Microhydro Systems: Advice From The Pros

Home-scale microhydro-electric systems can give the best renewable bang for the buck. With the right situation and implementation, you can have a low-impact, low-maintenance, reliable system that supplies clean energy over the long haul.

As with any renewable energy system, the dividing line between a dream and a working project includes education, experience, and expertise. When dealing with something as powerful and fragile as a flowing watercourse can be, it’s important to find people who have “been there and done that.”

Here, 12 hydro experts share the perspective of decades of hydro experience and wisdom. The group’s experience includes off-grid hydro living; system design, specification, and installation; engineering, consulting, and contracting; and equipment design and manufacturing. Read on and consider whether you have the right site, situation, and motivation to pursue energy from falling water.

Q: What’s the first step to identifying a good hydro site?

The two primary components of hydro-electric power are head (vertical drop) and flow. A good site needs a combination of these two. Higher head sites may be more cost-effective to tap, since you can use smaller pipe and less water. Ideally, you want water tumbling down the hillside—this is one sign of a potential hydro site. Water that is dead “flat” won’t do much for you—if there is no head, there is no power.

If you double the head, you double the power available. The same is true if you double the flow. Higher head is the least expensive way to generate more power. Increasing the head increases the water pressure, which requires more robust components, but doesn’t add significant cost to the turbine. On the other hand, more flow requires a physically larger turbine to handle the mass. As a general rule, higher flow requires more steel, which drives up the cost. A good home-scale system might have a vertical drop in the range of 40 to 200 feet.

A steady flow from a perennial stream is ideal. Seasonal streams that suffer wide fluctuations in flow linked to wet and dry seasons can be designed for, but require compromises in the design parameters.

Look for a good site rather than the closest site. With high-voltage transmission coupled to modern MPPT controllers and grid-connected inverters, wire cost for longer distance is often not the biggest issue. Other good attributes are a convenient and environmentally friendly intake site, easy access and permitting, and a relatively short pipe run.

Before you even consider hydro sites, realistically assess your energy needs. A common error is overestimating actual electricity needs. We live in a wasteful society, and use a lot more energy than is necessary due to inefficient appliances and lack of attention to conservation. The trouble with overestimating your energy needs is that it makes systems larger and more expensive, and often such large and expensive projects have a way of not getting done. In a hydro system, building a system for a wasteful home may mean using more materials and taking a larger portion of the stream flow.

Q: What types of water sources are not appropriate for microhydro systems?

Because available power comes from head and flow, water sources with little flow or little head will not work. Flat-water rivers are difficult or impractical to capture energy from, which is why we see few if any products on the market for this type of site. Large, gently flowing rivers like the Amazon, Nile, and Mississippi are generally unsuitable for any microhydro systems other than paddle-wheel floating designs that seldom generate more than a token amount of power. A “low-head” site typically needs to dam the whole river or divert a large amount of water in a canal to create some head.