Systems under test
We are currently evaluating the performance of two solar domestic hot water systems, similar in size and specification that would be found in a 2-3 bedroom family house. One system uses a flat-plate collector and the other an evacuated tube system using heat pipes.
The two collectors are mounted side by side on a south facing pitched roof and are connected to identical systems as follows:
- 166 litre Gledhill Sunspeed 2 vented twin coil solar cylinder
- Resol Flowcon S Pump Station with flow meter
- 18 Litre Expansion Vessel
- 2 x 7.5m Pre-Insulated Stainless Steel Fleixble DN16 piping
- Both cylinders are joined to the same hot water outlet to ensure a balanced loading
- A Resol Deltasol M solar controller is used to regulate the systems
Why are we doing this?
To help us fully understand how different designs of solar collectors work in the UK climate, by recording and analysing performance over a long period of time taking into account:
- Light levels and incidence angles
- Wind speed
- Ambient temperatures
- System operating temperatures
- Varying hot water demand profiles
Most solar thermal collectors on the market, including the ones Barilla sell, will have undergone EN12975-2 testing for both durability and performance. This test procedure is carried out by recognised testing institutes to defined ISO standards. A report is then produced that includes some parameters to describe the performance of the collectors, notably the converion efficiency, heat loss factors and thermal capicitance. This is intended to allow a standardised method of comparing collectors and predicting their annual output.
The main problem is that most of the testing is performed under steady-state generic conditions, that is at a constant irradiation and at a near normal angle of incidence. No account is made for the real effects of diffused light or wind. EN12975-2 does make a provision for a more complicated quasi-dynamic test that includes these factors, but we believe this is little used due to its expense and complexity.
Whilst our testing will not conclude for some time to come, we are pleased to show you the system in action - especially if you are new to solar thermal. It gives you the opportunity to see when solar thermal will and won't produce meaningful energy in our climate throughout the year.
How the data is logged
The experiment is managed by a Resol DeltaSol M Controller that allows independent control of the two solar thermal systems on test. With the use of 12 input sensors and a light meter to record the necessary data, the information is logged in real-time (in an ASCII text format) to a PC via a Resol RS-Com unit.
The schematic showing the live temperature and global irradiation is produced using the Resol Service Centre Software and is updated on this web page every minute.
Presenting the graphical data is more involved, the raw data is automatically processed by some bespoke analysis software that we have written. The software averages the data over 10 minute intervals then uploads it to our web server every few minutes. The graphs on this web page are then produced from this averaged data. We have graphs for this experiment going back to the 1st August 2009, you are welcome to view the data for any day back to this start date using the calendar provided.