Big solar and small batteries can break even

We did a complete solar and battery analysis for a home that has neither! The homeowner wants 13.2 kWs of solar and a 8.2 kWh BYD battery which, by our estimates, might actually break even!

This week, we'll look into a solar system with a BYD battery we designed from scratch.

One VIC home can expect a savings of $780 a year or $2.15 a day for installing a 8.2 kWh BYD battery

Build Your Dreams batteries are modular, smaller and cheaper alternatives to the Telsa Powerwall batteries that have dominated the market. They also seem to be getting very close to breaking even, meaning they just might pay themselves off before they run out of warranty.

In the chart below, we plotted the battery's daily savings relative to the possible solar credits that could be earned if the solar was sold to the grid for 5.2¢, we call that the Solar Opportunity Cost.

The graph above only takes into account 2024 so far, meaning there is still more data to be collected and used until Dec 31st. But so far, things are looking pretty optimistic.

In the beginning, you might notice a dip in the savings for about two weeks. This indicates a significant decrease in energy consumption for the home, which would most likely have been a holiday where no one was home.

Overall, though, the battery is working well. Given that this home plans to install 13.2 kW of solar on the roof, it can fully charge the battery almost every night. The smaller battery almost always reaches peak charge levels and then can discharge at night when cheaper power is needed. Even in winter, we predict reaching a high charge level, given that the solar system is much larger than the battery.

This home uses more power at night so the battery gets a full discharge cycle each night

This battery works so well for this home because it suits their lifestyle of consuming quite a lot of energy at night. They are also planning to install a large solar system to offset their energy consumption during the afternoon hours. The excess can then be stored in a battery for later that evening. At night, as their time-of-use pricing kicks in, they can start to draw power from their battery to offset their 49¢ peak priced energy. This saves them around $2.15 a day by using their battery. Two dollars and some change doesn't sound like much, but if we extrapolate that over ten years, it comes to roughly $7,850 in savings!

Because this home already has a consumption profile that is skewed towards the evening hours a battery will benefit them more rather than a house that consumes more energy during daylight hours or has less consumption at night. Each home is different and so you would need to take into account your own circumstances.

The lost value of selling the solar is around $125 a year, which brings the ten-year battery value down to $6,650

$7,850 in battery savings does sound good, but it's not quite the full story. We need to consider that storing solar energy does not mean selling it. For this home, they could sell their solar at 5.2¢ a kW, which means they are missing out on $125 a year in credits there. This opportunity cost is around 34¢ a day at the current rate things are trending. If we could maintain that feed-in-tariff credit for the next ten years they would lose out on around $1,250 in possible solar credits.

Now subtract those lost solar credits from the original battery savings and the battery down to $6,650, which is still great value for a 8.2 kW battery!

The battery will most likely cost a little bit more once we consider install costs. However, if it can make it, the battery will most likely break even within fifteen years. Which is not even taking into account rising energy costs and falling feed-in tariff credits!

This battery and solar setup is the closest to breaking even I have seen so far. The battery's utilisation might not be perfect, as it will stay fully charged quite often in the afternoon. Ideally we'd prefer it to be in a perfect sweet spot where the battery is charging and discharging more often, but given such a large solar system this realistically won't happen. In any event, the battery is usually fully discharged each night so overall it balances out.

We designed this solar system entirely from scratch using energy consumption history and weather station data

This homeowner accessed their entire energy consumption history via their SolvingZero dashboard, and they got up and running in a few minutes.

Once they had full access to their hourly consumption history, we could model how a solar system might save them money every hour of the day. This level of detail and savings was simply impossible before.

With their solar analysis in hand we took it one step further and modelled in this 8.2 kWh battery to see how that might save them money on their evening energy consumption. Thats how we ended up with this battery analysis!

You can also try out modelling a solar system for you house simply by creating a SolvingZero dashboard by linking your energy history. It only takes about two minute and a few clicks, its super simple and its free!