Maximum Demand Explained

Regarding off-grid power systems, the maximum demand is the highest average demand, or load, over a 30-minute period. This is determined by estimating which appliances will be used simultaneously during the highest consumption period. However, this is not always easy to estimate, as each household or business uses different appliances at different times. The total maximum demand is required to select an appropriate off-grid inverter to meet the maximum demand load. If the maximum demand is calculated incorrectly, the selected inverter may be undersized, leading to an overload and system shutdown, causing a blackout.

Summer Vs Winter consumption

Depending on where you live and the local climate, the summer and winter consumption values can vary greatly depending on what appliances are used for heating and cooling, plus hot water. Other high-consumption appliances like EV chargers can also dramatically increase year-round consumption.

Summer - Off-grid solar systems are generally much more reliable in summer as the days are much longer and brighter than in winter. A correctly sized solar system should easily produce enough energy to cover the loads and recharge the battery.

Winter - In contrast to summer, winter consumption in cooler locations is generally much higher due to heating loads, and solar generation is often far lower due to poor weather and shorter days. With this in mind, off-grid solar systems are generally designed and sized around winter consumption and loads.

Off-grid system sizing and energy consumption

The size and cost of an off-grid solar system are directly proportional to the amount of energy the household uses per day. This means the more energy a house uses, the more solar and batteries that will be required to power the home, along with a larger backup generator with longer runtime during poor weather. All this equates to a greater upfront cost. In contrast, a more efficient home will require less solar and a smaller battery. With this in mind, when designing and building an off-grid home, energy efficiency and smart passive solar design should be a top priority, especially in temperate (cooler) climates.

EV charging loads

Charging an EV can require a significant amount of energy depending a how far you drive per day and how often you charge from home. For example, if you only drive short distances, such as less than 40km per day, then you might only need to charge once or twice a week, and you could even charge on weekends during the day directly from solar. However, if you need to commute over 100km daily for work, you may need to charge every night and consume 20kWh or more per charge. This would almost completely drain an average-size (25kWh) off-grid battery system and require frequent backup generator use.

Of course, a large off-grid battery system of 50kWh or more storage capacity could cover the EV charging loads as well as the household consumption, but this would also come at a far higher cost and require a large solar array. In summary, EV charging off-grid is possible, but it depends on how far you drive daily and when you are home to recharge. Learn more in the Home EV solar charging explained article.