The latest news in the home energy storage sector has focused on the cost of the powerwall. After increasing its price since October 2020, Tesla has recently increased the price of its famous home battery storage product, the Powerwall, to $7,500, the second time in just a few months that Tesla has increased its price. This has also left many users feeling confused and uncomfortable.
While the option to purchase a home energy storage has been available for many years, the price of deep cycle batteries and other required components has been high, the equipment bulky and requires a certain level of knowledge to operate and maintain. This has meant that until now residential energy storage has been largely limited to off-grid applications and energy storage enthusiasts.
Rapidly falling prices and developments in lithium-ion batteries and related technologies are changing all this. The new generation of solar storage devices are cheaper, more cost-effective, streamlined and aesthetically pleasing. So back in 2015, Tesla decided to put its expertise to work by launching the Powerwall and Powerpack to manufacture battery packs for electric vehicles and produce energy storage devices for use in homes and businesses.
The Powerwall energy storage product has become very popular with customers who have solar power for their homes and want to have back-up power, and has even become very popular in recent virtual power plant projects. And more recently, with the introduction of incentives for home battery storage in the U.S., it has become difficult for customers to obtain a Tesla Powerwall as the demand for energy storage grows. last April, Tesla had announced that it had installed 100,000 Powerwall home storage battery packs. Around the same time, CEO Elon Musk said that Tesla was working to increase production of the Powerwall due to increasing delivery delays in many markets. It is because demand has long outstripped production that Tesla has been raising the price of the Powerwall.
Elements of choice
When considering solar + storage options, you will encounter many complex product specifications which complicate the costing. For the buyer, the most important parameters during the evaluation, besides cost, are the capacity and power rating of the battery, depth of discharge (DoD), round-trip efficiency, warranty and manufacturer. These are the important factors that affect the time cost of long-term use.
1. Capacity and power
Capacity is the total amount of electricity a solar cell can store, measured in kilowatt hours (kWh). Most home solar cells are designed to be 'stackable', meaning you can include multiple cells in a solar plus storage system to get extra capacity.
Capacity tells you the capacity of a battery, but not how much power it can deliver at a given moment. To get the full picture, you also need to consider the power rating of the battery. In solar cells, the power rating is the amount of electricity that the cell can deliver at one time. It is measured in kilowatts (kW).
Cells with a high capacity and a low power rating will deliver a small amount of power for a long time (enough to run some critical equipment). Batteries with low capacity and high power ratings will keep your entire home running, but only for a few hours.
2. Depth of discharge (DoD)
Due to their chemical composition, most solar cells need to retain some charge at all times. If you use 100% of the battery's charge, its lifespan will be significantly reduced.
The depth of discharge (DoD) of a battery is the used battery capacity. Most manufacturers will specify a maximum DoD for optimum performance. For example, if a 10 kWh battery has a DoD of 90%, do not use more than 9 kWh before charging. In general, a higher DoD means you will be able to utilise more of the battery capacity.
3. Round trip efficiency
The round-trip efficiency of a battery represents the amount of energy that can be used as a percentage of its stored energy. For example, if 5 kWh of power is fed into the battery and only 4 kWh of useful power is available, the round-trip efficiency of the battery is 80% (4 kWh / 5 kWh = 80%). In general, a higher round-trip efficiency means that you will get more economic value out of the battery.
4. Battery life
For most uses of domestic energy storage, your batteries will be "cycled" (charged and discharged) on a daily basis. The more a battery is used, the more its ability to hold a charge decreases. In this way, solar cells are like the battery in your mobile phone - you charge your phone every night to use it during the day, and as your phone gets older you start to notice that the battery is running low.
The typical range of life of a solar cell is 5 to 15 years. If solar cells were installed today, they would probably need to be replaced at least once to match the 25 to 30 year lifespan of the PV system. However, just as the lifespan of solar panels has increased significantly over the last decade, solar cells are expected to follow suit as the market for energy storage solutions grows.
Proper maintenance can also have a significant impact on the lifetime of solar cells. Solar cells are greatly affected by temperature, so protecting them from freezing or sweltering temperatures will extend the life of the cells. When a PV cell drops below 30°F, it will require more voltage to reach maximum power. When the same cell rises above the 90°F threshold, it will become overheated and require less charge. To address this issue, many leading battery manufacturers, such as Tesla, offer temperature regulation. However, if you purchase a cell that does not have one, you will need to consider other solutions, such as an enclosure with grounding. Quality maintenance work will undoubtedly affect the lifetime of the solar cell.
As the performance of a battery will naturally degrade over time, most manufacturers will also guarantee that the battery will maintain a certain capacity for the duration of the warranty. So, the simple answer to the question "How long will my solar cell last?" This depends on the brand of battery you buy and how much capacity will be lost over time.
Many different types of organisations are developing and manufacturing solar cell products, from automotive companies to technology start-ups. A large automotive company entering the energy storage market may have a long history of manufacturing products, but they may not offer the most revolutionary technology. In contrast, a technology start-up may have a brand new high performance technology but not a proven track record of long-term battery functionality.
Whether you choose a battery made by a start-up or a long-established manufacturer depends on your priorities. Evaluating the warranties associated with each product can provide you with additional guidance when making your decision.
BSLBATT has over 10 years of factory experience in battery research and manufacturing. If you are currently struggling to choose the most cost effective powerwall, please feel free to consult our engineers to advise you on the best solution.