It’s been nearly a year since the solar panel installation on the gym roof of the Gulf Islands Secondary School. And we’ve had a summer of glorious sunshine. It’s time to see how the actual output of electricity compares with expectations.
Here’s a quick reminder on the project specifics:
- A small team from School District 64 and the Salt Spring Community Energy Group installed an array of 84 solar photovoltaic panels on the school roof.
- To change the direct current (DC) from the panels into the AC alternating current that the grid uses, the output from the array is fed to three inverters in the gym electrical room. These output the correct voltage for the school system as well as incorporating the required safety and monitoring circuits to meet the standards of BC Hydro.
- Although the rated output of the array of panels is 21 kilowatts (kW) we had expected the usual small losses at various stages – the panels themselves, the wiring and inverters – to reduce the maximum power into the grid to around 17 kW on very sunny days.
So how has it performed? In two words: beyond expectations. During May, June and July we regularly saw the output above 18 kW with some days over 19kW – a system efficiency of over 90% compared to the industry norm of 80%. This is attributable to the care taken in the design and installation of the system.
Of course that’s not the whole story. We also need good performance on average days and even during overcast conditions. Using the historical sunshine figures for Victoria airport and plugging those into a solar prediction program produced by the National Renewal Energy Laboratory (NREL) in the US, we produced expected output figures for the system for the months that were not unusually sunny.
For the calendar year from January to end-December, the program predicted an output off 24,570 kilowatt hours or units of electricity. We surpassed that by early October, with a further 2800 units expected in the remaining months.
A graph of the monthly output so far this year is included. The dark grey lines are the actual output while the light gray show the forecast. Note that the expected dip in June, in what it is usually an intermittently rainy month, did not happen in 2015. This result means that the amount of money available for the winner of next year’s solar scholarship will be more than expected.
We have concluded that the extra output is due not only to the unusually fine weather conditions this year but also to the “Sunny Salt Spring” Mediterranean microclimate we enjoy, together with a system that is operating at higher than expected efficiencies.
Have there been any problems? Not really. There were a couple of BC Hydro grid power outages for a few hours each. The system automatically shut down as it is supposed to do for safety reasons. When the grid came back up everything started up and reconnected automatically, meaning we only lost the value of a few hours output.
One area that still needs work is the monitoring system to show the school how much electricity is being produced from the sun. This work is well in hand. We are still looking for a suitable electric vehicle charging station at the school. We are hoping to install this early in the new year.