FAQs

The ARES device can accurately measure all types of soiling. It has been designed to measure the same soiling type that is affecting the monitored plant and therefore covers all soiling types.

ARES accurately measures the instantaneous and daily soiling loss by comparing the irradiance difference between two identical large-area reference cells. One cell is washed daily, while the other is left to soil naturally. The Wash Extension hardware automatically cleans one reference cell on a daily basis, eliminating the need for manual cleaning.

Irradiance values are derived from the short-circuit current (temperature compensated) of the reference cell.

By default, ARES outputs data every 5 minutes. This frequency can be adjusted remotely. If you prefer even more resolution, you can connect the ARES device to the Wash Extension battery (12V) via the M12 cable. Higher resolution data draws more power than the default frequency.

Yes. Soiling buildup is often a very slow and gradual process that takes days or even months to show an obvious trend.

The internal battery draws very little power during the night because it goes into a deep-sleep state. The battery remains well-charged, even in the dark winter months. ARES cannot detect soiling at night, so it does not output data and consume battery power then.

All ARES devices have an integrated cellular modem that communicates with the nearest cellular tower. A secure connection is made to the Fracsun cloud and a message that contains the data is published.

ARES utilizes an internal E-SIM, which is a chip-based SIM card. There is no slot for an external SIM card.

In the United States, ARES connects to the AT&T LTE M1 network. Globally, ARES is powered by over 350 carriers across the world and automatically connects to the best networks across 2G/3G/LTE.

For poor cellular reception, you can install a higher gain external antenna. For sites with no reception at all, you can directly connect to an onsite data logger using Modbus RS-485. In this case, you cannot view the data in the portal.

No it does not. That being said, we have found that most network failures only last a couple hours and that ARES is still able to generate an accurate daily soiling loss value during these events, even with the missing irradiance data from that downtime.

No, but it can communicate over Modbus RS-485. You also may be able to use a Modbus TCP/IP to Modbus RS-485 converter if only TCP/IP is available.

We apply a nano-scale hydrophobic coating to the clean reference cell only. The coating, combined with a daily high pressure water spray, greatly reduces the need for mechanical cleaning on that sticky / hard soiling. That being said, we would recommend visual inspections during site visits to verify the efficacy of the cleaning.

The combination of the hydrophobic coating and daily high pressure spray are often enough to remove sticky soiling.

ARES uses polycrystalline large-area reference cells. The cells are standard size 156 x 156mm and the glass is 200 x 200mm.

The accuracy of our soiling measurement with a thin-film plant greatly depends on the thin-film technology used. CIGS, popular in First Solar modules, correlates well with our soiling station due to a similar spectral response seen in polycrystalline. CdTe and a-Si technologies don't correlate as well due to their different spectral responses, but we can still make decent correlations.

Because the polycrystalline reference cells may degrade at different rates over time, a simple calibration must be performed to match the cells as close together as possible using software-based scaling.

Preferably a calibration should occur once a year.

Fracsun uses a very simple automatic calibration process, which can be activated remotely in the portal or writing to Modbus registers. It should occur when both reference cells are completely cleaned.

When a shadow is cast over the ARES unit, vastly different clean and soiled irradiance values can result in erroneous soiling values. These soiling values are just instantaneous ones and should be ignored.

Any slope / inclination of 5 degrees or more is best. For tracking systems, the automated spray must occur when the nozzles are pointed towards the ground (not the sky).

Any slope / inclination of 5 degrees or more is best. For tracking systems, the automated spray must occur when the nozzles are pointed towards the ground (not the sky).

ARES can work on flat rooftops, but the angle must be slightly adjusted to at least 5 degrees so that the water from the daily spray flows away from the cell.

Yes, a soiling station can be moved from one location to another. Don't forget change the device coordinates in the Portal.

No. ARES does not need the Wash Extension to measure soiling. The Wash Extension's purpose is to automatically rinse ARES's clean reference cell on a daily basis. This process can also be scheduled manually by a local site resource.

The Wash Extension is an accessory for the ARES soiling monitoring station. The Wash Extension stores and automatically pumps water up to the high-pressure spray nozzles on the ARES device. While it's not required, almost all of our customers use it.

16 gallons (60 liters) of water when fully filled.

The Wash Extension reservoir needs to be refilled once a year in its default configuration (1 wash per day).

Distilled water or filtered water (RO + DI preferred) with a TDS value of less than 20 ppm. Under no circumstances should tap water be used. Tap water contains minerals that will build up on the solar glass after each wash, affecting the irradiance measurement and soiling accuracy.

1 wash per day. The Wash Extension can be configured to wash up to 3 times per day.

Typical maintenance includes annual water tank filling, pump replacement after 5yrs, battery replacement after 7yrs, and incidental damage from vegetation mitigation (mowers, sheep, etc).

9am local time. The Wash Extension can be configured to wash at any hour of the day.

Yes, it can work in freezing conditions. Please read our Winterization instructions.

In non-winter operation, there are no chemicals used within the reservoir.

Yes. The Wash Extension supports Modbus RS-485 communication. Please read the Modbus documentation for more information.

This greatly varies on the PV plant, dust type, and source of the soiling. We can perform a virtual site evaluation if you can share some details about your plant. The general recommendation would be 1 to 2 devices per 5MW.

The ends of a tracker row are often the best location to install ARES for accessibility reasons. For northern-hemisphere projects, installing on the south end of a row is recommended because the Wash Extension has less shading. For south-hemisphere projects, installing on the north end of a row is recommended.

Yes, you can use ARES to monitor soiling on ground-facing bifacial modules. However, when lower albedo is present, the soiling accuracy may not be as good. Generally speaking, if we are able to measure irradiance values of at least 200 W/m^2 on the ground-facing ARES, the data should be good enough to get a soiling loss value. Irradiance measurements under 100 W/m^2 w will start to have an error, so values below that threshold will likely be trimmed when calculating the daily soiling loss/ratio. Fracsun is continually researching the newest solar technologies, and results for measuring bifacial soiling look promising.

Yes. The daily soiling loss value is calculated using modified clean and dirty insolation values. Fracsun's calculation algorithm combs through the day’s irradiance data to clean up the insolation data by weight irradiance values (higher irradiance caries more weight than lower irradiance), removing irradiance values under a specific threshold, and removing irradiance values that are very far apart from each other (mostly due to shading).