How Storage can Enhance your Solar Rooftop Project

February 26, 2021

One of the critical constraints of current solar setups compared with traditional fuel-based generating systems has always been its inability to provide schedulable power. Failure to control its energy source, the Sun in case of Solar Energy leads to an inability to provide the same energy the load requires. This means you must run the system in conjunction with a flexible source, grid power, in most cases. Depending on grid power for your captive solar plant comes with strings attached. Net-metering regulation varies from state to state and is becoming increasingly strict as utilities continue to resist the business model. In the absence of a grid, the current solar system discontinues working until a reference voltage is provided. Diesel Genset integration comes with its issues and does not offer the kind of linear savings one would expect due to constraints with the genset technology. Adding energy storage technology to the solar generating system provides much-needed flexibility and helps circumvent most of these issues. It provides the ability to work in an off-grid mode, thus providing backup to the critical load during blackouts. Valuing energy resilience can increase the benefits of having storage as a part of your solar system.

In the absence of net-metering regulation, a battery can be used to size the solar system to the maximum area available instead of sizing just for the baseload. The battery can be used for supply-demand matching, thus significantly increasing the solar power in the total power mix. This can lead to more considerable savings in your energy cost compared to the only solar system due to the system’s increased size. Since releasing the stored energy is easily customizable, the same power can benefit from demand reduction or reduce peak tariff time consumption. This freedom to use the same energy storage asset to value stack, to provide backup, ramp up PV production, reduce peak time charges, etc., is what makes it attractive. Though the market of providing grid services from behind the meter storage assets does not currently exist in India, it is safe to say, with current policy direction, that it’s not a question of if, but when; when will this market open up. This can potentially provide an additional revenue stream in the future from your battery asset.

Typically, net-metering regulation capacity restriction is lower of the sanctioned load or present maximum limit (1 MW in most states). There is a use case for energy storage that I would like to highlight for states where the net-metering capacity restriction is on AC capacity instead of DC capacity. Depending on the irradiation levels and project conditions in such cases, DC capacity is 20-30% oversized than the AC capacity. Anything more leads to clipping losses, meaning Inverter will clip any excess power being generated by panels than its capacity. So, 500 KW inverter will cut any power above 500 KW being feed into it, leading to losses. By combining the energy storage on the DC side of the system through a DC-DC converter, the system can be designed to store this excess energy in such cases. As everyone is aware, solar production is a bell curve producing peak power only for a few hours. One needs to size the battery to store only this peak power of a few hours above the inverter nameplate reading. This can help one design the system with DC capacity way over 20-30% meaning more low-cost solar energy can be generated with the same AC capacity. A consumer can now take the benefit of net-metering along with increase solar generation. Even with the increased landed energy cost because of storage, customers can benefit from more enormous savings due to more production. Again, the energy stored can be dispatched based on a customizable logic, enabling value stacking as described above.

As battery pack prices continue to decrease and more behind the meter customized battery products make their way into the market, it is a matter of time before we start seeing most solar rooftop projects having some storage component.

Nimesh Gupta

Consultant, New Products & Electric Vehicle