diff --git a/assets/js/components/Battery/BatteryExperimental.vue b/assets/js/components/Battery/BatteryExperimental.vue
index 187defdd5..e70144406 100644
--- a/assets/js/components/Battery/BatteryExperimental.vue
+++ b/assets/js/components/Battery/BatteryExperimental.vue
@@ -117,8 +117,8 @@ export default defineComponent({
 			return this.gridChargePossible || this.gridChargeLimit !== null;
 		},
 		gridChargeTariff() {
-			const { forecast, smartCostType } = this.state;
-			return smartCostType === SMART_COST_TYPE.CO2 ? forecast?.co2 : forecast?.grid;
+			const { co2, grid } = store.uiForecast.value;
+			return this.state.smartCostType === SMART_COST_TYPE.CO2 ? co2 : grid;
 		},
 		smartCostLimitProps() {
 			return {
diff --git a/assets/js/components/BottomTabs/Bar.vue b/assets/js/components/BottomTabs/Bar.vue
index 15085db8a..ca456f318 100644
--- a/assets/js/components/BottomTabs/Bar.vue
+++ b/assets/js/components/BottomTabs/Bar.vue
@@ -53,7 +53,6 @@ import MoreItem from "./MoreItem.vue";
 import { defineComponent, type PropType } from "vue";
 import type {
 	FatalError,
-	Forecast,
 	Sponsor,
 	EvOpt,
 	AuthProviders,
@@ -74,7 +73,6 @@ export default defineComponent({
 		battery: { type: Object as PropType<Battery> },
 		batteryGridChargeActive: Boolean,
 		batteryMode: { type: String as PropType<string> },
-		forecast: { type: Object as PropType<Forecast> },
 		vehicles: { type: Object as PropType<Record<string, Vehicle>>, default: () => ({}) },
 		authProviders: { type: Object as PropType<AuthProviders>, default: () => ({}) },
 		sponsor: { type: Object as PropType<Sponsor>, default: () => ({}) },
diff --git a/assets/js/components/ChargingPlans/ChargingPlan.vue b/assets/js/components/ChargingPlans/ChargingPlan.vue
index 96eeda0bc..2c6c29c66 100644
--- a/assets/js/components/ChargingPlans/ChargingPlan.vue
+++ b/assets/js/components/ChargingPlans/ChargingPlan.vue
@@ -38,7 +38,7 @@ import formatter from "@/mixins/formatter";
 import minuteTicker from "@/mixins/minuteTicker";
 import { optionStep, fmtEnergy } from "@/utils/energyOptions.ts";
 import { defineComponent, type PropType } from "vue";
-import type { CURRENCY, Forecast, PlanStrategy, Vehicle } from "@/types/evcc";
+import type { CURRENCY, UiForecast, PlanStrategy, Vehicle } from "@/types/evcc";
 
 export default defineComponent({
 	name: "ChargingPlan",
@@ -71,7 +71,7 @@ export default defineComponent({
 		vehicleSoc: Number,
 		vehicleLimitSoc: Number,
 		vehicleNotReachable: Boolean,
-		forecast: Object as PropType<Forecast>,
+		forecast: Object as PropType<UiForecast>,
 	},
 	emits: ["open-modal"],
 	data() {
diff --git a/assets/js/components/ChargingPlans/ChargingPlanModal.vue b/assets/js/components/ChargingPlans/ChargingPlanModal.vue
index 9a4784ebe..ba86cf036 100644
--- a/assets/js/components/ChargingPlans/ChargingPlanModal.vue
+++ b/assets/js/components/ChargingPlans/ChargingPlanModal.vue
@@ -48,7 +48,7 @@ import PlansSettings from "./PlansSettings.vue";
 import api from "@/api";
 import type {
 	CURRENCY,
-	Forecast,
+	UiForecast,
 	PlanStrategy,
 	RepeatingPlan,
 	SMART_COST_TYPE,
@@ -70,7 +70,7 @@ export default defineComponent({
 		vehicles: { type: Array as PropType<Vehicle[]>, default: () => [] },
 		smartCostType: String as PropType<SMART_COST_TYPE>,
 		currency: String as PropType<CURRENCY>,
-		forecast: Object as PropType<Forecast>,
+		forecast: Object as PropType<UiForecast>,
 	},
 	data() {
 		return {
diff --git a/assets/js/components/ChargingPlans/PlansSettings.vue b/assets/js/components/ChargingPlans/PlansSettings.vue
index 0f28eb8ff..fe71da0c2 100644
--- a/assets/js/components/ChargingPlans/PlansSettings.vue
+++ b/assets/js/components/ChargingPlans/PlansSettings.vue
@@ -73,7 +73,7 @@ import { debounceLeading } from "@/utils/debounceLeading";
 import { defineComponent, type PropType } from "vue";
 import type {
 	CURRENCY,
-	Forecast,
+	UiForecast,
 	PlanResponse,
 	PlanStrategy,
 	PlanWrapper,
@@ -115,7 +115,7 @@ export default defineComponent({
 		vehicle: Object as PropType<Vehicle>,
 		vehicleLimitSoc: Number,
 		planOverrun: Number,
-		forecast: Object as PropType<Forecast>,
+		forecast: Object as PropType<UiForecast>,
 	},
 	emits: [
 		"static-plan-removed",
diff --git a/assets/js/components/Energyflow/Energyflow.vue b/assets/js/components/Energyflow/Energyflow.vue
index 4ced5d80e..6113693ec 100644
--- a/assets/js/components/Energyflow/Energyflow.vue
+++ b/assets/js/components/Energyflow/Energyflow.vue
@@ -328,7 +328,7 @@ import {
 	type Battery,
 	type Meter,
 	type CURRENCY,
-	type Forecast,
+	type UiForecast,
 	type UiLoadpoint,
 } from "@/types/evcc";
 
@@ -371,7 +371,7 @@ export default defineComponent({
 		prioritySoc: { type: Number },
 		bufferSoc: { type: Number },
 		bufferStartSoc: { type: Number },
-		forecast: { type: Object as PropType<Forecast>, default: () => ({}) },
+		forecast: { type: Object as PropType<UiForecast>, default: () => ({}) },
 	},
 	data: () => {
 		return {
diff --git a/assets/js/components/Forecast/Chart.vue b/assets/js/components/Forecast/Chart.vue
index 39905f6df..27f4115e1 100644
--- a/assets/js/components/Forecast/Chart.vue
+++ b/assets/js/components/Forecast/Chart.vue
@@ -42,7 +42,7 @@ import "chartjs-adapter-dayjs-4/dist/chartjs-adapter-dayjs-4.esm";
 import { registerChartComponents, commonOptions } from "../Sessions/chartConfig";
 import formatter, { POWER_UNIT } from "@/mixins/formatter";
 import colors, { lighterColor } from "@/colors";
-import type { CURRENCY, ForecastSlot, SolarDetails, TimeseriesEntry } from "@/types/evcc";
+import type { CURRENCY, UiForecastSlot, UiSolarDetails, UiTimeseriesEntry } from "@/types/evcc";
 import { ForecastType, highestSlotIndexByDay } from "@/utils/forecast";
 
 registerChartComponents([
@@ -64,9 +64,9 @@ export default defineComponent({
 	components: { Bar },
 	mixins: [formatter],
 	props: {
-		grid: { type: Array as PropType<ForecastSlot[]> },
-		solar: { type: Object as PropType<SolarDetails> },
-		co2: { type: Array as PropType<ForecastSlot[]> },
+		grid: { type: Array as PropType<UiForecastSlot[]> },
+		solar: { type: Object as PropType<UiSolarDetails> },
+		co2: { type: Array as PropType<UiForecastSlot[]> },
 		currency: { type: String as PropType<CURRENCY> },
 		selected: { type: String as PropType<ForecastType> },
 	},
@@ -452,7 +452,7 @@ export default defineComponent({
 			now.setMilliseconds(0);
 			this.startDate = now;
 		},
-		filterSlots(slots: ForecastSlot[] = []) {
+		filterSlots(slots: UiForecastSlot[] = []) {
 			if (!slots) {
 				return undefined;
 			}
@@ -462,7 +462,7 @@ export default defineComponent({
 					new Date(slot.end) >= this.startDate && new Date(slot.start) <= this.endDate
 			);
 		},
-		filterEntries(entries: TimeseriesEntry[] = []) {
+		filterEntries(entries: UiTimeseriesEntry[] = []) {
 			return entries.filter(
 				(entry) =>
 					new Date(entry.ts) >= this.startDate && new Date(entry.ts) <= this.endDate
@@ -491,7 +491,7 @@ export default defineComponent({
 				}, 100);
 			}
 		},
-		yMax(slots: ForecastSlot[] = []): number | undefined {
+		yMax(slots: UiForecastSlot[] = []): number | undefined {
 			const max = this.maxValue(slots);
 			if (!max) return undefined;
 			const fixedValues = slots.every((slot) => slot.value === max);
@@ -499,29 +499,29 @@ export default defineComponent({
 			const topSpace = fixedValues ? 3 : 1.15;
 			return max * topSpace;
 		},
-		yMaxEntry(entries: TimeseriesEntry[] = [], scale: number = 1): number | undefined {
+		yMaxEntry(entries: UiTimeseriesEntry[] = [], scale: number = 1): number | undefined {
 			const maxValue = this.maxEntryValue(entries);
 			if (!maxValue) return undefined;
 			// use scale and unscaled to determine max scale
 			return Math.max(maxValue * scale, maxValue) * 1.15;
 		},
-		maxIndex(slots: ForecastSlot[] = []) {
+		maxIndex(slots: UiForecastSlot[] = []) {
 			return slots.reduce((max, slot, index) => {
 				return slot.value > (slots[max]?.value || 0) ? index : max;
 			}, 0);
 		},
-		minIndex(slots: ForecastSlot[] = []) {
+		minIndex(slots: UiForecastSlot[] = []) {
 			return slots.reduce((min, slot, index) => {
 				return slot.value < (slots[min]?.value || 0) ? index : min;
 			}, 0);
 		},
-		maxValue(slots: ForecastSlot[] = []) {
+		maxValue(slots: UiForecastSlot[] = []) {
 			return slots[this.maxIndex(slots)]?.value || null;
 		},
-		maxEntryValue(entries: TimeseriesEntry[] = []) {
+		maxEntryValue(entries: UiTimeseriesEntry[] = []) {
 			return entries[this.maxEntryIndex(entries)]?.val || null;
 		},
-		maxEntryIndex(entries: TimeseriesEntry[] = []) {
+		maxEntryIndex(entries: UiTimeseriesEntry[] = []) {
 			return entries.reduce((max, entry, index) => {
 				return entry.val > (entries[max]?.val || 0) ? index : max;
 			}, 0);
diff --git a/assets/js/components/Forecast/GridDetails.vue b/assets/js/components/Forecast/GridDetails.vue
index 012febe7f..c9c567d25 100644
--- a/assets/js/components/Forecast/GridDetails.vue
+++ b/assets/js/components/Forecast/GridDetails.vue
@@ -50,7 +50,7 @@
 <script lang="ts">
 import { defineComponent, type PropType } from "vue";
 import formatter from "@/mixins/formatter";
-import type { CURRENCY, ForecastSlot } from "@/types/evcc";
+import type { CURRENCY, UiForecastSlot } from "@/types/evcc";
 import { isStaticTariff } from "@/utils/forecast";
 
 const MAX_HOURS = 96;
@@ -60,8 +60,8 @@ export default defineComponent({
 	name: "GridDetails",
 	mixins: [formatter],
 	props: {
-		grid: { type: Array as PropType<ForecastSlot[]> },
-		feedin: { type: Array as PropType<ForecastSlot[]> },
+		grid: { type: Array as PropType<UiForecastSlot[]> },
+		feedin: { type: Array as PropType<UiForecastSlot[]> },
 		currency: { type: String as PropType<CURRENCY> },
 		showFeedin: { type: Boolean, default: true },
 	},
@@ -81,7 +81,7 @@ export default defineComponent({
 		toggleFeedin() {
 			this.$emit("toggle-feedin");
 		},
-		summarize(slots?: ForecastSlot[]): { avg: string; range: string } | null {
+		summarize(slots?: UiForecastSlot[]): { avg: string; range: string } | null {
 			const upcoming = this.upcomingSlots(slots);
 			if (upcoming.length === 0) return null;
 			const values = upcoming.map((s) => s.value);
@@ -94,7 +94,7 @@ export default defineComponent({
 			const fmtMax = this.fmtPricePerKWh(max, this.currency, false, true);
 			return { avg: `⌀ ${fmtAvg}`, range: `${fmtMin} – ${fmtMax}` };
 		},
-		upcomingSlots(slots?: ForecastSlot[]): ForecastSlot[] {
+		upcomingSlots(slots?: UiForecastSlot[]): UiForecastSlot[] {
 			if (!Array.isArray(slots)) return [];
 			const now = new Date();
 			return slots
diff --git a/assets/js/components/Forecast/PriceChart.vue b/assets/js/components/Forecast/PriceChart.vue
index 01d47a0d0..12a1d17d2 100644
--- a/assets/js/components/Forecast/PriceChart.vue
+++ b/assets/js/components/Forecast/PriceChart.vue
@@ -23,32 +23,32 @@ import {
 import colors, { lighterColor } from "@/colors";
 import formatter from "@/mixins/formatter";
 import chartMixin from "./chartMixin";
-import type { CURRENCY, ForecastSlot } from "@/types/evcc";
+import type { CURRENCY, UiForecastSlot } from "@/types/evcc";
 
 export default defineComponent({
 	name: "PriceChart",
 	mixins: [formatter, chartMixin],
 	props: {
-		grid: { type: Array as PropType<ForecastSlot[]>, required: true },
-		feedin: { type: Array as PropType<ForecastSlot[]> },
+		grid: { type: Array as PropType<UiForecastSlot[]>, required: true },
+		feedin: { type: Array as PropType<UiForecastSlot[]> },
 		currency: { type: String as PropType<CURRENCY> },
 		zoom: { type: Boolean, default: false },
 	},
 	computed: {
-		slots(): ForecastSlot[] {
+		slots(): UiForecastSlot[] {
 			return filterForecastSlots(this.grid, this.startDate, this.endDate);
 		},
-		feedinSlots(): ForecastSlot[] {
+		feedinSlots(): UiForecastSlot[] {
 			return this.feedin
 				? filterForecastSlots(this.feedin, this.startDate, this.endDate)
 				: [];
 		},
-		markPoints(): { coord: [string, number]; value: string }[] {
+		markPoints(): { coord: [number, number]; value: string }[] {
 			const slots = this.slots;
 			if (!slots.length) return [];
 			const minIdx = minSlotIndex(slots);
 			const maxIdx = maxSlotIndex(slots);
-			const points: { coord: [string, number]; value: string }[] = [];
+			const points: { coord: [number, number]; value: string }[] = [];
 			if (slots[minIdx]) {
 				points.push({
 					coord: [clampStart(slots[minIdx]!.start, this.startDate), slots[minIdx]!.value],
@@ -144,9 +144,9 @@ export default defineComponent({
 	},
 	methods: {
 		priceSeries(
-			slots: ForecastSlot[],
+			slots: UiForecastSlot[],
 			color: string,
-			points?: { coord: [string, number]; value: string }[]
+			points?: { coord: [number, number]; value: string }[]
 		): Record<string, unknown> {
 			const avg = slots.length ? slots.reduce((a, s) => a + s.value, 0) / slots.length : 0;
 			const gradientDown = avg >= 0;
diff --git a/assets/js/components/Forecast/SolarChart.vue b/assets/js/components/Forecast/SolarChart.vue
index 97476d9ec..a2b825683 100644
--- a/assets/js/components/Forecast/SolarChart.vue
+++ b/assets/js/components/Forecast/SolarChart.vue
@@ -19,17 +19,17 @@ import colors, { lighterColor } from "@/colors";
 import formatter, { POWER_UNIT } from "@/mixins/formatter";
 import chartMixin from "./chartMixin";
 import { highestSlotIndexByDay } from "@/utils/forecast";
-import type { SolarDetails, TimeseriesEntry } from "@/types/evcc";
+import type { UiSolarDetails, UiTimeseriesEntry } from "@/types/evcc";
 
 export default defineComponent({
 	name: "SolarChart",
 	mixins: [formatter, chartMixin],
 	props: {
-		solar: { type: Object as PropType<SolarDetails> },
-		rawSolar: { type: Object as PropType<SolarDetails> },
+		solar: { type: Object as PropType<UiSolarDetails> },
+		rawSolar: { type: Object as PropType<UiSolarDetails> },
 	},
 	computed: {
-		entries(): TimeseriesEntry[] {
+		entries(): UiTimeseriesEntry[] {
 			return (this.solar?.timeseries || []).filter(
 				(e) => new Date(e.ts) >= this.startDate && new Date(e.ts) <= this.endDate
 			);
@@ -43,8 +43,8 @@ export default defineComponent({
 			}
 			return max;
 		},
-		markPoints(): { coord: [string, number]; value: string }[] {
-			const points: { coord: [string, number]; value: string }[] = [];
+		markPoints(): { coord: [number, number]; value: string }[] {
+			const points: { coord: [number, number]; value: string }[] = [];
 			const days = [
 				{ energy: this.solar?.today?.energy, day: 0 },
 				{ energy: this.solar?.tomorrow?.energy, day: 1 },
diff --git a/assets/js/components/Forecast/SolarDetails.vue b/assets/js/components/Forecast/SolarDetails.vue
index 18414ba69..6741e65b6 100644
--- a/assets/js/components/Forecast/SolarDetails.vue
+++ b/assets/js/components/Forecast/SolarDetails.vue
@@ -19,13 +19,13 @@
 <script lang="ts">
 import { defineComponent, type PropType } from "vue";
 import formatter, { POWER_UNIT } from "@/mixins/formatter";
-import type { SolarDetails } from "@/types/evcc";
+import type { UiSolarDetails } from "@/types/evcc";
 
 export default defineComponent({
 	name: "SolarDetails",
 	mixins: [formatter],
 	props: {
-		solar: { type: Object as PropType<SolarDetails> },
+		solar: { type: Object as PropType<UiSolarDetails> },
 	},
 	computed: {
 		days(): {
diff --git a/assets/js/components/Forecast/ValueChart.vue b/assets/js/components/Forecast/ValueChart.vue
index 6041fa6cb..37ef1af49 100644
--- a/assets/js/components/Forecast/ValueChart.vue
+++ b/assets/js/components/Forecast/ValueChart.vue
@@ -22,7 +22,7 @@ import {
 import colors from "@/colors";
 import formatter from "@/mixins/formatter";
 import chartMixin from "./chartMixin";
-import type { ForecastSlot } from "@/types/evcc";
+import type { UiForecastSlot } from "@/types/evcc";
 
 export type ValueChartType = "co2" | "temperature";
 
@@ -31,13 +31,13 @@ export default defineComponent({
 	mixins: [formatter, chartMixin],
 	props: {
 		type: { type: String as PropType<ValueChartType>, required: true },
-		rates: { type: Array as PropType<ForecastSlot[]>, required: true },
+		rates: { type: Array as PropType<UiForecastSlot[]>, required: true },
 	},
 	computed: {
 		color(): string {
 			return (this.type === "co2" ? colors.co2 : colors.temperature) || "";
 		},
-		slots(): ForecastSlot[] {
+		slots(): UiForecastSlot[] {
 			return filterForecastSlots(this.rates, this.startDate, this.endDate);
 		},
 		yMin(): number {
@@ -46,7 +46,7 @@ export default defineComponent({
 			return Math.min(0, Math.floor(Math.min(...this.slots.map((s) => s.value))));
 		},
 		markPoints(): {
-			coord: [string, number];
+			coord: [number, number];
 			value: string;
 			label?: Record<string, unknown>;
 		}[] {
@@ -55,7 +55,7 @@ export default defineComponent({
 			const minIdx = minSlotIndex(slots);
 			const maxIdx = maxSlotIndex(slots);
 			const points: {
-				coord: [string, number];
+				coord: [number, number];
 				value: string;
 				label?: Record<string, unknown>;
 			}[] = [];
diff --git a/assets/js/components/Forecast/ValueDetails.vue b/assets/js/components/Forecast/ValueDetails.vue
index d3bd3fed9..33ddb8abc 100644
--- a/assets/js/components/Forecast/ValueDetails.vue
+++ b/assets/js/components/Forecast/ValueDetails.vue
@@ -20,7 +20,7 @@
 <script lang="ts">
 import { defineComponent, type PropType } from "vue";
 import formatter from "@/mixins/formatter";
-import type { ForecastSlot } from "@/types/evcc";
+import type { UiForecastSlot } from "@/types/evcc";
 import type { ValueChartType } from "./ValueChart.vue";
 
 const MAX_HOURS = 96;
@@ -31,10 +31,10 @@ export default defineComponent({
 	mixins: [formatter],
 	props: {
 		type: { type: String as PropType<ValueChartType>, required: true },
-		rates: { type: Array as PropType<ForecastSlot[]> },
+		rates: { type: Array as PropType<UiForecastSlot[]> },
 	},
 	computed: {
-		upcomingSlots(): ForecastSlot[] {
+		upcomingSlots(): UiForecastSlot[] {
 			if (!Array.isArray(this.rates)) return [];
 			const now = new Date();
 			return this.rates
diff --git a/assets/js/components/Forecast/echarts.ts b/assets/js/components/Forecast/echarts.ts
index dab60032e..f0ed5a3b4 100644
--- a/assets/js/components/Forecast/echarts.ts
+++ b/assets/js/components/Forecast/echarts.ts
@@ -1,7 +1,7 @@
 import * as echarts from "echarts/core";
 import colors from "@/colors";
 import escapeHtml from "@/utils/escapeHtml";
-import type { ForecastSlot } from "@/types/evcc";
+import type { UiForecastSlot } from "@/types/evcc";
 import { BarChart, LineChart } from "echarts/charts";
 import {
   GridComponent,
@@ -31,7 +31,7 @@ export const FONT_FAMILY = "Montserrat, sans-serif";
 
 export function markPointLabel(
   color: string,
-  data: { coord: [string, number]; value: string; label?: { offset?: [number, number] } }[],
+  data: { coord: [number, number]; value: string; label?: { offset?: [number, number] } }[],
   startDate?: Date,
   endDate?: Date
 ) {
@@ -249,24 +249,24 @@ export function forecastYAxis(overrides: Record<string, unknown> = {}) {
   };
 }
 
-export function clampStart(ts: string, startDate: Date): string {
-  return new Date(ts) < startDate ? startDate.toISOString() : ts;
+export function clampStart(ts: number, startDate: Date): number {
+  return Math.max(ts, startDate.getTime());
 }
 
 export function filterForecastSlots(
-  slots: ForecastSlot[],
+  slots: UiForecastSlot[],
   startDate: Date,
   endDate: Date
-): ForecastSlot[] {
+): UiForecastSlot[] {
   if (!Array.isArray(slots)) return [];
   return slots.filter((s) => new Date(s.end) > startDate && new Date(s.start) <= endDate);
 }
 
-export function minSlotIndex(slots: ForecastSlot[]): number {
+export function minSlotIndex(slots: UiForecastSlot[]): number {
   return slots.reduce((min, s, i) => (s.value < (slots[min]?.value ?? Infinity) ? i : min), 0);
 }
 
-export function maxSlotIndex(slots: ForecastSlot[]): number {
+export function maxSlotIndex(slots: UiForecastSlot[]): number {
   return slots.reduce((max, s, i) => (s.value > (slots[max]?.value || 0) ? i : max), 0);
 }
 
diff --git a/assets/js/components/Loadpoints/Loadpoint.vue b/assets/js/components/Loadpoints/Loadpoint.vue
index a84e70f6c..799b56dc8 100644
--- a/assets/js/components/Loadpoints/Loadpoint.vue
+++ b/assets/js/components/Loadpoints/Loadpoint.vue
@@ -125,7 +125,7 @@ import type {
 	CHARGER_STATUS_REASON,
 	Timeout,
 	Vehicle,
-	Forecast,
+	UiForecast,
 	SMART_COST_TYPE,
 	BATTERY_MODE,
 	LoadpointUi,
@@ -251,7 +251,7 @@ export default defineComponent({
 		fullWidth: Boolean,
 		gridConfigured: Boolean,
 		pvConfigured: Boolean,
-		forecast: Object as PropType<Forecast>,
+		forecast: Object as PropType<UiForecast>,
 		lastSmartCostLimit: Number,
 		lastSmartFeedInPriorityLimit: Number,
 		vehicleKnown: Boolean,
diff --git a/assets/js/components/Loadpoints/Loadpoints.vue b/assets/js/components/Loadpoints/Loadpoints.vue
index dff4fd0d4..de3b9a148 100644
--- a/assets/js/components/Loadpoints/Loadpoints.vue
+++ b/assets/js/components/Loadpoints/Loadpoints.vue
@@ -98,7 +98,7 @@ import type {
 	Timeout,
 	Vehicle,
 	BATTERY_MODE,
-	Forecast,
+	UiForecast,
 	CURRENCY,
 } from "@/types/evcc";
 import ChargingPlanModal from "../ChargingPlans/ChargingPlanModal.vue";
@@ -123,7 +123,7 @@ export default defineComponent({
 		batteryConfigured: Boolean,
 		batterySoc: Number,
 		batteryMode: String as PropType<BATTERY_MODE>,
-		forecast: Object as PropType<Forecast>,
+		forecast: Object as PropType<UiForecast>,
 	},
 	emits: ["id-changed"],
 	data() {
diff --git a/assets/js/components/Loadpoints/SettingsModal.vue b/assets/js/components/Loadpoints/SettingsModal.vue
index b538da28a..02a2ef657 100644
--- a/assets/js/components/Loadpoints/SettingsModal.vue
+++ b/assets/js/components/Loadpoints/SettingsModal.vue
@@ -169,7 +169,7 @@ import SmartCostLimit from "../Tariff/SmartCostLimit.vue";
 import SmartFeedInPriority from "../Tariff/SmartFeedInPriority.vue";
 import SettingsBatteryBoost from "./SettingsBatteryBoost.vue";
 import { defineComponent, type PropType } from "vue";
-import { PHASES, CURRENCY, SMART_COST_TYPE, type Forecast, type UiLoadpoint } from "@/types/evcc";
+import { PHASES, CURRENCY, SMART_COST_TYPE, type UiForecast, type UiLoadpoint } from "@/types/evcc";
 import api from "@/api";
 
 const V = 230;
@@ -206,7 +206,7 @@ export default defineComponent({
 		tariffGrid: Number,
 		currency: String as PropType<CURRENCY>,
 		multipleLoadpoints: Boolean,
-		forecast: Object as PropType<Forecast>,
+		forecast: Object as PropType<UiForecast>,
 	},
 	data() {
 		return {
diff --git a/assets/js/components/Savings/Savings.vue b/assets/js/components/Savings/Savings.vue
index 5238947f3..45ea11598 100644
--- a/assets/js/components/Savings/Savings.vue
+++ b/assets/js/components/Savings/Savings.vue
@@ -268,7 +268,7 @@ import settings from "@/settings.ts";
 import { defineComponent, type PropType } from "vue";
 import type {
 	CURRENCY,
-	Forecast,
+	UiForecast,
 	StatisticsIndicator,
 	StatisticsPeriod,
 	SelectOption,
@@ -293,7 +293,7 @@ export default defineComponent({
 		sponsor: Object as PropType<SponsorType>,
 		currency: String as PropType<CURRENCY>,
 		telemetry: Boolean,
-		forecast: Object as PropType<Forecast>,
+		forecast: Object as PropType<UiForecast>,
 		tariffGrid: Number,
 	},
 	data() {
diff --git a/assets/js/components/Site/Site.vue b/assets/js/components/Site/Site.vue
index 9c3c44307..3deedb592 100644
--- a/assets/js/components/Site/Site.vue
+++ b/assets/js/components/Site/Site.vue
@@ -80,7 +80,7 @@ import type {
 	Battery,
 	Meter,
 	CURRENCY,
-	Forecast,
+	UiForecast,
 	Notification,
 	ConfigStatus,
 	HemsConfig,
@@ -147,7 +147,7 @@ export default defineComponent({
 		smartCostAvailable: Boolean,
 		smartFeedInPriorityAvailable: Boolean,
 		fatal: { type: Array as PropType<FatalError[]>, default: () => [] },
-		forecast: Object as PropType<Forecast>,
+		forecast: Object as PropType<UiForecast>,
 		hems: Object as PropType<ConfigStatus<HemsConfig, HemsStatus>>,
 		evopt: { type: Object as PropType<EvOpt> },
 	},
diff --git a/assets/js/components/Tariff/SmartCostLimit.vue b/assets/js/components/Tariff/SmartCostLimit.vue
index c8b908060..bfc389835 100644
--- a/assets/js/components/Tariff/SmartCostLimit.vue
+++ b/assets/js/components/Tariff/SmartCostLimit.vue
@@ -24,7 +24,7 @@ import { defineComponent, type PropType } from "vue";
 import api from "@/api";
 import { setLoadpointLastSmartCostLimit } from "@/uiLoadpoints";
 import settings from "@/settings";
-import { type CURRENCY, type ForecastSlot, SMART_COST_TYPE } from "@/types/evcc";
+import { type CURRENCY, type UiForecastSlot, SMART_COST_TYPE } from "@/types/evcc";
 
 export default defineComponent({
 	name: "SmartCostLimit",
@@ -41,7 +41,7 @@ export default defineComponent({
 		loadpointId: String,
 		possible: Boolean,
 		lastLimit: Number,
-		tariff: Array as PropType<ForecastSlot[]>,
+		tariff: Array as PropType<UiForecastSlot[]>,
 	},
 	computed: {
 		isCo2(): boolean {
diff --git a/assets/js/components/Top/TopNavigationArea.vue b/assets/js/components/Top/TopNavigationArea.vue
index 2a7f137ef..48aa0e375 100644
--- a/assets/js/components/Top/TopNavigationArea.vue
+++ b/assets/js/components/Top/TopNavigationArea.vue
@@ -44,7 +44,7 @@ export default defineComponent({
 				co2Configured: store.state.tariffCo2 !== undefined,
 				currency: store.state.currency,
 				telemetry: store.state.telemetry,
-				forecast: store.state.forecast,
+				forecast: store.uiForecast.value,
 				tariffGrid: store.state.tariffGrid,
 			};
 		},
diff --git a/assets/js/components/Vehicles/Vehicle.vue b/assets/js/components/Vehicles/Vehicle.vue
index 704077d5c..168a2c067 100644
--- a/assets/js/components/Vehicles/Vehicle.vue
+++ b/assets/js/components/Vehicles/Vehicle.vue
@@ -95,7 +95,7 @@ import { defineComponent, type PropType } from "vue";
 import {
 	CHARGE_MODE,
 	type BATTERY_MODE,
-	type Forecast,
+	type UiForecast,
 	type VehicleStatus,
 	type Vehicle,
 	type LoadpointUi,
@@ -146,7 +146,7 @@ export default defineComponent({
 		chargerStatusReason: String,
 		phaseAction: String,
 		phaseRemainingInterpolated: Number,
-		forecast: Object as PropType<Forecast>,
+		forecast: Object as PropType<UiForecast>,
 		planActive: Boolean,
 		planEnergy: Number,
 		planProjectedStart: String,
diff --git a/assets/js/store.ts b/assets/js/store.ts
index 8e6224552..64f020a72 100644
--- a/assets/js/store.ts
+++ b/assets/js/store.ts
@@ -1,7 +1,8 @@
-import { reactive } from "vue";
+import { computed, reactive } from "vue";
 import type { State } from "./types/evcc";
 import { convertToUiLoadpoints } from "./uiLoadpoints";
 import { useDebouncedComputed } from "./utils/useDebouncedComputed";
+import { expandForecast } from "./utils/forecast";
 import settings from "./settings";
 
 function setProperty(obj: object, props: string[], value: any) {
@@ -43,9 +44,14 @@ const uiLoadpoints = useDebouncedComputed(
   50
 );
 
+// derived forecast with slots expanded to objects with unix milliseconds; lazy,
+// only computed while a forecast consumer is mounted
+const uiForecast = computed(() => expandForecast(state.forecast));
+
 export interface Store {
   state: State; // raw state from websocket
   uiLoadpoints: typeof uiLoadpoints;
+  uiForecast: typeof uiForecast;
   offline(value: boolean): void;
   update(msg: any): void;
   reset(): void;
@@ -54,6 +60,7 @@ export interface Store {
 const store: Store = {
   state,
   uiLoadpoints,
+  uiForecast,
   offline(value: boolean) {
     state.offline = value;
   },
diff --git a/assets/js/types/evcc.ts b/assets/js/types/evcc.ts
index 82b2826fb..47b4fb642 100644
--- a/assets/js/types/evcc.ts
+++ b/assets/js/types/evcc.ts
@@ -1272,32 +1272,11 @@ export interface Slot {
   selectable?: boolean | null;
 }
 
-/** A forecast value at a point in time. */
-export interface TimeseriesEntry {
-  /** Forecast power in W. */
-  val: number;
-  /**
-   * Time of the forecast value.
-   * @format date-time
-   */
-  ts: string;
-}
+/** A forecast time slot as [start, end, value] array. Start and end are unix seconds. Value unit depends on the forecast type. */
+export type ForecastSlot = [number, number, number];
 
-/** A forecast value for a time slot. */
-export interface ForecastSlot {
-  /**
-   * Start of the time slot.
-   * @format date-time
-   */
-  start: string;
-  /**
-   * End of the time slot.
-   * @format date-time
-   */
-  end: string;
-  /** Forecast value of the time slot. Unit depends on the forecast type. */
-  value: number;
-}
+/** A forecast value at a point in time as [ts, val] array. ts is unix seconds, val is power in W. */
+export type TimeseriesEntry = [number, number];
 
 /** Expected solar production energy of a day. */
 export interface EnergyByDay {
@@ -1337,6 +1316,33 @@ export interface Forecast {
   temperature?: ForecastSlot[];
 }
 
+// Ui* variants of the forecast wire types, expanded to objects with unix
+// milliseconds by expandForecast in utils/forecast
+
+export interface UiTimeseriesEntry {
+  ts: number;
+  val: number;
+}
+
+export interface UiForecastSlot {
+  start: number;
+  end: number;
+  value: number;
+}
+
+export interface UiSolarDetails extends Omit<SolarDetails, "timeseries"> {
+  timeseries?: UiTimeseriesEntry[];
+}
+
+export interface UiForecast {
+  grid?: UiForecastSlot[];
+  co2?: UiForecastSlot[];
+  solar?: UiSolarDetails;
+  planner?: UiForecastSlot[];
+  feedin?: UiForecastSlot[];
+  temperature?: UiForecastSlot[];
+}
+
 export interface SelectOption<T> {
   name: string;
   value: T;
diff --git a/assets/js/utils/forecast.test.ts b/assets/js/utils/forecast.test.ts
index cbb99c5ce..51bf03524 100644
--- a/assets/js/utils/forecast.test.ts
+++ b/assets/js/utils/forecast.test.ts
@@ -1,56 +1,81 @@
 import { describe, expect, test } from "vite-plus/test";
-import { findLowestSumSlotIndex, isStaticTariff } from "./forecast";
+import { expandForecast, findLowestSumSlotIndex, isStaticTariff } from "./forecast";
+
+describe("expandForecast", () => {
+  test("expands slots to milliseconds", () => {
+    expect(expandForecast({ grid: [[1735689600, 1735693200, 0.25]] }).grid).toEqual([
+      { start: 1735689600000, end: 1735693200000, value: 0.25 },
+    ]);
+  });
+
+  test("expands the solar timeseries", () => {
+    expect(expandForecast({ solar: { scale: 1, timeseries: [[1735689600, 1000]] } }).solar).toEqual(
+      { scale: 1, timeseries: [{ ts: 1735689600000, val: 1000 }] }
+    );
+  });
+
+  test("handles missing input", () => {
+    expect(expandForecast(undefined)).toEqual({
+      grid: undefined,
+      co2: undefined,
+      solar: undefined,
+      planner: undefined,
+      feedin: undefined,
+      temperature: undefined,
+    });
+  });
+});
 
 describe("findLowestSumSlotIndex", () => {
   test("finds lowest sum with span of 4", () => {
     const slots = [
-      { start: "2025-01-01T00:00:00Z", value: 10 },
-      { start: "2025-01-01T00:15:00Z", value: 8 },
-      { start: "2025-01-01T00:30:00Z", value: 6 },
-      { start: "2025-01-01T00:45:00Z", value: 4 }, // sum 28 (index 0)
-      { start: "2025-01-01T01:00:00Z", value: 2 }, // sum 20 (index 1)
-      { start: "2025-01-01T01:15:00Z", value: 3 }, // sum 14 (index 2)
-      { start: "2025-01-01T01:30:00Z", value: 5 }, // sum 13 (index 3) lowest
-      { start: "2025-01-01T01:45:00Z", value: 7 }, // sum 17 (index 4)
+      { start: 1735689600000, value: 10 },
+      { start: 1735690500000, value: 8 },
+      { start: 1735691400000, value: 6 },
+      { start: 1735692300000, value: 4 }, // sum 28 (index 0)
+      { start: 1735693200000, value: 2 }, // sum 20 (index 1)
+      { start: 1735694100000, value: 3 }, // sum 14 (index 2)
+      { start: 1735695000000, value: 5 }, // sum 13 (index 3) lowest
+      { start: 1735695900000, value: 7 }, // sum 17 (index 4)
     ];
     expect(findLowestSumSlotIndex(slots, 4)).toBe(3);
   });
 
   test("returns -1 when not enough slots", () => {
     const slots = [
-      { start: "2025-01-01T00:00:00Z", value: 10 },
-      { start: "2025-01-01T00:15:00Z", value: 8 },
+      { start: 1735689600000, value: 10 },
+      { start: 1735690500000, value: 8 },
     ];
     expect(findLowestSumSlotIndex(slots, 4)).toBe(-1);
   });
 
   test("handles exact span length", () => {
     const slots = [
-      { start: "2025-01-01T00:00:00Z", value: 5 },
-      { start: "2025-01-01T00:15:00Z", value: 3 },
-      { start: "2025-01-01T00:30:00Z", value: 2 },
-      { start: "2025-01-01T00:45:00Z", value: 1 },
+      { start: 1735689600000, value: 5 },
+      { start: 1735690500000, value: 3 },
+      { start: 1735691400000, value: 2 },
+      { start: 1735692300000, value: 1 },
     ];
     expect(findLowestSumSlotIndex(slots, 4)).toBe(0);
   });
 
   test("finds lowest at end", () => {
     const slots = [
-      { start: "2025-01-01T00:00:00Z", value: 10 },
-      { start: "2025-01-01T00:15:00Z", value: 10 },
-      { start: "2025-01-01T00:30:00Z", value: 1 },
-      { start: "2025-01-01T00:45:00Z", value: 1 },
-      { start: "2025-01-01T01:00:00Z", value: 1 },
+      { start: 1735689600000, value: 10 },
+      { start: 1735690500000, value: 10 },
+      { start: 1735691400000, value: 1 },
+      { start: 1735692300000, value: 1 },
+      { start: 1735693200000, value: 1 },
     ];
     expect(findLowestSumSlotIndex(slots, 3)).toBe(2);
   });
 
   test("returns first index when multiple equal sums", () => {
     const slots = [
-      { start: "2025-01-01T00:00:00Z", value: 2 },
-      { start: "2025-01-01T00:15:00Z", value: 2 }, // sum 4
-      { start: "2025-01-01T00:30:00Z", value: 2 }, // sum 4 (same)
-      { start: "2025-01-01T00:45:00Z", value: 2 },
+      { start: 1735689600000, value: 2 },
+      { start: 1735690500000, value: 2 }, // sum 4
+      { start: 1735691400000, value: 2 }, // sum 4 (same)
+      { start: 1735692300000, value: 2 },
     ];
     expect(findLowestSumSlotIndex(slots, 2)).toBe(0);
   });
@@ -67,18 +92,18 @@ describe("isStaticTariff", () => {
 
   test("returns true when all values are identical", () => {
     const slots = [
-      { start: "2025-01-01T00:00:00Z", end: "2025-01-01T00:15:00Z", value: 0.25 },
-      { start: "2025-01-01T00:15:00Z", end: "2025-01-01T00:30:00Z", value: 0.25 },
-      { start: "2025-01-01T00:30:00Z", end: "2025-01-01T00:45:00Z", value: 0.25 },
+      { start: 1735689600000, end: 1735690500000, value: 0.25 },
+      { start: 1735690500000, end: 1735691400000, value: 0.25 },
+      { start: 1735691400000, end: 1735692300000, value: 0.25 },
     ];
     expect(isStaticTariff(slots)).toBe(true);
   });
 
   test("returns false when values differ", () => {
     const slots = [
-      { start: "2025-01-01T00:00:00Z", end: "2025-01-01T00:15:00Z", value: 0.25 },
-      { start: "2025-01-01T00:15:00Z", end: "2025-01-01T00:30:00Z", value: 0.3 },
-      { start: "2025-01-01T00:30:00Z", end: "2025-01-01T00:45:00Z", value: 0.25 },
+      { start: 1735689600000, end: 1735690500000, value: 0.25 },
+      { start: 1735690500000, end: 1735691400000, value: 0.3 },
+      { start: 1735691400000, end: 1735692300000, value: 0.25 },
     ];
     expect(isStaticTariff(slots)).toBe(false);
   });
diff --git a/assets/js/utils/forecast.ts b/assets/js/utils/forecast.ts
index a5c14d114..df2bfa4b8 100644
--- a/assets/js/utils/forecast.ts
+++ b/assets/js/utils/forecast.ts
@@ -1,4 +1,12 @@
-import type { ForecastSlot, TimeseriesEntry, SolarDetails } from "@/types/evcc";
+import type {
+  Forecast,
+  ForecastSlot,
+  SolarDetails,
+  UiForecast,
+  UiForecastSlot,
+  UiTimeseriesEntry,
+  UiSolarDetails,
+} from "@/types/evcc";
 import deepCopy from "./deepClone";
 
 export enum ForecastType {
@@ -7,6 +15,34 @@ export enum ForecastType {
   Co2 = "co2",
 }
 
+function expandSlots(slots?: ForecastSlot[]): UiForecastSlot[] | undefined {
+  return slots?.map(([start, end, value]) => ({ start: start * 1000, end: end * 1000, value }));
+}
+
+function expandSolar(solar?: SolarDetails): UiSolarDetails | undefined {
+  if (!solar) return undefined;
+  const { timeseries, ...rest } = solar;
+  return {
+    ...rest,
+    timeseries: timeseries?.map(([ts, val]) => ({ ts: ts * 1000, val })),
+  };
+}
+
+// The API publishes forecast slots as [start, end, value] and solar entries as
+// [ts, val] with timestamps in unix seconds. Expand them to objects with unix
+// milliseconds so components can keep using named fields and `new Date(...)`.
+export function expandForecast(forecast?: Forecast): UiForecast {
+  const { grid, co2, solar, planner, feedin, temperature } = forecast ?? {};
+  return {
+    grid: expandSlots(grid),
+    co2: expandSlots(co2),
+    solar: expandSolar(solar),
+    planner: expandSlots(planner),
+    feedin: expandSlots(feedin),
+    temperature: expandSlots(temperature),
+  };
+}
+
 // return the date in local YYYY-MM-DD format
 function toDayString(date: Date): string {
   const year = date.getFullYear();
@@ -17,9 +53,9 @@ function toDayString(date: Date): string {
 
 // return only slots that are on a given date, ignores slots that are in the past
 export function filterEntriesByDate(
-  entries: TimeseriesEntry[],
+  entries: UiTimeseriesEntry[],
   dayString: string
-): TimeseriesEntry[] {
+): UiTimeseriesEntry[] {
   const now = new Date();
   return entries.filter(({ ts }) => {
     const isPast = new Date(ts) < now;
@@ -36,7 +72,7 @@ export function dayStringByOffset(day: number): string {
 }
 
 // return the highest slot for a given day (0 = today, 1 = tomorrow, etc.)
-export function highestSlotIndexByDay(entries: TimeseriesEntry[], day: number = 0): number {
+export function highestSlotIndexByDay(entries: UiTimeseriesEntry[], day: number = 0): number {
   const dayString = dayStringByOffset(day);
   const dayEntries = filterEntriesByDate(entries, dayString);
   const sortedEntries = dayEntries.sort((a, b) => b.val - a.val);
@@ -45,7 +81,7 @@ export function highestSlotIndexByDay(entries: TimeseriesEntry[], day: number =
   return entries.findIndex((entry) => entry.ts === highestEntry.ts);
 }
 
-export function adjustedSolar(solar?: SolarDetails): SolarDetails | undefined {
+export function adjustedSolar(solar?: UiSolarDetails): UiSolarDetails | undefined {
   if (!solar?.scale) return solar;
 
   const { scale } = solar;
@@ -65,14 +101,14 @@ export function adjustedSolar(solar?: SolarDetails): SolarDetails | undefined {
   return result;
 }
 
-export function isStaticTariff(slots?: ForecastSlot[]): boolean {
+export function isStaticTariff(slots?: UiForecastSlot[]): boolean {
   if (!Array.isArray(slots) || slots.length === 0) return false;
   const firstValue = slots[0].value;
   return slots.every((slot) => slot.value === firstValue);
 }
 
 export interface SlotWithValue {
-  start: string | Date;
+  start: string | number | Date;
   value: number;
 }
 
diff --git a/assets/js/views/Battery.vue b/assets/js/views/Battery.vue
index ac289a532..c4da374b6 100644
--- a/assets/js/views/Battery.vue
+++ b/assets/js/views/Battery.vue
@@ -75,8 +75,8 @@ export default defineComponent({
 			return this.gridChargePossible || this.gridChargeLimit !== null;
 		},
 		gridChargeTariff() {
-			const { forecast, smartCostType } = this.state;
-			return smartCostType === SMART_COST_TYPE.CO2 ? forecast?.co2 : forecast?.grid;
+			const { co2, grid } = store.uiForecast.value;
+			return this.state.smartCostType === SMART_COST_TYPE.CO2 ? co2 : grid;
 		},
 		smartCostLimitProps() {
 			return {
diff --git a/assets/js/views/Forecast.vue b/assets/js/views/Forecast.vue
index 5527b5780..cbd2678ff 100644
--- a/assets/js/views/Forecast.vue
+++ b/assets/js/views/Forecast.vue
@@ -173,7 +173,7 @@ export default defineComponent({
 	},
 	computed: {
 		forecast() {
-			return store.state?.forecast || {};
+			return store.uiForecast.value;
 		},
 		forecastAvailable() {
 			return !!(
diff --git a/assets/js/views/Main.vue b/assets/js/views/Main.vue
index 5ee1d5b52..1bda56894 100644
--- a/assets/js/views/Main.vue
+++ b/assets/js/views/Main.vue
@@ -2,6 +2,7 @@
 	<Site
 		:notifications="notifications"
 		v-bind="state"
+		:forecast="uiForecast"
 		:selected-loadpoint-index="selectedLoadpointIndex"
 	/>
 </template>
@@ -22,6 +23,11 @@ export default defineComponent({
 	data() {
 		return store;
 	},
+	computed: {
+		uiForecast() {
+			return store.uiForecast.value;
+		},
+	},
 	head() {
 		const title = store.state.siteTitle;
 		if (title) {
diff --git a/core/site_tariffs.go b/core/site_tariffs.go
index 14c2bdb79..e9790a020 100644
--- a/core/site_tariffs.go
+++ b/core/site_tariffs.go
@@ -10,6 +10,7 @@ import (
 	"github.com/evcc-io/evcc/tariff"
 	"github.com/evcc-io/evcc/util"
 	"github.com/jinzhu/now"
+	"github.com/samber/lo"
 )
 
 type solarDetails struct {
@@ -25,6 +26,20 @@ type dailyDetails struct {
 	Complete bool    `json:"complete"`
 }
 
+// forecastRates publishes rates as [start, end, value] with the timestamps in
+// unix seconds. The forecast is the largest payload evcc sends and RFC3339
+// timestamps are two thirds of it.
+func forecastRates(rr api.Rates) [][]float64 {
+	// keep nil for empty rates: shards are published without omitempty
+	if len(rr) == 0 {
+		return nil
+	}
+
+	return lo.Map(rr, func(r api.Rate, _ int) []float64 {
+		return []float64{float64(r.Start.Unix()), float64(r.End.Unix()), r.Value}
+	})
+}
+
 // greenShare returns
 //   - the current green share, calculated for the part of the consumption between powerFrom and powerTo
 //     the consumption below powerFrom will get the available green power first
@@ -101,18 +116,18 @@ func (site *Site) publishTariffs(greenShareHome float64, greenShareLoadpoints fl
 	}
 
 	fc := struct {
-		Co2         api.Rates     `json:"co2,omitempty"`
-		FeedIn      api.Rates     `json:"feedin,omitempty"`
-		Grid        api.Rates     `json:"grid,omitempty"`
-		Planner     api.Rates     `json:"planner,omitempty"`
+		Co2         [][]float64   `json:"co2,omitempty"`
+		FeedIn      [][]float64   `json:"feedin,omitempty"`
+		Grid        [][]float64   `json:"grid,omitempty"`
+		Planner     [][]float64   `json:"planner,omitempty"`
 		Solar       *solarDetails `json:"solar,omitempty"`
-		Temperature api.Rates     `json:"temperature,omitempty"`
+		Temperature [][]float64   `json:"temperature,omitempty"`
 	}{
-		Co2:         tariff.Rates(site.GetTariff(api.TariffUsageCo2)),
-		FeedIn:      tariff.Rates(site.GetTariff(api.TariffUsageFeedIn)),
-		Planner:     tariff.Rates(site.GetTariff(api.TariffUsagePlanner)),
-		Grid:        tariff.Rates(site.GetTariff(api.TariffUsageGrid)),
-		Temperature: tariff.Rates(site.GetTariff(api.TariffUsageTemperature)),
+		Co2:         forecastRates(tariff.Rates(site.GetTariff(api.TariffUsageCo2))),
+		FeedIn:      forecastRates(tariff.Rates(site.GetTariff(api.TariffUsageFeedIn))),
+		Planner:     forecastRates(tariff.Rates(site.GetTariff(api.TariffUsagePlanner))),
+		Grid:        forecastRates(tariff.Rates(site.GetTariff(api.TariffUsageGrid))),
+		Temperature: forecastRates(tariff.Rates(site.GetTariff(api.TariffUsageTemperature))),
 	}
 
 	// calculate adjusted solar rates
diff --git a/core/site_tariffs_test.go b/core/site_tariffs_test.go
new file mode 100644
index 000000000..023f55e5e
--- /dev/null
+++ b/core/site_tariffs_test.go
@@ -0,0 +1,69 @@
+package core
+
+import (
+	"encoding/json"
+	"testing"
+	"time"
+
+	"github.com/evcc-io/evcc/api"
+	"github.com/stretchr/testify/assert"
+	"github.com/stretchr/testify/require"
+)
+
+func TestForecastRates(t *testing.T) {
+	start := time.Unix(1735689600, 0)
+
+	for _, tc := range []struct {
+		desc  string
+		rates api.Rates
+		want  string
+	}{
+		{desc: "nil", rates: nil, want: "null"},
+		{desc: "empty", rates: api.Rates{}, want: "null"},
+		{
+			desc: "slots",
+			rates: api.Rates{
+				{Start: start, End: start.Add(time.Hour), Value: 0.25},
+				{Start: start.Add(time.Hour), End: start.Add(2 * time.Hour), Value: -0.1},
+			},
+			want: "[[1735689600,1735693200,0.25],[1735693200,1735696800,-0.1]]",
+		},
+	} {
+		t.Run(tc.desc, func(t *testing.T) {
+			b, err := json.Marshal(forecastRates(tc.rates))
+			require.NoError(t, err)
+			assert.Equal(t, tc.want, string(b))
+		})
+	}
+}
+
+func TestTimeseriesMarshal(t *testing.T) {
+	start := time.Unix(1735689600, 0)
+
+	for _, tc := range []struct {
+		desc string
+		ts   timeseries
+		want string
+	}{
+		{desc: "nil", ts: nil, want: "null"},
+		{desc: "empty", ts: timeseries{}, want: "[]"},
+		{
+			desc: "entries",
+			ts: timeseries{
+				{Timestamp: start, Value: 1000},
+				{Timestamp: start.Add(time.Hour), Value: 0},
+			},
+			want: "[[1735689600,1000],[1735693200,0]]",
+		},
+	} {
+		t.Run(tc.desc, func(t *testing.T) {
+			b, err := json.Marshal(tc.ts)
+			require.NoError(t, err)
+			assert.Equal(t, tc.want, string(b))
+
+			b, err = tc.ts.MarshalBytes()
+			require.NoError(t, err)
+			assert.Equal(t, tc.want, string(b))
+		})
+	}
+}
diff --git a/core/solar.go b/core/solar.go
index f9c243fde..3fa3fde88 100644
--- a/core/solar.go
+++ b/core/solar.go
@@ -17,6 +17,20 @@ func (ts timeseries) MarshalBytes() ([]byte, error) {
 	return json.Marshal(ts)
 }
 
+// MarshalJSON publishes entries as [ts, val] with the timestamp in unix seconds
+func (ts timeseries) MarshalJSON() ([]byte, error) {
+	if ts == nil {
+		return []byte("null"), nil
+	}
+
+	res := make([][]float64, 0, len(ts))
+	for _, e := range ts {
+		res = append(res, []float64{float64(e.Timestamp.Unix()), e.Value})
+	}
+
+	return json.Marshal(res)
+}
+
 type tsEntry struct {
 	Timestamp time.Time `json:"ts"`
 	Value     float64   `json:"val"`
diff --git a/scripts/state-schema/schemas.ts b/scripts/state-schema/schemas.ts
index 1aac76b72..179a6b53e 100644
--- a/scripts/state-schema/schemas.ts
+++ b/scripts/state-schema/schemas.ts
@@ -113,6 +113,13 @@ function normalizeNullables(schema: AnySchema): void {
         node.allOf = rest;
       }
     }
+    // openapi 3.0 cannot express tuple positions, document tuples as
+    // fixed-length uniform arrays; positional meaning lives in the description
+    if (Array.isArray(node.items)) {
+      const types = [...new Set(node.items.map((item: AnySchema) => item.type))];
+      if (types.length !== 1) throw new Error(`tuple with mixed item types not supported`);
+      node.items = { type: types[0] };
+    }
     // openapi 3.0 has no `const`, use a single-value enum
     if ("const" in node) {
       node.enum = [node.const];
diff --git a/server/mcp/openapi.json b/server/mcp/openapi.json
index c0312fa0e..8935f9d33 100644
--- a/server/mcp/openapi.json
+++ b/server/mcp/openapi.json
@@ -3320,29 +3320,13 @@
         ]
       },
       "ForecastSlot": {
-        "description": "A forecast value for a time slot.",
-        "type": "object",
-        "properties": {
-          "start": {
-            "description": "Start of the time slot.",
-            "type": "string",
-            "format": "date-time"
-          },
-          "end": {
-            "description": "End of the time slot.",
-            "type": "string",
-            "format": "date-time"
-          },
-          "value": {
-            "description": "Forecast value of the time slot. Unit depends on the forecast type.",
-            "type": "number"
-          }
+        "description": "A forecast time slot as [start, end, value] array. Start and end are unix seconds. Value unit depends on the forecast type.",
+        "type": "array",
+        "items": {
+          "type": "number"
         },
-        "required": [
-          "start",
-          "end",
-          "value"
-        ]
+        "minItems": 3,
+        "maxItems": 3
       },
       "EnergyByDay": {
         "description": "Expected solar production energy of a day.",
@@ -3363,23 +3347,13 @@
         ]
       },
       "TimeseriesEntry": {
-        "description": "A forecast value at a point in time.",
-        "type": "object",
-        "properties": {
-          "val": {
-            "description": "Forecast power in W.",
-            "type": "number"
-          },
-          "ts": {
-            "description": "Time of the forecast value.",
-            "type": "string",
-            "format": "date-time"
-          }
+        "description": "A forecast value at a point in time as [ts, val] array. ts is unix seconds, val is power in W.",
+        "type": "array",
+        "items": {
+          "type": "number"
         },
-        "required": [
-          "val",
-          "ts"
-        ]
+        "minItems": 2,
+        "maxItems": 2
       },
       "SolarDetails": {
         "description": "Solar production forecast.",
diff --git a/server/openapi.state.yaml b/server/openapi.state.yaml
index fac0068aa..4c137b9be 100644
--- a/server/openapi.state.yaml
+++ b/server/openapi.state.yaml
@@ -630,24 +630,12 @@ components:
           items:
             $ref: "#/components/schemas/ForecastSlot"
     ForecastSlot:
-      description: A forecast value for a time slot.
-      type: object
-      properties:
-        start:
-          description: Start of the time slot.
-          type: string
-          format: date-time
-        end:
-          description: End of the time slot.
-          type: string
-          format: date-time
-        value:
-          description: Forecast value of the time slot. Unit depends on the forecast type.
-          type: number
-      required:
-        - start
-        - end
-        - value
+      description: A forecast time slot as [start, end, value] array. Start and end are unix seconds. Value unit depends on the forecast type.
+      type: array
+      items:
+        type: number
+      minItems: 3
+      maxItems: 3
     GenericConfigStatus:
       description: Configuration and runtime status of an integration. Structure depends on configuration.
       type: object
@@ -1767,19 +1755,12 @@ components:
         - chargedKWh
         - solarPercentage
     TimeseriesEntry:
-      description: A forecast value at a point in time.
-      type: object
-      properties:
-        val:
-          description: Forecast power in W.
-          type: number
-        ts:
-          description: Time of the forecast value.
-          type: string
-          format: date-time
-      required:
-        - val
-        - ts
+      description: A forecast value at a point in time as [ts, val] array. ts is unix seconds, val is power in W.
+      type: array
+      items:
+        type: number
+      minItems: 2
+      maxItems: 2
     Vehicle:
       description: A configured vehicle.
       type: object