R
roamwood
As someone with a keen interest in solar I am a long term loiterer on this forum, so thought it was time I joined. I also have a puzzle I can't work out.
A year or two back I purchased some sunpower spr-90 90w panels for installation on my motor-home, and on my fathers. So far I have only installed my fathers but its performance is so much exceeding expectations that I am wondering what is going on!
A bit of background information: For a 90w panel they are very small at 1038mmx527mm and the blurb claims higher efficiencies as all the electrical pickups are on the rear of the cells. Although the installation manual said they could be used in strings, an extra note in the box said they should only be used individually which I thought was odd. Checking on the internet I found out that their was an issue with the panels being used in series that caused their performance to drop due to a build up of -ve charge over time. This effect was apparently fully reversible by making the aluminium frame of the panels positively charged. I decided to link the +ve panel output to the frame of the panel, which was the recommended course of action. To cover the risk that aluminium frame might come in contact with the -ve earth of the vehicle (only a slight risk as my dads camper has a fibreglass roof) I put a 5 amp fuse in the line between panels and the charge controller. I sized this on the claimed output of the panels 90w at 18v. I never expected to hit those sorts of figures as the panel is horizontal, so hardly optimal. That was all done late last year.
Jump forward to mid May and I'm on holiday with my Dad in the north of Scotland. The weather was great. He has quite a quite a sophisticated (but non MPPT) controller that monitors and records panel voltage and current, as well as battery voltages, so we were regularly checking it and getting high figures. One particularly sunny day we checked it to find zero output from the panels. The 5 amp fuse had blown. The solar controller recorded 6.4 amps and 21.5v at the time of failure, so 137w by my maths! I replaced the fuse with a 7.5 amp one and watched the output increase further during the day to 7.1amps at 22v, so around 156w. How can this be possible, in the North of Scotland with such a small panel, or am I missing something obvious??
Any thoughts would be much appreciated.
Mike
A year or two back I purchased some sunpower spr-90 90w panels for installation on my motor-home, and on my fathers. So far I have only installed my fathers but its performance is so much exceeding expectations that I am wondering what is going on!
A bit of background information: For a 90w panel they are very small at 1038mmx527mm and the blurb claims higher efficiencies as all the electrical pickups are on the rear of the cells. Although the installation manual said they could be used in strings, an extra note in the box said they should only be used individually which I thought was odd. Checking on the internet I found out that their was an issue with the panels being used in series that caused their performance to drop due to a build up of -ve charge over time. This effect was apparently fully reversible by making the aluminium frame of the panels positively charged. I decided to link the +ve panel output to the frame of the panel, which was the recommended course of action. To cover the risk that aluminium frame might come in contact with the -ve earth of the vehicle (only a slight risk as my dads camper has a fibreglass roof) I put a 5 amp fuse in the line between panels and the charge controller. I sized this on the claimed output of the panels 90w at 18v. I never expected to hit those sorts of figures as the panel is horizontal, so hardly optimal. That was all done late last year.
Jump forward to mid May and I'm on holiday with my Dad in the north of Scotland. The weather was great. He has quite a quite a sophisticated (but non MPPT) controller that monitors and records panel voltage and current, as well as battery voltages, so we were regularly checking it and getting high figures. One particularly sunny day we checked it to find zero output from the panels. The 5 amp fuse had blown. The solar controller recorded 6.4 amps and 21.5v at the time of failure, so 137w by my maths! I replaced the fuse with a 7.5 amp one and watched the output increase further during the day to 7.1amps at 22v, so around 156w. How can this be possible, in the North of Scotland with such a small panel, or am I missing something obvious??
Any thoughts would be much appreciated.
Mike