What size inverter do I need for my solar panels?

The inverter should typically be sized at 90-100% of the array DC rating. For a 4 kWp array, a 3.6-4.0 kW inverter is appropriate. Slight undersizing (DC:AC ratio of 1.1:1) is acceptable and cost-effective as panels rarely reach full rated output in UK conditions.

What is the difference between string and micro inverters?

String inverters connect panels in series and convert DC to AC centrally (one unit for the whole array). Microinverters are fitted to each panel individually. Micros perform better with shading as each panel operates independently, but cost more. String inverters are cheaper for unshaded arrays.

Should I get a hybrid inverter?

A hybrid inverter can manage both solar panels and battery storage. If you plan to add a battery within 2-3 years, installing a hybrid inverter now avoids the cost of replacing the inverter later. They cost 60-80% more than string inverters but save on future retrofit costs.

How long do solar inverters last?

String and hybrid inverters typically last 10-15 years with a standard 5-10 year warranty (extendable to 15-20 years). Microinverters often have 20-25 year warranties. Most homeowners will replace a string inverter once during the 25+ year life of their solar panels.

What is a power optimiser?

Power optimisers are DC-DC converters fitted to each panel that maximise individual panel output before feeding a string inverter. They offer similar shading benefits to microinverters but at lower cost. Systems like SolarEdge use this approach. They add about 40% to inverter system cost.

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Solar PV Inverter Calculator

Size and select the right inverter for your solar PV array. Compare string, hybrid, microinverters and optimisers with DC:AC ratio and cost estimates.

Array Size

Total DC capacity of panels

Inverter TypeString is cheapest, hybrid for battery

Electrical PhaseMost UK homes are single phase

Number of Strings

Panel strings (roof faces)

Price per Inverter

String inverter base cost

How We Calculate This

This calculator sizes solar PV inverters based on array capacity and installation requirements.

The formula

Inverter size = Array kWp × 0.95 (DC:AC ratio ~1.05:1)

DC:AC ratio: 1.0-1.2 is typical (slight oversizing of array is OK)
Single phase: up to ~5 kW per inverter
Three phase: up to ~10 kW per inverter (or 3 x single phase)
Microinverters: one per panel (250-500W each)

Frequently Asked Questions

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Last updated: March 2026

All calculations are estimates. Verify with your supplier.