There is a lot of talk about solar + storage or batteries attached to solar systems, but most systems do not come with a battery. There are some very good reasons for that. To help you decide if a battery is a good fit for your project, first you need to understand what they do and how they work.

What is a battery good for?

A battery attached to your solar array is like the battery in your cell phone or laptop. It gets charged by sunlight hitting your panels and will discharge that power in two ways.

  1. BACK UP POWER: If the power goes out for any reason at any time, your home will switch to battery backup power.
  2. LOAD SHIFTING/POWER STORAGE: The battery will store excess solar production to use later in the day or in the month.

Both of those sound awfully useful, but let’s dig a bit deeper and see if they make financial & practical sense in Las Vegas.

Batteries for backup power

Batteries are not included with solar systems by default because they are still quite expensive compared to the benefits. Almost every solar system in Las Vegas and surrounding areas is connected to the power grid (grid-tied). The power company’s grid acts like a virtual battery “storing” excess power production as credits on your power bill. Those credits then pay for the power you need at night. This is called Net Metering.

You can learn more about net metering on our How does solar work? page.

Unlike adding physical batteries – which can cost upwards of $6,000 per unit – you will not pay any additional cost for Net Metering to be your “virtual battery.”

You should understand that when the power goes out, a standard grid-tied solar system will shut off, too. This is required by electrical code and is in place for the safety of the utility workers while they restore power. Unexpected power coming from your house would be a hazard to them. As soon as the grid is back up, the system will wake up on it’s own and start making juice again.

Here in the Las Vegas valley, with our very stable power grid, we rarely see outages of more than a few minutes. In order to run your home off batteries for more than those few minutes, you would need at least 2 or more batteries, so spending an extra $6,000 – $12,000 or more to have backup power from a physical battery really doesn’t make financial sense – even with the NV Energy storage rebate.

Batteries for Load Shifting/Power Storage

Load shifting means storing power made at one time to use at a different time.

In order for load shifting to be beneficial to you financially, your power company needs to charge lower prices in the morning and higher prices in the evening – like they do in California, Arizona and Hawaii. This is called Time of Use pricing. Here in Nevada, customers pay the same rate for power all the time, so “load shifting” power from morning hours to late afternoon/early evening has no financial benefit. You can request TOU pricing, however the behaviour changes required to save money on that rate (such as not running your AC in the summer between 1-7pm) are more dramatic than most people want to live with.

Another way load shifting could help is if your power company has tiered rates. You pay so much per kwh up to 500 kwh on Tier 1, then more for 501-2,000 kilowatt hours on Tier 2 and maybe even more for 2,001 and above. This is really common in California, but again, most of the big utilities here, including NV Energy, do not have tiered pricing, so there is no financial benefit to load shifting.

The biggest reason load shifting makes no financial sense here though, is energy density.

The batteries most commonly talked about is the Tesla Powerwall. Each Powerwall holds 13 kilowatt hours of power and can deliver 5-7 kwh at a time. That’s not a whole lot of juice. In order for the Powerwall to work correctly, your also have to install a Tesla Gateway. If the power went out for a week and you wanted to stay cool in August, you’d need more than 1 battery.

Tesla’s Powerwall sizing page 

How long will a Powerwall will last in an outage?

Other brands of batteries such as LG Chem, Sonnen and Mercedes all store about the same amount of power and cost about the same per unit. At a cost of at least $6,000 each plus the required Gateway,  you can easily see why batteries are not included by default. Even with the NV Energy rebate of $3,000 for storage, unless you have a 24/7 need for backup (such as medical equipment that cannot be off for more than 5 minutes), the math just doesn’t pencil out in Las Vegas and surrounding areas right now.

So when are batteries a good idea?

If you MUST have critical loads in your home backed up 24/7, such as life support equipment, the cost of batteries might make sense for you.

If you live in the more remote areas and you do not have power to your home at all, an off-grid system with batteries is your answer. The system is not connected to the power grid at all. When the sun is up, the panels power your home and charge the batteries. Once the batteries are full, any extra power is shunted into the ground rod. If it’s cloudy or dark, your power will come from the batteries. Since you have no connection to the grid to supply back up power, this type of system is more difficult to design and quite a bit more expensive due to the number of batteries you’ll need to supply overnight power. Off grid systems use different types of batteries depending on cost.

Litium Ion types (Tesla Powerwall, LG Chem, Enphase, Mercedes, Sonnen): These type of batteries are very similar to the ones you’d find in your laptop or cell phone … only on a much bigger scale. They use various chemical makeups – mostly based on lithium. They can operate both on or off grid and can be used for either backup power, tier shaving or nighttime power. Batteries may require a separate inverter.

Deep Cycle Batteries: This type of batteries looks a lot  like boat or car batteries. They do not store as much power as the newer lithium ion chemistry types and need to be replaced more frequently. They also required a lot more user maintenance.

Robco can install either type of battery. If you’d like a quote or have questions, please give us a call at 702-614-4900.

Are batteries the answer if my existing solar system is not quite meeting my needs?

There are a lot of reasons your current system might not be meeting your power needs. You could have had someone move into the house, added a pool or spa or bought an electric car since you got solar. Maybe your system was sized based on square footage and not historical use.   Maybe your air conditioner is hitting end of life or you still have a single speed pool pump. Because batteries are still so expensive and store so little power, is is always less expensive to simply install more solar panels (roughly $1,000 per panel) or employ energy efficiency measures (swap out that old pool pump or replace that aging HVAC) to reduce demand. Even if we did not install your system, we can probably expand it. Click HERE for a quote.