The turn of the millennium was an inflection point for renewable energy—geothermal in particular. Assessing the scale and spread of geothermal expansion around 2000, though, is not just a question of output totals or new plant announcements. The underlying data, drawn from ISIC 3510—electric power generation, transmission, and distribution—offers both opportunity and complication. Within this code, geothermal operators are counted alongside coal, hydro, and gas, blurring distinctions that matter if the goal is to track a specific slice of the energy sector.
The process begins, inevitably, with a census of all ISIC 3510-registered firms in the target region. In countries with geothermal potential—think of Iceland, Italy, parts of the United States or the Philippines—the registry may number in the dozens, sometimes more. Some firms are large utilities managing mixed portfolios. Others are smaller companies, often joint ventures, created to develop a single field. The registry by itself, unfortunately, rarely distinguishes a geothermal operator from one focused on fossil or hydropower. That’s where project documentation, regulatory filings, and trade association lists come in, helping to sort firms by their actual generation mix.
The next step involves reviewing plant-level or project-specific records. Environmental permits, energy ministry reports, or sometimes technical conference proceedings often list geothermal plants by name, operator, commissioning year, and installed capacity. In some cases, licensing authorities publish centralized lists of all renewable energy projects, with fuel type included as a category. Where documentation is missing, news archives or local government records occasionally fill in the blanks, but not always. The gaps, for those who notice them, tell a story of their own.
Identifying geothermal capacity additions means tracing when new projects came online—and matching this timeline against the broader trend of sector expansion. Sometimes, capacity jumps are stepwise: a major field is tapped and several megawatts added in one burst. At other times, growth is incremental, reflecting upgrades, refurbishments, or incremental exploration successes.
Integrating thermal gradient data adds another layer. The viability of a geothermal project depends almost entirely on subsurface heat, typically measured as a thermal gradient. National geological surveys or academic research provide maps of high-potential zones. Overlaying the spatial distribution of geothermal plants (or at least their operators) onto these thermal maps reveals patterns of development and, occasionally, missed opportunity. Some projects spring up in the most promising hot spots; others cluster at the edge, their existence a function of land rights, infrastructure access, or regulatory incentive.
The correlation between thermal gradient and capacity additions is rarely as strong as intuition suggests. Political and economic factors intrude. In some regions, the best gradients lie under protected land, or too far from the grid to be profitable. Elsewhere, policy support or a history of oil and gas exploration primes local industries for geothermal investment, even where the thermal gradient is less than ideal. Mapping new capacity against gradient data highlights these mismatches—areas with high thermal potential but little development, and conversely, areas with investment despite only moderate gradients.
Throughout the process, documentation is crucial. Every decision—how firms were identified as geothermal operators, how missing data was interpolated, how spatial overlays were constructed—should be tracked. The reliability of the analysis depends as much on these details as on the data itself. Where records are ambiguous, or capacity figures are disputed, it is sometimes better to flag the uncertainty than to force a tidy summary.
Using ISIC 3510, in combination with thermal and project data, makes it possible to sketch the contours of geothermal expansion at a moment when the sector’s future was far from assured. The lines aren’t always sharp, and some stories slip the net. Still, for those prepared to weave together multiple sources and tolerate a little ambiguity, the pattern of geothermal growth in 2000 can be glimpsed, if not perfectly mapped.