Skip to content
07944 877 329 hello@solar-tech-support.co.uk
Alectrona Get a quote
Tariff configuration · Sunsynk

Sunsynk Not Charging on Cheap Rate — Octopus, Agile, Go and TOU Schedule Fixes

Battery should be charging overnight on Octopus Go/Agile but it's not. This is the most common Sunsynk configuration failure in the UK. BST/GMT clock offset and TOU schedule mismatch account for >80% of cases. We cover every tariff and every fix.
Free remote diagnostic pay only if we fix it — from £95 if remediable remotely
Book Sunsynk diagnosisSunsynk hub
  • Most common Sunsynk complaint
  • Usually a 30-minute configuration fix
  • Octopus Go, Agile, Intelligent, Flux
Not seeing overnight charging on cheap rate?

This diagnostic guide walks through every setting. Most cases are resolved by Step 2 — the BST/GMT clock offset.

Book your free remote diagnosticOctopus tariff guide

We configure Sunsynk for all major UK tariffs remotely in a single session.

5.0
Rated 5.0 on Google Read all 73 reviews

Wow... a firmware update to my inverter sent the whole system into meltdown – the battery discharged, and the house seemed to be drawing power, and the solar, who knows where that was going? Aghhh... A short email exchange with Roland and Solar Tech Support sorted the problem... the firmware had reversed a setting (from when it was installed), and the CT clamp needed to be reversed. As soon as I had done that, the world returned to normal. Thanks, Roland; there is no way I would have come to that conclusion. Would I recommend them? You bet! Worth the fee? You bet, again!

Pete Hawkins · Jul 2026 Google

My GivEnergy hybrid inverter + battery system had worked faultlessly for 3 years when it suddenly stopped charging and discharging the battery. On contacting my supplier, who had used a sub-contractor for the installation work, I was provided with an email address at GivEnergy but, as it turned out, this is only for GivEnergy Software who are not able to assist. A Google search led to the Solar Tech Support web site, which contains a wealth of helpful information. I requested a remote solar diagnostic, and after providing Ron access to my inverter, he was able to identify and fix the problem within minutes. I am very impressed by Ron’s expertise and knowledge, which included useful information on the current state of GivEnergy Ltd. I would thoroughly recommend Solar Tech Support.

Simon Riddle · Jun 2026 Google

I have a GivEnergy system consisting of two batteries, two inverters and a controlling EMS (Energy Management System) which has not worked since Nov 2025. After six months I discovered Solar Tech Support, reached out to them and Ron phoned me back – how often do you get that service? Could not be more helpful – worked directly with me over the phone, outside what I would call normal working hours. Lucid explanations and we were able to discuss the issues and history using camera and email history. As this was a very rare setup, Ron was able to access an EMS expert in the field to confirm the solution. One sunny day in, I am now only paying for standing charge and a few pence for spikes in grid consumption while battery catches up with house demand.

Ian · May 2026

Ron was extremely helpful and tried his best to repair/reset our GivEnergy inverter remotely. In the event he was unsuccessful but he couldn’t have been more helpful. If you have problems with a GivEnergy system please contact him. Highly recommended

Neil Crichton · Jun 2026 Google

Having had a recent solar instal and being concerned about various aspects of the work, I reached out to Solar Tech for advice. I received immediate engagement and first class advice. This was late evening and the company went above and beyond in providing assistance to me - high recommended.

John Szram · Jul 2026 Google

A superb service from Ron who went beyond the normal service received from other Tech support companies. I live abroad and was badly let down when my givenergy system failed (and the company went bankrupt) and the local supplier ran away from the problem. Ron sorted the problem and even accessed specialist coding for the inverter that would not be available for suppliers. Ron also ran a full diagnostic to insure that all was in good working order afterwards. Without Rons support and patient assistance I doubt I would ever have got the system back up and running. Well done and thankyou and you have a customer for the future.

Philip Davey · Jun 2026 Google

Safety Warning

Do not open your inverter or interfere with DC cabling. Solar panels produce live DC voltage whenever exposed to light. Always use your DC isolator switch and contact a qualified solar engineer for hands-on fault diagnosis.

Diagnosis steps

6-step diagnostic process

Work through these steps in order. Most cases are resolved by Step 2.

1

Confirm your cheap-rate tariff window from your energy bill

Check your energy supplier's portal or your latest bill for the exact cheap-rate hours. Common windows: Octopus Go 00:30–04:30 (GMT/BST) · Octopus Intelligent 23:00–06:00 plus peak windows · Octopus Flux off-peak 02:00–05:00 · Economy 7 approximately 00:30–07:30 (varies by region). Write these times down exactly — you'll need them for Step 2.

2

Check inverter clock and compare to local time

In SolarMan, go to Device → Information and check the inverter's current clock time. Compare it to your local time right now. If the inverter clock is 1 hour behind (e.g., showing 23:00 when it's actually 00:00 BST), this is the problem. During British Summer Time, many Sunsynk inverters don't auto-adjust the clock. The charge window will fire exactly 1 hour late as a result.

BST/GMT offset is the #1 cause: We find that approximately 80% of Sunsynk cheap-rate charging failures are due to the inverter clock being 1 hour off. It's usually a clock adjustment that happened automatically on your phone and laptop, but not on the Sunsynk.
3

Check Time of Use schedule in SolarMan

Navigate to Device → Settings → Time of Use. Find your charge window and verify the start and end times match your tariff window exactly. Common mistake: if Octopus Go is 00:30–04:30 but SolarMan shows 23:30–03:30, the window is offset by 1 hour. Correct it to 00:30–04:30.

Timezone note: Some Sunsynk installations have windows set to GMT times even during BST, or vice versa. Always use your local current time — not GMT or BST as separate entities. Your local time IS GMT or BST depending on the season.
4

Verify grid charge is enabled for the charge window

In SolarMan, check the grid charge settings (usually Device → Settings → Grid Charge). Confirm that grid charge is set to ON for the charge window. If disabled, the battery will only charge from solar generation, not from cheap-rate electricity. Grid charge must be ON for the system to force charge from the grid.

5

Check charge power target and SoC targets

In Device Settings, find the charge power limit (if set). If too low (e.g., 500W), the battery will charge very slowly during the window — a 5kWh battery might only gain 500Wh in 4 hours. Set charge power to the inverter's rated capacity for maximum charging during the window. Also verify SoC target is high (e.g., 90-100%) and minimum SoC is low (e.g., 10-20%) to allow meaningful charge/discharge cycles.

6

Monitor the next charging cycle and verify with SolarMan data

After making any adjustments, check SolarMan's battery SoC graph the following morning. Look for: battery SoC increasing during your charge window, grid power showing as positive import during the window, and battery reaching your target SoC by the end of the window. If charging still hasn't started, book a remote diagnostic — there may be a secondary issue.

Context

About cheap-rate tariff integration

Octopus Energy grew explosively across the UK from 2020 onwards, and many Sunsynk systems were installed without proper tariff-specific configuration. The combination of BST/GMT clock confusion, unclear SolarMan UI, and inconsistent Time of Use scheduling has created a situation where the majority of Sunsynk owners report that their cheap-rate charging doesn't work reliably. In reality, nearly all of these systems can be fixed in a single 30-minute remote session.

STS is a Sunsynk and Octopus specialist. We've configured hundreds of Sunsynk systems for Octopus Go, Agile, Intelligent, and Flux tariffs. The fix is always the same: correct the clock, verify the TOU window times, enable grid charge, and set appropriate SoC targets.

Most common issues (in order)
1. Inverter clock 1 hour off (BST/GMT changeover)
2. TOU window times offset by 30min–1 hour
3. Grid charge disabled in settings
4. SoC target too high — no headroom to charge
5. Charge power set too low — very slow charging
Related pages
Useful guides
FAQ

Cheap-rate charging questions

The most common cause is a BST/GMT clock offset. Check the inverter clock in SolarMan — if it's 1 hour behind your local time, that's the problem. Correct it to your current local time. Also verify your Time of Use window in SolarMan matches Octopus Go's window (00:30–04:30) exactly. If both are correct and charging still hasn't started, grid charge may be disabled — enable it in Device Settings.
Octopus Agile prices change every 30 minutes and are published by 4pm each day. The simplest approach is to set a conservative window (e.g., 23:00–05:00) that covers most cheaper periods. For advanced optimization, you can manually update your TOU schedule based on the Agile prices each day. We can configure this remotely as part of our tariff setup service, including setting up multiple windows for different patterns.
Not reliably. Many Sunsynk installations require a manual clock adjustment when clocks change in March and October. If your charge window is consistently 1 hour late (e.g., charging starts at 01:30 instead of 00:30), check the inverter clock in SolarMan and adjust it manually to match your local time. This is the #1 cause of Octopus cheap-rate charging failure and the easiest to fix.
A smart meter isn't strictly required for force-charging during cheap-rate windows with Sunsynk, but it helps your system track import and export accurately. Without a smart meter, you may not see real-time grid consumption data in SolarMan, making it harder to verify that charging is happening at the right times. Your installer or STS can check your metering setup during a diagnostic visit and recommend any upgrades needed for optimal performance.
Book

Octopus cheap-rate not working?

Tell us your tariff and what you're seeing. We'll check your SolarMan data and configure your system to work correctly with your Octopus tariff — most cases are fixed in a single session.

  • Not affiliated with Sunsynk Energy
  • Remote TOU configuration from £95
  • Octopus Go, Agile, Intelligent, Flux specialists

By submitting you agree to be contacted about your diagnostic request. We don't share your data with 3rd parties.

Call 07944 877 329 Book free diagnostic