Project Details

Power Calculations:

                                                     P= hv’gµ

• P= Power, watts, W
• h = Head, metres, m
• v’= volume flow rate, metre cubed per sec, m³/s
• g = gravity, metres per second per second m/s²
• µ = efficiency factor

The head was initially thought to be 25m from map contours, but a more simple approach revealed it to be 8.3m by simply using a measured length and repeating uphill.

v’, or the volume flow rate is indeed critical to the success of the project. The flow rate has been measured at 10-20L/s in summer, but more than 50L/s+ after rainfall and more commonly available in winter (via a timed bucket fill method). This is a crude measure but is fairly accurate under low flow conditions, under high flow conditions it is more difficult as it is nearly impossible to concentrate the whole of burn flow into a bucket. So the high flow measure there is by simply estimating the doubling or trebling in flow. Which was easier to read at the pond for cold water supply at the proposed 25m head inlet.

		km2	m2
Catchment area		1.6	1600000
Rainfall		1.5	m
Volume of rainfall in catchment		2400000	m3
Losses	10%	240000
Annual Flow		2160000	m3
Daily Flow		5918	m3/day
Flow / Hour		247	m3/hour
Flow/sec		0.07	m3/sec

The other method to calculate flowrate is to work back from the catchment area, as summarised in the above table which gives a flowrate of 70L/s. This is based on an annual rainfall of 1500mm which is likely in this area[i]. However the nature of rainfall in Scotland is that it will rain heavily for short periods and so the flow rate is likely to range from as low as 10L/s on after a dry summer spell to possible up to 100L/s after days of heavy rain. This was also backed up by looking at sepa flow data for local rivers.

• To conclude in winter the flowrate is likely to be in the order of 40L/s average, whereas in summer the average will be nearer 20L/s.

Power Generation:

Hydro¹

• Units: Metric
• Flow: 15.0 lps
• Used Flow: 10.4 lps
• Pipe Head: 8.5 m
• Pipe Length: 120 m
• Pipe Efficiency: 90 %
• Pipe Diameter: 110 mm (This value was locked and may not have been the diameter recommended by the calculator)
• Number of Powerspouts: 1 (This value was locked and may not have been the number recommended by the calculator)
• Nozzles: 2
• JetDiameter: 23.7 mm
• ActualPipeEfficiency: 84 %
• Speed: 442 rpm
• Output: 365 W
• TotalOutput: 365 W

Electrical[2]

• OuputVoltage: 351 V
• CableEfficiency: 90 %
• CableLength: 40 m
• LoadVoltage: 350 V
• ActualLoadVoltage: 350 V
• CableMaterial: Copper
• CableSize: 1.5 mm^2 (This value was locked and may not have been the size recommended by the calculator)
• CableAWG: 15 AWG
• CableCurrent: 1.0 A
• ActualCableEfficiency: 100 %
• ActualTotalOutput: 364 W

 

[i] From metoffice data, available online here: http://www.metoffice.gov.uk/climate/uk/ns/print.html, viewed 01/11/2011

[2] Data from the powerspout calculator available online here: http://www.powerspout.com/advanced-calculator/?ref=PS1593-0DE9F073