Technology
Power Optimisers
Per-panel DC electronics that keep conversion in one accessible box: the middle option between string and micro.
What a power optimiser is
A small sealed DC-DC converter that clips to the mounting rail behind a panel, with the panel’s leads going into it and its output joining the string. It does not convert DC to AC. That still happens in the central inverter, which stays in the loft or garage where it can be reached.
The optimiser’s job is to break the tyranny of the series string.
The problem it solves
Panels in a string are wired in series, so the same current flows through all of them. A shaded panel can only pass a reduced current, and that limits every panel behind it. Bypass diodes and half-cut cell construction soften this, but a shaded module still costs the string more than its own share of the roof.
An optimiser sits between its panel and the string and converts. It runs its own Maximum Power Point Tracker — continuously adjusting the voltage it draws from its panel to find the point where voltage multiplied by current is greatest — then delivers that power into the string at whatever voltage and current the string needs. The panel operates at its own optimum; the string operates at the inverter’s optimum. Neither has to compromise for the other.
That is the whole mechanism, and it explains precisely what optimisers do and do not achieve. They recover losses caused by panels differing from each other. They do not increase the light falling on the roof.
Where it is the right choice
Partial shading on an otherwise conventional roof: a chimney, a flue, a dormer cheek, a neighbour’s tree. Roofs where a small group of panels sits at a different pitch or orientation and there are not enough inverter trackers to separate them. Systems where the owner wants panel-level monitoring but not the cost of microinverters. Existing systems where shading was underestimated at the original design and a targeted retrofit is cheaper than a rebuild.
Where it is not
An unobstructed roof with a single orientation. There, every panel already operates at nearly the same point and there is no mismatch to recover. Optimisers add cost, add connections, and add devices under the array for no measurable gain. We will say so rather than include them by default.
Severely fragmented arrays across many orientations, or a requirement for no DC on the roof, point toward microinverters instead.
Installation implications
Each optimiser mounts on the rail and is connected before its panel is set down. Each adds two connections on the roof, and the quality of that connector work is what decides whether the array behaves in five years. Access matters for the same reason it does with microinverters: a failed optimiser is under a panel, and reaching it on a two-storey house is a scaffolding job.
Where the optimiser family requires a matched inverter, that pairing becomes a long-term commitment. It is worth knowing at the point of quotation, because it narrows the options when the inverter eventually needs replacing.
Specification, warranty and cost
Check three things: whether the optimisers must be fitted to every panel on the string or only to selected ones, whether a specific inverter is required, and what the shutdown behaviour is when the inverter powers down.
Optimiser warranty terms are usually longer than inverter warranty terms and differ by manufacturer. Read whether the cover extends to the labour and access needed to replace a roof-level unit, since that is often the larger part of the cost.
On price, optimisers sit between a plain string system and a microinverter system. Fitted selectively where shading actually occurs, they are frequently the best value answer to a difficult roof. Your written quotation will show the number fitted, where they go and what they add, so the decision is visible rather than bundled.
Specification considerations
These are the figures worth comparing when you are reading a quotation. The exact values for the products specified for your installation come from the manufacturer's current datasheet and are stated in your written quotation.
| What to look at | Why it matters |
|---|---|
| Function | A DC-DC converter fitted behind each panel, allowing that panel to operate independently within a string |
| Conversion point | DC to AC conversion stays in the central inverter; the optimiser only conditions DC |
| Tracking | Panel-level maximum power point tracking, with the string held at a fixed voltage by the inverter |
| Inverter pairing | Some optimisers require a matched inverter from the same manufacturer; others work with a range of units |
| Safety function | Most reduce panel voltage to a low level when the inverter shuts down, lowering DC voltage on the roof |
| Monitoring | Panel-level generation data, showing which module is underperforming |
| Retrofit | Can often be added to selected panels on an existing array rather than the whole roof |
Where it works, and where it does not
Strengths
- Recovers most of the output a string loses to partial shading, at lower cost than microinverters
- Conversion electronics stay in one accessible unit, so the most failure-prone part is not on the roof
- Panel-level monitoring identifies a failing or soiled module without a site visit
- Can be fitted only to the panels that are actually affected, rather than to the whole array
- Rapid shutdown behaviour reduces DC voltage on the roof when the inverter is off
Limitations
- Adds a device behind every fitted panel, each with connections that must be made and weathered properly
- Costs more than a plain string inverter and buys nothing on an unshaded roof
- Some systems tie you to a specific inverter manufacturer, limiting future replacement choices
- A failed optimiser is under a panel, so replacement needs roof access even though the inverter does not
- Does not remove the single point of failure — the central inverter still takes the whole array down if it fails
This page covers one component. For how the whole thing fits together, see solar panels and battery storage.
Common questions
Do I need optimisers on every panel?
Usually not. Optimisers earn their cost on the panels that actually behave differently from their neighbours — the ones under a chimney shadow, on a lower course near a parapet, or at a different pitch. Fitting them to a whole unshaded array is a common way of adding cost without adding generation. Some manufacturers require all-or-nothing on a string, which is a genuine constraint, but where selective fitting is permitted we design it that way.
Optimisers or microinverters?
Optimisers keep the expensive conversion electronics in one accessible box and cost less; microinverters give full per-panel AC independence and no DC on the roof, and cost more. For moderate shading on an otherwise conventional roof, optimisers are usually the better value. For heavily fragmented arrays, or where DC on the roof is unacceptable, microinverters make more sense.
Can optimisers be added to a system I already have?
Sometimes. It depends on whether your existing inverter is compatible, and some optimiser families require a matched inverter. Where it works it is a targeted fix — add devices to the affected panels rather than rebuild the array. Where it does not, we would look at whether the shading is better addressed by restringing or by an inverter change. That assessment starts with reading the actual generation data.
Will optimisers fix a north-facing roof?
No. Optimisers recover losses caused by mismatch between panels. They do not create light. A north slope receives substantially less irradiance across the year, and no electronics change that. What optimisers do fix is a good roof partly spoiled by a shadow, or two orientations that would otherwise fight each other on one tracker.
Related services
- Solar panel installationSurvey, design, roof works, electrical works and commissioning for a domestic solar PV system.
- System monitoring and optimisationGetting proper data out of a system, then changing its settings so it earns more from the same hardware.
- Solar health checkA one-off independent assessment of an existing system, with a written report on its condition and performance.
- Solar panel repairsFault diagnosis and repair on arrays that have stopped working, or never quite worked properly.
The technology behind it
- InvertersWhat the inverter does, how MPPT works, and how the four architectures compare honestly against each other.
- String invertersThe conventional central inverter: how strings are designed, where it is the best value, and where it is the wrong choice.
- MicroinvertersOne inverter per panel mounted on the roof: what per-panel conversion buys, and what it costs.
- Monitoring systemsWhat generation, consumption and battery data actually tells you, and what a system needs fitted to produce it.
- Solar panelsWhat a domestic solar panel is, how it is built, and which specifications on the datasheet actually matter.
Property and roof guides
- North-facing and shaded roofsSometimes the answer is no. Where it is not, per-panel electronics, a different roof, an outbuilding or a ground mount.
- East-west roofsLess annual total than south, a flatter daily curve, higher self-consumption — and a design that pairs naturally with storage.
- Victorian terracesNarrow slate slopes, party walls, rear back-additions and scaffolding through a shared alley — terraced solar on its own terms.
- 1920 to 1965 homesInterwar and early post-war housing: hipped roofs, clay and early concrete tile, central chimneys and modest incoming supplies.
See it on a real installation
Further reading
- Roof orientation and shadingHow aspect, pitch and obstructions change what a roof can produce, and what can be done about shading.
- String inverter vs microinvertersHow central and module-level conversion differ in shading tolerance, servicing, monitoring and failure behaviour.
- Signs your solar system is underperformingHow to tell a genuine fault from normal seasonal variation, and the checks worth doing before calling anyone out.
Where we work
Information reviewed on 2026-08-23.
Not sure which specification suits your roof?
We design around the property rather than fitting the same system to every house. Tell us the postcode and we will explain what we would specify and why.
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