• Sonny Rivers

Off-Grid Solar

The off-grid lifestyle is one of independence, self-sufficiency, and self-reliance. Whether it's just being practical or trying to achieve an ideal, living off-grid can offer greater resilience compared to homes that are entirely 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 to avoid a high grid-interconnection cost.


How it works


Your home will be powered by a high-capacity battery installed in the garage or a mechanical room and are connected to your electrical panel much like an ordinary appliance. The solar power system generates power for the home's electrical loads while simultaneously charging the battery throughout the day. At night, the stored energy is discharged from the battery to power the home.


It is never reliable to depend on one system. A standby generator is required, especially for winter environments, to ensure an additional power source is available on demand. Combined, solar plus a generator offers a continuous, reliable power supply.

Sizing a system


To properly size the system, we need to first estimate the electricity needs throughout the year. The number of occupants, the major appliances, and square footage are some of many factors that contribute to determining the minimum system capacity.


An average, small to medium sized home uses about 12,000 kWh per year (kWh/Year), or an average of 30 kWh to 40 kWh per day (kWh/Day). However, every home and its occupants are unique and seasonal needs vary (usually, the highest power consumption occurs during the winter).


Smaller and more efficient homes (especially newly-built) can reduce energy requirements significantly below average through construction methods and an airtight building envelope. Selection of equipment and appliances are also important. (More on this below and on our FAQ page.)


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


(See Power vs. Energy post for more detail on this.)


Energy use


The solar array is sized to provide for the highest energy need during the shortest days (i.e. winter), but not necessarily the worst-case scenario. Since a backup generator will be on standby, solar should try to cover the bulk of power requirements.


Recommendations:

  • Heat is needed most when there is the least sunshine. Installing two or more heating sources (propane furnace, heat pump, biomass, electric) is highly recommended.

  • South-facing windows to capture the winter sun, with awnings that provide shade during the summer, are excellent.

  • Air-tightness of the building and high R-value insulation are very important. (Mechanical ventilation is also required.)

  • Air-conditioning is a great match with solar since it is used most when there is the most sunshine. Heat pump systems are preferable to central units, but neither should not be oversized. Mini-split units that condition specific rooms are a great choice, and whole-house fans can be very effective as well.

  • For water heating, install a hot water tank fitted with 3800W elements. (Do not install an on-demand electric water heater.) Propane on-demand water heaters are good, especially when paired with an electric tank preheated by solar.

  • Well pumps are often a high-power load. Larger pumps must be fitted with a soft-start or VFD controller to minimize lock-rotor amps (starting power). A cistern with a pressure pump and tank can also be a great option.

  • 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.

  • Clothes dryers are major loads, so propane models are preferred for off-grid homes. Otherwise, a smaller electric dryer may be used on a sunny day.

  • Geothermal systems (a.k.a. ground-source heat pumps) are efficient 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 alternatives.


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 snow storms 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 me maintained regularly, especially before winter.


Consultation


When planning a new construction project or total home renovation, reach out to us for further consultation.

ABOUT US

Black Hills Solar specializes in solar power, energy storage systems, and electrical services.

LOCATION

Rapid City, Black Hills, South Dakota

Serving Counties:

Pennington, Meade, Custer, Fall River, Lawrence, Butte, Weston, Crook

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