Solar savings. Octopus Agile overnight charging. SEG export payments. And now a fourth income stream: Axle Energy’s Virtual Power Plant, which pays me £1 per kWh whenever the National Grid needs extra power.

If you have a home battery — Fox ESS, Givenergy, Sigenergy, SolaX, or Solis — you can join this too. Here’s exactly how it works and what it earns.

What is a Virtual Power Plant?

The National Grid needs to balance supply and demand in real time. When lots of people put the kettle on at half time during a big match, or a cold snap hits and everyone turns the heating up, there’s a spike in demand that the grid needs to handle.

Traditionally this was done with gas peaker plants — expensive, dirty generators that spin up just for these moments. A VPP does the same thing using thousands of home batteries instead.

When the grid is stressed, Axle tells all its connected batteries to export electricity at the same time. From the grid’s perspective, it looks like a large power station suddenly coming online. From your perspective, your battery discharges for an hour and you get paid.

Axle Energy — how it works with Fox ESS

Axle Energy launched a specific partnership with Fox ESS, which means the integration is clean and doesn’t require any complex setup. It works entirely through software — no new hardware.

The basic mechanics:

Axle connects to your Fox ESS inverter remotely
When a “grid event” is called (typically 4 times per month), Axle triggers your battery to export at maximum rate
Events last around 60 minutes
You get paid £1 per kWh exported
Guaranteed minimum of £10/month even if no events occur

For my 10.3kWh Fox ESS setup:

Battery can export at 3kW
In a 60-minute event: 3kWh exported
Payment: £3 per event
4 events/month = £12/month
Annual: ~£144/year

Not life-changing on its own, but it’s completely passive income on top of everything else the battery already earns.

Does it interfere with Predbat?

This was my main concern when I signed up. The answer is: not really, if you use Events-Only Mode.

Axle offers two modes:

Fully Optimised Mode: Axle takes over battery scheduling entirely, using their AI to plan charge/discharge around your tariff and solar forecast. This replaces Predbat.

Events-Only Mode: Axle only touches your battery during grid events. The rest of the time, Predbat runs as normal. This is what I use.

In Events-Only Mode, if a grid event is called at 7pm, Axle exports from the battery for an hour. After the event, control returns to Predbat and normal scheduling resumes. I can also skip events in the Axle app if I need the battery reserved for a specific reason — though in practice I never do.

What happens to my battery during an event?

During a 60-minute export event at 3kW, my 10.3kWh battery loses about 3kWh of charge. If I was at 80% SOC (8.24kWh), I’d finish the event at around 50%.

Predbat then knows the battery is depleted and will schedule overnight charging to top it back up — at cheap Agile rates. So the event costs me the cheap electricity I use to refill overnight, minus the £3 I earned from the event.

At typical cheap overnight Agile rates (5–8p/kWh), refilling 3kWh costs 15–24p. Earning £3 for that same energy is a very good deal.

Does it affect battery warranty?

Axle explicitly states the software operates within manufacturer limits to protect warranty and battery health. For Fox ESS, this means:

Battery isn’t discharged below the minimum SOC threshold
Charge/discharge rates stay within spec
The 10,000-cycle battery lifespan isn’t materially impacted by 4 extra discharge cycles per month

Over 10 years at 4 events/month: ~480 extra cycles. On a battery rated for 10,000+ cycles, this is negligible.

Go to vpp.axle.energy — use my referral link and we both get a bonus
Create an account and enter your inverter details
Connect your Fox ESS account (you’ll need your Fox Cloud credentials)
Choose Events-Only Mode (if you’re using Predbat)
That’s it — you’ll get notified before each event

The setup takes about 15 minutes. There’s no contract and you can leave at any time.

Sign up with my referral link → vpp.axle.energy/landing?ref=R-NGTUFBIZ — you get a welcome bonus on top of the £1/kWh event payments, and so do I. It’s the same free service either way.

What it adds to the payback calculation

Adding VPP earnings to my overall income from the solar + battery setup:

Income stream	Annual value
Solar self-consumption (vs 28p grid)	~£590
Octopus Agile smart charging saving	~£220
SEG export earnings	~£124
Axle VPP events	~£144
Total	~£1,078/yr

That moves the annual return up by 15% simply by signing up to a free service. On an £8,500 system, that’s a payback period of roughly 7.9 years instead of 9.

Who else supports Axle?

Currently supported inverters (as of mid-2026):

Fox ESS ✓
Givenergy ✓
Sigenergy ✓
SolaX ✓
Solis ✓
SolarEdge (via separate partnership) ✓

Tesla Powerwall uses its own demand response via the Tesla app (Powerwall Time-Based Control and Virtual Power Plant features) — so if you have a Powerwall you’d use that rather than Axle.

GoodWe ESA users: GoodWe’s new Octopus Kraken integration covers some of this functionality. Axle support for GoodWe may be coming.

Bottom line

If you have a supported battery and you’re not on Axle, you’re leaving money on the table. It takes 15 minutes to set up, runs completely automatically, and earns you ~£144/year for doing nothing.

The only reason not to sign up is if you’re on Fully Optimised Mode elsewhere (like Octopus Saving Sessions) and can’t have two services controlling your battery simultaneously. In Events-Only Mode, Axle sits alongside Predbat and Agile without conflict.

👉 Join Axle with my referral link — we both get a bonus, and it’s free either way.

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Axle Energy VPP — I get paid £1/kWh just for having a battery