site requirements for microhydro

Before you make any investment in a microhydro system you should first try and determine if the site you are contemplating is appropriate for this type of energy generation.  It is not enough to simply have a river or stream on or near your property.  Some factors you should consider include:

• legal considerations
• water head level
• flow at the turbine
• pipeline
• distance to transmission system

Legal Considerations - To begin with, you will need to have ensured that the property you are considering using, from the intake at a river or pond, to the end of the tailwater flow back into the river or stream, is all within the boundaries of your property.  In addition, you need to consider any impact that any diversion you might make of a river or stream, for example to create a head pond, might have on those downstream of you.  Most states have regulations under which it is illegal to significantly reduce the flow to those downstream of you.  Normally, this is not a problem since you will be returning the water to the source once it has run through the water turbine but it is still an issue to be aware of. 

Water Head Level - If you are planning on using a high head type of turbine you need to measure the vertical drop from the location of your water intake to the point where you will be placing the turbine.  The greater the drop the more head pressure will be generated because of gravity. if the vertical drop you have available within your property is too small to create the minimum head pressure you need for your turbine then you will need to reconsider the layout of your system or you may need to switch to more of a low head type of turbine. There are several approaches you can take to measuring the head level for you site which are covered in the next section.

Water Flow at the Turbine Intake - In order to capture the flow you usually need to channel the flow into a pipe using a temporary dam or weir placed in the river or stream you are using. Determine where the best place would be for the intake such that it requires the smallest head pond. If you live in the southwest or other locations where the river flow varies from year to year you may wish to measure the flow during the different seasons.  You wouldn't want to invest in the water turbine system and then discover that your stream is reduced to a trickle in the summer when you were planning on using its energy to run your air conditioning.  Also, keep in mind how much the flow you are doing will impact fish and other animals downstream.  If the grade is shallow and you must cover a significant distance in order to get an adequate head pressure then you could be causing damage to the local ecosystem.

Pipeline - In order to create the head pressure you will need to run pipe from the intake upstream down to the turbine. This pipe is often referred to as the penstock. If the grade is shallow then this could mean a significant amount of piping which could then raise your overall project costs.  There is friction and loss of energy whenever the water runs through the pipes.  In general, the larger the diameter of the pipe the less energy will be lost.  Most water turbine piping systems use standard polyethylene (PVC) pipes or hoses.  This kind of piping comes in continuous coils and is flexible which means it can be run over rough terrain.  When you evaluate your site determine what path this pipe can take and to what extent it can be buried to minimize its impact on the environment.  Burying the pipe may not always be possible in rocky terrain.

Distance to Transmission System - If you wish to use an on the grid system then a key cost consideration is the distance from the turbine to the electric meter in your home.  If this is a significant distance then you will need to account for the cost of running the wiring.  Similarly, if you are doing an off-the-grid system and are running the electricity to your battery bank the wiring costs would need to be considered.  There is always some loss of energy in any transmission.  Generally, it is safe to assume about a 10% loss of energy from the turbine to the meter or battery system if the distance is significant.