Creating a Resilient Home

Intermediate

Inside this Article

In a heating-dominated climate, solar gain and good insulation can keep a home cozy without much energy.
In a cooling-dominated climate, earth-coupling and shading the home from the sun can make a home comfortable without much energy input.
With its Secure Power Supply feature, SMA America’s line of TL-US inverters can provide up to 1.5 kW of AC power when the grid is down but the sun is shining.
Portable solar power systems can provide emergency power for communication, lighting, and battery charging.
This AC-coupled system includes battery backup, integrated with a batteryless grid-tied photovoltaic system.
A solar water heating system can often provide adequate hot water, even without utility power.
Solar ovens like the StarFlower can bake without combustible fuel and without heating up the home.
The same energy that grows your fruits and vegetables can also dry your harvest.
Solar pumping systems can be AC-powered, DC-powered, or PV-direct (batteryless).
Having on-site rainwater collection and storage is a valuable addition to a home’s resiliency.
Electric cars are becoming more commonplace, and can be charged directly from solar-electric systems.
Electric-powered vehicles come in many sizes and shapes to meet different needs of range, climate, load capacity, and charging resource.

A resilient home can weather whatever comes its way, and still provide its inhabitants with what they need to survive—and thrive.

Thermal Resilience

Whether the climate in your area is getting hotter, cooler, wetter, or drier, the ability of your home to deal with changing conditions is an important aspect of its resilience. A key tenet of resilience is that houses be able to maintain habitable conditions in the event of an extended power outage or interruption in heating fuel—this is referred to as passive survivability. In the absence of energy input, a resilient house shouldn’t get too cold in winter or too hot in summer—it should keep residents safe, which is different from comfort.

Although there is debate about what constitutes safe conditions, since that varies depending on the age, health, and metabolism of the occupants as well as relative humidity, a reasonably safe temperature range is 50°F to 90°F. This goal can be achieved with a highly insulated building envelope, along with passive solar heating and natural cooling. As would be expected, more insulation is required in colder climates (see “Insulation Recommendations” table).

In addition to insulation levels, passive solar gain and cooling-load-avoidance measures are very important in ensuring passive survivability. Window area should be greater on the south side of the house (in the northern hemisphere) than on the east and west, and thermal mass should be provided to store passive solar heat.

In new construction, house size is another very important consideration. Building smaller, more space-efficient houses is an excellent way to keep heating and cooling requirements minimal—even though the energy use per square foot may be higher.

Energy Resilience

Electricity. Generators can offer electricity resilience as long as fuel lasts, but the greatest resilience is from PV systems with battery banks. (Electricity generated from microhydro systems can also provide resilience, given a constant stream flow and good head, but good hydro resources are uncommon.) All off-grid systems include batteries, but the majority of PV systems are batteryless grid-tied, which won’t work during a power outage.

For a grid-tied PV system, the resilient PV solution can operate in grid-tied mode normally, but switch to stand-alone if the grid goes down. In this case, the power requirements during a power outage can be limited to critical loads, thus minimizing the size of the battery bank.

A lower-cost option is the SMA America Sunny Boy TL inverter with secure power supply (SPS) that provides power during power outages, only while the sun is shining on the array. This option can provide daytime recharging for cell phones and laptop computers, power other small loads, and even power a freezer or refrigerator.

For those who already have a batteryless grid-tied PV system without SPS, a battery-based system can be added through AC-coupling. The second system can operate without the grid, and essentially fools the batteryless system into thinking it is the grid and still operating. In this way, AC loads can continue running up to the capacity of the combined systems during the day, and up to the capacity of the battery-based system when there’s no sun.

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Comments (1)

Frank Heller's picture

You seem to forget the most resilient system is one which can be maintained and repaired by the home owner; including redundancy. The more rural your residence, the more widespread the disaster--storms, floods, ice storms, etc. the harder it will be to get your dealer/installer to your place esp. if you aren't plowed out or your power is out for several days.

When all factors are weighed the propane or natural gas fueled backup generator is the one left standing. ....care for a photo of a rack of PV panels on a neighbor's house covered with ice and snow, and left that way for weeks?

Another impact is the effect of 'smart meters' which can be moderated from outside your home, altering the flow of power to it; or other grid restrictions on the flow of power into the grid under net metering

Local hydro-powered grids distributing power to restored mill buildings or small mill 'villages' are being seriously considered in Maine. Properly designed they can withstand flooding and even droughts; there are thousands of tidal mill sites which are immune to most disaster and use fairly simple technology like efficient water wheels powered by either flowing water or impounded water. They operate like they did in the 15th century with a large impound and a metered flow that is released during low tide.

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