A New Era in Home-Owner Hydro

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"Just in Colorado, there are probably dozens of places that could be doing this," says Scott. "Few people realize how fairly simple it is."

Although AC systems cost $7,000 to $20,000 and up, they provide much more electricity than a battery-based system at a cheaper per unit cost, often including a surplus that can heat a hot tub, radiant floor, greenhouse, or what have you. But one principal advantage of an AC system—no batteries—is also a principal constraint. An AC system must be big enough to start a refrigerator motor, with power left over to meet evening and morning peaks. For this reason, most AC systems are 3 kW or bigger, with 5 to 8 being optimal. Below 2 kW, you'll have to go with DC and an inverter.

There is rarely any need to agonize over the AC versus DC choice, because generally speaking it doesn't exist. At nine of 10 sites, AC isn't an option. The reason has to do with head and flow.

Sizing Your System's Potential

Short of having our computer size your system's potential, the chart below will give you a good idea of how much output in watts you may expect per different gpm (gallons per minute), for varing feet of head. Multiply the number of watts by 24-watt-hours to get the total number of watt-hours generated in one day. Divide this by system voltage to get your amp-hour per day output.

Hydro Physics

"What's your head and flow?"

Call Powerhouse Paul to talk hydro and that's the first question he'll ask. These variables dictate everything—how much power can be produced, what type of turbine is best, what size penstock pipe is required, and so forth.

Head (or "drop" or "fall") is the vertical distance between the intake at top and turbine at bottom. Flow is the quantity of water passing through the turbine.

Hydropower texts are replete with arcane equations, but the relationship between head and flow is not complicated. To determine your site's power potential, multiply the two. For example, a site with 10 units of flow and one unit of head will produce 10 units of energy, as will a site with one unit of flow and 10 units of head.

In the equation, head and flow are equally valuable. On the ground, though, head trumps. Yes, power can be generated at heads as low as three feet, but this re quires tremendous quantities of water, large turbines, expensive diversion structures, and expert planning. For backyard applications, you'll want at least 15 feet of head, and preferably 50 feet or more. On the other hand, you don't need much flow. Microhydro isn't really "garden hose" technology, but in terms of water required, it's close.

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