Do I need batteries?
Battery technology is an expensive component of a home electrical system, so consideration of how and when batteries can be used in conjunction with solar power is important. The electricity generated by a rooftop solar panel array can only be used at the time of generation unless an energy storage system is in place. Fortunately, there are multiple options for delayed electricity use, which is also called net metering or net billing. Batteries are needed in a solar energy system if an electric grid is not available and the only power to the home is what is generated on-site. If the home is on the power grid, the ability to send power to the grid can play the same role as batteries. Depending on the details of a power buyback program, batteries may or may not be necessary.
Power grids can be used instead of batteries
Net metering with an electrical grid is based on the net value of transactions between you and the power company. During periods when your solar panels are producing more energy than your home is using, energy can be metered and sent to the grid for use by other customers. When solar panels are not producing enough energy, your home draws from the grid to fill the energy demand. The end effect is a reduced power bill because you are able to utilize your captured solar power at times other than when it was captured.
However, the ability to sell power back to the grid is highly dependent on rules and regulations. In some cases, power companies do not have an option of receiving energy, and even those that do may not pay for your solar power at the same rate that you are purchasing energy from the company. Given that there are many caveats, the case may be that batteries are a better choice than selling back to the grid for shifting solar power use.
Roles of household scale batteries
Home scale energy storage batteries are simply large batteries that can store enough energy to supply household needs. Some older forms consist of large tubs containing batteries that are heavy and unsightly, while new units such as the Tesla Powerwall, are elegant household additions. Rapidly improving battery technology is making batteries more economical than ever. The choice to include batteries in your energy system comes down to your energy security needs and infrastructure options.
Some households install batteries simply as a backup energy supply to replace conventional generators. The batteries can be charged from any source, even the power grid. If your solar panel installation delivers much less energy than the demand of your home, net metering is not as necessary. The power will simply be used as soon as it is generated since homes have constant energy draws, even if only from the refrigerator. Batteries in this situation could provide a little power shifting, but would mostly provide energy security.