Those who own and those who aspire to own a water turbine are equally interested in how much electricity can be expected. This concept of electrical productivity must not be understood as being the same as the installed capacity of a scheme, which is the maximum power it can produce from the head and flow available at the site. Whilst not the same as installed capacity, clearly installed capacity is a major determinant of productivity.
Rather, productivity is a measure of how well the installation performs over time and many are the factors beyond installed capacity which contribute to it. To give an answer to how productive a scheme is requires some way of capturing energy output with respect to time and then a way of presenting it. In this diary entry I want to outline how I record and display such information for my scheme.
The two plots I find most useful are these:
1. Cumulative energy output displayed by year:
2. Daily energy output displayed by year:
These two plots both use the same data. It is captured automatically from the inverter via a Bluetooth feed to a desk-top display device. The inverter I use is a German SMA WindyBoy and the desk-top device is an SMA Sunny Beam. The latter is now not marketed and because it is no longer supported by SMA with updates, the latest versions of some computer operating systems are not able to download data from it. I have to keep alive an old laptop using an out-of-date operating system just for the purpose of downloading data from the Sunny Beam.
Generally though, the system has proved very robust. It seamlessly accepted energy data from a new solar installation I had put in last year, capturing and displaying this on Sunny Beam alongside the hydro data. The Sunny Beam has memory capacity to store several months of hydro and solar generation before it starts to over-write the oldest data. My habit is to download data to a computer each month where it can be displayed in an MS Excel spreadsheet and then used to construct graphs such as those above.
As data from successive years is added, so the usefulness and interest value of keeping these records increases. Each year is different depending on how much rainfall there is, yet also there are regular patterns to each year as can be seen in the daily energy output graph above.
In the cumulative graph, it is the slope of the plot which reveals the rate at which energy is being harvested: the steeper the slope in comparison to previous years, the more productive that year is proving to be. As can be seen, the present year is, so far, better than the two previous ones but the daily energy plot shows that as this month of June starts, the daily yield is dipping below what it was in 2013-14. The next four months, which are the drier months of the year, will determine how the whole year works out. Whether I can keep generating through August and September will determine if I reach my target of 4000 kWh in the year.
Collecting this data adds greatly to the enjoyment of operating a Powerspout and the technology required, though sophisticated, is not expensive. Market competition has kept prices down because it has been developed for the mass solar market. It is certainly something worth considering.