Sighten now offers comprehensive storage modeling functionality! Sighten users can add DC and AC batteries to projects and model storage behavior to estimate overall homeowner savings for the project.
Storage modeling overview
Sighten storage modeling allows users to add batteries to a project with charge/discharge behavior, solar-supply power, and grid-supply power taken into account.
- The daily energy profile chart on the Project page allows users to see how batteries will meet and impact usage needs.
- Admins have control over which batteries are available in their organization via the Settings page and admins can add new batteries at any time.
Battery modeling – there are three ways to model storage charge and discharge schedules through Sighten: PV Self-Consumption, Advanced TOU Self-Consumption, and Backup Power.
- PV Self-Consumption: whenever the PV system generates more kWh than is needed for the current load, all excess energy is sent directly to the battery (charge). Once the battery has reached capacity, all excess energy will be sent to the grid. When the PV system does not meet the need of the current load, the battery will discharge the exact amount of kWh required to meet the current load. The battery will discharge until the minimum state of charge bound (reserve capacity) is reached.
- Advanced TOU Self-Consumption: solar production is used to fully charge the battery during all off-peak hours. The home is 100% powered by the grid during this time until the battery is 100% charged, at which point solar solar production is used to meet the current load instead of charging the battery. As soon as on-peak or active shoulder rates occur, the battery discharges to serve 100% of the homeowner’s load during the peak window(s). All solar production will go directly back to the grid during this time.
- If battery cannot meet 100% of current load, solar production will be applied to offset additional consumption until there is 100% load offset.
- If battery meets 100% of current load, solar production will be sent back to the grid.
- Backup Power: the battery will charge from excess solar production but there will be no discharge from the battery at any time during normal grid operation. This ensures that the battery is always fully available to discharge during unpredictable blackouts or for other circumstances where backup power is needed.
Stringing – all DC batteries will require an inverter. Batteries can be strung with their own inverter (AC-coupled) or strung together with an existing project inverter (DC-coupled).
- Storage - AC - no inverter selection required. It is assumed that the inverter is included in the battery, so there is no option to add an inverter for AC batteries.
- Storage - DC - includes inverter selection in the "add battery" section or an inverter can be added in the "inverter" section.
Storage chart (daily) - the daily energy profile chart shows usage, solar production, battery charging, and battery discharging behavior. Add a battery, click "Calculate", and then use this chart to evaluate how much of the daily load is met by solar + storage versus the grid.
Battery sizing - generally with residential storage, 1 or 2 batteries will meet the full load need of most homes when the goal is PV self-consumption (storing the daytime solar production for use in the evening). The daily energy profile chart can be used to compare usage and generation sources with different numbers of batteries - add a second battery if there is load in the evening / at night that is not met by the discharge from a single battery. After adding a second battery, the daily energy profile chart will show the evening / nighttime load met by the discharge of the additional battery versus 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 and make an impact on the evening / nighttime load.
Multiple batteries – when the battery count is incremented, a battery of the same manufacturer and model is added to the project; the batteries are considered to be stacked.
- If two different manufacturer or model AC-coupled batteries are added to a project, the more efficient battery will be charged first; the same applies to DC-coupled battery systems.
- If DC-coupled and AC-coupled battery systems are both added to a project, then the DC-coupled battery system will be charged first, and the AC-coupled battery system will be discharged first.
State of charge - there are bounds on the state of charge to ensure a longer life for the battery as this is used in real-world applications to prevent degradation. The bounds are default percentages for charging and discharging the battery, and a battery's usable capacity automatically factors this in.
Losses – each battery has its own round-trip efficiency that is applied when discharging the battery. Inverter efficiency and loss is applied to DC-coupled DC batteries on discharge, applied to AC-coupled DC batteries on charge and discharge, and not applied to AC batteries as this is assumed to be included in the AC battery’s round trip efficiency.
- For DC-coupled batteries, Sighten reverses the impact of the inverter losses on the AC solar generation to approximate DC excess solar power flowing to the battery directly from the solar system when charging.
- There is no thermal modeling, so batteries stored indoors and outdoors will be modeled identically.
Degradation – Sighten does not currently model battery degradation. All calculations assume the battery does not degrade over time, thus the battery capacity remains constant. In real-world applications, batteries degrade over time implying a decrease in savings and more solar production going to the grid.
Chemistry-agnostic – batteries of different chemistries, e.g. lithium-ion and lead acid, are modeled identically for charge/discharge, capacity, and losses.
Backup power & "islanding" - for off-grid or large backup power applications, there are limitations both for the battery technologies and Sighten battery modeling, which is generally designed for grid-tied systems.
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