Solar Batteries & Energy Storage

Solar Batteries & Energy Storage

These days a lot of solar PV customers are inquiring about solar batteries and how they can store their solar power. A solar PV owner can harness the power of the sun by day, using it to produce clean solar energy, but what happens at night? When the sun is no longer out and shining on your solar array, you must then pull energy from the utility grid to sustain electricity at night or on cloudy days. Batteries offer you the opportunity to store clean solar energy for later use in this instance. It sounds like a simple solution but there is much to consider before making a solar battery purchase and upgrading your PV system. Let’s begin with some pros and cons:

The Pros:

  1. Energy Independence - Aside from having backup power when the sun is out or when the utility grid may be down, solar batteries offer energy independence. By using power that was stored from your solar array and less from the grid, you are reducing your reliability on the utility’s energy, as well as reducing your electric bill. Though a lot of utility companies have a feed in tariff, the compensation for sending excess power into the grid is typically less than what you’d pay to use energy from the grid. Storing your excess energy ultimately reduces any financial loss from feeding power into the grid, as well as lowering your bill.
  2. Load Shifting - For customers on rates that change according to on-and-off peak hours, batteries can allow you to load shift. This means you can move the energy consumption from peak hours to another part of the day when rates are cheaper. Ultimately you will be using stored energy from the battery during the utility’s peak hours. Time of use tariffs are more common with commercial properties but can also be for residential utility customers as well.
  1. Energy Trading - The battery software can give you the ability to trade energy. The battery can communicate with net metering to know when to feed the grid to maximize profits, based on your home’s usage habits, the grid demand, weather, and future energy rates.
  1. Reduce your carbon footprint - a complete solar system consisting of the solar array and a backup battery will further reduce the use of the grid and your carbon footprint. The utility grid still uses power generated from carbon emitting resources.
  2. Off-Grid - for those interested in going off-grid and being completely energy independent, energy storage allows you to do so. You may need a larger PV system to cater to all of your electrical needs, and even a little extra to charge the battery but it is definitely possible to be completely off-grid and 100% self-sufficient.

The Cons:

  1. Expensive - batteries can be an expensive upgrade to your PV system. You may want to consider calculating your return on investment (in which PurePoint Energy can be of assistance) along with your utility rates before purchasing. However, with technology advancements the cost of batteries are coming down and will become more affordable over time, the same way solar panels have in the past.
  2. Lifespan - the lifespan of the solar battery is also something to consider. With the current technology available expect to replace the battery at least once throughout the life of the PV system.
  3. Design Complexity - designing a PV system can get more complex when adding a battery. It is important that the battery system is sized correctly, including the right cables and switches. The battery also has to be stored in a place that is cool with the appropriate amount of ventilation.

Are Solar Batteries Worth It?

Whether or not solar batteries are worth it depends on your values, flexibility goals, and your current generator and utility costs. If you want any of the following then solar batteries are worth it.

 1. Save on monthly utility expenses.

 2. To cut your carbon emissions.

 3. More energy flexibility/independence.

What should you look for when comparing solar battery options?

When comparing battery options there are a few different categories you should consider:

  1. Capacity – the total amount of electricity that the battery can store. This is measured in kilowatt hours.

a. Most batteries are stackable, giving the ability to include multiple batteries in your design for increased amount of storage.

b. Consider the power rating as well. This is the amount of electricity that a battery can deliver at once. The power rating can be the difference in having the ability to run a few small appliances at once, or the entire home at once.

  1. Battery lifespan – the range of useful lifespan.

a. A typical battery lifespan is between 5-10 years.

b. A typical solar PV system has a lifespan of 30 years. You will likely replace the battery once during the life of your solar system.

c. Protecting the battery from extreme temperatures (below 30 degrees or above 90 degrees) will help preserve its life.

  1. Warranty – the battery warranty will guarantee a certain number of cycles and/or years of useful life. Battery performance degrades naturally overtime, so most manufacturers guarantee that it keeps a certain amount of its capacity over the course of the warranty.
  2. Depth of Charge (DoD) – the amount of a battery’s capacity that has been used. Most batteries have to retain some charge at all times because of their chemical composition.

a. If you use 100% of its charge, you can significantly shorten the useful life.

b. You should never deplete your battery. For example, if the DoD on a 10 kWh battery is 90%, you should not use more than 9 kWh before recharging it.

  1. Round-trip-efficiency – is the amount of energy that can be used in ratio to the amount of energy that it took to store the energy. For example, feeding 5 kWh into your battery and getting 4 kWh out of it of useful electricity means the battery has an 80% round-trip-efficiency.
  1. A higher round-trip-efficiency means more economic value.
  1. Manufacture – take the time to consider the company that is manufacturing your battery. There are many different types of companies producing batteries these days. Evaluating the different companies and their warranties is a must. For example, there may be an automotive company that is entering the solar battery market with a long manufacturing history in general, but hasn’t been in the solar battery industry long. Or there may be a tech start-up company that can offer revolutionary new technology but does not have the long manufacturing history of the automotive company. You must choose a manufacturer that you are comfortable with and trust based on your individual priorities.

What are the most popular solar batteries currently on the market?

  • Tesla Power Wall
    • Lithium ion battery similar to the one used in Tesla cars.
    • Capacity of 13.5 kWh, enough to power essential appliances for 24 hrs.
    • Price with supporting software is around $7,500.
    • Warrantied 10 years for daily charging and draining.
    • Minimum guaranteed capacity of 70%.
    • Comes with integrated inverter and can be used with or without solar.
    • Software allows you to manually manage your consumption to minimize electric bill.
  • Sonnen Eco
    • Lithium ferrous phosphate battery.
    • Capacity starts at 4 kWh.
    • Average price (of 4kWh model) is $9,950.
    • Warrantied for 10 years of daily charging and draining.
    • Minimum guaranteed capacity of 70%.
    • Comes with integrated inverter and self-learning software to manage self-consumption and time-of-use when your solar array is connected to the grid.
  • LG Chem Resu
    • Only LG model sold in the United States.
    • Lithium ion battery.
    • Capacity of 2.9-12.4 kWh and usable capacity of 9.3 kWh (60%).
    • Average price is between $6,000-7,000.
    • Warrantied for 10 years of daily charging and draining.
    • Has a sleek unobtrusive design that is more aesthetically pleasing.

Batteries are a great option to become more self-reliant and eco-friendly when it comes to energy consumption. As more batteries are being connected to the grid, the smarter the grids will become, upgrading the utility infrastructure for the future. As technology and prices improve, we expect to see more complete energy systems being installed. If you are interested in learning more or would like a free quote for solar energy storage on your commercial or residential property, please contact PurePoint Energy. We are your local solar energy storage experts and look forward to hearing from you.

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