Energy Storage

• As back-up power to keep devices running during a power outage. 
  When combined with solar, appropriately sized batteries can potentially run loads indefinitely because the solar recharges them during the day. 
• To increase the amount of solar you use onsite, behind the meter.
  If the rate at which you sell your excess solar energy to your utility — either net metering or avoided cost — is low, or if you have high demand charges, a battery can be helpful, although it is complicated to calculate potential financial benefits. Note that storage won’t save summer solar for winter usage, but it does help with using daytime production during the night. 
• Off-grid solar and storage systems.
  These can provide power in a range of situations. Storage enables places that are not already grid-connected to have electrical systems. High energy loads become expensive quickly, so energy efficiency is critical.

Storage capacity is the most important factor in designing your system, although the peak and continuous load of the devices you plan to use is also a factor. 

1.  Inverter to change the DC power of the battery into the AC power that your house and appliances require. If you have or are also getting solar you might be able to get one inverter that serves the needs of your battery and your solar system. Some systems integrate the inverter into the battery. 
2. Transfer switches are required for using your home system when grid power is down. This is a safety issue: it’s essential not to feed power back onto lines that technicians might be fixing. Some inverters and batteries have switches built in, but in most situations, this will be a separate component that must meet your utility’s requirements. A more manual option particularly for portable battery systems is to move the plug from the normal outlet to the battery to back up one or more appliances that are in close proximity. 

An average home storage system to cover critical loads (10kWh) should cost around $15,000 and is highly dependent on how much and how long you want to run devices. Expect to pay around $1,300/kWh. 

Batteries do wear out with use and will need to be replaced. The timing depends on how frequently you discharge and recharge (cycle) the battery. Under normal usage a good battery can last 10 years or more.

1.  Ask your solar installer. 
   Even if you don’t plan to include storage right away, if your installer knows you might want storage in the future, they can design the system to be “storage ready.” Always ask what storage training or certifications they have to make sure they are up to date on the rapidly changing options available. 
2.  Prioritize your needs.
   Storage is expensive, so you will need to decide which devices are critical to keep running and how long you want to run them. That will help you determine the system size (and cost) that is right for you.
3.  Determine your budget.
   A typical home system will cost $15,000-25,000. Look for rebates or rate benefits from your utility or state. 

Here are several studies digging into the opportunities for adding storage to renewable energy production like solar and wind.