About the Hybrid Solar + BESS
A hybrid solar-plus-storage plant co-optimises PV and battery capacity to deliver a firmer, more dispatchable output than solar alone — shifting midday generation into evening peaks or meeting round-the-clock (RTC) and peak-power contracts. The design question is the ratio of BESS energy (MWh) to solar capacity (MW) that meets the offtake at the lowest cost.
Formula
Firmed output & BESS ratio depend on the offtake profile
- Solar (MW)
- PV capacity, usually oversized vs the grid connection
- BESS (MWh)
- Storage energy to shift/firm the required hours
- Offtake
- Contract shape: peak-power, RTC, or grid-firming
How to calculate it
- 1Define the target output shape — evening peak, RTC, or a firm dispatch profile.
- 2Oversize solar relative to the grid-connection/PPA capacity so surplus midday energy charges the battery.
- 3Size the BESS energy to cover the required shift/firming hours at the contract power.
- 4Co-optimise the solar-to-BESS ratio and connection size against capex, curtailment, and the PPA to minimise levelised cost.
Worked example
A peak-power contract might pair an oversized solar field with a few hours of BESS so that clipped midday energy is stored and dispatched into the evening peak; an RTC contract needs a larger solar oversize and more storage hours to cover the night.
What you can calculate
- PV + BESS sizing
- Self-consumption
- Export limit
- Solar clipping
Standards & references
Frequently asked questions
Why combine solar with a battery in a hybrid plant?
Solar alone is intermittent and peaks at midday, when it is least valuable. Adding storage lets the plant shift energy to evening peaks, firm its output, and meet RTC or peak-power contracts — turning variable solar into a more dispatchable, higher-value product.
What is the right BESS-to-solar ratio for a hybrid?
There is no single ratio — it is set by the offtake shape. A simple evening-peak shift needs only a few hours of storage and modest solar oversize; a round-the-clock contract needs heavy solar oversizing and many hours of BESS. The ratio is co-optimised against capex and the PPA.
You might also need
Power Rating
Size BESS power output in kW/MW for peak shaving, backup, or grid services based on C-rate and capacity
OpenEnergy-to-Power Ratio
Determine optimal E/P ratio for use-case (1C backup, 0.25C arbitrage, 2C frequency regulation)
OpenAutonomy / Backup Time
Calculate backup duration from capacity, load, and DoD — validate against IS 16270 backup requirements
OpenRound-Trip Efficiency
Compute RTE from charge/discharge efficiency and auxiliary losses — benchmark vs IEC 62933 ≥85%
OpenDC/AC Architecture
Compare DC-coupled vs AC-coupled BESS architecture for efficiency, cost, and application suitability
OpenUsable Capacity
Derive usable energy from nameplate capacity applying DoD, temperature, and aging derating factors
Open