Rooftop Solar: Four Times Versus a 400% Increase

Four times the original amount means a 300% increase. A 400% increase means five times the original amount. The distinction matters whenever a story describes rapid growth.

A recent US rooftop-solar report provides a useful reason to check both wording and numbers. EIA's October 16 small-scale solar article uses “quadrupled” in its title but prints endpoints of 18,812 and 92,979 gigawatt-hours (GWh). Those endpoints imply roughly 4.94 times the starting amount, not exactly four times.

Source-check note, October 20: the headline and endpoints do not reconcile exactly. EIA's current Electric Power Monthly table 1.1.A also lists a different, preliminary 2025 total of 93,148 GWh. We keep the published article's arithmetic and the table's separate version distinct below; we cannot establish why they differ. This is an explanation of growth language, not a claim that the discrepancy has been corrected by EIA.

Start with an unambiguous example

Suppose an invented solar system produces 100 units of energy in one period and 400 units in a comparable later period. These are teaching numbers, not a household-output forecast.

The multiple is the new total divided by the old total:

400 ÷ 100 = 4 times.

The increase is only the extra amount: 400 − 100 = 300 units. Divide that increase by the original 100 and multiply by 100:

300 ÷ 100 × 100 = 300%.

Enter 100 as the original value and 400 as the new value in the Percentage Increase Calculator. The result is 300%. The original 100 units are already included in the new total; they are not part of the increase.

Compare the two phrases

To apply a 400% increase, add four copies of the starting amount to the one you already had. That leaves five copies. A useful rule is:

Growth multiple = 1 + percentage increase ÷ 100.

In reverse, subtract one from the multiple and multiply by 100. Avoid ambiguous wording such as “four times more” when “four times as much” or an explicit percentage would be clearer.

Audit the numbers printed in the solar article

Use the Standard Calculator for 92,979 ÷ 18,812: approximately 4.94.

Then use the Percentage Increase Calculator, with original 18812 and new 92979. The result is about 394.25%. These are two descriptions of the same endpoint arithmetic: the final amount is roughly 494.25% of the starting amount, while the increase is about 394.25%.

This calculation alone cannot settle a source-definition or revision question. EIA's annual summary table identifies 18,812 GWh as estimated small-scale photovoltaic generation for 2016. The current monthly table labels 93,148 GWh as its preliminary 2025 total. Using that separate pair gives approximately 4.95 times, or 395.15% growth. Do not silently substitute the monthly number into a quotation of the October 16 article, or imply these are observed full-year 2026 figures.

Keep units and definitions aligned

Both inputs must describe the same quantity in the same units. Gigawatt-hours measure energy generated; gigawatts measure generating capacity. A ratio between energy and capacity would not answer this growth question.

Neither national growth calculation predicts the performance of a particular roof. It also does not estimate household bill savings, export payments, installation payback or avoided emissions. Those questions require additional inputs and an appropriate model.

Try your own growth comparison

Choose two comparable quantities and enter them in the Percentage Increase Calculator. Divide the new quantity by the original in the Standard Calculator as a cross-check. For another distinction between two percentage descriptions, read the EV sales-share example.

All three EIA sources above were checked October 20, 2026. The hero is an original generated illustration of rooftop panels, not evidence of measured output. The unresolved source-version difference remains visible rather than being treated as a verified correction.