Planning for Off-grid Systems -- Load Estimation

The first step in planning a solar installation requires as accurarate as possible estimation of the electrical loads for your building. This not only provides essential input into correctly sizeing a system, it clarifies what type of electrical lifestyle that you expect and require. If your expectations are for everything the same as you have in the city, then if you have an average home, then you would have a daily load of about 19 to 24 kWh per day. This is based on different sources that studied electrical use patterns.

Usually an off-grid system would use about 20% of what they might use when grid connected. However on off-grid house uses other energy sources, mostly propane for high electrical consumption appliances such as a kitchen range, clothes dryer, and hot water heating, so just taking the average value and multiplying by 20% does not give a useful answer.

Examples of documented off-grid homes

A number of houses that have a published electrical load plan will indicate how much electricity some people use. All but one of these examples the people involved are committed to concervation to reduce their electrical and other energy needs. Only one, the Amish house electrification was done in recent times simply due to the cost of off grid power was less than the cost of running hydro lines to a newly purchased property. They were intending to replicate the lifestyle thet had in the city, with a modest amount of concervation. Details of all of these houses can be obtained by reading the studies detailing these buildings.

Category Item A B C D
Average daily Electrical power used (kHw) 0.6 2 5.8 6
Number of occupants 1 2 4 4
Heating Central heat- automatic Propane or Oil forced air central heating furnace
Heating Heat - Propane radiant heating, via condensing instantaneous DHW
Heating Kitchen range - propane 4 burner and oven no electricity or wood X X X
Water Basic running water, Low flow water pump DC powered X X
Water Conventional running water, AC powered water pump, high pressure. X X
Hot Water Hot water heater, Propane storage, with standing pilot no electricity required
Hot Water Hot water heater, Instantaneous Propane requires electricity.  X
Lighting Minimal electric lighting X X
Lighting Moderate electric lighting X
Lighting Generous electric lighting X
Refrigeration Propane refrigeration X
Refrigeration DC electric refrigerator, high efficiency for solar homes X
Refrigeration DC electric freezer, high efficiency for solar homes
Refrigeration Electrical refrigeration, 18 cu ft best energy star 330 kWH / year 120VAC X
Kitchen appliances Microwave oven + 1 appliance, or two kitchen appliances at the same time X X X
Kitchen appliances Electric dishwasher
Laundry Propane dryer, has 120VAC  electric motor, name brand product X
Laundry Electric Clothes washer X X X
Laundry Steam Iron 1/2hr / week, 
Ceaning Vacuum cleaner X X X X
Fans Ceiling fans X
Fans Bathroom exhaust fans
Fans Kitchen exhaust fan
Entertainment TV HD, LED X X X
Entertainment Satellite TV set top box
Entertainment DVD player or VCR X X
Entertainment Radio X
Computer Laptop computer X X X
Computer Desktop computer X
Computer iPhone Cell phone charger X X
Computer High speed Internet access via satellite or terrestial wireless
Computer WiFI router X
Computer SOHO office electronic equipment (printers, fax, scanner, desktop computers) X

A) 0.6 kWh 1 person residence in NS, #12 in in CHMC study of of-grid houses

B) 2.0 kWh 2 person residence in BC, #2 in in CHMC study of of-grid houses

C) 5.8 kWh 4 person former 6 bedroom Amish home, in Nov 2013 edition of Home Power magazine.

D) 6.0 kWh 4 person residence in BC, #3 in in CHMC study of of-grid houses

Three examples of well documented energy efficient homes as drawn from a CMHC study of 12 Canadian off-grid homes. This study includes houses that went off grid from 1980 to 1997. These were selected by CHMC to identify the amount of electricity these homes were using.

Since this study goes back in time, these homes in the CHMC study were not designed to use CFL and LED lighting that we have today, and HD LED TV are quite different to the CRT technology that existed 17 years ago. None of these has 120VAC refrigeration, which is now an option. 120VAC domestic refrigeration appliance efficiency has improved, and is now no longer prohibitve for off-grid use. DC powered refrigeration models are even more efficient. Seventeen +  years later, the cost of PV panels in particular is far less than when these were commissioned. Therefore a house implemented today would include some different choices, when solar panels are a fraction of the price prevailing when these houses were built. Prices have dropped from $76.67/Watt in 1977 to around $1/Watt in 2014.

The Amish house was converted to electricity in 2012 when panel prices were in the range of $2 to $1 a watt. This is documented in the Nov 2013 edition of Home Power magazine. This is a 6 bedroom house occupied by 4 people, located in NY state. They wished to have a lifestyle similar to living on the grid in a city. They bought a house that had no indoor plumbing or electricity. The cost for a 0.5 mile grid connection was more than they spent on the solar installation. They did a detailed load estimate, and came up with a average daily load of 5.8kWh. One unusual item is they had a spring fed cistern, and can use a shallow well pump. They still retained the non-electrically operated heating system installed by the previous owners. They found in practice they used 4-5 kWh per day on weekends. Their system includes 4kW of solar modules, and a Generac propane backup generator.

Example loads for various sized cottages and homes

The columns contains hours/day use. Lighting contains bulb on hours/day, based on 5 hrs a day use, with multiple bulbs.

Click on the column heading title to see the detailed breakdown of this building.

Category Loads Hunt Camp Small cabin weekend use Typical Weekend Use Cottage 7 day a week cottage Deluxe cottage year round home Delux year round home
Heating Central Forced Air, propane 8
Heating Radiant hot water, propane (3) 7
Heating HRV Heat Recovery Ventilation 8
Water DC pump (1) 4.26 4.26
Water AC pump 0.5 1 1 1 1
Hot water Power Vent 1.05 1.05
Lighting 13W CFL 10 20 30 30 40 60 60
Refrigeration 12V Sundanzer 5.83W 24
Refrigeration 120VAC 18 cuft 311kw/yr 24 24 24 24 24
Refrigeration 120VAC Freezer 5 cuft 24 24
Kitchen appliances Microwave 0.42 0.58 0.75 0.75 1.00 0.17 0.17
Kitchen appliances Keurig coffee maker 0.13 0.13
Kitchen appliances toaster 0.17 0.17
Kitchen appliances Dishwasher (Loads) (2) 0.50 0.50 0.50 0.50 0.50
Laundry Clothes washer (loads) (2) 0.29 0.29 0.29 0.29
Laundry Propane dryer (loads) (2) 0.29 0.29 0.29 0.29
Laundry Steam Iron 0.50 0.50 0.50 0.50
Grooming Hair dryer 5 min per use 0.08 0.08 0.08 0.08 0.08
Cleaning Vacuum cleaner   0.14 0.14 0.14 0.14
Fans Ceiling 6 6 12
Fans Bathroom 1 2 2
Entertainment iPhone charger 3 3 3 3 3 6 6
Entertainment HD TV LED 25" 2 3
Entertainment HD TV LED 42" 3 3 3 3
Entertainment HD TV LED 65" 3
Entertainment Satellite set top 2 2 2 2 2 2
Entertainment Radio 1 2 2 2 1 1 1
Entertainment Blue ray/DVD player 1 1 1 1 1
Entertainment Stereo 2 2 2
Computer Laptop recharge 2 2 2 3 3
Computer High speed Internet + WiFi 2 2 3 3
Computer Desktop + monitor 0.5 0.5
Generator heater battery carb, oil heaters winter only yes yes
Inverter  Inverter standby or search mode 12 8 8 8 8 6 6
Total kWh/day 1.54 2.3 4.57 5.04 5.87 7.337 7.35
Minimum Inverter 2 2 3.6 3.6 3.6 7 7
Simultaneous use high wattage plug in appliance use
One kitchen or other plug in appliances at a time or 1500W total  
Two kitchen or other plug in appliances at a time or 3000W total  
Three kitchen or other plug in loads at a time or 4500W total  

These plug in small kitchen appliances such as a toaster, or electric kettle use 1500W, a microwave use 1000W to 1200W,  a coffee machine may use up to 1500W, depending on the model. Due to inverter limitations, you are restricted in the simultaneous use of these items. This restriction can be reduced by using a larger inverter capacity than listed, and in the case of a smaller building, select 120/240VAC instead of 120VAC only inverters.

(1) A typical Shurflo DC deep well water pump can lift 140’ and provide 30 psi pressure to a pressure tank. This is about 1/3 of city water pressure. An average city household uses 329 litres per person, so if we assume there is hot water, and the hot water is heated by wood, or an older technology standing pilot propane heater. Then making an assumption that the water use is ½ of the city rate, and for 4 persons, 660l is required per day. That requires the pump to run for 4.26 hours per day. If the well is shallower, the flow rate will be higher . If it is a shallow well (under 30’) then it operates at 3.28 l/min and uses 21.6W. This cuts the power budget by more than ½ for the same amount of water.

(2) Dishwasher, run once every 2 days, or 1/2 a load per day. Similarly appliances marked (load) the hours use column entry is the number of loads per week / 7, to yield % of a load theretically done each day. For washing, 2 loads a week is 2/7 or .29.

(3) Why use an instantaneous propane hot water heater in a year round home, instead of a propane standing pilot storage tank? The later choice does not require any electricity to operate, and it is tolerant of hard well water. The instantaneous DHW heater ‘s only benefit is a more efficient consumer of propane, at a much higher equipment cost. However this should not be used on a well with any significant amount of mineral content or with corrosive properties.


The smaller examples assume a portable, manual start generator that is kept indoors, or at least warm enough to start. When needed it is wheeled outside and plugged in and started.  Stationary generators require heaters in cold weather, similar to car block heaters. This heat comes as a load on the house battery. All year round they require a trickle charge to keep the generator’s starter battery charged.

Year round home assumptions

The deluxe year round home is assumed to be a new construction, or major renovation where the owner's preferred type of heating system can be installed. The focus is on the best electrical efficiency for the heating system, and the lowest propane use. Often radiant floor is the prefrred selection, due to lowest electrical load and the most uniform heat.

The standard year round home has a forced air furnace, probably from an upgrade from a wood burning furnace. This can be  due to the ducts and plenums are  already in place. It could also be for new construction where the lower cost furnace installation is more important than the electrical load of running the furnace.