Solar Inverters: String, Micro & Optimisers Explained

It depends entirely on your roof. For a simple, unshaded south-facing roof, a quality string inverter from Fronius, SMA, or Solis is the best value solution — there is no point paying for optimisers when your panels all operate at the same irradiance. For roofs with multiple aspects (common in our service area), partial shading from chimneys or trees, or east-west flat roof configurations, we recommend Sigenergy with P-series optimisers. Enphase microinverters are reserved for the most complex installations where panel-level independence genuinely matters.

A standard string inverter carries a 5–10 year warranty and can realistically last 12–15 years with good maintenance. This means most homeowners will need at least one inverter replacement in a 25-year system life, costing approximately £600–£1,500 including labour. Sigenergy optimisers and Enphase microinverters carry 25-year warranties and should last the full system life without replacement — partly offsetting their higher upfront cost.

MPPT (Maximum Power Point Tracking) is the algorithm an inverter uses to extract the maximum power from your solar panels at any given moment. Every solar cell has an optimal voltage and current combination that produces peak power — this varies continuously with temperature, light intensity, and shading. A string inverter uses one MPPT channel for a string of panels, so shading one panel drags down the others. Optimisers and microinverters give each panel its own MPPT, eliminating this effect.

Yes, but the method varies. Hybrid inverters (like the Sigenergy AIO or Sigenergy Home Hub) combine the solar inverter and battery inverter in one unit — the cleanest and most integrated solution for new installations. Alternatively, an AC-coupled battery (like the Tesla Powerwall or Sonnen) connects on the AC side of your existing inverter and works with any inverter type. For advice on the best configuration for your existing system, see our retrofit battery guide.

Both are excellent, professional-grade inverters used by quality installers worldwide. The distinction is really about whether you need panel-level optimisation. Fronius (and SMA, Solis) make excellent string inverters for straightforward installations. Sigenergy bundles its inverter with the P-series optimiser ecosystem — if your roof would benefit from panel-level MPPT, Sigenergy is the clear choice. If your roof is unshaded and single-aspect, a Fronius Primo or GEN24 offers comparable performance at lower cost.