Why it matters
The rear side is where the estimates differ
The front of a panel sees the sky, and most yield tools handle that well. The rear sees the ground under and between the rows, the backs of the rows in front, and a slice of sky. How much light reaches it changes with the sun's height, the share of diffuse light, the row spacing and height, and above all what the ground is made of.
A single yearly bifacial gain, or a fixed albedo typed into a yield tool, hides all of that. The rear can give a few per cent in one month and several times as much in another. Over bare ground it gives one figure; over a light surface laid on purpose, a much larger one.
A reflected typical year puts the rear side on the same hourly footing as the front. It tells you what the rear will earn, month by month, at your site, with your mounting, on your ground. It lets you compare grounds and layouts before anything is built, and it gives the plant a figure to be measured against once it runs.
The method is Namindo's own. It works from first principles, hour by hour, and it is the same calculation behind the trial in Namindo's ARENA Launchpad application and its published site results.
What you receive
An hourly year, and the totals that matter
Hourly file
8,760 hours
Every hour of the typical year: sun position, the weather year's sky and temperature, front-plane irradiance, rear-plane irradiance, the ground-reflected part of it, module temperature, and energy per kWp.
Cases side by side
Bare against treated
Your ground as it is, and each surface or layout you want to test, run on the same hours so the difference is the ground and nothing else. Gain is given hour by hour, by month and for the year.
Summary
Monthly and yearly tables
Front and rear irradiation, energy per kWp, rear-side gain and bifacial gain for each month and the year, with a short note of the inputs used.
Carried to the inverter
Clipping at your ratio
The extra rear energy is run through your inverter at your DC to AC ratio, so the gain you see is the gain you sell, not the gain the panels make.
Heat and ageing
Warmer modules, dirtier ground
Module temperature follows the extra light, and a treated surface can be run as new and as aged, so the year shows what the ground gives after it has weathered.
Your own data in
Satellite or measured albedo
Use a public typical year, a commercial satellite dataset you already hold, or your own albedometer record. We are not tied to one source.
Columns in the hourly file
| Column | Content | Unit |
|---|---|---|
time_local, time_utc | Hour ending, site time and UTC | |
sun_elev, sun_az | Sun elevation and azimuth | degrees |
ghi, dhi, dni, t_air, wind | From the weather year used | W/m², °C, m/s |
poa_front | Irradiance on the front of the module | W/m² |
poa_rear, rear_ground | Irradiance on the rear, and the part of it reflected from the ground | W/m² |
t_module | Module temperature | °C |
e_bare, e_case, gain | Energy per kWp on bare ground and for your case, and the gain | Wh/kWp, % |
Files come as CSV and as OpenOffice spreadsheets, downloaded from your own webdoli login, so the people you choose can fetch them and nobody else can.
What the field tells us
Why a bifacial estimate needs the whole year, and the whole plant
The spread
Estimates from 4 to 17 per cent
Published estimates of the bifacial gain over monofacial range from about 4 to 17 per cent. Resource analysts warn that a gain promised and not delivered damages investors' trust in the technology. The ground is the largest single unknown.
Modelled against measured
Light ground covers, two answers
A developer's modelling of a white agricultural cover under trackers gave about 3 to 4 per cent more energy, but did not pay, partly because the inverters clipped more. A measured trial of white films under trackers, against a reference, gave about 9 per cent, with modules about 2.6 °C warmer and some of the gain lost to dirt on the film.
What we take from it
Count everything the ground changes
A reflected year has to carry the rear gain through to the inverter, the module temperature and the cover's ageing, hour by hour. That is what ours does, and why we set it against measured data wherever we can.
Sources: Solargis on albedo and investor trust; 7X Energy in pv magazine, 2021; high-albedo ground covers on trackers in Brazil, ISES Solar World Congress 2025.
What we need from you
Six inputs
- Site: coordinates, or the weather file you want used. Without one, we use a public typical year for the site.
- Mounting: fixed tilt and azimuth, a single-axis tracker with its limits and backtracking, or a carport or pergola frame.
- Rows: row spacing, height above ground, and the module layout on the table.
- Module: make and model, or its bifaciality and temperature response.
- Ground: what is there now, and any surface you are thinking of laying. A measured albedo, if you have one, is welcome.
- Cases: the layouts or grounds you want compared, and the inverter DC to AC ratio for each.
In-house examples
Sixteen sites, three continents
Namindo's own modelling, shown as a worked example: rear-side gain on fixed racks, as a share of front-side energy, over bare ground and over a treated ground surface, each run on the site's public typical year.
Eight of the sixteen sites shown: five in Australia, three in India. All sixteen, with trackers and a lighter treatment, are on the large farm modelling page. A second in-house example, carports and pergolas in the eight Australian capitals with the hourly year behind buttons, is on Namindo BIPV designs.
How to order
Five steps
- Send the inputsEmail the six inputs above, or as many as you have. A layout drawing and the module data sheet are usually enough.
- We confirm and quoteWe check the inputs, agree the cases with you, and confirm the price and delivery date.
- We run the yearNamindo engineers run each case hour by hour and check the results against the site's sky and the published sites.
- You download the filesThe hourly files and summary tables go into your webdoli login, as CSV and OpenOffice.
- Track it once built (optional)When the plant runs, we log its weather and output and set them against the same model each hour. Each new year can be run as a reflected actual year beside the typical one. See the Comparator.
Who it is for
Owners, designers, lenders and researchers
Bifacial yield for a project or a bid; choosing between grounds, heights and spacings; carport and building-integrated designs; a basis for a field trial or a grant application.
The method
Namindo's own, and licensed
The model and the recipe behind it are Namindo's own work and are not disclosed. The results are yours to use in your design, your yield report or your application. Engineering firms that want to run it themselves can ask about a licence.
Ask for a reflected typical year
Send your site, mounting and ground to info@webdoli.com or call +61 426 087 878. We work from Australia, Indonesia and India, for sites anywhere.