Most of the water calculations are based on a standardized temperature of 20.2 C or 68.4 F. Most water sources applicable to these small turbines run much colder. As water temperature decreases is becomes somewhat thicker. Its velocity decreases and results in a lower flow rate. There is an ugly formulae for figuring the flow rate decrease but it works out to be very close to the fluidity index if taken as a percentage. We get some of the power potential back with an increase in density. There is an intimidating calculus equation for this one. For mechanical power estimates this is adequate. Hydro-electric turbines however have an alternator attached that has a non-linear torque/output curve. The last column in the table shows what the expected power estimate should be as a percentage based on my own observations and experience on my own products as well as others.
| Water temperature | Flow rate % | Turbine | |
|---|---|---|---|
| Temp C | Temp F | Fluidity Index | Power estimate |
| 0 | 32 | 55.8 | 50% |
| 1 | 33.8 | 57.76 | |
| 2 | 35.6 | 59.78 | 60% |
| 3 | 37.4 | 61.76 | |
| 4 | 39.2 | 63.8 | |
| 5 | 41 | 65.84 | 70% |
| 6 | 42.8 | 67.9 | |
| 7 | 44.6 | 70.01 | |
| 8 | 46.4 | 72.15 | 80% |
| 9 | 48.2 | 74.28 | |
| 10 | 50 | 76.47 | 85% |
| 11 | 51.8 | 78.64 | |
| 12 | 53.6 | 80.89 | |
| 13 | 55.4 | 83.14 | 90% |
| 14 | 57.2 | 85.4 | |
| 15 | 59 | 87.69 | |
| 16 | 60.8 | 90 | 95% |
| 17 | 62.6 | 92.35 | |
| 18 | 64.4 | 94.71 | |
| 19 | 66.2 | 97.1 | |
| 20 | 68 | 99.5 | 100% |
| 21 | 69.8 | 101.94 | |
| 22 | 71.6 | 104.4 | |
| 23 | 73.4 | 106.86 | |
| 24 | 75.2 | 109.38 | |
| 25 | 77 | 111.91 | |
| 30 | 86 | 124.89 | 110% |
| 35 | 95 | 138.4 | |
| 40 | 104 | 152.45 | |
| 45 | 113 | 167 | 120% |