The off-grid lifestyle is one of energy independence and greater resilience compared to utility-powered homes.
The best case for an off-grid power system is during new construction, when there is the most opportunity to maximize energy efficiency and save money on the often high cost of connecting to the utility. However, any property including large family homes and even whole communities can be powered by their own solar and battery micro-grid.
Already connected to the grid but interested in energy independence? See - Hybrid Power Systems.
How it works
High-performance lithium batteries are installed in the garage or a mechanical room and are connected to your electrical panel much like an ordinary appliance. The solar power system, also connected to an electrical panel, 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.
When extra power is needed (mainly during winter), a propane powered backup generator keeps the power on while the battery is recharged. Combined, solar plus a generator offers a continuous, reliable power supply.
Sizing a system
To properly size the system, we need to estimate the electricity needs throughout the year. The number of occupants, major appliances, and square footage are some of many factors that contribute to power and energy requirement.
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 their occupants are different and seasonal needs vary (with most power needed during the winter).
Smaller and more efficient homes (especially newly-built) can reduce energy requirements significantly below average. For the best results, there are several guidelines and recommendations to follow.
Selection of equipment and appliances are a key consideration. Any given appliance has its own power requirement (load) needed to operate, which varies significantly.
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 large family homes, electric heating, and/or inefficient buildings
The solar array is sized to provide for nearly all electricity needs, especially to meet the highest energy need during the shortest days (i.e. winter). If a smaller solar power system is desired, propane can be used for heating, cooking and clothes drying.
Though possible to generate a share of heating energy from solar panels, heat is needed most when there is the least sunshine. The best practice is to use propane and/or biomass (wood or pellet stoves) for space heating.
Air-tightness of the building and high R-value insulation are very important.
South-facing windows to capture the winter sun (passive solar heating) are recommended.
Air-conditioning is readily accommodated by solar since it is needed most when there is the most sunshine. However, air conditioning is a major energy consumer, and is best when controlled with a smart thermometer. Inverter-air-conditioners and mini-splits are an excellent choice. Larger air-conditioners must be fitted with soft-starting controllers to apply power more efficiently during start-up. Whole-house fans are exceptionally effective when paired with smaller A/C systems.
Water heating is one of the largest loads alongside air-conditioning. Tanks are preferred, whereas on-demand electric water heaters are incompatible (in most cases). On-demand propane water heaters are acceptable, especially when paired with an electric tank preheated by solar. Large tanks are best when custom-fitted with low-power heating elements. Hybrid electric-propane tanks are also an option.
Heat pumps are efficient appliances for heating and cooling, including water heating. However there are caveats to their favorability and the options should be considered on a case-by-case basis.
Clothes washing machines are easily powered by an off-grid power system, especially newer high-efficiency models.
Clothes dryers are major loads, so propane models are preferred for off-grid homes. Otherwise, a small electric clothes 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.
Well pumps are often major loads, but can be accommodated. Larger pumps must be fitted with a soft-starting controller. It is also best to use a pressure tank, and for even greater resilience, a well-to-cistern system is an excellent choice.
Of the many kitchen appliances you may use, any that plug into a wall outlet are a fine choice. Induction cooktops are excellent. Large electric ovens, however, are a major load. If regular oven use is expected, a propane model may be favorable.
Given the number of considerations for household load selection and energy management, keep in mind that the presence of a back-up generator means that at any time it is possible to power large loads as much as needed.
A propane-fueled standby generator (8 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 used. But during the inevitable week of snow storms or consecutive days of heavy cloud cover, the back-up generator ensures that the loads and battery remain powered and charged as much as necessary.
When planning a new construction project or total home renovation, reach out to us for a free consultation.