Solar Arrays Guide

A solar array is simply a collection of solar panels working together as a single system. Whether it’s 10 panels on a domestic roof or 10,000 panels on a commercial site, the fundamental principles of how they’re wired, how the inverter handles their output, and how shading affects performance all follow the same rules. Understanding how a solar array works helps you make better decisions about system design, inverter choice, and shading mitigation.

This guide covers the fundamentals of solar array design: series and parallel wiring, string inverters versus microinverters and power optimisers, and the considerations that differ between residential and commercial arrays in the UK.

Key Takeaways

• A solar array is a group of solar panels connected together and wired to an inverter, it’s the complete panel installation, not a single panel.
• Panels connected in series increase voltage; panels connected in parallel increase current. String inverters require series-connected strings within specific voltage windows.
• Shading one panel in a series string reduces the output of the entire string, not just that panel, this is the key limitation of string inverter systems.
• Microinverters and power optimisers mitigate shading losses by enabling panel-level maximum power point tracking.
• Most residential UK arrays use string inverters, which are cost-effective and reliable for unshaded or lightly shaded roofs.
• Commercial arrays above 3.68kW per phase require a G99 DNO notification; above 50MW they require a Development Consent Order.

What Is a Solar Array?

The term “solar array” refers to the complete assembly of solar panels in an installation. A single panel is just a panel; connect several panels together, wire them to an inverter, and you have an array. The inverter converts the DC electricity generated by the array into usable 230V AC electricity.

Array sizes are described in kilowatt-peak (kWp), the total rated power of all the panels at standard test conditions. A domestic array might be 4kWp (10 × 400W panels). A commercial array might be 100kWp, 500kWp, or more. The configuration of how the panels connect within that array, in series, in parallel, or a combination, affects the voltage and current the inverter must handle, and has significant implications for how the system behaves under partial shading.

Series vs Parallel Wiring

Solar panels can be connected in series (positive terminal of one panel to negative terminal of the next) or in parallel (all positive terminals together, all negative terminals together). The electrical effect is quite different.

In a series connection, voltages add up while current stays the same. Connect 10 panels each rated at 40V open-circuit voltage in series, and the string voltage is 400V. This high voltage allows thin, long cable runs with low resistive losses, which is why string inverters, which accept high-voltage DC input, are efficient for long cable runs from a large roof to a central inverter.

In a parallel connection, currents add up while voltage stays the same. Connect the same 10 panels in parallel and the current is 10 times that of a single panel, but the voltage remains at 40V. High current requires thicker, more expensive cable to manage safely and efficiently, parallel connections are used within microinverter or optimiser systems at the panel level but are less common for connecting large groups of panels to a single inverter.

Most residential string inverter systems use a combination: panels are connected in series to form “strings” (typically 8 to 14 panels per string depending on panel and inverter voltage specifications), and multiple strings are connected in parallel at the inverter’s DC input. This gives a manageable voltage (typically 600 to 800V for residential inverters) while allowing larger arrays than a single string would support.

The Shading Problem in Series Strings

The most important practical implication of series wiring is how shading affects performance. In a series circuit, current must be the same throughout the circuit. If one panel is shaded and its current output drops, the entire string is limited to that panel’s reduced current, not just the shaded panel.

In practice, a single panel at 50% output due to shading can reduce the entire string’s output by 50% or more, depending on the inverter’s MPPT (Maximum Power Point Tracking) response. On a roof with even mild shading, a chimney stack casting a shadow across two panels for a few hours each day, the energy loss from a string inverter system can be 10 to 20% of annual generation, much more than many homeowners expect.

Microinverters: Panel-Level Conversion

Microinverters address the shading problem by placing a small inverter on each panel rather than a single large inverter for the entire array. Each panel’s DC output is independently converted to AC at the panel itself. Because there’s no series string, shading on one panel doesn’t affect any other panel, each operates independently at its own optimum.

The advantages are significant for shaded roofs: annual generation loss from shading is limited to the shaded panels only. Microinverters also provide panel-level monitoring, making it easy to identify a single underperforming panel. And because the system outputs AC from each panel, DC cable runs are minimal, a safety advantage as there’s no high-voltage DC wiring on the roof.

The disadvantage is cost: microinverters cost more per watt than string inverters, and with one unit per panel there are more potential points of failure. For unshaded roofs, the additional cost of microinverters is hard to justify in financial terms alone, a string inverter delivers comparable performance at lower cost. Enphase is the dominant microinverter brand in the UK market.

Power Optimisers: A Middle Ground

Power optimisers (such as those made by SolarEdge or Tigo) sit behind each panel and perform DC-to-DC optimisation, allowing each panel to operate at its individual MPPT operating point regardless of what other panels in the string are doing. The panels are still wired in series to a conventional string inverter, but the optimisers decouple individual panel performance so that shading on one panel doesn’t pull down the whole string.

Power optimiser systems are typically cheaper than full microinverter systems but more expensive than plain string inverters. They’re a good choice for roofs with moderate shading or complex shapes requiring panels on different pitches or orientations within the same array. SolarEdge inverters are designed specifically to work with their HD-Wave optimisers and offer sophisticated monitoring at the panel level.

Residential vs Commercial Arrays

Domestic solar arrays in the UK are typically 3 to 6kWp, sized to match the household’s daytime electricity consumption and available south-facing roof area. They use single-phase string inverters, connect to the domestic electricity supply, and require a G98 DNO notification (for systems up to 3.68kW) or G99 DNO approval (for systems above 3.68kW).

Commercial arrays range from 10kWp on a small retail premises to hundreds or even thousands of kilowatts on industrial buildings and solar farms. Commercial installations typically use three-phase inverters, require G99 DNO approval (and sometimes detailed grid studies for large systems), and must comply with additional Health and Safety requirements for working at height, electrical safety, and fire risk management. Full Expensing capital allowances allow UK businesses to deduct the full cost of commercial solar in the year of purchase, a significant financial incentive.

Expert Insights From Our Solar Panel Installers

One of our senior solar panel installers with over 15 years of experience in residential and commercial solar commented: “For a clean south-facing roof with no shading, a plain string inverter is almost always the right choice, it’s cost-effective, reliable, and the technology has been proven for 25+ years. Where we recommend optimisers is when there’s genuine complexity: multiple roof planes, a chimney causing seasonal shading, or a customer who wants panel-level monitoring for peace of mind. Microinverters make sense for genuinely difficult shading scenarios or where the DC cable safety aspect of no high-voltage rooftop wiring is a specific priority.”

Frequently Asked Questions

Summing Up

Understanding how a solar array is configured, series strings, MPPT, and the role of the inverter, helps you make better decisions when commissioning a new installation or troubleshooting an existing one. For most unshaded UK roofs, a string inverter with series-connected panels is the cost-effective standard. Where shading, complex roof shapes, or multiple orientations create challenges, power optimisers or microinverters provide meaningful generation improvements. Our MCS-certified installation team can assess your roof, advise on the right configuration for your specific situation, and provide a free, no-obligation quote.

Updated April 2026