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Free Solar PV Calculators, Design Tools and Software

Updated: January 2024. Below is a list of free solar calculators that can be used in the design of solar PV systems. These calculators are free to use or download, all excellent resources for anyone looking to install or understand more about solar PV systems.

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UK Solar Radiation Map

Solar PV Output Estimate

PVGIS Estimation Utility

The PVGIS Estimation Utility is a great way to understand a proposed solar PV system's relationship with the sun based on it's location. If you have an understanding of this relationship as well as the access to the historical solar radiation data for your location that the PVGIS provides, you can prepare power output estimates (kWhrs), optimise system designs and have a very good idea of how a solar PV system will perform at a given location before a solar PV system is commissioned.

Using this utility will give you the basic information needed to work out (1) the optimum pitch of a solar PV array based on it's location and height above sea level, (2) the amount of solar radiation available to a given location and (3) an estimated power output figure for the proposed solar PV system. Understanding the movement of the sun over a solar PV installation site is key to optimising the performance and power generation of a PV system, the PVGIS is a great tool to use for this.


This tool underestimates the efficiency of modern solar panels and overestimates (default settings) the power losses that we would expect from a well designed solar PV array. That said, when used as a tool to really understand what's going on between a solar PV array, it's location and the sun, it's superb.


SMA Logo Sunny Design - Solar PV Calculator

SMA Sunny Design

SMA is the world's leading manufacturer of solar PV inverters and solar PV monitoring systems. SMA's Sunny Design software is a free to download and an incredibly powerful solar PV calculation tool.

SMA Sunny Design software generates detailed .pdf reports based on simple inputs such as the number and type of panels used in the design, the basic location details, the aspect i.e. (N, S, E, W) and the roof pitch. The software also helps in cable size calculations to minimise power losses.

A nice feature we have found when using this software is the ability to directly compare the performance of different solar panel types, makes and models directly against the details of the solar PV installation site. Most solar PV manufacturers panels and modules are already listed in the SMA Sunny Design database, you also have the option to input your own solar PV module data.


Only applicable to solar PV systems that use SMA solar inverters. Location details are quite general, the design will be based on the solar radiation data available for the nearest large town to the installation site.


Fronius Solar-creator - Solar PV Design Calculator

Fronius Solar-creator

Fronius have been manufaturing high quality solar inverters in Austria since 1992. Fronius' Solar-creator is a free online configuration tool.


Only applicable to solar PV systems that use Fronius solar inverters.

Link: Fronius Solar-creator

Renusol Solar Configuratoresign Tool - Solar PV D

Renusol PV Configurator 3

Renusol have been manufacturiring solar PV mounting systems in Cologne, Germany since 1997. The Renusol PV configurator is an excellent online configuration tool that allows the user to produce very detailed information and measurements when modelling mounting solar panels in a variety of different conditions.


Only applicable to solar PV systems using Renusol mounting equipment.

Link: Renusol PV Configurator 3

SolarEdge Designer - Solar PV Design Tool

SolarEdge Designer

The SolarEdge Designer is an impressive tool using the latest technology to optimise the design and components of a PV system. The designer includes electrical calculations and accurate environmental information.


Only applicable to solar PV systems using SolarEdge solar inverters and optimisers.

Link: SolarEdge Designer

Schletter Solar PV Mounting Design Calculation Tool

The Schletter Configurator v3

The Schletter Group is a global leader in photovoltaic mounting, manufacturing mounting systems for roofs, fa├žades and solar parks. The downloadable configurator has very detailed structural analysis capabilities enabling detailed loading assesment and verification.


Only applicable to solar PV systems using Schletter mounting equipment.

Link: The Schletter Configurator v3

In Balance Energy 16 x Solar PV Panels On Roof Landscape

In Balance Energy - Solar PV System Sizing & Yield Calculator

Our very own calculator for working out roof layouts, solar panel numbers and system sizing. Low tech, but hopefully useful, quick and worthy of being on the list.

This calculator will help you to quickly work out how many large (60 cell) solar panels could fit onto a roofspace if the basic roof measurments (length x width) are known. Figures are also provided for power outputs (kWhrs) based on MCS irradiance datasets.


Will not give 100% accurate measurements for all large solar panels which come in a range of sizes. Unable to design non square PV arrays, for example when mounting solar panels on gable ends.

URL: solar_panels_pv_calculator.html

In Balance Energy Flat Roof Solar Panel Mounting

In Balance Energy - Flat Roof Solar PV Array Spacing / Shade Calculator

Another one of our awesome solar calculators, this one is for working out the minimum spacing between panel rows for solar panels mounted on flat roofs.

This calculator takes into account the shading found when mounting solar panels at different pitches and at different lattitudes. We have assumed that no shading on the panels is acceptable i.e no self shading even at the winter solstice, this would be a particularly important consideration for off-grid systems or any other solar PV systems using batteries.

URL: lambda_row_spacing_calculator.html

Free Solar PV Design Tools and Software

The design tools and software listed below are free general tools that also lend themselves nicely to be used as solar PV system design tools.

Carbide Depot Logo

Carbide Depot Trigonometry Calculator

We have been using this simple but effective free web tool for years. Always available with no annoying ads. Perfect for quickly working out roof measurements and roof pitches. Carbide Depot have also built a length, area conversion tool and loads of other calculators and tools to use when working with metal.


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Mains/Grid Isolation and Surge Protection

Mains/AC Surge Protection Solar PV Systems

A whole house surge protector is installed to provide protection from transient overvoltages originating from the mains/grid. A whole house surge protector is installed directly inline and as close as possible to the incoming mains/grid supply meter, this allows for surge protection for all circuits and equipment including solar inverters, routers, stereos and other sensitive electrical equipment within the network. The addition of a 100Amp lockable isolator also allows for safe and convenient isolation of all electrical equipment within the network including consumer units, solar inverters, battery storage units and EV chargers from the mains/grid in one place.

Surge protectors are in compliance with the recently updated 18th edition amendment 2 of BS7671.

Mains/Grid Isolation and Surge Protection


Solar PV Surge Protection (DC Surge Protection)

DC Surge Protection Solar PV Systems

DC surge protection devices (SPDs) are installed between the solar panels and the solar inverter to protect both the solar inverter and the downstream electrical equipment from transient overvoltages of an atmospheric origin impacting the electrical system via the DC side of the system / the solar panels.

DC Surge protectors are in compliance with the recently updated 18th edition amendment 2 of BS7671.

Solar PV Surge Protection (DC Surge Protection)

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Articles: Further Information, Calculators & Solar Inverter Fault Codes

Lots of articles, calculators and technical information including links for further reading. Covering a range of topics related to the installation and maintenance of solar photovoltaic and electrical systems in the UK.

/Solar PV Information Articles

Engineering Recommendation G98

Grid Connections for Micro-Generators including Solar PV Systems and Elecricity Storage Systems in the UK. Under 16Amps Per Phase, grid synchronised.

How to provide power to a house using a portable generator

In this article we show you how to power your home using a portable diesel, petrol or LPG generator. We look at changeover switches, the importance of earthing, generator loadings, how to isolate non essential loads. We ask where to locate the generator when it's in operation, how best to safely isolate the grid mains power supply and switch to a generator supply.

Ground Faults, Isolation (ISO) Faults, RISO Low Faults and Insulation Resistance Faults with Solar PV Systems

After a number of years exposed to wind, rain, snow, ice and sometimes animals; solar panel systems can start to develop faults. The most common faults we find related to exposure are ground faults, isolation (ISO) faults, RISO low faults and insulation resistance faults. In this article we take a look at what these faults are, the possible causes and what steps are taken to identify and resolve them.

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We are located in Wanborough, very close to Swindon in Wiltshire, Southern England, UK. From here we service clients within a 90 minute driving radius including the towns, cities and regions below:

Swindon: Abingdon, Aldbourne, Amesbury, Andover, Banbury, Basingstoke, Bath, Berkshire, Bicester, Blunsdon, Box, Bracknell, Bradford on Avon, Bridgwater, Bristol, Buckingham, Burford, Burnham on Sea, Calne, Camberley, Cardiff, Carterton, Cheltenham, Chippenham, Chipping Norton, Chipping Sodbury, Cirencester, Corsham, Cricklade, Devizes, Didcot, Evesham, Eynsham, Faringdon, Frome, Fleet, Glastonbury, Gloucester, Gloucestershire, Hampshire, Henley-on-Thames, Highclere, Highworth, Hook, Hungerford, Keynsham, Kingsclere, Lambourn, Lechlade, Ledbury, Ludgershall, Lyneham, Maidenhead, Malmesbury, Marlborough, Marshfield, Melksham, Minety, Newbury, Newport, Oxford, Oxfordshire, Pewsey, Purton, Ramsbury, Reading, Ross on Wye, Royal Wootton Bassett, Salisbury, Shaftesbury, Shalbourne, Slough, Southampton, Stow, Stratford upon Avon, Stroud, Swindon, Tewkesbury, Thatcham, Tidworth, Trowbridge, Wanborough, Wantage, Warminster, Weston Super Mare, Wiltshire, Winchester, Windsor, Witney, Wokingham, Worcester, Wroughton and Yate.

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