Smart Home Battery Storage Integration: SolarEdge, GivEnergy and Tesla Powerwall — App Control and Tariff Shifting

Quick Answer: Home battery storage in the UK is installed under MCS (Microgeneration Certification Scheme) with G98 (single-phase systems up to 16A/phase) or G99 (above 16A or three-phase) notification to the DNO. Common UK platforms are GivEnergy (3.6–13.5 kWh), Tesla Powerwall 3 (13.5 kWh), SolarEdge Home Battery (10 kWh modules), Sonnen and Fox ESS. All offer app control, but only the Tier-1 platforms (GivEnergy, Powerwall, SolarEdge) have mature API integrations with Octopus tariffs (Cosy, Agile, Intelligent Octopus Go) for tariff-shifted charging. Integration with broader smart-home (Home Assistant, KNX, Loxone) typically uses Modbus TCP locally or the manufacturer cloud API.

Summary

Battery storage has gone from a niche addition to solar PV to a near-default upgrade. Falling battery prices, time-of-use tariffs from Octopus, and the steady extension of charging windows mean a battery can pay back in 6–9 years even without solar PV. For solar PV customers the case is stronger — self-consumption rises from 30–35% (no battery) to 75–85% (battery sized to overnight load).

The wiring and notification side is straightforward in principle: the battery either sits on the DC side of a hybrid inverter, or on the AC side via its own inverter, with metering at the consumer unit. The complications are around DNO notification timing (G98 vs G99), CT clamp placement, and the cybersecurity / commissioning workflow that determines whether the battery actually participates correctly in the customer's smart home and tariff shifting.

This article covers the integration side — platform choice, app/API control, smart-home wiring touchpoints, tariff strategies and how to spec a system that will work three years from now when the tariff lineup has changed. The notification rules and DNO process are noted but not exhaustively covered.

Key Facts

• MCS — installer and product certification required for ECO scheme, Smart Export Guarantee and most insurance compliance
• G98 — type-tested microgenerators ≤16A/phase per phase; installer-notifies DNO post-install
• G99 — full DNO connection application required for >16A/phase or three-phase battery systems
• Battery chemistry — LFP (LiFePO4) dominant; safer thermal characteristics than NMC; longer cycle life
• Round-trip efficiency — Tier 1 batteries 88–94% (DC); typically 80–88% measured AC-AC
• Cycle life — LFP batteries warranted 6,000–10,000 cycles at 80% depth of discharge
• Octopus Agile — half-hourly variable tariff; export pricing matches import
• Octopus Intelligent Go — fixed cheap window (11.30pm–5.30am 7.5p/kWh as of 2026); plus dynamic charging slots
• Octopus Cosy — 3 cheap windows daily (4am–7am, 1pm–4pm, 10pm–midnight)
• Smart Export Guarantee (SEG) — minimum export tariff scheme; rates vary 1.5–15p/kWh
• Common UK platforms — GivEnergy, Tesla Powerwall 3, SolarEdge Home Battery, Fox ESS, Sonnen, Solax
• API / integration maturity — GivEnergy excellent, Tesla good, SolarEdge good (since 2024 Home Assistant integration), Fox ESS variable
• Modbus TCP — local protocol exposed by most hybrid inverters for Home Assistant / Loxone / Hubitat integration
• Battery sizing for tariff-shifting only — 8–13 kWh for a typical household (no PV)
• Battery sizing with PV — 5–10 kWh; sized to overnight load not to PV peak
• Inverter sizing — hybrid inverters from 3 kW (single battery) to 8 kW; 3-phase from 5 kW upwards
• EPS (Emergency Power Supply) — most Tier 1 batteries offer backup output (1.5–5 kW continuous) during grid outages
• Whole-home backup — needs automatic transfer switch and DNO permission; significantly increases scope
• Vehicle-to-home (V2H) — emerging; Wallbox Quasar 2, Indra V2H, Volvo EX90; G99 plus manufacturer-specific commissioning

Quick Reference Table

Detailed Guidance

Battery sizing — first principles

A common mistake is sizing battery to PV peak. The right approach is sizing to overnight load.

For a typical UK household with:

• 8 kWh/day total electricity use
• 60% load between 4pm and 11pm (cooking, lighting, TV)
• A 4 kWp PV system generating 3,400 kWh/year

The overnight + early-evening load is approximately 5 kWh. A 5–7 kWh battery covers most of this. A 13 kWh battery is oversized — and the marginal kWh shifted at 7.5p instead of 28p doesn't pay back in a reasonable horizon.

For a household without PV, tariff-arbitrage sizing is different: size to cover all-day daytime load at the cheap rate. 8 kWh is a useful minimum; 10–13 kWh is the sweet spot.

Hybrid inverter vs AC-coupled

Two topologies:

1. DC-coupled / hybrid inverter — single inverter handles PV input, battery charge/discharge and grid interface. Higher efficiency, simpler wiring, lower cost. Examples: GivEnergy AC3, SolarEdge Energy Hub, Solax X-Hybrid.
2. AC-coupled — separate PV inverter (existing or new) plus a battery with its own inverter. Useful for retrofits to existing PV systems with non-hybrid inverters. Examples: Tesla Powerwall 3 (built-in inverter), Enphase IQ Battery, GivEnergy AC1.

For a new install with PV, DC-coupled is generally preferable. For retrofit to a 2015-era PV system with a working string inverter, AC-coupled is the practical option.

G98 vs G99 notification

• G98 applies to type-tested generators ≤16A per phase per device. For single-phase domestic, this means up to about 3.68 kW continuous. Installer registers the install with the DNO within 28 days of energisation.
• G99 applies above 16A/phase or any three-phase install. Application to DNO required BEFORE installation; DNO can take 4–12 weeks to respond.

A typical 5 kW hybrid inverter for a 5 kW PV + 13.5 kWh battery is G99. Plan the timing — DNO approval drives the install date.

Wiring and CT clamp placement

A battery system needs a CT (current transformer) clamp on the incoming live tail to measure grid import/export. Critical placement rules:

• Clamp the live tail BEFORE the consumer unit
• Orient with the arrow pointing from grid towards consumer unit (or as specified by manufacturer)
• Keep the CT wire <30m from the inverter or use a recommended extension
• If the property has a parallel henley block (e.g. EV charger fed separately), the CT must enclose ALL incoming lives — usually means a different CT location or a combined-feed busbar

Incorrect CT placement is the single most common commissioning fault. Symptoms: battery exports to grid instead of supplying house load; or battery charges from grid when it shouldn't.

App / API control and tariff shifting

For the customer to benefit from time-of-use tariffs, the battery must charge during cheap windows and discharge during expensive ones. Three implementation patterns:

1. Scheduled (basic) — set a fixed daily charge window in the manufacturer's app. Works for Octopus Go, Intelligent Octopus Go, Cosy. Doesn't adapt to Agile pricing.
2. Tariff-aware (advanced) — manufacturer integrates with Octopus API; battery checks pricing daily and charges during cheap slots. GivEnergy's "Octopus Bills" feature does this. Tesla's tariff schedule does it with manual setup.
3. External automation (expert) — Home Assistant, OctoPi, or a custom controller reads the Agile pricing API and writes setpoints to the battery over Modbus or cloud API. Maximum flexibility; requires technical commissioning.

For most customers, pattern 1 or 2 is adequate. Pattern 3 is for technically-engaged customers or where the battery is part of a larger automation system (Loxone, KNX with energy management, Home Assistant).

Backup / EPS configuration

Most Tier 1 batteries can supply a "backup output" of 1.5–5 kW continuous when the grid drops. Two configurations:

• Single-circuit backup — battery feeds a single dedicated socket or critical-load circuit (often the freezer, router, gas boiler control). Cheap and simple. No DNO concerns since the inverter automatically disconnects from the grid.
• Whole-home backup — automatic transfer switch (ATS) isolates the property from the grid during outage; battery supplies the whole consumer unit. Requires careful sizing (5 kW won't run an electric shower), and DNO sign-off on the changeover scheme.

For most customers, single-circuit backup is the sensible scope. Whole-home backup adds £1–3k and needs careful load profiling.

Integration with the wider smart home

Three integration patterns:

• Cloud API integration — Home Assistant, Hubitat or commercial controllers poll the manufacturer's cloud API. Works for GivEnergy, Tesla, Enphase, Fox ESS. Latency 30–60 seconds.
• Local Modbus TCP — same controllers connect directly to the inverter over LAN using Modbus TCP. Latency <1 second. Required for KNX / Loxone setups.
• Manufacturer ecosystem — GivEnergy + EVS, Tesla + Wall Connector, SolarEdge + EV Charger — single vendor manages the whole system.

Where the customer has a KNX or Loxone home automation system already, Modbus TCP integration is the standard. The battery's inverter exposes registers for SoC, charge/discharge power, grid power, PV power — the controller orchestrates against these values.

Frequently Asked Questions

Do I need MCS to install a battery for the customer?

You need MCS for the install to qualify for SEG (Smart Export Guarantee) and to satisfy most home insurance policies. MCS is also required for the customer to qualify for ECO4 grants. A non-MCS install is technically legal but commercially much harder to justify.

Can I add a battery to an existing 2015 solar PV system?

Yes — AC-coupled batteries (Tesla Powerwall 3, Enphase, GivEnergy AC1) are designed for retrofit. The existing PV inverter stays in place; the battery has its own inverter that connects on the AC side with a CT clamp on the grid tail.

How long does G99 approval take?

Typically 4–12 weeks depending on the DNO and the local network constraints. For a 5–10 kW system on a single-phase domestic supply, expect 4–8 weeks. Apply early — DNO sign-off is the gating item for the installation date.

What's the lifetime of a home battery?

Tier 1 batteries are warranted 10 years at typically 60–70% retained capacity. Real-world LFP batteries have shown 90%+ retention at 10 years if cycled within manufacturer guidelines. Cycle life is 6,000–10,000 cycles at 80% DoD — exceeds the warranty term for a single-cycle-per-day household.

Can I integrate the battery with my heat pump?

Yes — pattern matters. Direct integration via Modbus to a heat pump (Mitsubishi, Vaillant, Daikin) is rare; more common is using Home Assistant or the manufacturer app to coordinate. Cosy tariff alignment is the typical strategy: heat pump runs during cheap windows; battery charges during the same windows.

Regulations & Standards

• BS 7671:2018+A2:2022 — Wiring Regulations; Section 712 (PV) and Section 826 (LV electrical installations generally)

• G98 — Engineering Recommendation; type-tested microgenerators

• G99 — Engineering Recommendation; non-type-tested or larger generators

• MCS Installer and Product certification — required for SEG and most grant schemes

• BS EN 50549-1 — requirements for generating plant in parallel with distribution networks

• BS EN 62619 — safety requirements for secondary lithium cells and batteries for industrial applications

• IEC 62933 series — Electrical Energy Storage Systems

• Smart Export Guarantee (Ofgem) — mandatory export tariff scheme since 2020

• PSTI Act 2024 — applies to connected battery management systems

• MCS — Microgeneration Certification Scheme — official UK installer/product certification

• Energy Networks Association — G98/G99 — DNO notification engineering recommendations

• Ofgem — Smart Export Guarantee — SEG policy and tariff list

• Octopus Energy — Tariffs and Smart Battery Integration — tariff-shifting commercial details

• GivEnergy — API documentation — example of a mature manufacturer API

• smart heating controls — heat pump and tariff-window alignment

• smart home consumer unit considerations — Type B RCBO, Class T2 SPD for battery + inverter circuits

• part p implications smart home — battery installs are notifiable; CPS schemes

• smart home system specification — battery placement in a multi-system specification