The Powerwall: Tesla’s home battery and backup in Quebec, a comprehensive review

The Powerwall is a lithium-ion type battery from the American manufacturer Tesla. It was marketed on April 30, 2015 and is now available in two different models (Powerwall 1 and Powerwall 2) with 6.4 kWh and 13.5 kWh of capacity respectively.

Like any other type of battery, the Powerwall recharges with the electricity generated by the solar panels and stores it for later use. It can also be charged by the Hydro-Québec network when the solar panels no longer generate electricity (ie at night).

A Powerpack version is available for commercial or industrial use, where a multitude of batteries are combined to generate up to 232 kWh of storage.

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The table below shows the technical characteristics of the two Powerwall models. These are taken from Tesla’s official website.

Capacity is defined as the amount of energy stored. The higher the capacity, the greater the autonomy it provides. It is therefore more advantageous to obtain the Powerwall 2 since it offers greater autonomy.

The 100% discharge depth means that the Powerwall can be fully discharged without affecting its useful life. The manufacturer mentions this since this is not the case for all the batteries available on the market today. Indeed, several battery technologies (ie. Lead-acid, Nickel-Cadmium) suggest a maximum discharge depth of 50 to 75%. Lithium-ion batteries are therefore more advantageous since they offer more energy per battery.

The bearable power by the Powerwall represents the sum of the powers of the devices in operation simultaneously that the Powerwall can manage. For example, if you are billed at the Hydro-Québec’s D Rate (the most common residential rate in Quebec), the maximum power peak tolerated is 65 kW. This 65 kW is more than enough to allow you to carry out several tasks simultaneously without worrying about the power demand generated since it is only very rarely achieved (not to say never for the majority of households, even if you have a swimming pool or a spa). In the case of homes that take their electricity from a Powerwall, the power peak must be of 7 kW maximum. Being almost 10 times less than the power peak tolerated by Hydro-Québec’s network, daily activities must be shifted. Indeed, explained by the Peukert effect, the capacity of a battery decreases exponentially when the intensity of the discharge current increases linearly. In other words, this means that if you don’t want to drain the energy contained in your Powerwall too quickly, you will have to be careful with the number of devices that you decide to operate at the same time. The figure below shows the battery discharge time decrease (y-axis) versus its discharge current intensity increase (x-axis). It is therefore essential to be aware of our energy behavior when using batteries.

One cycle corresponds to a complete charge and discharge of the Powerwall. Assuming that a full cycle is performed daily, a lifetime of 5000 cycles is equivalent to 13.7 years.

How many Tesla Powerwalls would I need in Quebec?

According to Hydro-Québec, a 2,000 square foot single-family home that does not have a pool or a spa consumes an average of 25,000 kWh of electricity per year. This consumption is theoretically equivalent to 70 kWh/day. However, given that our average winter electricity consumption is two to three times greater than our average summer electricity consumption, dividing this 25 000 kWh by the number of days in the year would not be representative of average daily electricity consumption. Indeed, this division would only bear witness to an average value of low and large values. Let’s suppose that in winter your electrical demand is 120 kWh/day and that it fluctuates around 45 kWh/day for the rest of the year.

 If you want your Powerwall to offer you at least one full day of autonomy in the worst possible scenario (for a winter day), you will need nine Powerwalls (120 kWh/day ÷ 13.5 kWh/Powerwall = 9 Powerwall). It would cost you 97 200 $ (before taxes and without installation fees).

 If the same calculation is repeated for the best possible scenario (one day of autonomy for a summer day), you will need three Powerwalls (45 kWh/day ÷ 13.5 kWh/Powerwall = 3 Powerwalls). It would cost you 32 400 $ (before taxes and without installation fees).

 Following the same logic as for the two previous scenarios, those who would want only one Powerwall would meet 30% of their energy needs in an average summer day against 12% in an average winter day.

As mentioned earlier, a Powerwall would give you 13.5 kWh of energy, which would allow you to perform only certain basic functions. The table below shows the energy required for the operation of typical household appliances.

The table above shows how easy it is to consume 13.5 kWh of energy. Indeed, knowing that the 13.76 kWh of the table does not take into account heating (which accounts for 60% of our overall energy consumption), the use of washer and dryer (both very energy-consuming) and the use of a multitude of other devices (vacuum cleaner, dehumidifier, fan, video game console, dvd player, sound system, coffee machine, etc.) this amount of energy is very little. It is even more important to remember that the 13.76 kWh of energy required to operate these devices can easily double if several devices are operating at the same time (Peukert effect). In addition, considering the power that can be supported by the Powerwall (5 kW continuous and 7 kW maximum), not all the devices listed in the table above could operate simultaneously. Compromises would have to be made.

Do not forget that an average daily electricity consumption for a Quebec household is 45 kWh in non-winter period and 120 kWh in winter. 13.5 kWh is therefore very little considering its purchase cost of 10800 $.

Could opting for dynamic pricing make your Tesla Powerwall profitable in Quebec?

Hydro-Québec has offered dynamic pricing since 2019 that adjusts the price of electricity according to demand. This pricing is offered in two separate rates, either in Flex D rate or in D rate with the winter credit option. In both cases, the rate is applicable for a period of 100 hours in winter, from December 1 to March 31 inclusively and allows you to save money when you reduce your electricity consumption during peak hours (from 6 am to 9 am and from 4 p.m. to 8 p.m.).

The goal of dynamic pricing is to better distribute electricity demand in order to relieve the public network during peak hours and allow it to meet all the demand alone. Knowing that imports of electricity are necessary when the network is not able to meet all our needs, it is to our advantage to better manage our consumption.

The Flex D rate means that the purchase price of electricity is lower during off-peak hours and higher during peak hours. The image below (taken from the Hydro-Quebec website) shows the pricing structure. The price of electricity drops 22 to 30% during off-peak hours and increases from 534 to 822% during peak hours.

Rate D with the winter credit option means that the price of electricity is the same as that of Rate D (without option), but a 50¢ credit is offered for each kWh saved during hours of spikes. The image below (also from the Hydro-Quebec website) shows the pricing structure.

Hydro-Québec estimates that with Rate D with winter credit option, $ 70 in savings can be made for every $ 1,000 of your electric bill. For the Flex D rate, $ 100 in savings are achievable for every $ 1,000 of your electric bill. The Flex D tariff gives you the opportunity to save more but requires much more discipline given the very large increase in the price of electricity during peak periods.

As for those living outside Quebec, the principle of dynamic pricing remains the same. The only difference is in the value of the monetary reward, which varies depending on the region and the supplier’s production costs.

Dynamic pricing becomes attractive to those with a Powerwall since it allows its users to better distribute their electrical demand. Indeed, the Powerwall can recharge during off-peak hours and discharge during peak hours, which means that the demand for electricity is zero during peak hours. This means that savings can be made with your Powerwall. However, depending on the magnitude of your energy consumption, the annual savings achievable seem to be still too small to allow you to monetize your Powerwall.

The Tesla Powerpack, the commercial version of the Powerwall backup solution

As mentioned earlier, a Powerpack version is available for commercial or industrial use. A Powerpack can have up to 16 batteries and have a maximum capacity of 232 kWh. The table below shows the technical characteristics of a Powerpack. These are also from the official Tesla website.

It should be noted that several Powerpacks can be connected in series or in parallel in order to increase the voltage or the total capacity of the system. Thus, a company wishing to have an energy capacity of 500 kWh could have five Powerpacks connected in parallel.

Conclusion

Ultimately, although the acquisition of a Powerwall offers the possibility of being self-sufficient in energy for a certain time, its too high cost makes it unfortunately unattainable for most of the population.

It is still very interesting for individuals who can afford it given the comfort and peace of mind it provides. Indeed, knowing how essential electricity is in our daily life, being able to be independent during crisis situations is very attractive. In addition, in the case of dynamic pricing, the Powerwall allows you to save money by offering you the possibility of better distributing your electricity demand during peak periods. In the case of an off-grid installation or in a place where power failures are frequent, the installation of a Powerwall is also significantly advantageous.

Do not hesitate to contact us to start the installation process for your Tesla Powerwall. Our partners are certified to install the Powerwall. We will be happy to help you achieve energy self-sufficiency.

*Update* : As for April 2020, the cost of the Powerwall is 9250 $ CAD, supporting hardware is 1550 $ CAD. We estimate installation costs to be between 2500-4500 $ CAD. That means a total installed cost of around 13300-15300 $ CAD.

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