ᐅ Insufficient solar output; how to set up three flat-plate collectors

Hello everyone,

We have been living in our beautiful house for several months now, which came with quite a few construction issues. We have managed to resolve most of them, but we are unsure whether our solar system is working correctly.

Here are the key details of our system:
We have a Vaillant solar system with three horizontal flat-plate collectors connected in series, one above the other. Total net surface area: 7.05m² (76 ft²)
Flow rate of the solar fluid: 2 l/min (0.53 gal/min) (the operating manual requires at least 3 l/min (0.79 gal/min), with a recommended flow of 4.6 l/min (1.22 gal/min))
Flow velocity in the circuit: 0.13 m/s (0.43 ft/s) (the manual requires a minimum of 0.4 m/s (1.31 ft/s); otherwise, the Vaillant venting system will not function properly)
Circulation pump type: Wilo RS25/7-3P; power consumption Stage 1: 62 W; Stage 2: 92 W; Stage 3: 132 W; set to Stage 2 as Stage 3 did not noticeably increase the volume flow.

According to Vaillant, this is a low-flow system and everything is fine.
But is that really the case?

We received a tip from a heating technician to check whether the system is set up for three flat-plate collectors, since factory settings often only cater to two collectors. We have searched through the manuals but could not find any setting options.
The controller is the Vaillant auroMATIC 620 model.

Despite repeated follow-ups with the plumbing company that installed the system and Vaillant, we have received no response or feedback for months.

We would greatly appreciate any insights or advice based on experience.

Good luck,
Thomas

Hello,

Capone2000 schrieb:
....but we don’t know if the solar system is working correctly.

What do you mean by correctly? How many kWh were actually "harvested," and how many were predicted? Who planned this nonsense?

Regards

What exactly is correct, we don’t really know in this case. We only know that what is stated in the operating manual does not match what our system actually produces. It has been in operation since April and has generated 1310 kWh since then. The best month was May with 552 kWh.

Capone2000 schrieb:
What exactly is correct in this case, we don’t really know. We only know that what is in the user manual does not match what our system delivers.

What is the discrepancy between the user manual and the actual output? How is the actual result measured (kWh)?

Best regards

€uro schrieb:
What is the discrepancy between the operating manual and the actual delivery? How is the actual output measured (kWh)?

Regards.

The achievable output (kWh) is not stated anywhere. I only have the above-mentioned information from the operating manual regarding circulation volume, flow velocity, etc. The output is determined by the Vaillant auroMATIC controller. It shows on the display how much energy has been produced per month.

Capone2000 schrieb:
.....The achievable yield (kWh) is not provided anywhere.

Usually, there should be a yield forecast before the system installation; otherwise, how can the result be evaluated.

Capone2000 schrieb:
..I only have the above-mentioned information from the operating manual regarding circulation volume, flow velocity, etc.

If the manufacturer specifies an optimal circulation volume, it should also be practically realized. The specification is not meaningless.
It is surprising that the flow rate does not increase at the next higher pump speed.
Either there is air in the system, or the pressure losses of the system are too high, so the pump is already operating at the end of its performance curve.
The advice from a builder is strange: either it is genuinely measured (mass flow, supply temperature, return temperature), in which case appropriate sensors must be installed in the hydraulic circuit, or it is estimated via software using "parameters." This comment would refer to that. However, I would have little confidence in that yield display.
I always see opportunities for control here, sometimes with surprising results.

Best regards.