IS IT COST-EFFECTIVE TO INSTALL A STORAGE BATTERY AT HOME?

In recent years, photovoltaics has experienced tremendous growth among individuals in North America and energy storage, in the same way, is experiencing unprecedented growth. However, one question remains essential for Canadian consumers, is buying an energy storage battery really a good solution?

Various studies have shown that when a photovoltaic system does not have a storage system, the self-consumption rate is generally between 20 and 50%. This means that a large part of the electricity produced by the solar panels is not used and is injected into the Hydro-Québec electricity grid for a fee. On the other hand, if a storage battery is connected to the installation, the rate of self-consumption increases significantly, with some professionals claiming that it can reach up to 100%.

Indeed, by storing excess energy, it becomes possible to accumulate unconsumed electricity for later use. This is particularly useful during the night, when there are outages on the Hydro-Québec grid or when the solar installation fails to fully cover the electricity needs, because the battery can then provide the necessary energy. Thus, the use of a storage battery reduces dependence on fluctuations in solar production as well as on the national electricity grid.

THE DIFFERENT TYPES OF SOLAR STORAGE BATTERIES

Note: The energy storage capacity of a home battery can be measured in ampere-hours (Ah), watt-hours (Wh) or kilowatt-hours (kWh).

The power of a battery is measured in watts (W) or kilowatts (kW), and can be calculated by multiplying the maximum current indicated in amperes (A) by the nominal voltage indicated in volts (V). For example, a battery declaring a maximum current of 200 A at a voltage of 12.7 V will have a maximum power of 2,540 W (or 2.54 kW).

In the residential market, the two most commonly used types of batteries are lithium and lead-acid batteries. As for lead-acid batteries, they come in three different forms depending on their technology: open lead-acid batteries, gel batteries and AGM batteries. AGM batteries are still widely available due to their lower cost and the fact that they were historically the only ones available before the rise of lithium technology. However, they are gradually losing ground to lithium batteries which offer many advantages, including a much higher energy density, a much lighter weight or an energy capacity that remains stable over several years for high-end lithium batteries such as those we offer at Volthium.

• The lithium battery is currently the most popular in the market due to its advanced performance. This type of battery has the advantage of being both compact and lightweight, in addition to having a considerably longer life than lead-acid batteries. Within the

Lithium technology, there are different chemical formulations. For example, the LiFePo4 (lithium-iron-phosphate, or LFP) battery is known to be safer (with less risk of fire), more durable (with a longer lifespan) and more flexible (able to withstand deep discharge) better than conventional lithium-ion batteries. However, they have slightly less energy density. However, not all lithium batteries are created equal and we must be careful of bad marketing practices. You can refer to our article Explain the price difference in the market between LFP batteries to learn more.

• The open lead-acid battery uses a solution of sulfuric acid and water as an electrolyte. This type of battery is the most economical on the market, but these batteries offer the shortest life and low energy density. For these reasons, this technology is recommended only for occasional use. Another disadvantage of the open lead-acid battery is that it releases hydrogen.

• The AGM (Absorbent Glass Mat) battery, just like the open lead-acid battery, also uses sulfuric acid, but it is more airtight thanks to the presence of glass fibers that act like a sponge. It has a longer lifespan than the open lead-acid battery but much shorter than a lithium battery, it is suitable for daily use, making it slightly more expensive. In addition, AGM technology prevents the release of hydrogen. On the other hand, it is a technology that today is overtaken by lithium batteries because of its lower energy density, its heavier weight and its limits of use.

• The gel battery uses a composition of sulfuric acid and silicic acid, which gives a gel-like texture to the electrolyte. This version is the most durable and easy to maintain among lead-acid batteries. As a result, it is also the most expensive lead technology.

USING A STORAGE BATTERY: LIFETIME AND DEPTH OF DISCHARGE

To evaluate the economic profitability of a home battery, it is important to understand a few technical concepts, such as depth of discharge and service life.

The depth of discharge, also known as DoD (depth of discharge), is the maximum recommended level of discharge for a battery before recharging. It is usually expressed in volts, but is often translated as a state of charge from 0 to 100%. It is essential to note that a lead-acid battery can never be completely discharged at the risk of being severely damaged and drastically reducing its lifespan. To better understand, let’s take the example of a storage battery with a capacity of 1 kilowatt hour (kWh). Generally, the depth of discharge of a lead-acid battery is 50%, so you could use only 0.5 kWh of the stored energy before you need to recharge the battery. On the other hand, for lithium batteries such as those we offer at Volthium, you can discharge your battery entirely without damaging its lifespan or storage capacity, giving you access to the full energy storage capacity of the battery. For comparison, a single 12V 400Ah battery from Volthium would replace 8 AGM batteries.

The life of a battery is closely related to its depth of discharge. It is measured and expressed in number of charge/discharge cycles. The lifespan varies depending on the battery technology and can range from 400 to 6,000 cycles, depending on the specific measurement methods used by the manufacturer.

As a general rule, lithium batteries offer many cycles and therefore a much longer life than other batteries.

A LOOK AT PROFITABILITY

In the first table below, an assessment of the amount of energy stored and destocked in a 1 kWh battery over its lifetime was performed, and was measured in cycles. This amount of energy depends mainly on the type of battery, the number of cycles performed and its storage capacity. Other factors such as ambient temperature and type of use (intensive, repeated deep discharges, high power demands) also have a considerable impact on the life of a battery.

The formula used to calculate these values is as follows:

Total quantity stored and destocked = depth of discharge x storage capacity x number of cycles.

In the second table, you will find the cost of each kilowatt-hour stored and destocked in a
battery with a capacity of 1 kWh throughout its lifetime. To achieve this result, here is the formula that
was used:
Cost = Battery price/Total quantity stored and destocked

POINT POWER CONSUMPTION AND HYBRID SYSTEM

One of the major problems encountered by Hydro-Québec is the low energy capacity available on the grid during peak hours, which does not allow all consumers connected to the grid to operate all their devices without having network outages at times.
The solution to this low energy capacity at peak times is called “peak shaving”. The principle is simple: store solar electricity or cheaper electricity (outside peak hours)
In a storage battery, use battery energy when grid electricity is at peak times, recharge batteries through your solar installation or when kWh prices are lower (off-peak hours). And in this way, you reduce your electricity bill without disrupting or changing your daily activities.
To summarize, the goal of “peak shaving” is:

• Have fully automatic energy redundancy during outages
• Be able to take advantage of the 30% discount all winter with Hydro-Québec and thus make the benefits of
  equipment
• Contribute to the reduction of the carbon footprint and avoid buying energy urgently for
  energy peaks

It should be noted, however, that to optimize the profitability of a hybrid system, it is recommended to opt for the dynamic rate of your electricity supplier such as the flex D rate that Hydro-Québec can offer. This will save you a lot of money! At Volthium we have been working for several years to develop batteries perfectly adapted to hybrid or autonomous systems in order to optimize peak shaving. Thanks to the quality of our storage solutions, we are now partners with Hydro-Québec and we currently provide Hydro-Québec with backup batteries for telecommunications towers and infrastructure, and other departments, including research in Shawinigan. But how to establish the “Peak shaving” easily, tomorrow morning, at home for example? For an average bungalow, we are talking about the purchase of 20KWH of batteries, and a residential hybrid inverter of 15KWH. Most houses have a 200 Amp panel. The 15KWH residential hybrid inverter we mention can be installed easily and quickly by a master electrician and can support the entire 200A panel during peak periods.

There is therefore no need for an electrical sub-panel as seen in homes with a generator. In fact, with the new hybrid inverters available on the market, the entire electrical panel will be redirected to home batteries during peak consumption hours. Consumers do not realize anything and have no manual action to perform. Hydro-Québec’s consumption will then be 0 KWH when the rate is the highest. When the peak period ends, the hybrid inverter abandons power via the batteries and transfers the entire panel to Hydro-Québec’s inlet automatically, quickly, and without interruption. From then on, the batteries will charge at low prices (or through solar panels) and they will be full and available for the next peak period. But this is not the only advantage; During power outages, the batteries will take over entirely, and this, automatically, allowing you to maintain your autonomy until Hydro-Québec technicians, whose workforce is never large enough during outages, can intervene!