What’s worth buying long-term?
Enter offer prices for up to ten modules and see which set produces the most energy at the lowest price - accounting for degradation, operating temperature and installation type. In seconds, with no sign-up.
- 1 Add modulesUp to ten panels from the database, each with its offer price
- 2 Set conditionsCurrency, cell temperature, installation type
- 3 Read the resultLCOE, lifetime energy and a shareable PDF
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Add at least two panels to compare, or load the worked example back.
The result
Panel watts times the installation baseline, times a temperature factor from the module’s own coefficient, times what degradation has left. Each module degrades on its own datasheet curve where the manufacturer publishes one, and on the 2% / 0.55% convention where it does not.
Those thirty annual figures added up - kilowatt-hours one module produces over the analysis horizon. Higher is better, and it is the half of the answer price alone cannot tell you.
Offer price divided by lifetime energy gives cost per kilowatt-hour. The 0-100 score weights lifetime energy at 45%, cost per kWh at 40% and warranty length at 15%, normalised across the set you entered.
What this does not model. Energy price inflation, inverter and installation cost, local irradiance variation, shading, or degradation warranties that differ from the datasheet curve. It compares modules against each other, not a full system business case. Talk to an installer before you buy.
Questions
Levelised cost of energy is what one kilowatt-hour ends up costing you over the module's life: the offer price divided by every kilowatt-hour that module produces in thirty years.
It is the only number that lets a more expensive panel win - and often it does. A module 20% dearer that produces 30% more energy is the cheaper purchase. Sticker price answers what you pay today; cost per kWh answers what you get for it.
Accurate enough to rank modules against each other, not to predict your electricity bill.
Degradation comes from each module's own datasheet where we have it - it is one of the things that separates two panels, so we do not average it away. Where a manufacturer publishes no curve we fall back to the industry convention: 2% in year one, 0.55% every year after. Annual yield comes from an installation-type baseline unless you override it.
Not modelled: irradiance variation, shading, inverter losses, energy price inflation. Two modules simulated under identical assumptions can be compared; the absolute kWh figure is an estimate.
A module is rated at 25 °C, and a working roof sits 20 to 50 °C above the air temperature. Every degree above 25 costs you the module's temperature coefficient in output.
Typical values run from -0.26 %/°C (excellent) to -0.34 %/°C (poor). At 55 °C that is the difference between losing 7.8% and 10.2% of rated output - every hour the sun is up, for thirty years.
Over that horizon the gap between two otherwise similar panels is usually worth more than the price difference between them.
A 0-100 composite, weighted: lifetime energy at 45%, cost per kWh at 40%, warranty length at 15%.
Each input is normalised across the modules you entered - so the score is relative to your own set, not to the whole database. Adding a cheaper module moves everyone else's score down. Where every module in the set shares a warranty length, that dimension separates nothing and splits evenly.
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We do not store your prices against any identity, and the calculator carries no affiliate links - nobody pays us to rank their module higher.