Solar House Design Considerations

In our vast experience with using solar house design, we’ve dealt with a fair number of people who have built a Solar House and did not connect to the power company for their electricity usage. Instead, they use a combination of solar panels and a battery backup to produce, store and use their energy. They’ve gone off-grid utilizing Solar House Design principles.

The motivation for a Solar House Design can be one of several reasons:

• Customers can’t cost-effectively get the power company to bring power to their property. They have to gain access rights, clear the right-of-way, and pay thousands of dollars to bring service out. Once they do, they are also charged a monthly power bill from the power company!
• Having the power company bring power out to their property, makes getting power easier and attracts neighbors! Most of these customers want to live away from people.
• They hear about what happens when the utility grid goes down for an extended timeframe, and they want to be prepared for this type of extended grid outage.
• Preparing for the worst, so they want to live far away from people when it happens and want to sustain the well-being of those people living on their compound when the rest of civilization falls apart.

In any of these cases, you CAN go off-grid. But we recommend taking these considerations into account when designing and constructing your off-grid home:

Keep the AMOUNT of electric power needed to a minimum. Most houses in the US are built with 200A service. This size service is excellent for running many loads. Off-grid inverters typically have only a 25-40A output with the ability to surge to 50A for a short period. You’ll need 4-5 inverters operating in parallel to provide the same power output that the grid can provide your house. That’s a lot of power.

Minimize What Your Off-Grid System Requires

LED lighting and anything that will minimize your electrical footprint. For example, consider a tankless water heater. Also, think about using any appliance that is Energy-Star rated and uses the least amount of electricity compared to peers.

Minimize your big loads. Big electrical loads are those that have large heating elements. These include your:

• Oven
• Range Top
• Electric Central Heat
• Hot Water Heater
• Electric Clothes Dryer

Whatever you can run off propane or natural gas here, that’s what you need to do. It keeps your solar/battery system size to a minimum. Gas prices are relatively low, and it is plentiful. So get a large propane tank at your new house (500 gal capacity) and run piping to these appliances.

Note: If you are worried that gas becomes scarce in an extended outage, think about having an electrical backup for these items. But don’t plan for electrical power for them unless you have the budget for it. Remember, anything that heats should be run off of gas.

Minimize HVAC

Solar house design is not easy in the south because summers here are sweltering. However, it would be best if you looked at installing a high-efficient, high-SEER HVAC system to keep your home cool in the summer. A typical residential 5-ton HVAC compressor/air handler unit uses too much electricity to make it a viable option in off-grid living (unless you want to run a Generator when the HVAC runs). There are several options, from using mini-split units to specific solar-powered HVAC systems that are available.

HVAC will use as much energy as ALL of your other loads combined, so we recommend starting your design work here. Minimizing HVAC can cut solar/battery system costs in half.

Double-Insulate. Generating heated or cooled air is costly. Once you do, you want to keep this conditioned air as long as possible. Insulate your entire house with the best materials you can buy and provide extra insulating, if possible. Get the most efficient windows and doors and make sure openings are sealed tight. Add an extra layer of insulation to the attic. Spray foam AND provide batting insulation. Any extra money you spend here will see multiple returns in your electrical generation system’s effectiveness and minimal use.

Use Fire for Heat in Solar House Design

A Fireplace or Stove goes along with using gas appliances for any heating load. Consider a wood-burning stove for heat and food prep in the winter. Southern homes don’t need this as much, but homes built up north sure do. Burning wood (or fuel pellets) is cost-effective, and that source of fuel will likely always be available in a prolonged outage.

Consider Digging In

Homes that are partially buried or are underground can conserve energy. These homes are cooler in the summer and warmer in the winter. They don’t get hit with the elements as much, and the ground around them insulates. Homes dug into sides of a mountain or have a large basement area underground use a lot less energy than above-ground homes. If your home doesn’t require as much power, your solar system’s production capacity is also reduced.

Orientation for Solar House Design

You want a substantial south-facing roof face for your solar panels, or at least have an unshaded area available for a ground-mounted system. How you orient your house on the property can affect solar loads, so discuss this with your Architect.

Extend Eaves for Energy Savings

Extended eaves prevent the high sun in the summer from penetrating the house but allowing the lower sun in the winter to provide radiant heat.

There’s more about orientation techniques here

Water for Off-Grid Living

If you want to live off-grid electrically, I’m sure you want to live without being tethered to city water. You’re going to need a well and pump to get water from the ground. Most likely, it will be 220V that uses more electricity when it runs. Consider getting a larger bladder tank to hold the water. When the pump runs, it runs for a longer time pumping up the tank, which uses less electricity than running multiple times pumping a small tank. You don’t want to run the pump to deliver the water directly. In other words, it shouldn’t run every time you turn on a faucet.

You can do rainwater harvesting and other water recycling techniques, but these are difficult to install for the return you get. With a good, deep well and pump, water is plentiful and safe.

DC Appliances

DC-run appliances may be a bad idea. Consider that DC appliances take power directly from the battery bank (which stores energy in DC) rather than converting the DC-to-AC with an inverter and losing some energy through the conversion process. You can get DC refrigerators and freezers, and other common household appliances if you search around.

Inverters today are efficient…95%+. That means they lose some energy during the DC-to-AC conversion process, but no more than is lost through the wires bringing electricity to your appliance. The most significant factor is the replacement. If one of the DC-run appliances goes out, your ability to get a replacement is limited. You can’t just go down to your local Home Depot or Lowes and pick one out because they don’t have any! Instead, you have to find one online and order if they are in stock for delivery in 1-2 weeks. If you have to have one appliance on AC, it makes sense to me to have ALL of your appliances on AC.

Note: A DC-run well pump is an exception. Sometimes the well is located far away from the central solar/battery system, and getting electricity out to it is difficult. Having a few solar modules and a battery bank can allow you to run a well pump off DC without an inverter.

Tracking the Electrical Load of Your Appliances

Consider installing a load center/electrical panel tracking device so you can see your primary appliance’s electricity consumption. Knowing where your electricity is going is key to helping to minimize it. (This goes for your on-grid houses, too!)

For Solar House Design become a Minimalist

A good bet is minimizing your life. Determine what you do not need. Going off-grid is a lifestyle change. When you are grid-tied, you turn on the light and don’t think twice about it not coming on (unless you didn’t pay your bill this month!). When you are off-grid, you need to think about the weather and sunshine, the charge on the batteries, and the amount of energy you are consuming.

Blow drying your hair (using an appliance with a heating element) uses a large amount of electricity. So does the coffee pot. If the toilet doesn’t stop running because the handle is stuck, that can force the well pump to run excessively and drain your battery bank. You always have to keep energy consumption in the back of your mind. If you aren’t ready for this thought process, you might not be prepared for off-grid living.
These are the tips that we’ve learned or seen in action during our many years of designing and installing off-grid solar systems. Feel free to contact us and provide your recommendations for good off-grid house design.