Sighten now offers battery modeling! You can add DC and AC batteries to projects and model storage behavior to estimate overall homeowner savings for the project.
Battery Modeling Overview
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- The daily usage chart on the Project page allows users to see how the battery will meet usage needs.
- Admins have control over what batteries are available under Settings and can add any batteries they're using themselves without needing to wait for Sighten to make updates.
Battery modeling – there are three ways to model storage charge and discharge schedules through Sighten: PV Self-Consumption, Advanced TOU Self-Consumption, and Back-up Power.
- PV Self-Consumption: whenever the PV system generates more kWh than is needed for the load, then all excess energy is sent directly to the battery. Once the battery has reached capacity, all access energy will be sent to the grid. When the PV system does not meet the need of the load, then the battery will discharge the exact amount of kWh required to meet the load. The battery will discharge until the minimum state of charge bound is reached.
- Advanced TOU Self-Consumption: Production is used to fully charge the battery during all off-peak hours. The home is 100% powered by grid during this time until the battery is 100% charged. As As soon as on-peak or rates occur, the battery discharges to serve 100% of the homeowner’s consumption during the peak window(s). All production will go directly back to the grid during this time.
- If battery cannot meet 100% of consumption needs, production will be applied to offset additional consumption to get to 100%.
- If battery meets 100% of consumption needs, production will sent back to the grid.
- Back-up Power: The battery will charge from excess production but there will be no discharge from the battery. This will ensure that the battery is always available to discharge during unpredictable blackouts or for other circumstances.
Stringing – All DC batteries will require an inverter. It can be strung with its own inverter (AC-coupled) or strung together with an existing project inverter (DC-coupled).
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Battery sizing - generally with residential, 1 or 2 batteries will meet the needs of most homes when the goal is PV self-consumption (storing the daytime solar production for use in the evening). The daily chart can be used to compare what usage will be with different numbers of batteries - add a 2nd battery if there is a lot of usage in the evening / at night that cannot be met by the battery supply. You will then be able to see how much of the evening usage is covered by the discharge of the additional battery vs pulled from the grid. If there is no noticeable difference with the additional battery, it is likely that the PV system must be larger to charge the additional battery.
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Methodology & Limitations
- Backup power & "islanding" - use cases for 2+ batteries can arise if the homeowner has a big consumption load (much higher than typical) or want to isolate loads from the grid ("islanding" or off-grid applications). For off-grid or large backup power applications, there are limitations both for the battery technologies and our modeling, which is designed for grid-tied systems.
- No battery degradation is modeled. The tool does not model battery degradation - it assumes capacity stays the same over the years. In reality, batteries degrade and the rate at which capacity degrades depends on charge and discharge behavior, including depth of discharge. Sighten modeling is based on best-practice cycling and depth of discharge assumptions, which protect battery life over time when followed.
- No battery thermal modeling - this is the temperature's impact on battery performance. The tool has no thermal model - batteries stored indoors and outdoors are modeled identically.
- No difference in battery modeling based on battery chemistry/battery type. The tool is chemistry-agnostic, meaning batteries of different chemistries, ie Lithium-ion and Lead Acid, are modeled identically for charge/discharge, capacity, and losses.
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