Off-Grid Passive Solar Earthship
Located close to BLM land with gorgeous views of the San Juan Mountains in southwestern Colorado, this passive solar, modified earthship-style house is off the grid and generates all of its own electricity.
The house is a modified two-story earthship that has a berm around on the northern side of the ground floor. It is situated on an east-west axis with the front of the house dominated by windows that face true south. The rest of the graceful, curving walls that envelop the house are composed of stacked, recycled tires that have been filled with compressed earth.
The tire wall is approximately 100 linear feet in length, extends 8 feet above ground and 10 feet below the ground. (Disclosure! I helped to build the back wall of this house. It was my first building experience, as I spent a week with the Krebs in the hot summer sun pounding dirt into the tires.) A compressed air tamper was used to pound the slightly damp dirt into each tire. Michael Reynolds, the inventor / creator of the earthship style of building, has said that about 300 pounds of dirt fills each tire. It really is amazing how much dirt can be used to fill a tire.
Approximately 2,000 tires were used to create the structure. When asked about the experience in obtaining the tires, Stu Krebs said, “We went around to tire shops and many of them were really happy to give them away. One shop even paid us to take them.” It saved the tire shop from having to pay a fee to dump them in a landfill. Soon after they started building, they quickly learned that it was a good idea to pick through the tires in order to get obtain tires of a similar size to create a more level wall. The furthest south – north distance within the house is approximately 30 feet. Adobe mud has been used to cover the tires.
Tip learned: If building with tires, find tires that are a similar size so that a uniform level wall can be created.
Because it is an earthship-style house, the rammed earth in the tires is the foundation as well as the insulation for the structure.
The building is almost entirely composed of thermal mass; in the form of dirt that has been pounded into the tires, while floor at the ground level is a concrete slab (below the one pictured to the right). The main living space on the upper level has a wooden floor with a strip of thick ceramic tile near the row of double pane windows to further boost the amount of thermal mass in the building.
A specifically engineered overhang allows the lower winter sun through the windows to warm the structure, while the summer sun does not enter. The picture to the left was taken after the spring equinox in April, and shows the sun’s reach in the spring, when only a sliver of sunlight enters the house. Their passive solar house typically tends to be on the cooler side during the spring.
The house is powered by a photovoltaic (PV) array that is located on the ground, a short distance from the main dwelling.
The Krebs bought the solar panels and built the frames for them. They built both metal and wooden frames. The metal frames have an open back, while the wooden frames have been painted white and enclose the back of the solar panels.
After using the system, they found out that the solar panels in the metal frames are more efficient because they allow the solar panels to stay cooler.
The solar panels in the wooden frame have a wooden back that acts as a blanket layer that causes the solar panels to heat up and do not work as efficiently as the cooler ones.
Tip learned: Solar panels that are cooler operate more efficiently.
The electricity from the PV array is stored in batteries, then travels through an inverter before reaching the house. When the sun does not provide enough energy for the house, a propane generator is used.
The generators (they have a backup diesel generator in addition to the propane one) are on one side of the wall, while the battery storage, dc disconnect and inverter are housed on the other side of the tire wall.
The batteries are stored in the wooden box to the lower right hand side of the inverter and dc disconnect box.
Inside the House
The occupants enjoy the natural light that drapes the house in sunlight and have constructed insulated shades to help retain the heat in the winter. While the winter temperatures frequently dip below freezing, when the sun is out, the house is typically around 65. On one of the coldest mornings of the winter, that happened after the sun had not been out for a few days, the lowest temperature in the house was 40 degrees. In the summer time, when temperatures soar above 100, the hottest temperature in the house hovers around 80 degrees.
When living in a house located off of the main electrical grid, regular housing appliances are scrutinized more carefully for their use of electricity. After doing research, and debating between a gas or an electric refrigerator, they chose to have an electric refrigerator because they were larger and had more choices available within their design. A refrigerator, however, is one of the appliances that uses a large portion of electricity. Because both a refrigerator and espresso maker are regularly in use in the morning and running at a time when the sun is just starting to provide the potential for solar electricity again, the propane generator is run in the morning to augment the solar electrical system. The generator is run again in the evening to charge up the batteries, in large part to power the refrigerator through the night.
Solar Thermal Hot Water
Solar thermal hot water panels supply the household needs for hot water exclusively during the summer, while an on-demand flash propane water heater can kick in when the sun alone can not adequately heat the water.
The hot water can also be piped into the ground floor because the cement floor has been plumbed for radiant heat. Either the solar thermal hot water or the flash propane hot water can be the source of the in floor heat.
The owner builders are still working on the finishing touches of the house. Future plans include the building of two greenhouses that will be constructed on the front of each end of the house. They would also like to add an additional layer of insulation to surround the outside tires in order to create a warmer and more stable inside temperature.
A shed that measures 20 by 50 was first built as a test before work on the main house began. The shed, on the left hand side of the picture, because it is smaller, with the distance from north to south being shorter and able to absorb and radiate heat energy more efficiently, is warmer than than the larger house in colder weather. Distance matters in passive solar design.
Tip learned: In passive solar design, the depth of the house, from the source of heat to when the heat is absorbed in the thermal mass should be minimized.
Designer / Builder: Owners – Stuart and Barbara Krebs
Size: 3500 square feet
Time: 10 years
If you have any questions, feel free to comment and I’ll try to find an answer.