
+++ b/tests/hems.sql
@@ -0,0 +1,14 @@
+DROP TABLE IF EXISTS `grid_sessions`;
+CREATE TABLE `grid_sessions` (
+  `id` integer,
+  `created` datetime,
+  `finished` datetime,
+  `type` text,
+  `grid_power` real,
+  `limit_power` real,
+  PRIMARY KEY (`id`)
+);
+
+INSERT INTO `grid_sessions` VALUES (1,'2025-05-01 08:00:00.0+02:00','2025-05-01 09:30:00.0+02:00','consumption',5000,4200);
+INSERT INTO `grid_sessions` VALUES (2,'2025-05-02 14:00:00.0+02:00','2025-05-02 15:00:00.0+02:00','feedin',3500,3000);
+INSERT INTO `grid_sessions` VALUES (3,'2025-05-05 10:00:00.0+02:00','2025-05-05 11:00:00.0+02:00','consumption',4800,4200);
diff --git a/util/config/config.go b/util/config/config.go
index 36340004e..a566a3c6e 100644
--- a/util/config/config.go
+++ b/util/config/config.go
@@ -76,7 +76,14 @@ func (d *Config) Delete() error {
 	return db.Instance.Delete(Config{ID: d.ID}).Error
 }
 
-func Init() error {
+func init() {
+	db.Register(func() error {
+		return SetupSchema()
+	})
+}
+
+// SetupSchema is used for testing
+func SetupSchema() error {
 	return db.Instance.AutoMigrate(new(Config))
 }
 
diff --git a/util/csv/writer.go b/util/csv/writer.go
new file mode 100644
index 000000000..5589d10f3
--- /dev/null
+++ b/util/csv/writer.go
@@ -0,0 +1,147 @@
+package csv
+
+import (
+	"context"
+	"encoding/csv"
+	"fmt"
+	"io"
+	"reflect"
+	"strings"
+	"time"
+
+	"github.com/evcc-io/evcc/util/locale"
+	"github.com/fatih/structs"
+	"github.com/nicksnyder/go-i18n/v2/i18n"
+	"golang.org/x/text/language"
+	"golang.org/x/text/message"
+	"golang.org/x/text/number"
+)
+
+type Config struct {
+	I18nPrefix string // e.g., "sessions.csv" or "config.hems.csv"
+}
+
+func formatValue(mp *message.Printer, value any, digits int) string {
+	if rv := reflect.ValueOf(value); rv.Kind() == reflect.Pointer && rv.IsNil() {
+		return ""
+	}
+
+	switch v := value.(type) {
+	case float64:
+		return mp.Sprint(number.Decimal(v, number.NoSeparator(), number.MaxFractionDigits(digits)))
+	case *float64:
+		return mp.Sprint(number.Decimal(*v, number.NoSeparator(), number.MaxFractionDigits(digits)))
+	case time.Time:
+		if v.IsZero() {
+			return ""
+		}
+		return v.Local().Format("2006-01-02 15:04:05")
+	default:
+		return fmt.Sprintf("%v", value)
+	}
+}
+
+func writeHeader(ctx context.Context, ww *csv.Writer, structType any, i18nPrefix string) error {
+	localizer := locale.Localizer
+	if val, ok := ctx.Value(locale.Locale).(string); ok && val != "" {
+		localizer = i18n.NewLocalizer(locale.Bundle, val, locale.Language)
+	}
+
+	var row []string
+	for _, f := range structs.Fields(structType) {
+		csvTag := f.Tag("csv")
+		if csvTag == "-" {
+			continue
+		}
+
+		caption, err := localizer.Localize(&locale.Config{
+			MessageID: i18nPrefix + "." + strings.ToLower(f.Name()),
+		})
+		if err != nil {
+			if csvTag != "" {
+				caption = csvTag
+			} else {
+				caption = f.Name()
+			}
+		}
+
+		row = append(row, caption)
+	}
+
+	return ww.Write(row)
+}
+
+func writeRow(ww *csv.Writer, mp *message.Printer, structVal any) error {
+	var row []string
+	for _, f := range structs.Fields(structVal) {
+		if f.Tag("csv") == "-" {
+			continue
+		}
+
+		digits := 3
+		if format := f.Tag("format"); format == "int" {
+			digits = 0
+		}
+
+		val := formatValue(mp, f.Value(), digits)
+		row = append(row, val)
+	}
+
+	return ww.Write(row)
+}
+
+// WriteStructSlice writes a slice of structs to CSV format with localized headers
+func WriteStructSlice(ctx context.Context, w io.Writer, slice any, cfg Config) error {
+	if _, err := w.Write([]byte{0xEF, 0xBB, 0xBF}); err != nil {
+		return err
+	}
+
+	lang := locale.Language
+	if language, ok := ctx.Value(locale.Locale).(string); ok && language != "" {
+		lang = language
+	}
+	if lang == "" {
+		lang = "en"
+	}
+
+	tag, err := language.Parse(lang)
+	if err != nil {
+		return err
+	}
+
+	ww := csv.NewWriter(w)
+
+	if b, _ := tag.Base(); b.String() == language.German.String() {
+		ww.Comma = ';'
+	}
+
+	sliceVal := reflect.ValueOf(slice)
+	if sliceVal.Kind() == reflect.Pointer {
+		sliceVal = sliceVal.Elem()
+	}
+	if sliceVal.Kind() != reflect.Slice {
+		return fmt.Errorf("expected slice, got %T", slice)
+	}
+
+	var structType any
+	if sliceVal.Len() > 0 {
+		structType = sliceVal.Index(0).Interface()
+	} else {
+		structType = reflect.New(sliceVal.Type().Elem()).Elem().Interface()
+	}
+
+	if err := writeHeader(ctx, ww, structType, cfg.I18nPrefix); err != nil {
+		return err
+	}
+
+	mp := message.NewPrinter(tag)
+	for i := 0; i < sliceVal.Len(); i++ {
+		row := sliceVal.Index(i).Interface()
+		if err := writeRow(ww, mp, row); err != nil {
+			return err
+		}
+	}
+
+	ww.Flush()
+	return ww.Error()
+}
diff --git a/util/csv/writer_test.go b/util/csv/writer_test.go
new file mode 100644
index 000000000..a54634d25
--- /dev/null
+++ b/util/csv/writer_test.go
@@ -0,0 +1,127 @@
+package csv
+
+import (
+	"bytes"
+	"context"
+	"os"
+	"strings"
+	"testing"
+	"time"
+
+	"github.com/evcc-io/evcc/server/assets"
+	"github.com/evcc-io/evcc/util/locale"
+)
+
+func init() {
+	assets.I18n = os.DirFS("../../i18n")
+	_ = locale.Init()
+}
+
+type TestStruct struct {
+	ID       int       `json:"id" csv:"-"`
+	Name     string    `json:"name"`
+	Value    float64   `json:"value"`
+	OptValue *float64  `json:"optValue,omitempty"`
+	Created  time.Time `json:"created"`
+}
+
+type TestStructs []TestStruct
+
+func TestWriteStructSlice_Empty(t *testing.T) {
+	var buf bytes.Buffer
+	slice := TestStructs{}
+
+	ctx := context.WithValue(context.Background(), locale.Locale, "en")
+	err := WriteStructSlice(ctx, &buf, &slice, Config{
+		I18nPrefix: "test.csv",
+	})
+
+	if err != nil {
+		t.Errorf("Expected no error, got %v", err)
+	}
+
+	output := buf.String()
+	if !strings.Contains(output, "Name") {
+		t.Errorf("Expected header with 'Name', got: %s", output)
+	}
+}
+
+func TestWriteStructSlice_WithData(t *testing.T) {
+	var buf bytes.Buffer
+	val := 42.5
+	slice := TestStructs{
+		{
+			ID:       1,
+			Name:     "Test",
+			Value:    123.456,
+			OptValue: &val,
+			Created:  time.Date(2024, 1, 1, 12, 0, 0, 0, time.UTC),
+		},
+	}
+
+	ctx := context.WithValue(context.Background(), locale.Locale, "en")
+	err := WriteStructSlice(ctx, &buf, &slice, Config{
+		I18nPrefix: "test.csv",
+	})
+
+	if err != nil {
+		t.Errorf("Expected no error, got %v", err)
+	}
+
+	output := buf.String()
+
+	if !strings.HasPrefix(output, "\xEF\xBB\xBF") {
+		t.Error("Expected UTF-8 BOM at start")
+	}
+
+	lines := strings.Split(strings.TrimPrefix(output, "\xEF\xBB\xBF"), "\n")
+	if len(lines) < 2 {
+		t.Fatalf("Expected at least 2 lines (header + data), got: %d", len(lines))
+	}
+
+	expectedHeader := "Name,Value,OptValue,Created"
+	if lines[0] != expectedHeader {
+		t.Errorf("Expected header: %s\nGot: %s", expectedHeader, lines[0])
+	}
+
+	if !strings.Contains(lines[1], "Test,123.456,42.5,2024-01-01") {
+		t.Errorf("Expected data row to contain Test data\nGot: %s", lines[1])
+	}
+}
+
+func TestWriteStructSlice_GermanLocale(t *testing.T) {
+	var buf bytes.Buffer
+	slice := TestStructs{
+		{Name: "Test", Value: 123.456},
+	}
+
+	ctx := context.WithValue(context.Background(), locale.Locale, "de")
+	err := WriteStructSlice(ctx, &buf, &slice, Config{
+		I18nPrefix: "test.csv",
+	})
+
+	if err != nil {
+		t.Errorf("Expected no error, got %v", err)
+	}
+
+	output := buf.String()
+	lines := strings.Split(output, "\n")
+	if len(lines) > 1 && !strings.Contains(lines[1], ";") {
+		t.Errorf("Expected German CSV to use ';' separator, got: %s", lines[1])
+	}
+}
+
+func TestFormatValue_NilPointer(t *testing.T) {
+	var nilPtr *float64
+	result := formatValue(nil, nilPtr, 3)
+	if result != "" {
+		t.Errorf("Expected empty string for nil pointer, got: %s", result)
+	}
+}
+
+func TestFormatValue_ZeroTime(t *testing.T) {
+	result := formatValue(nil, time.Time{}, 3)
+	if result != "" {
+		t.Errorf("Expected empty string for zero time, got: %s", result)
+	}
+}