Increasing battery size will increase the battery utilisation

Let's compare two different battery sizes to see if one can achieve significantly higher savings than the other.

In this article, I looked at how increasing the battery size can also increase the utilisation rate of a battery, increasing its value to you, the homeowner!

Increasing the battery utilisation rate by almost 10% when upgrading from 8 to 11 kWhs of battery for an extra $130 in savings

Battery utilisation means how often the battery is really in use, charging and discharging, rather than sitting empty or fully charged when solar energy is abundant or not available.

Two weeks ago I finished a solar and battery analysis for a home outside Melbourne. The home currently has no solar or batteries, so the homeowner wanted to know how much they could save on their energy bills by installing both at the same time. For now though, we are going to focus on two different battery sizes we modelled for the home.

The chart below shows how often this home would use an 8.2 kWh and an 11 kWh battery if they had a 13.2 kWh battery. Ideally, we want to see as little white space in the graph as possible, which would tell us that the battery is charging and discharging in full cycles regularly.

More often than not, the battery completes a full cycle of charging to its maximum capacity and then discharges a fair bit, depending on the demands of that day. There is a bit of white space in March, which is most likely due to the homeowner going on holiday for a few weeks.

A smaller battery is utilised less often, discharging its full capacity faster.

Following on from the graph above, I calculated how often the two batteries sit at full capacity and how often they sit completely empty.

In the table below, we can see the smaller battery has a lower overall utilisation rate primarily because it discharges all of its energy faster and then sits empty for longer. In contrast, the larger battery can discharge more power to the home over a longer period of time and thus is in use for longer.

While a smaller battery will be cheaper, it won't necessarily mean you will get a higher utilisation rate.

Perhaps if we were to buy energy from the grid while energy is cheap, charge the battery, store it and use it later in the day, we could turn the tides a bit here. But buying grid energy to charge a battery is an extra level of analysis, and I've done it once before. In a past article, I wrote about the savings and costs of buying energy for a battery

But outside of buying energy and storing it, using a smaller battery clearly means it will run out of stored power faster, and when it's sitting empty, it's a battery with wasted potential. But before we start to get too sour here, let's look at how much savings we are really leaving on the table by buying a smaller less utilised battery.

This house would save roughly $130 more a year with the bigger battery

For some context, this home uses a lot of power at night, so they are already playing to the strengths of a battery. Meaning the energy stored in either battery size will most definitely be used each night.

The last row of the chart below shows a rough average of what kind of savings could be achieved with each battery size.

Below is an explanation of each row:

• Savings so far are from late January to late August (this is all the data we had available for this home)

• Savings per day is the daily average of the previous savings

• Solar opportunity cost is the money they could have earned if they sold the energy to the grid for 5.2¢ instead of storing it

• Real savings per day is the daily savings minus the solar opportunity cost

• Savings per year is the estimated total savings for a full year

The home in this analysis is on a peak/off-peak energy plan, and we optimised the battery to discharge during their peak hours. Also, they already use quite a lot of their power in the evenings so the battery is covering their highest costs and highest peak consumption times.

All in all, the battery's savings look pretty favourable. Given these very rough averages, and depending on the cost and installation of a BYD battery, a BYD battery for this home could break even in its lifetime. Of course, they also get the benefits of storing renewable energy in their home and having blackout protection too!

There are some important factors that we left out of this analysis

One important variable not included in this analysis is the fact that energy costs continue to rise year on year. Unfortunately, I misplaced my crystal ball, so I couldn't factor in the price of energy for the next ten-plus years. I could factor in a small multiplier on the prices, but I need to do more research on market trends. That said, as costs rise and feed-in tariff prices continue to decrease, this battery will look more financially attractive each year.

Another variable left out of this analysis is the rate of battery degradation over time. Battery degradation is an ongoing science, and after talking to an expert on batteries recently, I am not going to try to predict it. As he pointed out, the jury is still undecided on how large of an issue battery degradation really is. These two factors could be taken into consideration to make a more complete analysis. And, as I mentioned in the dot points above, we only had around seven months of the homes energy consumption history to use, so we had to make some assumptions, ideally we have at least one year of full data to work with.

Nonetheless, some analysis is better than flying blind. This is certainly one of the more optimistic analysis I've done, partly because this home is quite well suited to benefit from a battery, by using more energy in the evening they maximise the value of the battery.

You can get your own solar and battery analysis without getting off the sofa

SolvingZero is purpose-built to make analysing your energy as easy as possible. The dream is you can connect to your energy without getting up from your sofa, no need to connect a device or have a sparkie visit your home.

While we are still working on making battery analysis open to everyone, we already have a solar analysis tool available to use right now. If you want to see how much you can save by installing solar then take one minute to link your energy to your own SolvingZero dashboard, its free!