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Solar panel optimisers sit behind each panel and let it produce power independently from the rest of the string. If one panel is shaded or dirty, the others keep working at full output instead of being dragged down. Two brands dominate the UK market: Tigo and SolarEdge.
For most UK homes, Tigo optimisers are the better choice. They work with any existing string or hybrid inverter, cost less per unit, and Tigo’s own data across 105,000 sites in 122 countries shows an average 8.7% energy gain from reclaimed mismatch losses. SolarEdge optimisers only work with SolarEdge inverters but offer tighter integration and SafeDC shutdown.
What is the Best Solar Power Optimiser?
Two manufacturers supply the optimisers you can realistically buy in the UK. They both perform per-panel MPPT but differ on compatibility, monitoring, and built-in safety features. Your inverter brand is often the deciding factor.
Tigo vs SolarEdge: Side-by-Side
| Feature | Tigo TS4-A-O | SolarEdge P505 |
|---|---|---|
| Compatibility | Any inverter | SolarEdge only |
| MPPT | Per-panel | Per-panel |
| Monitoring | Via Tigo CCA + Cloud | Via SolarEdge portal |
| SafeDC/Shutdown | Optional (TS4-A-S model) | Built-in |
| Price per unit | ~£35-50 | ~£40-55 |
| Warranty | 25 years | 25 years |
| Best for | Retrofit, mixed systems | New SolarEdge installs |
Tigo power optimisers
They are small enough to tuck away at the back of a panel, come with clips for secure mounting, and have longer leads that make wiring to the next panel easier.
Positives
Tigo’s global dataset of 105,000 sites across 122 countries shows an average 8.7% energy gain from mismatch loss recovery (Tigo global performance dataset, 2024). Their Photon test results white paper sets out shading improvement data:
| Condition | Improvement | Value |
|---|---|---|
| No shading at all | Increased energy yield | 1.5% – 1.7% |
| Horizontal shade | Energy gain improvement | 20.8% |
| Shade from pole | Energy gain improvement | 9.7% |
| Shading from a tree | Energy gain improvement | Data not provided |
NREL field data on optimisers across UK-style roof conditions shows gains of 3-4.5% under light shading, 15-18% under moderate shading, and 18-22% under heavy shading, compared to a plain string inverter setup.
Works with any inverter: Tigo optimisers sit on the DC string before the inverter, so they work with string, hybrid, or any third-party inverter. This makes them the only practical option when retrofitting optimisers to an existing system.
Negatives
Monitoring hub costs extra: Panel-level monitoring requires purchasing the Tigo CCA hub separately. It costs roughly the same as 4-5 optimisers and is not needed for performance, only for visibility into what each panel is doing.
SolarEdge power optimisers
Small enough to fit behind a solar panel, the P505 comes with pre-wired MC4 connectors and mounting clips, making it straightforward to install on a new system.
Positives
SolarEdge’s PV Performance white paper reports the following improvements compared to a string inverter without optimisers:
| Condition | Improvement | Value |
|---|---|---|
| No shading at all | Increased energy yield | 1.5% – 1.7% |
| Horizontal shade | Energy gain improvement | 34.6% |
| Pole | Energy gain improvement | 9.7% |
| Shading from a tree | Negative effect reduction from 24% | to 9% |
At light, moderate, and heavy shading, a SolarEdge optimiser system improves energy harvest by 1.9%, 5.0%, and 8.4% respectively, compared to a string inverter system without optimisers.
Built-in SafeDC shutdown: SolarEdge optimisers reduce string voltage to a safe level when the inverter is switched off. This is a requirement in some markets and valued by installers for roof safety.
Integrated monitoring: Panel-level data feeds directly into the SolarEdge monitoring portal with no separate hub purchase required.
Negatives
Only works with SolarEdge inverters: SolarEdge optimisers run a proprietary protocol and only work on strings connected to a SolarEdge inverter. They cannot be retrofitted to a system with a different inverter brand.
Reliability
Optimisers add components to each panel, so a fair question is whether the added hardware is a liability. Field data suggests not: optimisers have an early failure rate of around 0.076%, compared to 0.89% for string inverters. Both carry 25-year warranties from Tigo and SolarEdge, which aligns with typical panel lifespans.
What Do Optimisers Add to the Cost?
Fitting optimisers adds roughly £30-50 per panel to the system cost. On a 10-panel install that is £300-500 extra. Whether that pays back depends on how much shading your roof gets. On a fully unshaded south-facing roof the gains are modest (1.5-1.7%). On a partially shaded or awkward roof, the case is much stronger.
Independent Verification
A study by the University of Southern Denmark tested both SolarEdge and Tigo optimisers and found results in line with the manufacturers’ shading claims. The study also notes that optimisers can have a small negative effect in completely uniform conditions, which matches the 1.5-1.7% baseline figures above.
A 2019 paper from the University of Campinas found a general positive effect across all conditions, based on the argument that panels degrade at different rates and thermal inefficiency means even an unshaded string rarely runs at uniform output.
My Take
I used Tigo optimisers on a north-west facing string with intermittent shading.
In my experience, Tigo’s optimisers perform in line with the stated benefits. I cannot speak to their longevity as I have had them since May 2023 and so far they are working well.
Summary
Tigo and SolarEdge are the two realistic options for UK buyers. Tigo’s inverter-independence and lower unit cost make them the default choice for most installs, including retrofits. SolarEdge’s built-in SafeDC and integrated monitoring are useful if you are already buying a SolarEdge inverter. For a broader look at how optimisers fit into a system, see the guide to solar panel optimisers and the inverter comparison.
