# Tides: Correlation Prices it moves with, and why Source page: https://www.materialinsights.org/energy/e_tides/correlation/ Tides are a free, predictable flow driven by the Moon and Sun. Their value depends on the cost of barrages or underwater turbines at the few sites with large tidal ranges or strong streams, such as the Gulf of Khambhat. No public price Tides has no public monthly price series: A free natural flow; no market price, only capture costs. #### What its price moves with Energy [TdP Tidal and ocean-current power](https://www.materialinsights.org/energy/e_tidal_power/)Main converter Tidal barrages and tidal stream turbines turn tides into electricity. High building costs mean only a few plants run, such as La Rance in France and Sihwa in Korea. Output is predictable years ahead. No public price for tidal and ocean-current power, so the link is explained in words only. Commodity [Cem Cement](https://www.materialinsights.org/commodities/cement/)Capture cost Tidal barrages are large concrete dams across estuaries, so cement and construction costs dominate. This is why barrage schemes, including proposals for Gujarat, have stalled on cost. Civil works also take many years to build. Not enough overlapping price history to measure. Commodity [St Steel](https://www.materialinsights.org/commodities/steel/)Capture cost Tidal stream turbines and barrage gates use large steel structures that must resist seawater. Steel prices weigh on the cost of each project. Corrosion protection and regular maintenance at sea add further cost to every steel part. Not enough overlapping price history to measure. Commodity [REE Rare earths](https://www.materialinsights.org/commodities/rare_earths/)Capture cost Many tidal stream turbines use permanent-magnet generators, which need neodymium. Rare earth prices and supply rules affect device costs. China controls most magnet supply, so export rules are a risk for tidal developers. No public price for rare earths, so the link is explained in words only. Energy [HyD Hydropower dams](https://www.materialinsights.org/energy/e_hydro_dams/)Similar technology Tidal barrages use low-head turbines similar to river dams, and draw on the same suppliers. Tides are predictable, unlike river flows, but barrages also harm estuary habitats, as dams do rivers. Not enough overlapping price history to measure. How to read these numbers **Correlation of monthly changes** (the number in the coloured pill) compares how much each price moved, month by month, since 2006 or the first month both series exist. It runs from −1 to +1: near +1 the two usually rise and fall in the same months, near 0 there is no link, and a negative number means they tend to move in opposite directions. Above 0.7 is strong, 0.4 to 0.7 moderate, 0.2 to 0.4 weak. **12-month changes** compare year-on-year moves, which shows whether two prices share the same cycles even when the month-to-month noise differs. **Price function** is a straight-line fit of the two prices on logarithmic scales: price ≈ k × (partner price)^β. β is how much this price moves, in per cent, for a 1% move in the partner over the whole period, and R² is the share of the variation the fit explains. Two prices that both drift up with inflation can fit well without any real link, so read it together with the monthly correlation. **Lead or lag** checks whether the monthly correlation is clearly higher when one price is shifted by 1 to 6 months. Correlation is not cause. The reasons on each card explain the economic link; the numbers show how strongly it has shown up in prices. Proxy series are US producer price indexes or related prices and can blur the real link. Data: World Bank Commodity Price Data (Pink Sheet), October 2026; US Bureau of Labor Statistics producer price indexes, IMF primary commodity prices and US EIA prices via FRED, Federal Reserve Bank of St. Louis, retrieved November 2026. Calculations by this site. ## Other sections - [Summary](https://www.materialinsights.org/energy/e_tides/index.md) - [Overview](https://www.materialinsights.org/energy/e_tides/overview/index.md) - [How energy resides](https://www.materialinsights.org/energy/e_tides/resides/index.md) - [Abundance](https://www.materialinsights.org/energy/e_tides/abundance/index.md) - [Fluctuation in time](https://www.materialinsights.org/energy/e_tides/time/index.md) - [Across the Earth](https://www.materialinsights.org/energy/e_tides/geography/index.md) - [Impact on nature](https://www.materialinsights.org/energy/e_tides/nature/index.md) - [Relationships](https://www.materialinsights.org/energy/e_tides/links/index.md)