This 1970s house was updated with a 2.2 kW solar electric array, geothermal heating and cooling, and rainwater collection system. The main bathroom was fitted with a Caroma Sydney dual-flush toilet and water was further budgeted through the use of an evapo-transpiration sensor for irrigation.

2.2 kW solar PV system with 12 Mitsubishi MF180 panels
Fronius grid-tied invertor
4-ton Waterfurnace geothermal heat pump with 180-foot-deep vertical well field and desuperheater to provide domestic hot water

All Energy Star appliances
Low-flow, dual-flush toilet
Electric clothes dryer with exhaust plumbed to HVAC to provide humidity during dry winter months
Rotary clothes-drying line for summer use
Compact fluorescent, LED, and dimmable incandescent lighting
2,400-gallon rainwater collection system
South-facing, drought-tolerant plantings and runoff-reducing landscaping
Intelligent irrigation system with evapo-transpiration sensor for watering only when needed
Pair of Swedish Blue ducks, replacing bi-annual petrochemical pesticide applications to garden
100% organic horse manure, replacing periodic hydrocarbon-derived chemical fertilizer
1990 Honda CRX HF getting 53 mpg, and also a bicycle, replacing a 2001 Volvo V-70 that maybe once got 28 mpg on the highway

$21,000 minus $2,000 federal tax credit, $4,000 state rebate, $4,000 Great River Energy rebate. Final cost: $11,000.