In 1978, my wife and I bought a 190-acre farm near Ithaca, New York, consisting of an 1840s-era farmhouse, a barn, pastures for our horses, lots of room for vegetable gardens, and a sizable woodlot for our wood heater, which backs up an oil-fired boiler and gas furnace. The farm was a great place to raise our kids; gives us a sense of security in an uncertain world; and allows us to be closer to the land and its resources.
Weaving Wind into the Energy Mix
Our loads were fairly typical for an older home. While we did not do a comprehensive energy audit and efficiency upgrades, we focused on the biggest energy load—heating. I redesigned our heating system to provide comfortable temperatures to fewer rooms. And we added a lot of insulation and then hired a local firm to add even more insulation to replace the vermiculite in the walls that had settled.
A few years ago, Art Weaver, an installer and builder of wind turbines, came to our place. We sat on our deck and watched the leaves blow in the wind as he told us about the benefits of wind energy. We seemed to have more wind than most of our neighbors because of our hilltop location.
Our home is grid-tied, but I was concerned about the security and robustness of our nation’s electricity grid. I wanted to be as prepared as possible for outages, and installing a wind-electric system seemed a good way to diversify our energy sources for greater protection against utility failures.
Art studied the wind, topography, and surrounding trees, on which he based the tower height. A tower height of 120 feet was chosen, to raise the turbine 30 to 40 feet above mature trees in the area. This height gets the turbine above the most turbulent boundary layer and into much smoother winds. Smoother winds mean less turbine yawing—with less yawing you increase energy production and decrease wear.
In June 2013, the Weaver 5 wind turbine began producing energy. I read the meter faithfully and could see that it was going to fall short of our consumption, which hovers around 20 kWh per day. The daily wind fluctuations didn’t surprise me as much as the seasonal changes did. I decided to add solar-electric modules and batteries to the system to further decrease dependence on fossil fuels—a key goal.
Pairing the PV Array
I wanted enough renewable electricity to be self-sufficient in the event of a lengthy grid failure, without having to resort to fossil fuels. This meant an allocation of at least 5 kW of PV to supplement wind for household consumption, and a little more than 5 kW of additional PV for the charging our electric car, a Nissan Leaf.
The wind system was originally a batteryless grid-tied system, with 3 kW and 7 kW SMA Windy Boy inverters. The 3 kW inverter is used at lower wind speeds (lower start voltage) and the 7 kW is used at higher wind speeds (higher start voltage). The addition of an 11.4 kW PV system, along with whole-house battery backup, required that the wind system also be able to charge the new 15.4 kWh lithium-ion battery. The solution was to AC-couple the SMA wind inverters to the AC load port of a 10 kW Princeton Power Systems DRI-10 inverter, which is able to accommodate a high-voltage lithium-ion battery. The PPS has four bidirectional ports—two DC ports (used for PV and battery) and two AC ports (used for grid and load). The Weaver 5 wind controller was also upgraded (by the manufacturer) to sense battery and load status in addition to grid status, and to safely control wind turbine output according to the availability of these loads.