Wind Energy

There is no single minimum wind speed threshold for electricity production from wind turbines, as it depends on the turbine size, design, height, and other factors. However, here are some general guidelines on the minimal wind speeds required:

  • Most commercial scale horizontal axis wind turbines today need average annual wind speeds of at least 6-7 miles per hour (mph) or 10-11 km/h to be viable for electricity generation.
  • Smaller residential vertical axis turbines can start generating power at lower wind speeds of around 5 mph or 8 km/h. But their energy output is still low at this speed.
  • For commercial scale turbines, the cutoff-in speed is around 7-9 mph (11-14 km/h) when they will begin spinning and generating some power. Output is limited at these minimum speeds.
  • The optimal operating range for full power generation is around 15-35 mph (24-56 km/h) for large modern utility-scale wind turbines.
  • Cutoff-out speeds when turbines shut down for safety are usually 55-65 mph (88-105 km/h).
  • For a wind farm to produce a substantial amount of its maximum capacity, average wind speeds need to be closer to the optimal range and have at least 12-13 mph (19-20 km/h) averages.
  • Areas with average annual wind speeds of less than 6-7 mph are generally not suitable sites for wind farms without taller turbines that can capture higher altitude winds.

So while turbines can start generating at lower wind speeds, significantly productive wind energy generation requires careful siting in locations with adequately strong wind resources. Higher turbines can take advantage of faster winds at increased heights.

Is Zanzibar suitable?

Here are some details on average wind speeds in Zanzibar:

  • The average annual wind speed across Zanzibar is approximately 9-10 knots or 10-12 mph (16-19 km/h).
  • Wind speeds are highest during the kaskazi season from December to March when the prevailing wind blows from the northeast. Average wind speeds can reach 15-20 knots (17-23 mph or 28-37 km/h) during this period.
  • The lowest wind speeds occur during the monsoon season from April to early June when wind direction reverses and blows from the southwest. Speeds can drop below 5 knots (6 mph or 9 km/h) on average.
  • Winds pick up again during the kusi season from June to September with averages of 10-15 knots (11-17 mph or 18-28 km/h).
  • The inland areas of the islands tend to have lower wind speeds compared to along the coastlines.
  • The highest average wind speeds are observed in northern and eastern coastal regions which are most exposed to the prevailing winds. Sites like Ras Nungwi see higher consistent wind.
  • Outside of the main cities, much of Zanzibar remains sparsely populated. Offshore winds are less obstructed allowing for harnessing of wind energy.

Summary

So in summary, Zanzibar has modest average wind speeds suitable for small-scale wind turbines, especially in coastal areas and during the windy kaskazi season. Large scale wind farms would require especially windy sites.

Based on the moderate average wind speeds in Zanzibar, there is some potential for wind energy, but it may not be an ideal location for large-scale wind farm development:

  • The annual average wind speeds of 9-12 mph are on the lower end of what is considered economically viable for utility-scale wind power. The minimum is usually around 10-11 mph.
  • However, wind speeds do reach optimal generation levels for periods during the kaskazi and kusi seasonal winds. Target speeds are around 15-35 mph for most large turbines.
  • Smaller scale wind development using smaller turbines that can operate at lower wind speeds may be more feasible across more areas of Zanzibar.
  • The offshore winds are likely stronger than onshore and could support offshore wind farms. But offshore development costs are higher.
  • Being an archipelago, the land area is constrained, further limiting onshore wind farm potential. And competing land uses like tourism and agriculture reduce suitable open sites.
  • Interconnection to transmit wind power from Zanzibar to mainland Tanzania may be challenging and costly. Local demand may not be enough to justify large projects.
  • Wind project permits and policy frameworks are still emerging in Tanzania, adding development uncertainty.

So in summary, while Zanzibar has wind resources that could be harnessed in a limited capacity, it is not an ideal wind power location compared to sites with stronger and more consistent wind speeds. Smaller distributed wind development is likely a better fit than major utility-scale wind farms for Zanzibar.