Storage and dispatch
Pair a run with a load, a bank, and a grid that is not always there.
Reviewed
What this is for
What the site does with the year the array made, including the hours the grid is not there. A yield figure says what an array makes. It says nothing about the load, the bank, or an interruption. Without storage a grid-tied inverter must disconnect for the whole of an interruption, so a solar-only system covers none of it however bright the day. That is why "with a battery" and "without" are two models to compare rather than a checkbox.
The engine is generation-only and never sees a kilowatt-hour of load. Dispatch reads a completed run afterwards, so one 8,760 serves any number of banks and interruption steps.
Steps
- Open Storage. Until you have a model, the page is empty. A model pairs a simulation with the site's load, the bank on a design, and however much interruption you want to test against. The comparison worth running first is the same site with a battery and without one. Create the first model.
- Same head as financials: Save writes, Save and compute writes and runs the year. Not ready to compute names what is missing - a run, a consumption profile, or a supply group when an interruption step is set - and pressing the button before then is refused with the same list. A design is not required: no bank is the baseline worth running.
- The bank is fitted to a design on the Battery tab, because it is hardware - not an assumption about the world. It is saved with the model by the same two buttons; every model pointing at that design sees it and each of their stored dispatches is dropped. If the bank's own datasheet does not state its round-trip efficiency or its usable depth of discharge, a notice beside the bank says so and names the assumed figure: the dispatch divides by both, so either one sets what every stored kilowatt-hour is worth. A missing charge or discharge limit is not assumed unless you ask: the dispatch refuses and names the figure, and Use the default rate under the notice fills it at the rate set under Catalogue on the settings screen, as a multiple of the bank's usable capacity an hour. That choice belongs to the bank, so Save keeps it, and from then on the notice, the Discharge limit tile and the stored result all say the limit was assumed. Use the datasheet only takes it back. Stated limits run from a quarter of a bank's capacity to three times it, so the default is a floor rather than a typical value: enter the real figure from the datasheet when you have it. The notice describes the battery in the picker, so choosing another one changes it straight away, before you save.
- Strategy: self-consumption, backup only, or time-of-use arbitrage. Arbitrage with no tariff on the site has no price signal and behaves as a backup reserve. Set the schedule on Grid connection; the model reads the site's tariff when it is next saved. Until then the head shows Unsaved changes and says the site's grid connection has changed, so Save is there to press. Reserve fraction is a fraction (
0.3, not 30). May charge from the grid is a separate flag. - Once computed, the strip leads with self-sufficiency (of load served without the grid). A model nobody has computed renders a dash, not
0%. Results tab: self-consumption of what the array made, self-sufficiency of what the site used, typical autonomy from a full bank, worst outage, unserved load, interruptions covered in full. Cycles a year and Bank lasts say what the strategy does to the bank's warranted cycles. - Does the bank fill? answers the question a buyer asks first: will these panels charge this battery, and by when. Days filled counts the days the array alone brought the bank back to full, and Usually full by is the hour it typically got there, in the site's standard time. A model computed before these figures existed shows a dash and asks you to compute again. The panel under the tiles breaks it down by month: days filled, the usual time, and on the days it fell short, how far it got and how many kilowatt-hours short of full that was. A month the array fills on fewer than half the days that needed it is also named in How this was modelled. A typical day charts the bank's average charge across 24 hours for the month you pick. It opens on the month the array fills the bank least. Where another month fills it more often, the month it fills it most is dashed behind for comparison. It is an average, so a month where half the days fill draws a curve that never quite reaches the top. The table is what says how often it got there.
- Consumption is the project's profile, the same one financials reads. Choose it on Setup; it is edited on Consumption, and Set up consumption takes you there while the project has none.
If the site names no supply group and the interruption step is zero, the grid is modelled as available in every hour. Set a step above zero with no group and the model is not ready to compute until the group is chosen on Grid connection.
Financials re-dispatch a matching model (the same run and the same consumption profile) even if it was never computed here, so the bill and the storage strip can still describe one site.
Tips and common mistakes
- Do not expect dispatch to rewrite the production cell. It reads the run.
- There is no separate save for the battery. Save and Save and compute on the head write the bank and the model's inputs together.
- Clearing the battery picker removes the bank from the design entirely.
- A day the grid helped fill is not counted as filled by the array. With May charge from the grid on, those days get their own column, so a small array beside a grid-charged bank does not look big enough.
- On backup only the bank is held full while the grid is up, so most days show under Stayed full. The fill figures then describe the days after an interruption drew the bank down.
- A bank drawn down after dark has no sun to refill it until the next morning. That is not a short day. Days are judged on the hours the array is generating.
- Creating or cloning a storage model needs a plan that includes the outage and battery model. Without one, the button is refused with a sentence naming the plan that carries it.