Solar yield too low; how to adjust three flat collectors

Hello everyone,

for several months now we have been living in our beautiful house, which came with quite a few construction problems. We have managed to get most of the problems under control, but we do not know if the solar system is working correctly.

Here are the key data of our system:
We have a Vaillant solar system with 3 horizontal flat plate collectors connected in series. Total net area: 7.05m²
Circulation volume of the solar fluid: 2l/min (according to the operating instructions minimum required is 3l/min, recommended is 4.6l/min)
Flow velocity in the circuit 0.13m/s (required according to the operating instructions minimum 0.4m/s otherwise the Vaillant venting system has no effect)
Circulation pump type Wilo RS25/7-3P; power consumption stage 1: 62W; stage 2: 92W; stage 3: 132W; stage 2 is set as stage 3 brought no noticeable increase in the volume flow.

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

Now we received a tip from a heating engineer to check whether the system is also set for three flat plate collectors, because often only a 2-collector setting is provided at the factory. We have now searched the manuals but found no possibility of adjustment anywhere.
The controller is the auroMATIC 620 model from Vaillant.

Despite repeated inquiries at the plumbing company that installed the system for us, as well as at the manufacturer Vaillant, we have received neither a response nor feedback for months.

We would be very happy about an experience report or help.

Best regards
Thomas

Hello,

....but with the solar system we don't know if it is working correctly.

What does correctly mean? How many kWh were actually "harvested", how many were forecasted? Who planned this nonsense?

Best regards

What exactly correct means we do not know in this case either. We only know that what is stated in the operating manual does not correspond to what our system delivers. It has been in operation since April and has generated 1310kWh since then. The best month was May with 552kWh.

What exactly "correct" means we do not know in this case. We only know that what is stated in the operating manual does not correspond to what our system delivers.

How large is the discrepancy between the operating manual and the actual delivery? How is the actual result determined (kWh)?

Best regards

How large is the discrepancy between the operating manual and the actual delivery? How is the actual result determined (kWh)?

v.g.

The achievable yield (kWh) is not specified anywhere. I only have the above-mentioned information from the operating manual regarding circulation volume, flow velocity, etc. The determination of the yield is done by the Vaillant auroMATIC controller. It shows me on the display how much power was generated per month.

.....The achievable yield (kWh) is not indicated anywhere.

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

..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 here, it should also be practically realized. The specification is not pointless. It is surprising that the throughput does not increase at the next higher pump level. Either there is air in the system, or the pressure losses of the system are too high, so that the pump is already operating at the end of its characteristic curve. The tip from a heating technician is strange: Either it is really measured (mass flow, supply temperature, return temperature), then corresponding sensors must be installed in the hydraulic circuit, or it is estimated by software with "parameters." This comment would be aimed at that. However, I would have little trust in the yield display. I always see control options here, sometimes with surprising results.

Best regards