• Sonny Rivers

Off-Grid Solar

The off-grid lifestyle is one of independence, self-sufficiency, and self-reliance. Whether to achieve an ideal lifestyle, have autonomy, or be practical for the situation, living off-grid can offer greater resilience compared to homes that are dependent on the grid. (Homes that are already grid-connected can attain a similar degree of autonomy as a "backup system".)

The ideal scenario for an off-grid home is during new construction, when there is the most opportunity to build optimally, maximize energy efficiency, and avoid a high grid-interconnection cost.

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 so in a winter climate. The majority of energy consumption in most buildings is related to heating (and cooling).

A quality building envelope is key to ensure energy conservation where needed most. Efficient homes have a high insulation value (R-40 walls, R-60 ceiling), and air-tight envelope, and heat-recovery ventilation (HRV) to keep the air fresh without temperature loss. New homes, when built for energy conservation, can operate with high-performance modern appliances using one-third of the energy use of an average American home.

Heating is very energy-intensive and needed most when there is the least sunshine. Multiple sources for heat and power are recommended for improved resiliency and efficiency throughout the seasons. Propane, biomass (wood), and a backup generator are standard in most off-grid homes. A standby generator steps in during short days and winter weather, but gets minimal use for most of the year.

How it works

The home is powered by a battery (or set of batteries) installed in the garage or a mechanical room, usually where the main electric breaker panel is located. 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 step in if the battery gets low.

Sizing a system

The number of solar panels and capacity of battery are 'sized' to provide for nearly all electric usage, with the exception of some occasional generator use. Even when sizing a very high solar capacity, an auxiliary power source is generally preferred to guarantee uninterrupted power.

The power capacity needed depends mainly on the construction quality, square footage, number of occupants, and major appliances. The home's roof might be designed to accommodate the necessary number of solar panels (at the right tilt and orientation), or a nearby open space on the ground might be used. But since a new home has no history of energy use, sizing larger and/or being able to readily increase the power system capacity are common practice to ensure all needs can be met.

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). 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 20% of average to over 500% of average energy use in some cases.

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 home

15 kW for larger homes

20 kW+ for the largest single-family homes

Major Appliances

Here I will list the larger and more significant appliances with considerations for how to select from the options. Most smaller appliances and electronics that are not used continuously are less significant, but user behavior is ultimately responsible for actual energy consumption.

  • Mechanical ventilation is essential for high efficiency homes with a tight building envelope (confirmed by a blower-door test). Also known as heat-recovery ventilators (HRVs), they exchange indoor air with filtered outdoor air without losing/gaining heat.

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

  • Newer, efficient central air conditioners are one option (avoid oversizing: it is better to run at lower power for more time).

  • Heat-pumps are very efficient provide for both cooling and heating.

  • Mini-split units for cooling specific rooms.

  • Whole-house fans can be very effective to ventilate hot, stale air quickly.

  • Space heating with electric is usually limited to milder periods, and for small and highly-efficient homes. Heat pumps are excellent for heating in spring/autumn, while a propane furnace or biomass (wood/pellet stove) heater serves additional heat during the coldest periods.

  • For water heating, a large hot water tank with electric elements (or a hybrid electric/propane tank) is preferred. Never use an on-demand electric water heater, but on-demand propane water heating is a fine choice. A combination of a smaller electric tank that preheats water going to a smaller on-demand propane water heater can offer advantages for both options.

  • Many well pumps require a high-power start and must be fitted with a soft-start capacitor (smaller pumps) or VFD controller (larger pumps). 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 with less energy.

  • For the kitchen, an induction cooktop is the best choice, but a standard electric range is acceptable also. If used, a gas stove or oven should be well ventilated.

  • There are many options for efficient dish washing machines.

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

  • Conventional clothes dryers (heaters) are extremely energy intensive, inefficient, and also destructive to fabrics; they should not be used in most cases. New heat pump dryers are strongly recommended, as they use significantly less energy (without the damaging side effects).

  • Geothermal systems (a.k.a. ground-source heat pumps) are efficient and can work better than air-sourced heat pumps in the winter, but should be considered very carefully. The actual effectiveness of a geothermal system depends on the location, and the costs to install may be very high compared to air-source heat pumps.

  • Internet connectivity is essential for monitoring and updating solar and battery power systems. Purchase a new modem and router that is listed for efficiency. Avoid rental units provided by internet service providers, which may be outdated and inefficient. In the most remote areas, Starlink may be the best or only choice.

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 over all, and the benefits of better appliances in general.