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.

BACK UP POWER: If the power goes out for any reason at any time, your home will switch to battery power and your lights will stay on. 

LOAD SHIFTING/POWER STORAGE: The battery will store power you make in the morning to use later in the day or overnight.

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

Batteries for back up power.

Batteries are not included with solar systems by default because they are still quite expensive compared to the benefits. Most systems in Las Vegas and surrounding areas are 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. Unlike adding a physical battery, you will not pay any additional cost for this “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 Las Vegas, with our very stable power grid, we rarely see outages of more than a few minutes, so spending an extra $6,000-$10,000 to have backup power from a physical battery really doesn’t make sense.

Batteries for Load Shifting.

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, most 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.

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, we don’t have this here (except for Boulder City) so there is no financial benefit to load shifting.

The batteries most commonly talked about hold 13 kilowatt hours of power and can deliver 5-7 kwh at a time. That’s not a whole lot of juice. Running an average Las Vegas air conditioner for 8 hours would take 20 kilowatt hours or more. So if the power went out for a week and you wanted to stay cool in August, you’d probably need more than one battery. At a cost of $6,000 to $8,000 each, you can easily see why batteries are not included by default. The math just doesn’t pencil out in Las Vegas and surrounding areas right now.

So when are batteries a good idea?

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.

Robco can install either type of battery.