Hydro Power is the conversion of the energy in moving water to electrical or mechanical energy using a turbine or waterwheel. From backyard, single resident systems made from recycled car parts, to grand scale projects such as those on the Colorado river in the western United States, people are harnessing the energy of water moving down a gradient. The size and application of a Hydro Power system can vary widely. Microhydro systems are specifically those systems that are not grand in scale. Damming a river usually will not qualify as microhydro, but partially diverting a stream into a holding tank and running the water into a small hydro-electric turbine or pelton wheel is more along the lines of what the term microhydro refers to.

The following article is a brief overview of the more technical aspects and considerations needed to design and construct a microhydro system.

## Hydropower Sizes

Size Power Output Typical Use
Large >10MW Usually part of a large grid.
Small 1MW-10MW Usually grid intertied. (up to 50MW in Canada)
Mini 100kW-1,000kW (1MW) Community and industry. Often grid intertied.
Micro 1kW-100kW Small low energy consuming community, small industry, rural high energy consuming household. Usually off-grid.
Pico <1kW Radio tower, low energy consuming household, charging station. Almost always off grid.

Please note that these are averages, many different communities classify hydropower somewhat differently.

## Equation

The amount of energy $\,E$ released by lowering an object of mass $\,m$ by a height $\,h$ in a gravitational field is:

$\,E=mgh$ where $\,g$ is the acceleration due to gravity.

Converting these units, a common field equation to measure the maximum power available in a moving body of water is:

$\,P_{max}={\frac {Q_{max}*H_{max}*e_{max}}{K}}$ Where:

• Pmax=Maximum Power Available (kW)
• Qmax=Flow (Volume/time)
• Hmax=Head (Vertical drop in ft)
• emax=Efficiency of the turbine (use a value of 1 for max power available)
• K=Unit conversion factor (see table below for some common values)
For Q measured in K is equal to
ft3/min 708 (ft4)/(min*kW)
ft3/sec (CFS) 11.8 (ft4)/(sec*kW)
l/sec 334(l*ft)/(sec*kW)
gal/min (GPM) 5302 (gal*ft)/(min*kW)

To find the actual power you will get from that moving body of water, calculate Pnet with the following changes made.

$\,P_{net}={\frac {Q_{net}*H_{net}*e_{net}}{K}}$ Where:

• Pnet=The net power extracted from the river, not including loss in delivery from power station to load (kW)
• Qnet=Flow (Volume/time) - Only take a portion of the max flow (%take). For delicate streams this may be a small percentage of the total flow.
• Qnet=Qmax*%take
• Hnet=Head (Vertical drop in ft) - This is the actual head that you have available due to losses from friction. Calculate friction loss using tables based on the materials you use for diversion (e.g. PVC).
• Determine equivalent length of pipe by adding actual length of pipe and equivalent lengths of fittings based on tables using pipe size.
• Find Frictional Pressure Loss Ratio (FPL) coefficient in ftloss/ftpipe based upon flow rate and pipe size
• calculate Hloss=equivalent length of pipe * FPL

Hnet=Hmax-Hloss

• enet=Efficiency of the turbine - Always between 0 and 1, usually between .5 and .9 depending on the turbine type and flow rate. A value of 0.78 is a good guess for modern turbines in average conditions.
• K=Unit conversion factor (see table above for some common values)

Note that these equations are static in time. You must run these equations for with a resolution high enough to cover periods of variation (e.g. monthly river data).

## Water Wheels

Probably the most accessible technology for hydro power is the water wheelW. It can be built entirely from local materials. Only the generator has to be brought in. For small systems a modified motor or car alternator can be used.

• The vertical undershot water wheel is most appropriate for relative low head situations even if it is the least efficient of all water wheels. You should avoid building an undershot wheel with straight buckets and go for either a Poncelet wheel or a Zuppinger wheel which can both double the efficiency. They have an efficiency of about 30%, but enclosed like a breast shot of up to 70%.
• The breast shot is next when the head is large enough. Here the water enters at a height similar to the axle height. It is more complicated to build and needs a structure that encases the wheel to function with high efficiency. If done correctly it uses the weight of the water and its impulse. It can have an efficiency of about 85% if it's well-built.
• The over shot wheel needs the most head of the water wheels. Under optimal conditions with steel buckets it can have an efficiency of up to 80%.
• The back shot wheel can be seen as an cross between a breast shot wheel and an overshoot wheel. The water enters at the top of the wheel but the buckets are like a breast shot wheel. The direction of rotation is the same as in a breast shot wheel. The efficiency can exceed that of the breast shot.
• Horizontal water wheels apart from museum pieces are today found mainly in the Himalaya region in the form of the ghatta. That version is a primitive version of a turbine.