• Sonny Rivers

Off-Grid Solar

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

The best case for an off-grid power system is during new construction, when there is the most opportunity to build optimally, maximize energy efficiency, and avoid a high grid-interconnection cost. Existing homes that are already grid-connected can attain a similar degree of autonomy as a backup system.

Every home should be built for a high degree of efficiency, but especially homes in a winter environment and off-grid homes with a conscientious energy footprint. A well-designed home may cost more or be smaller than today's conventional build, but like in Europe, our new homes can have one-third of the energy use of an average North American home. The building envelope is key, for a leak-free home with a high insulation value (R-40 walls, R-60 ceiling) and heat-recovery ventilation (HRV).

Multiple sources of power and heat further improve resiliency, such as propane, backup generator, biomass, etc. Heating is very energy-intensive and is needed most when there is the least sunshine, so electric is best for secondary heat. As long as electricity use is met by solar for most of the time during the darkest months, there will be minimal generator run-time and for the rest of the year, solar power will exceed the average needs (including cooling).

How it works

Your home is powered by a battery (or set of batteries) installed in the garage or a mechanical room. The power system is connected to your main electrical panel in place of the grid. Solar panels provide the home's power directly while simultaneously charging the battery throughout the day. At night or whenever needed, stored energy is discharged from the battery to power the home. And when there is above average power use and below average sunshine, the automatic standby generator will step in if the battery get's 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 occassional generator use and winter heating. Actual energy use is fairly predictable but may also change over time, so aiming larger from the start or starting small with the option of future expansion may be considered.

The system capacity needed will be estimated based on the square footage, type of construction, number of occupants, and major appliances. Actual system options also depend on space available for the solar array.

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 our opinion, average is inefficient and it is possible to live just as comfortably with two-thirds or even one-third of average electricity use if building new or performing a complete renovation with new insulation.

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 small home or cabin

10 kW for a moderately-sized home

15 kW for larger homes

20 kW+ for the largest family homes

Major Appliances

  • 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.

  • New and efficient central air conditioners can be used, but avoid oversizing; it is better to run at lower power for more time is better.

  • Heat-pumps efficiently provide for both cooling and heating.

  • Mini-split units that condition specific rooms are a great choice.

  • Whole-house fans can be very effective as well.

  • Space heating with electric is usually secondary to a main heating system such as a propane furnace. Usually only a small, highly-efficient home could consider electric heat as the primary and use a generator to support electric heat. A propane furnace or biomass heater is usually necessary. (With combustion, attention should be given to ventilation and air quality, so properly ventilate propane appliances and the room they occupy, and when possible it may be preferable to use an outdoor burner.)

  • For water heating, it works best to use a larger hot water tank re-fitted with 3800W elements. Alternatively, a combination of a smaller electric tank that preheats water going to a smaller on-demand propane water heater can offer advantages for both. (Never use an on-demand electric water heater.)

  • 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 greater resiliancy, the well pump can fill a cistern for water storage at the surface, and then a pressure pump provides water on-demand with less energy.

  • For cooking, install an induction cooktop (best) or a standard electric range. We don't recommend using a gas stove or oven, but if used it should be well ventilated.

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

  • Conventional clothes dryers are extremely energy intensive, inefficient, and even destructive to clothing. New heat pump dryers use significantly less energy and are better for the clothes. Alternatively a propane dryer, or smaller electric dryers can be used conscientiously.

  • 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.

In most cases, the cost of high efficiency appliances will be relatively high in exchange for lower energy use, but their benefits will result in savings on the solar power system sizing, enhanced reliabilty over all, and other features.

Propane generator

A propane-fueled standby generator (14 kW to 20 kW) is essential for an off-grid system, especially in a winter environment. In most cases solar will meet >90% of annual electricity needs, and for most of the year the generator is not needed. But during an inevitable week of snowstorms or consecutive days of heavy cloud cover, the back-up generator ensures that the loads remain powered and battery recharged. A larger generator is especially necessary to power electric heat. Generators should be maintained regularly, especially before winter.