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Off-Grid Solar

The off-grid lifestyle is one of independence, self-sufficiency, and self-reliance. Whether to achieve an ideal, achieve autonomy, or eliminate the cost of a grid interconnect, living off-grid can offer greater resilience compared to homes that are dependent on the grid.


Note: A home that is already grid-connected can attain a similar degree of autonomy, and is called a battery backup system.


However, off-grid solar is not for everyone and may not be practical in every situation. In some cases, the amount of power a home (or the occupants) consumes is excessive and better suited to a grid connection (and high power bills). Some people do not like to have an energy budget, monitor their usage, or limit their power use to what's available on a daily basis. But others are very keen to maximize efficiency and conservation. It is also essential that homeowners become familiar with how their power system works. Our expert advice will help guide you, and the information below offers a good start for the essentials so you can plan ahead and get the best results.


The best-case scenario for an off-grid home is always during new construction when there is the most opportunity to build optimally, maximize energy efficiency, and avoid the grid-interconnection costs.


Building Efficiency


A high-performance home will always be more reliable and cost-effective (over time) than a conventional, energy-intensive home built at a budget price. This is especially true for off-grid homes, and even more important in a winter climate. The majority of energy consumption in most buildings is related to heating and cooling, so optimizing performance and efficiency for climate control is significant. The costs of having a higher-quality home and appliances can be offset by not requiring as large of a power system while being more reliable overall.


A quality building envelope is very important to ensuring energy conservation where it is needed most. Efficient homes have:

  • High insulation value (R-40 walls, R-60 ceiling, under slab and footing insulation),

  • an air-tight envelope (confirmed by a blower-door test),

  • and energy-recovery ventilation (ERV) to keep the air fresh and control humidity with minimal energy loss.

New homes, when built for energy conservation, can get down to one-third of the energy use of an average American home. This in turn reduces the capacity and cost of the power system while providing a more comfortable and reliable home overall.


Winter capacity / Heating


Rule of thumb: if the power system capacity is sufficient for the wintertime, it will be sufficient for the rest of the year. This is especially due to the largest energy consumer of all - space heating. Adding to the challenge, heat is needed most when there is the least sunshine.


It is best to have two or more sources for heat other than resistive electric elements. For primary heating, it is usually best to have a combination of:

  • a heat pump (for milder temperatures) and

  • a propane furnace and/or wood/biomass stove (for freezing temperatures).

Heat pumps always reduce overall heating needs, within the limits of their heat source and ambient temperature. A secondary source is essential in most cases. Only high-efficiency homes may rely on electric heat (or heat pumps) primarily.


Ultimately, the preferred heating options will vary depending on factors including the building size and layout, exposure to sun and wind, ducting and ventilation options, and more. With some guidance, an expert HVAC contractor can offer what is best for your situation.


How the system works


The home is powered by a battery (or bank of batteries) installed in the garage or a mechanical room, usually where the main electric breaker panel is located. If all equipment is located in one room, the wall space required is typically around 6 feet square, and floor clearance from the wall of about 3 to 4 feet.

  • Solar panels provide the home's power directly while simultaneously charging the battery throughout the day.

  • Stored energy in the battery is available any time it is needed.

  • Whenever there is above-average power use and below-average sunshine, the standby generator (typically 14 to 20 kW) will automatically turn on if the battery gets low or power usage gets high.

  • Sometimes systems use an automatic transfer switch to run the home directly from the generator when the battery is low until solar has recharged the battery sufficiently. Other systems allow the generator to charge the battery through the inverter and don't require a transfer switch.

  • System functionality and battery longevity can be improved with the use of a smart breaker panel for automatic load controls.

Sizing a system


The number of solar panels and capacity of the battery is 'sized' to provide for nearly all electric power usage (the generator may cover about 5%-10% annually when needed most). Even when sizing a very large solar/battery capacity, a standby generator is still necessary to guarantee uninterrupted power. In some cases, homeowners will choose to have two generators for maximum reliance (in case one generator needs service).


An average South Dakota home uses about 12,000 kWh per year (kWh/Year), or an average of 30 kWh to 40 kWh per day (kWh/Day). In most cases, energy consumption is highest in the wintertime. Every building and its occupants are unique, so each situation needs to be considered individually.


A combination of construction quality, appliance efficiency, and conscientious occupants/users factor together to determine if a home will consume as little as 30% of the average or up to 5x the average.


The power capacity of the battery system must be able to meet, at a minimum, the single largest load. Generally, power requirements are as follows:


5 kW for a cabin

10 kW for a small/moderately-sized efficient home

15-20 kW for larger homes

20 kW+ for the largest single-family homes with unmoderated energy use


Major Appliances


Larger appliances are the most significant, especially those that are used often. Smaller appliances and electronics are less significant (unless they are running continuously).


The following guidance is here to help you plan your home to achieve the best experience with off-grid living.


Ventilation

  • A blower-door test is recommended to test the air-tightness of the building and address leaks.

  • Mechanical ventilation is essential for high-efficiency homes with a tight building envelope.

  • Also known as heat-recovery ventilators (HRVs), mechanical ventilation systems exchange indoor air with filtered outdoor air with minimal heat gain/loss.

  • Energy-recovery ventilators (ERVs) are like HRVs, but also manage humidity.

  • Whole-house fans (large exhaust fans) are a good alternative to an active mechanical ventilation system. These large vent fans are manually controlled, and rapidly exhaust air from the home when windows are open (on a nice day). Unlike mechanical ventilators, the air is not filtered and temperature/humidity will not be recovered or controlled.

HVAC

  • Air-conditioning works very well with solar since cooling is needed most when there is the most sunshine.

  • Air-sourced heat pumps are very efficient for cooling and can be installed as part of a central-air ducted system/furnace or wall mount.

  • Mini-split heat pumps are very good for cooling individual rooms. Multiple units may be used to serve certain areas of the home only as needed.

  • High-efficiency central air conditioners are acceptable. Avoid oversizing: it is typically more efficient to run at lower power for more time.

  • Ground-sourced heat pumps can be effective, but have a high cost and don't work well in all situations. Like solar power systems, they should be used only when carefully planned, with expert guidance, and in the right locations.

  • Electric (resistive) heat is limited to use in milder temperatures in smaller spaces and highly-efficient homes. Whole-house heating is, on average, a very high energy requirement. Alternate heat sources are strongly recommended when off-grid at (or above) our latitude. Larger homes may prefer to have more than two heating sources and/or multiple zoned systems.

  • Air-source heat pumps are recommended and are excellent for heating in spring/autumn, and do well to supplement the main heat source even during sub-freezing temperatures.

  • A propane furnace or biomass (wood/pellet stove) heater serves as the primary heating source and is used most during the coldest periods. At least one of these options is essential.

  • Ground-source heat pumps can be effective but may be inefficient in some cases, depending on the nature of the ground source. Results may vary considerably, so these should only be used in some cases.

Water

  • For water heating, a large hot water tank with electric elements (or a hybrid electric/propane tank) is preferred. With a timer or controller, extra solar power can be used to heat the tank during the day and not require energy at night.

  • An on-demand propane water heater can also be a good choice.

  • Do not install an on-demand electric water heater (as the power requirement is too high in most cases).

  • A combination of a small electric tank that preheats water going into a small on-demand propane water heater can offer the advantages of both options.

  • Many well pumps require a high-power start and therefore need to be fitted with a soft-start capacitor (for smaller pumps) or VFD controller (for larger pumps) to run efficiently and not overload the battery system.

  • For even greater resiliency, the well pump can fill a cistern for water storage at the surface during the day, and a small pressure pump (or gravity) can provide water pressure on demand with minimal power any time.

Kitchen

  • Induction cooktops are easily the best choice, though a standard electric range is acceptable also. If using gas, properly ventilate.

  • Most new refrigerators and freezers are energy efficient and don't require special consideration. Ice-makers will use a lot more energy, however.

  • Dishwashers are relatively efficient and represent a small share of energy use. Dishwashers can actually be more energy-efficient than hand washing, especially when using efficiency settings.

Laundry

  • Newer clothes washing machines are very energy efficient. A high-extraction (fast-spinning) washer is recommended to reduce energy use for drying.

  • Propane/Gas vented dryers are a good choice that requires little electricity. They are affordable, readily available, and serviceable.

  • Electric, vented (hot-air, resistive electric heating element) clothes dryers are extremely energy-intensive, inefficient, and potentially damaging to fabrics. However, they are the most affordable and widely used. A lower-powered option (under 5 kW) is preferable. Smaller dryers are not more energy-efficient, but they demand less power at one time in exchange for a longer drying cycle, which is generally more suitable with battery power. A high-powered dryer can be fine when running while there is sunshine or while the generator is running; at night it may trigger the generator to turn on in order to support the high load or recharge the batteries.

  • A condenser dryer (typically called "ventless" or unvented) is like a vented dryer except the extracted moisture is collected in a tank that must be emptied. These use a little more power than a vented dryer and actually dry clothes faster, but their efficiency isn't significantly different from a vented dryer.

  • A heat pump dryer is another unvented dryer that uses a heat pump to dry clothes at room temperature, using significantly less energy than other technologies. Also, heat pump dryers are more gentle on fabric, reducing damage. These are excellent in many ways but have a higher price tag and there are fewer options available. Like other unvented dryers, they have a water reservoir that needs to be emptied.

Electronics

  • Most electronics use relatively little power to run, so electronics are not often much to consider. However, some electronics use power even when not being used, so using power strips or smart switches to turn off power to home entertainment systems and gaming consoles when not in use is beneficial.

  • Internet connectivity is essential for monitoring and updating solar and battery power systems and is usually left on at all times, so choosing a newer, efficient option is best. Avoid rental modems/routers provided by internet service providers, as they may be outdated and inefficient. Satellite-based internet modems use much more power than a regular modem/router, so sometimes it is best to turn them off overnight. Starlink is a relatively low-energy satellite system.

As with buildings, the cost of high-efficiency appliances will be higher in exchange for lower energy use and overall quality. The benefits will result in savings on the solar power system size, enhanced reliability, and higher performance overall.


Thanks for reading this guide!