Battery sizing is not just a capacity calculation. Powerlily models storage hour by hour so you can compare products and configurations, understand seasonal behaviour, test backup resilience, and connect the technical result to customer value.
Prepare the project inputs
Battery analysis depends on the solar design, customer consumption, utility rate, and selected storage equipment. Before comparing configurations, confirm:
- The solar array and annual production have been calculated and saved.
- The customer’s monthly bills, interval data, or load profile are as complete as possible.
- The current utility tariff, export credit, time-of-use periods, and demand charges are configured correctly.
- The battery and inverter records contain usable capacity, electrical limits, coupling type, and charge and discharge capabilities.
- The intended backup architecture and microgrid interconnection device are represented.
Choose the storage architecture
Confirm whether the design is AC-coupled or DC-coupled and whether the battery has its own inverter or depends on a hybrid inverter. The architecture affects conversion paths, power limits, equipment requirements, and how solar can charge the battery.
For backup systems, include the required isolation or microgrid interconnection equipment and identify whether the design supports whole-home or partial-home backup.
Build a battery configuration
Select the battery product and quantity, then review total usable energy and available charge and discharge power. More kilowatt-hours increase stored energy, but inverter power and equipment limits determine how quickly loads can be served or the battery can be recharged.
When comparing configurations, change one meaningful variable at a time. Examples include battery quantity, usable reserve, coupling type, backup load, or operating strategy.
Understand hourly state of charge
Powerlily uses an 8,760-hour framework to model the battery’s state of charge throughout the year. The analysis follows solar production, customer load, tariff conditions, reserve behaviour, and equipment limits instead of assuming the battery performs the same way every day.
Review where the battery repeatedly reaches its minimum or maximum state of charge. Long periods at either boundary can show that the configuration is undersized, oversized, power-limited, or constrained by the selected operating strategy.
Set the reserve behaviour
The reserve determines how much usable energy is held back instead of being consumed for everyday bill savings. A larger reserve can improve outage readiness but reduces the energy available for self-consumption or tariff optimization.
Explain the trade-off clearly to the customer. A system optimized for maximum bill savings may behave differently from one designed to maintain a substantial emergency reserve.
Review seasonal operating ranges
Compare the battery’s state-of-charge behaviour across seasons. Solar production, heating or cooling loads, daylight hours, and rate periods can produce very different winter and summer outcomes.
A configuration that appears comfortable during high-production months may spend much more time near reserve during the least favourable season.
Test worst-case no-sun backup
Use the no-sun or backup analysis to estimate how the selected configuration supports the defined loads without new solar production. Review both stored energy and maximum power. A battery may contain enough energy for the period but still be unable to start or sustain the required loads.
Do not describe a generic number of backup hours without stating the assumed loads, starting state of charge, reserve, and whether solar recharge is included.
Evaluate time-of-use operation
For time-of-use rates, review when the battery charges and discharges relative to the tariff periods. The analysis can show whether stored energy is available during expensive import periods and whether grid charging or solar charging is part of the intended strategy.
Confirm that the selected behaviour is permitted by the utility, incentive program, equipment, and interconnection agreement.
Evaluate demand-charge management
For tariffs with demand charges, compare the battery’s power and energy against the customer’s load peaks. A useful configuration must have enough discharge power to reduce the peak and enough stored energy to sustain the reduction for the required duration.
Model demand-charge savings conservatively when interval data is incomplete or the customer’s operations may change.
Compare long-term economics
Compare configurations using the same production, consumption, tariff, escalation, and financial assumptions. Review equipment cost, bill savings, demand-charge savings, replacement assumptions, and the value assigned to backup.
Keep resilience and financial return separate when necessary. Backup capability may be valuable to a customer even when it does not produce the shortest payback.
Compare battery options
Use quote options when the customer should compare solar-only, smaller-storage, larger-storage, whole-home, or partial-home configurations. Calculate each option independently and make the differences in capacity, power, reserve, backup assumptions, and economics visible in the proposal.
Final review checklist
- Solar production and customer consumption inputs are current.
- The utility tariff and export rules are correct.
- Battery usable capacity and power limits match the product.
- AC- or DC-coupling is represented correctly.
- The required inverter and interconnection equipment are included.
- Reserve and operating strategy match the customer’s priority.
- Seasonal state-of-charge behaviour has been reviewed.
- Backup claims state the load and solar assumptions.
- Time-of-use or demand-charge savings are supported by the model.
- Proposal pricing matches the analyzed configuration.
