Paul Lambert · Sheffield

I taught four homes to buy electricity at the right time.

Since 2024 I've been wiring batteries, solar and heat pumps into Home Assistant and letting half-hourly prices decide when they run. This is what I built, what worked, and what I'd tell anyone starting out.

See the homes → The tools I use
I had no idea these things could be done.” Read what Rob and Jon say →
Illustrated portrait of Paul with his German Shepherd puppy, Bob, in front of a house with solar panels at sunset
Me and Bob. He handles security. I handle the batteries.
What I'm working with

The price changes 48 times a day

On a half-hourly tariff like Octopus Agile, electricity can be almost free at 3am, expensive at 5pm, and occasionally negative, when you actually get paid to use it. Everything below is about moving usage into the green bars.

00:0006:0012:0018:0023:30
below 0pcheapaveragepeakIllustrative day, not live prices
Four homes, four different problems

What I actually built

One is my own house. The other three are properties I look after remotely. Different kit, different tariffs, different rules, which is exactly why there's no one-size-fits-all answer.

Running

Chester

  • GivEnergy All-in-One 13.5 kWh
  • 7.16 kWp solar, two arrays
  • Stiebel heat pump, SG-Ready
  • Agile import + Agile Outgoing
  • Predbat · Home Assistant on a mini PC

I set Predbat up from scratch here: solar forecasts corrected to the real roof angle, a learned household load forecast, and tariff comparisons running in the background. The battery charges in cheap slots, sells into the evening peak, and joins grid flexibility events through Axle when they're called.

82%
less electricity imported from the grid on the June bill, compared with before Predbat took over.
The time the grid was the problem

On sunny days the solar kept cutting out. The logs showed mains voltage above the 253V legal limit. I pulled the inverter data, wrote a formal complaint to the network operator, and kept a voltage limiter running in the meantime. They fixed it in September 2026. It now sits around 243V. How to check your own system →

Running · my house

Sheffield

  • Hive heating, 10 zones
  • Smart appliances and lighting
  • Agile import · Home Assistant

My own house is where I try ideas out first. Everything runs through Home Assistant, and I wrote the automations myself.

  • Ten heating zones with weather compensation, frost protection and an away mode that knows when I've left.
  • Washing machine, dishwasher and slow cooker are scheduled into the cheapest slots, with the solar forecast taken into account.
  • The lights change colour with the price, so everyone in the house can see when it's a good time to run things.
Running

Sheffield East–West

  • Fox ESS inverter + battery
  • East–west split solar array
  • Agile import + Agile Outgoing
  • Predbat · Axle Energy

This is a second Sheffield property, with the panels split across an east roof and a west roof. That gives a lower midday peak but a much longer solar day, from early morning into the evening, so the battery plan has to account for two forecasts rather than one.

  • Predbat plans charging and discharging around Agile prices and both solar forecasts.
  • Surplus is sold on Agile Outgoing when the evening price is worth it.
  • The battery joins Axle grid events when they're called.
Running

Wrexham

  • Fox ESS AC-coupled, ~18 kWh
  • 3.68 kWp solar on an old Feed-in Tariff
  • NIBE heat pumps · pool heating
  • Agile import
  • Predbat Cloud · Axle Energy

A rural property with an older Feed-in Tariff that pays well for generation. Octopus won't let you combine FIT with an export tariff, so keeping the FIT was the right call. That changes the whole strategy: day to day the battery doesn't export, it just soaks up solar and cheap overnight power. The only time it sends power back is during Axle grid events.

  • Predbat decides when the battery charges: from solar when the sun's out, and from the grid when its schedule spots a cheap slot.
  • It runs entirely on Predbat Cloud, with no Home Assistant needed. Proof you don't need a mini PC to do this.
  • Next: switching the pool heater and pump on price.
No battery? No solar? Start here

You don't need kit to save money

Not everyone has panels on the roof or a battery in the garage, and they don't need them to start. I've helped friends and family who have neither: we looked at their bills, moved them to a tariff that suited how they actually live, and worked out which jobs they could move to cheaper times of day.

Most of it is understanding the tariff. Once you know when electricity is cheap and when it's expensive, small changes add up without buying anything.

See the supplier I use →

Easy things to move to cheaper times

LaundrySet the washing machine or dryer on a timer for overnight or a midday dip.
DishwasherRun it late at night instead of straight after tea.
CookingSlow cookers and batch cooking can run in cheaper slots.
CarIf you have an EV, overnight charging on the right tariff makes the biggest difference of all.
AvoidHeavy use between about 4pm and 7pm, when half-hourly prices usually peak.
Do it yourself

You don't need me to run your system

Everything on this site is what I'd tell you if you asked. With Predbat Cloud there's no Home Assistant, no mini PC and nothing to install: you connect your inverter, your Octopus account and Axle, and it runs the battery for you. If you can follow a few setup screens, you can do this yourself.

I'm happy to help if you get stuck, but that's an offer, not a requirement. If you like building things yourself, I write up my Home Assistant projects on Gadgets Galore.

Predbat docs ↗ Predbat Cloud ↗ My Home Assistant builds ↗ Octopus Energy ↗
  1. Get a smart meterIt needs to send half-hourly readings. Most newer smart meters do; your supplier can confirm.
  2. Pick the Octopus tariff that suits youI use Agile, where the price changes every half hour, but a cheaper-overnight tariff or a fixed one may suit your home better. Add an export tariff if you sell solar or battery power back. Predbat plans around whichever you choose.
  3. Sign up to Predbat CloudCheck your inverter is on the supported list, then connect it. No Home Assistant or extra hardware needed.
  4. Connect your Octopus accountAdd your Octopus API key, found in your Octopus account under API access, so Predbat sees your actual rates.
  5. Connect Axle (optional)If your battery qualifies, add your Axle details and Predbat handles grid events for you. Those events pay when the network needs extra power.
  6. Give it a few weeksIt learns how your house uses power. Then tweak the reserve settings with the seasons.
For anyone starting out

What I've learned the hard way

Sort the tariff before the hardware

A battery on a flat-rate tariff has very little to do. A half-hourly or time-of-use tariff is what gives it a job.

Read the standing charge

A cheaper unit rate can be wiped out by a higher daily charge. Compare a full year, not the headline price.

If solar cuts out on sunny days, check the voltage

High grid voltage makes inverters shut down. Your inverter's own logs are the evidence the network operator needs. Read the guide →

Old Feed-in Tariffs change the maths

If you're on FIT, you can't usually add an export tariff with the same supplier. Work out which pays more before switching anything.

Forecasts drift, so keep an eye on them

Solar and load forecasts learn from your data. Bad data, such as cloud outages or clipped solar, teaches them the wrong thing.

Change settings with the seasons

I keep more battery in reserve from October to March and less in summer. A setup tuned in June won't be right in January.

The tools in the four homes

What I use, and why

These are the services running in the homes above. My own house runs on Agile with automations I wrote myself; the other three homes use all three of the services below. They aren't right for everyone, so check they fit your setup first.

Energy supplier

Octopus Energy

All four homes are on Octopus Agile, which gives the batteries prices to work with. Agile Outgoing pays for exports at Chester and the east–west house.

Check your meter is compatible and compare the standing charge with your current deal.

Referral link. A reward may be available to eligible customers.

Explore Octopus Energy ↗
Battery planning

Predbat

The brain at every home except mine: Chester, Wrexham and the east–west house in Sheffield. It plans charging and discharging around prices, solar forecasts and how much the house uses.

Predbat Cloud needs no Home Assistant or extra hardware, just a supported inverter. Tinkerers can also run it free in Home Assistant.

Referral link. Results depend on your system and tariff.

Discover Predbat ↗
Grid flexibility

Axle Energy

Chester, Wrexham and the east–west house all join Axle's grid events, which pay when the network needs extra help.

£1+ per kWh exported during the events I've taken part in, many times a normal export rate.

Check your battery and inverter qualify, and read the control settings before you sign up.

Referral link. Event payments vary, events aren't guaranteed, and your battery and inverter must qualify.

Explore Axle Energy ↗

Not energy, but worth knowing

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A B Corp mobile network. The Classic SIM has bills that drop every month, and the Smart SIM works alongside your main SIM for extra signal and free roaming abroad. Use my link and you get £5 off; I get £5 credit too.

Get £5 off Honest ↗

JamDoughnut

A cashback app that gives you money back instantly when you shop with brands you already use. It also runs daily competitions. Sign up with my link, or code 5SX1, for a free sign-up bonus.

Get the sign-up bonus ↗

About these links. If you sign up through one, UK99 may get a referral reward. It doesn't normally change what you pay. I only list things I use myself, and UK99 isn't affiliated with or endorsed by any of these companies.

In their words

What people say

I had no idea these things could be done.

Rob, SheffieldSolar and battery customer

Paul knocked on my door and offered me advice about making sure I had solar protection from the birds roosting, as he had noticed I was having solar installed.

Next we are sat having a drink and he's helping me with my MCS certificate, SEG export, then my tariff changes. I use Agile import and export now.

He set up Axle, who pay me £1 a kWh when the grid needs support, and Predbat brings everything together. I had no idea these things could be done.

I sold my fossil fuel car and now fill the car on negative electric days or cheap excess solar.

My installer installed the kit, showed me the app and left it to me. This is when you need Paul.

Bird protectionMCS & SEGAgile tariffsAxlePredbat

Not only was this my issue, it was the whole street's fix.

Jon, ChesterSolar and battery customer

Funny story how Paul and I met, but we are now good mates.

First time I met him, he asked about my solar and battery system, sat in my kitchen having a drink. I looked at him, as I had no idea I could get a return on my excess solar.

Within days he had me on Octopus Agile import and export, after sorting my SEG and Axle.

He found an issue with my home voltage and wrote the letter to the network operator, who came out and agreed with Paul. Not only was this my issue, it was the whole street's fix.

Paul has reduced my bill massively, to zero some months, but most importantly he has since become a good friend.

I tell all my friends, lol.

Agile tariffsSEGAxleVoltage fix

Real words from people I've helped, shared with their permission. Only spelling is corrected, and I don't edit out criticism.

For solar and battery companies

After-sales support your customers will actually use

I'm open to working with solar and battery installers, and already in talks with some, to look after their customers once the install is finished. Most people are handed a battery and an app and left to work it out. That's the part I'm good at.

  • The right tariff. Getting customers onto a tariff that suits their system, such as Agile import and export, and explaining how it works in plain English.
  • Battery optimisation. Setting up Predbat so the battery charges and exports at the right times, and tuning it through the seasons.
  • Grid events. Signing eligible systems up to Axle so customers earn from flexibility events.
  • Remote check-ins. Spotting problems early, like solar cutting out, a battery not charging or missing data, and working out the cause.
  • Fewer calls to your office. Customers get answers from someone who runs these systems every day.
4 homesmanaged across Sheffield, Chester and Wrexham, three of them remotely on GivEnergy and Fox ESS kit.
82%less grid import at Chester on the June bill after Predbat was set up.
243VChester's voltage after I took an overvoltage problem to the network operator and got it fixed.

I handle setup, software and support. Anything electrical stays with the installer.

Questions

Before you change anything

Will I get the same 82% result?

Probably not. That figure is from one house with a large battery, solar and a heat pump, tuned over months. Your result depends on your tariff, kit, usage and the season.

Do I need solar or a battery to start?

No. A half-hourly tariff can save money on its own if you can move things like washing and car charging to cheaper times. Predbat and Axle need a compatible battery.

Do I need you to set this up for me?

No. With Predbat Cloud you connect your inverter, your Octopus API key and Axle yourself, with no Home Assistant needed. Plenty of people set it up on their own. If you get stuck, message me and I'll point you in the right direction.

Are you a qualified installer?

No. I'm someone who's spent a lot of evenings getting this right in real homes. Anything involving wiring or your consumer unit needs a qualified electrician.

Do prices and offers stay the same?

No. Tariffs, referral rewards and supported hardware change often. Always check the provider's own website before you sign up.

Get in touch

Got a question about your energy?

Whether you're weighing up a tariff, stuck setting up a battery yourself, or you're an installer looking for after-sales support, send me a message. WhatsApp is the quickest way to reach me.

Mobile and WhatsApp 07775 766 477
Call
Free, friendly advice. I'm not a financial adviser or an electrician.