Energy charts and time-series export

The summary table gives you annual totals. The chart window and the time-series export give you the shape underneath them — hour by hour through a day, month by month through a year, and, when you need it, a full-year generation series in a file. Both come from the energy calculation, so run Calculate Energy first; both are unavailable until you have.

Three controls sit together: Calculate Energy, 📊 Show Energy Chart, and Export TMY data CSV with an interval selector beside it. TMY is a typical meteorological year — a single representative year assembled to stand for the long-run climate at the site, rather than any particular calendar year.

The daily view

The chart window opens on the daily view: one day of the year at a time, in two stacked charts sharing a time axis.

• 24 hourly bars of energy, in kWh per hour, in the upper chart.
• Hourly in-plane irradiance beneath it, in W/m² — the global tilted irradiance, GTI, striking the plane of the array rather than a horizontal surface.
• A slider across all 365 days, so you can walk the whole year one day at a time.
• A month jump, to move to a month directly instead of dragging.
• A crosshair readout that reads both charts at once. Move the pointer and it reports the time, the energy and the irradiance at that instant in both subplots together.

The two charts stacked this way are the point of the view. Energy is in-plane irradiance put through the plant's capacity and its losses, so the pairing gives you both numbers at a chosen hour: so many W/m² arriving, so many kWh coming out, on a plant of a known capacity. That is a check anyone can do on the back of an envelope, and it is the fastest way to catch a capacity or a loss assumption that is not what you thought.

One thing not to expect from it: the ratio between the two charts is not the same figure all year. The monthly performance figures follow IEC 61724-1, and the performance ratio inside them varies with module temperature — a hot month converts a given irradiance into less energy than a cool one. Comparing the same hour in January and in June is therefore comparing two slightly different conversion efficiencies, which is the behaviour you want and not an inconsistency.

The day slider is what makes it a design tool rather than a picture. Compare a day near the winter solstice against one near the summer solstice, at the same site: the peak height, the number of generating hours, and the total under the bars all move, and that swing is what the monthly view then aggregates.

Working the daily view

The monthly view

Switch to the monthly view for the whole year in one frame:

• Twelve bars of energy, in MWh per month.
• Twelve bars of irradiance, in kWh/m² per month.
• Annual totals for both.

This is the view to cross-check against the summary and against the report before either goes out. The annual irradiance total is the in-plane irradiation the whole calculation is built on, and the annual energy total is the year-one generation. A material disagreement with the figures you are about to issue is worth understanding before you issue them — the usual cause is an energy calculation that predates a change to the layout or the losses.

The same monthly data is published in the report as an IEC 61724-1 table — the international standard for photovoltaic performance monitoring, which defines reference yield, final yield and performance ratio month by month. See The PDF report.

Where the chart's data comes from

The chart is only as good as the series behind it, and the application will always draw something. It works down a priority list and uses the best source available:

Know which of these you are looking at before you use a chart to make a decision. A daily profile drawn from priority 3 is a clean, plausible-looking curve that contains no cloud, no haze and no real day-to-day variation — it will never show you the ragged afternoons that matter to a dispatch or a storage study. Its monthly totals are still sound; its hourly detail is a reconstruction.

The way to move up the list is to supply better weather data. An hourly file, or an hourly fetch from the automatic service, puts you at priority 1 or 2 — see Weather data.

Exporting the series

Export TMY data CSV writes the full-year series to a file. The interval selector beside the button sets the time step, and offers 1, 10, 15, 30 and 60 min. The default is 15 min.

Pick the interval to match what the series is for, not the finest one on offer. A 60-minute file is the smallest and is enough for an annual reconciliation; a 1-minute file is sixty times the size and, as below, contains no more weather detail than the source it was built from.

The per-interval energy relation

E (kWh) = capacity_kWp × GTI(W/m²)/1000 × PR × LID × (interval/60)

The LID factor is worth pinning down, because it decides which year the file describes. It is the 1st year degradation field and nothing else — the same one-off step applied to the annual figures, taken as 1 − 1st year degradation ÷ 100. So the exported series is a first-year series, consistent with the year-one energy in the summary, and the annual degradation rate does not enter it at all: there is no exported series for year 10. See Lifetime, degradation and P-values.

The relation is linear in irradiance, so the exported series has the same shape as the irradiance series it was built from. Two consequences the file records directly:

• Timestamps are local time. Values are therefore zero through the night and peak around solar noon. A series that peaks at midnight has been read with the wrong time base somewhere downstream, not exported wrongly.
• A sub-hourly interval does not create sub-hourly weather. Choosing 1 min gives you 1-minute rows, but the underlying irradiance resolution is whatever your weather source provided. Finer intervals give a finer grid, not more information.

The export needs an hourly series

The export requires an hourly series to work from — either an hourly weather file you loaded, or an hourly fetch from the automatic service. Monthly data alone is not enough, and the export is not available from it.

This is the one place where the choice of weather source is not a question of quality but of capability. If you need a generation series, arrange for hourly data before you plan the work around the export.

What the file contains, and what it is for

The file carries the full-year series at your chosen interval:

• Horizontal irradiance (GHI) — what arrives on a horizontal surface.
• In-plane irradiance (GTI) — what arrives on the plane of the array.
• Energy — the generation computed by the relation above.

Having all three in one file is what makes it checkable by someone else: a reviewer can re-derive the energy column from the irradiance column, your stated capacity and your stated performance ratio, without needing the application.

Typical uses:

• A dispatch or curtailment study. The generation profile against a connection limit or a scheduled export, interval by interval.
• A storage study. Sizing a battery against the daily shape and the ramp rates, where the annual total tells you nothing useful on its own.
• A tender or grid submission asking for sub-hourly generation. Set the interval selector to whatever the request specifies and export directly, rather than resampling an hourly file by hand.
• Reconciliation. Summing the energy column must reproduce the first-year energy in the summary. It is the quickest independent check that the run you are reporting is the run you think it is.

Where to go next