What is a home battery storage system?
A home battery storage system stores electricity and releases it later to run your home. It is wired into your consumer unit (fuse board), charges when electricity is cheap or when your solar panels make more than you use, and discharges when electricity would otherwise cost more.
The saving comes from the price gap. On Octopus Go, electricity is cheap between 00:30 and 05:30 every night. On Octopus Go 12M Fixed (GO-FIX-12M-26-10-14, checked 15 October 2026) that night rate is 9.4p per kWh, against 35.293p to 39.3081p per kWh at other times, depending on region. A battery buys at the night rate and saves you buying at the day rate.
The parts of a home battery storage system
Every system has the same jobs to do, whether the parts sit in one box or several.
| Part | What it does | On Habo's EcoFlow STREAM |
|---|---|---|
| Battery | Stores energy as direct current (DC). Capacity is measured in kWh. | EcoFlow lists the STREAM AC 5000 at 5,024 Wh, expandable with up to two Expansion Battery 5000 units to 15 kWh (EcoFlow UK). |
| Inverter | Converts DC from the battery into the alternating current (AC) your home uses, and back again when charging. Its rating in watts limits how much power the battery can supply at once. | Built in. EcoFlow says the STREAM host includes the battery and a grid-tied inverter (EcoFlow UK). Maximum grid-connected output for a single STREAM AC 5000 is 2,500 W, or 3,000 W with an Expansion Battery 5000 (EcoFlow UK). |
| Controller or gateway | Decides when to charge and when to discharge. Some systems add a separate gateway box to link several units or manage the grid connection. | Controls are in the unit. EcoFlow says the STREAM supports a STREAM Gateway to expand grid-connected power, with up to six units working together (EcoFlow UK). |
| Wiring and consumer unit | Connects the battery to your home's circuits through its own protected circuit at the consumer unit. | EcoFlow says the STREAM comes with a cable with stripped ends, no plug, and in the UK must be hardwired by a certified, registered electrician (EcoFlow UK). |
| Meter or CT clamp | Measures how much power your home is drawing from the grid, so the battery can match it instead of guessing. This is separate from your supplier's smart meter. | EcoFlow lists compatible meters, including the EcoFlow Smart Meter and Shelly 3EM, and a Smart Meter Dual CT option for overload protection (EcoFlow UK). |
| App | Lets you set the schedule, see what the battery is doing and change settings. | The EcoFlow app offers a custom mode that runs schedules by time and tariff rate, and an intelligent mode that uses tariff and weather data (EcoFlow UK). |
You also need a supplier smart meter to join a smart tariff. Octopus says Octopus Go needs a smart meter it can connect to (Octopus Energy).
How the parts work together
Here is a normal day on a time-of-use tariff:
- Overnight: the controller starts charging in the cheap window. The inverter turns grid AC into DC and fills the battery.
- Morning and evening: the meter or CT clamp sees your home drawing power. The controller tells the inverter to discharge, and the battery covers that demand up to its output rating.
- Big loads: if you use more than the inverter can supply, for example an oven and a kettle at the same time, the rest comes from the grid as normal.
- When it is empty: your home runs on the grid until the next cheap window.
Habo sets the timer schedule at installation, so the battery charges in your tariff's cheap window and runs your home afterwards without you managing it day to day.
Types of home battery storage system
AC-coupled
An AC-coupled battery has its own inverter and connects on the AC side, at your consumer unit. It does not need solar panels, and if you already have solar it sits alongside your existing solar inverter rather than replacing it. EcoFlow lists no solar input on the STREAM AC 5000, so it is an AC-coupled battery (EcoFlow UK).
DC-coupled
In a DC-coupled system, solar panels feed the battery on the DC side through the system's own solar inputs (MPPTs), before anything is converted to AC. Solar energy that is stored goes through fewer conversions, which suits new solar and battery installs. EcoFlow lists the STREAM 5000 with four solar inputs and up to 5,000 W of solar input power (EcoFlow UK).
Hybrid inverter systems
A hybrid inverter handles both solar panels and a battery in one box. It is common when solar and a battery are fitted together. If you already have solar, a hybrid system usually means replacing your existing solar inverter, which is a bigger job than adding an AC-coupled battery.
All-in-one vs modular
An all-in-one system puts the battery, inverter and controls in a single unit, so there are fewer boxes on the wall and fewer connections. A modular system lets you add battery modules later, or pair separate batteries with a separate inverter. The STREAM is both: an all-in-one main unit that can stack up to two Expansion Battery 5000 units, with up to six main units in one system (EcoFlow UK).
| Type | How it connects | Usually suits |
|---|---|---|
| AC-coupled | Own inverter, wired at the consumer unit | Homes without solar, or adding a battery to existing solar |
| DC-coupled | Solar panels feed the battery side directly | New solar and battery fitted together |
| Hybrid inverter | One inverter for solar and battery | New installs, or replacing an old solar inverter |
| All-in-one | Battery, inverter and controls in one unit | Simple installs with fewer parts |
| Modular | Battery modules added to a main unit or inverter | Starting small and expanding later |
For a wider look at the choices, see our guide to home battery storage options.
Do I need solar panels?
No. An AC-coupled battery on a time-of-use tariff charges from cheap grid electricity overnight and powers your home later in the day. Solar can be added, but it is not a requirement.
In winter, when solar panels make little, grid charging is what keeps a battery working. See battery storage without solar, or batteries with solar panels if you have them already.
What size home battery storage system do I need?
Size the battery to the electricity you use outside the cheap window, and check the output rating covers your usual evening use.
Look at your smart meter data for the hours outside your tariff's cheap window. If that is around 5 kWh a day or less, a 5 kWh battery can cover most of it. If it is more, the battery covers part of it, or you can add capacity. Check the usable capacity on the spec sheet, not just the headline figure. Output matters too: a battery that can only supply a set number of watts at once will leave big loads partly on the grid. For more detail, see our battery sizing guide.
Wiring, G98 and VAT
Wiring: a wired-in home battery storage system goes on its own circuit at your consumer unit. EcoFlow says the STREAM must be hardwired by a certified, registered electrician in the UK and should not be connected to a household socket to feed power in (EcoFlow UK). A plug-in battery in a socket does not power the whole home. See home battery installation rules in the UK.
G98: equipment up to 16 A per phase, about 3.68 kW on a single-phase supply, in total at the property, is installed and then notified to the network operator. Anything bigger needs a G99 application first (ENA G98 single premises guide). A single STREAM AC 5000 is listed at 2,500 W grid-connected output (EcoFlow UK). Your electrician confirms which route applies. See G98 vs G99.
VAT: batteries installed in homes, including a standalone battery storing electricity from the grid, are zero-rated until 31 March 2027, then revert to 5% (HMRC VAT Notice 708/6, section 2.19).
Where it goes: EcoFlow rates the STREAM AC 5000 IP65 for indoor or outdoor use, and lists it at 44.6 kg, 295 x 287 x 489 mm and under 30 dB (EcoFlow UK). Your electrician will look at your consumer unit and where the unit can be mounted.
What a home battery storage system costs and saves
Habo installs a 5 kWh EcoFlow STREAM from £2,499, electrician-wired (Habo pricing). Best case, Habo's 5 kWh EcoFlow STREAM saves up to about £453 to £527 a year, based on Octopus Go 12M Fixed (GO-FIX-12M-26-10-14, checked 15 October 2026), one full cycle a day and an assumed 90% round-trip efficiency (see how we worked it out). On £2,499 installed that is roughly an 18% to 21% equivalent savings-interest rate (see home battery vs savings account). Real savings will be lower, and there is no saving on a flat-rate tariff. For other systems, compare quotes on cost per usable kWh; see our home battery storage cost guide.
Backup in a power cut
EcoFlow says that in a power cut the STREAM switches to off-grid mode, its grid-connected port stops, and it supplies loads plugged into its own AC outlet, provided the battery has charge (EcoFlow UK). For a single STREAM AC 5000, EcoFlow gives 2,500 W as the off-grid output of that outlet. So backup covers what you plug into the unit, not your whole home. See home battery backup power.
What to look for when choosing a system
- Usable capacity: matched to what you use outside the cheap window.
- Output in watts: enough to cover your normal evening use.
- Coupling: AC-coupled if you have no solar or want to keep your solar inverter; DC-coupled or hybrid for a new solar and battery install.
- Expansion: whether you can add capacity later.
- Warranty: check the years, cycle terms and end-of-warranty capacity. EcoFlow lists a 10-year warranty for the STREAM AC 5000 (EcoFlow warranty policy).
- Installer: a registered electrician who wires it in properly and handles the G98 notification.
Frequently asked questions
A battery to store energy, an inverter to convert between the battery's DC and your home's AC, a controller (sometimes a separate gateway) that decides when to charge and discharge, the wiring into your consumer unit, a meter or CT clamp that measures what your home is using, and an app to set the schedule. On the EcoFlow STREAM the battery, grid-tied inverter and controls sit in one unit (EcoFlow UK).
An AC-coupled battery has its own inverter and connects on the AC side, at your consumer unit, so it works with or without solar panels and can sit alongside an existing solar system. A DC-coupled system takes solar power straight into the battery side through its own solar inputs, before it is converted to AC. EcoFlow lists no solar input on the STREAM AC 5000 and four solar inputs on the STREAM 5000 (EcoFlow UK).
No. On a time-of-use tariff such as Octopus Go, which is cheap between 00:30 and 05:30 every night, the battery charges from the grid overnight and powers your home later in the day. Solar can be added, but it is not required. See battery storage without solar.
Not on its own. A wired-in battery feeds your home's circuits through the consumer unit, but only up to its output rating, and anything above that comes from the grid as normal. EcoFlow lists a single STREAM AC 5000's maximum grid-connected output as 2,500 W, or 3,000 W with an Expansion Battery 5000 (EcoFlow UK). A plug-in battery in a socket does not power the whole home. In a power cut, the STREAM only supplies what is plugged into its own AC outlet (EcoFlow UK).
Batteries installed in homes, including a standalone battery that stores electricity from the grid, are zero-rated for VAT until 31 March 2027. From 1 April 2027 they revert to the reduced rate of 5% (HMRC VAT Notice 708/6, section 2.19).
G98 covers equipment up to 16 A per phase, about 3.68 kW on a single-phase supply, in total at the property. Your installer fits it and notifies the network operator; anything bigger needs a G99 application first (ENA G98 single premises guide). A single STREAM AC 5000 is listed at 2,500 W grid-connected output (EcoFlow UK). If you already have solar, the total can go over the limit. See G98 vs G99.
It depends on your tariff and how much you use outside the cheap window. Best case, Habo's 5 kWh EcoFlow STREAM saves up to about £453 to £527 a year, based on Octopus Go 12M Fixed (GO-FIX-12M-26-10-14, checked 15 October 2026), one full cycle a day and an assumed 90% round-trip efficiency. That is a best-case payback of about 4.7 to 5.5 years on £2,499 (see how we worked it out). Real savings will be lower, and there is no saving on a flat-rate tariff.
Get a home battery storage system fitted
Habo fits the EcoFlow STREAM, electrician-wired to your consumer unit, from £2,499 installed. Not a plug-in battery. Join the UK waitlist: Habo will try to serve anyone who registers in an area where we have an electrician. Nothing to pay today.
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