The site and the design
The bundled PVWatts TMY data tells the seasonal story: 5.51
kWh/m²/day in May, 2.95 in December, even with the array
tilted 42° for winter. Solar alone would need a much bigger
array and battery to survive November through February, right
when the heat pump and longer lighting hours push demand up. So
the design pairs 3.2 kW of solar with a 600 W wind turbine on an
18-meter tower; New England's winter winds fill the solar gap.
- Solar array: 3.2 kW, tilt 42°, facing due south
- Wind turbine: 600 W rated, 2.0 m rotor, 18 m tower,
5.5 m/s average site wind
- Battery bank: 400 Ah LiFePO4 at 48 V (19.2 kWh)
- Charge controller: MPPT; inverter: pure sine wave, 93%
- Loads: refrigerator and freezer, household LED lighting,
well pump, heat pump in the shoulder seasons, home office,
washing machine three cycles a week, TV; roughly 8 to
9 kWh/day
Things to try
Toggle the wind block off and watch the November and December
rows go red; that is when the turbine outshines the sun. Push
the tower height from 18 m to 24 m to see the cubed-velocity
scaling in the wind model. Or
change the terrain type from suburban to forested and watch the
same tower lose output to ground drag.
Open in calculator →
Frequently asked questions
Can solar and wind together run a house off-grid?
In the right climate, yes, and the pairing is the point. In
northern Vermont, solar production drops sharply from November
through February, exactly when heating and lighting demand
rise. Winter is also the windy season there, so a 600 W turbine
on an 18 m tower covers much of the shortfall the 3.2 kW solar
array leaves. Toggle the wind block off in this example and the
November and December rows go into deficit; that gap is what
the turbine exists to fill.
How big a battery bank does an off-grid house need?
This house draws roughly 8 to 9 kWh per day, including a heat
pump in the shoulder seasons, and carries a 400 Ah LiFePO4 bank
at 48 V, about 19 kWh, of which roughly 15 kWh is usable at an
80 percent depth-of-discharge target. That is not a week of
autonomy; it is a buffer that bridges a cloudy, windless
stretch while production catches up. Whole-house systems also
favor 48 V because the same watts flow at a quarter of the
current a 12 V system would need.
Does raising a wind turbine tower really help?
More than almost any other change. Wind speed increases with
height above the ground's friction layer, and turbine power
scales with the cube of wind speed, so a modest speed gain
compounds three times over. Push this example's tower from
18 m to 24 m and watch the winter wind numbers climb; raising
the hub is usually a better buy than a bigger rated wattage on
a short tower.
More worked examples
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How the calculator works