Green Building Forum - Keep those PV arrays clean or this will happen!!

Keep those PV arrays clean or this will happen!!

jms452 — Fri, 01 Jun 2012 11:46:01 +0100

Posted By: GotanewlifeYes I remember when last year I raised here the issue of my PV panels not performing as well as I expected in high summer and suggesting an automated watering/cleaning solution a couple of people pointed out that the risks and unintended consequences would outweigh any benefits. Right now though I do seem to have a little spare capacity so I might just do some experimentation myself. I only have one inverter for my 2 string 5kW system so one-sided cleaning not an option.

My panels are mounted in a dip in the roof so as to be the same hight as the surrounding tiless but with a good 40mm gap underneath and are mounted tight so I should be getting signification ventilation currents from the hot air rising albeit only up a 15 deg slope. Ambient shaded air temp high summer is often 35 deg so 60 deg on the panels a very real possibility!

Have you tried comparing your output with pvgis for a clear day - if your inverter logs the data last weekend was excellent. see:

http://www.greenbuildingforum.co.uk/forum114/comments.php?DiscussionID=9144&page=1#Item_7

Keep those PV arrays clean or this will happen!!

cbatjesmond — Fri, 01 Jun 2012 19:22:19 +0100

Posted By: jms452

Have you tried comparing your output with pvgis for a clear day

My project for the weekend is to run a cable to a 1-wire light-sensor on a front windowsill under the PV so that I can compare light levels, temperature and PV generation. Unfortunately at the moment, my cable only reaches the windowsill facing the opposite direction from the PV array! http://www.ccandc.org/cgi-bin/env?START=end-1w&END=now#lux

Once I've got some data, I'm hoping SteamyTea is going to derive a formula for me linking lux, C and W ... ;-)

-- Chris

Keep those PV arrays clean or this will happen!!

SteamyTea — Fri, 01 Jun 2012 21:59:31 +0100

Posted By: cbatjesmondI'm hoping SteamyTea is going to derive a formula for me linking lux, C and W ... ;-)

Are you now

Sure I have asked before, what make Inverter you got?

Keep those PV arrays clean or this will happen!!

cbatjesmond — Sun, 03 Jun 2012 13:44:42 +0100

It's a Fronius IG-15, photos and docs at http://www.ccandc.org/pv/#inverter

I'd like to think that there'll be a simple relation between insolation and power output, but I see wide differences between reported output from the inverter and what's recorded by the generation meter, so I suspect there would need to be a lot of hidden variables, e.g. panel temp, inverter temp, inverter efficiency at various temperatures and inputs ... and target output voltages (I suspect my generally high mains voltage - 3hr average 247.5V, max 253V, min 243V according to the inverter - costs me some efficiency), ... Would the resistance of the ~10m of cable inverter -> meter change depending on current (max 6.5A)?

This sounds like an excuse for a *lot* more sensors :-)