It is important that people understand the advantages and disadvantages of battery-based grid interactive inverter systems and straight grid-tie inverters. While cost and time of return on investment may be a large concern, it is equally important that the consumer understands what they are getting for their investment.
Value might be quantified in more than just dollars and cents. Even though the price of a battery based system represents a larger investment, there is a great deal of value and security in having an uninterruptable power supply for all or part of the loads in one’s home. It is a common misconception that just because a house has solar panels on the roof, there will be a source of power whenever there is a power outage. The only way this can happen is if the inverter is battery based. That means that the inverter runs on batteries rather than solar panels. Both types can and will use power from the photovoltaic array and put it into the grid. Both will disconnect from the utility in the event of a power outage, but the battery based inverter will continue to energize loads on the downstream side of the inverter while at the same time using the solar array to maintain a charge in the battery bank. Another advantage is multiple DC inputs. A straight grid-tie inverter will only run on solar panels. A battery based invert will make use of any DC sores that can charge the battery like wind generators, hydro, or traditionally fueled generators.
The advantage of a battery-less grid interactive inverter is a comparatively low upfront investment and not having to maintain a battery bank. Straight grid-tie inverter systems can cost up to half as much as battery based systems with the same solar output. Lead acid batteries need routine maintenance but batteries with other chemistries can be used that are maintenance-free and perform better than lead acid.
In the end, the client should know the options so he or she can make the best decision to meet their needs and wants. Many have had grid-tie inverters installed only to find out later that there is no electricity during a power outage. The bottom line is: what is it worth to you to have the security and comfort to know you will have electricity when the utility fails?