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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.


(A home that is already grid-connected can attain a similar degree of autonomy, which we call a "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) needs is excessive and better suited to a grid connection (and high power bills). Also, 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, while others are very keen to maximize efficiency and conservation. It is also essential that the homeowners are committed to becoming familiar with how the 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 a high grid-interconnection cost. Unfortunately, most average homes are not built to high standards in exchange for cost efficiency, but a retrofit home can become better suited to energy independence, especially during a complete remodel.


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.


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

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

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

  • and heat-recovery ventilation (HRV) to keep the air fresh without temperature 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 space-heating needs, which is generally the biggest energy consumer and is used most when there is the least sunshine.


It is best to have two sources of heat other than electric heat. 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).

Only the highest-rated (i.e. LEED-certified) homes may rely on electric heat (or heat pump) primarily.


Ultimate, the preferred heating options vary depending on several factors including the building size, complexity, floors, basement, and ducting and ventilation options. With this basic guidance, an expert HVAC contractor can offer what is best for your particular construction.


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 (with about 3-1/2 feet floor clearance off the wall).

  • 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, including overnight.

  • 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.

  • System functionality and reliability can be improved with the inclusion 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 (and size), appliance efficiency, and conscientious occupants/users factor together to determine if a home will consume as little as 30% of 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 tiny home or cabin

10 kW for a small/moderately-sized efficient home

15-20 kW for larger homes

20 kW+ for the largest single-family homes


Major Appliances


Larger appliances are the most significant, especially those that are used often. Smaller appliances and electronics (that are not used continuously) are less significant, but user behavior is ultimately responsible for actual energy consumption. Because of this, we focus most on the larger appliances.


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.

  • 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 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. Unlike mechanical ventilators though, 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. Some options are better than others:

  • Air-sourced heat pumps are very efficient for cooling and work as part of a central-air ducted system/furnace.

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

  • High-efficiency central air conditioners are acceptable, but avoid oversizing: it is better to run at lower power for more time.

  • Ground-sourced heat pumps are effective, but have a high cost and don't work well in all cases. They should be used only when carefully planned for with expert guidance.

  • Space heating with electricity is usually limited to milder temperatures, and for smaller and highly-efficient homes. At least two alternate heat sources are recommended, and larger homes may prefer to have more than two heating sources.

  • 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 to operate when temperatures are below freezing. 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. An on-demand propane water heating is a fine choice also, but never use an on-demand electric water heater. A combination of a small electric tank that preheats water going to a smaller on-demand propane water heater can offer the advantages of both options.

  • Many well pumps require a high-power start and may need to be fitted with a soft-start capacitor (smaller pumps) or VFD controller (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, with a small pressure pump to provide water on demand.

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 are actually more energy-efficient than hand washing, especially when using the 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.

  • Conventional (hot-air) electric clothes dryers are extremely energy-intensive, inefficient, and also destructive to fabrics. However, they are hard to avoid. A lower-powered option is preferred (under 5 kW). Smaller dryers are not necessarily more energy-efficient overall, but they demand less power at one time in exchange for a longer drying cycle, which is generally more suitable with battery power. A higher-powered dryer can be fine when running while there is sunshine, else it may need the generator for support.

  • A newer type of electric dryer uses a heat pump to dry clothes at room temperature, using significantly less energy than a conventional dryer. Also, heat pump dryers are more gentle on fabric, reducing damage. These are excellent in many ways but have a high price tag.

  • Propane-heated dryers are a good choice as long as they are properly ventilated.

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.

In most cases, the cost of high-efficiency appliances will be higher in exchange for lower energy use and overall quality, but their benefits will result in savings on the solar power system sizing, enhanced reliability overall, and the benefits of better appliances in general.


Thanks for reading this guide!