03-10-2018, 03:01 PM
What I aspire to is to have 1/3 of my panels pointed east, 1/3 pointed west, and 1/3 pointed south, all at a steep angle at least 45 degrees from horizontal. I already have 1/3 pointed south south-east at about 45 degrees and the remainder up on the roof about 15 degrees from flat pointing south south-east. The goal is "virtual tracking". Some will be productive in the morning, some in the afternoon. The south angled panels will angled right for the winter sun. In the summer the east and west facing panels will start pumping out power long before and after the south facing panels even get any sun. This only works if you invest heavily on panels. Certainly you should never spend any money on trackers or even fancy fixed supports if that money could be spent on buying and mounting another panel to an available fixed surface.
This strategy has merit even where the sun shines brightly. Here in Puna where there are so many clouds, it almost doesn't matter where the panels are pointed as long as there is a clear line of sight to some part of the sky. I have been outside on a cloudy day when the brightest part of the sky was to the north simply because the clouds were thinnest there. On such days square footage of panels trumps everything else. With this setup the charge controller would never see the sum of all the attached panels because they are all generating at different times, except on cloudy days when the sky was uniformly gray. Those days are not a problem for other reasons.
I have a regular electric resistance 240 volt AC water heater as my diversion load. My charge controller turns it on when battery voltage is above 55 volts (float voltage) and off when it drops to 54 volts. I run it on 120 volts AC so it draws a little over 1,000 watts instead of the 4,500 watts listed on the nameplate. I could also run it on 55 VDC and get about 500 watts diversion load. I don't think that an electric resistance load cares about AC vs DC although the switch contacts would.
ETA: If this is a diversion load you could take the 95VDC coming directly from the panels before it goes through the charge controller and send it to the water heater. The resistance element wouldn't care what voltage it was getting. Wattage would be somewhere between 500 and 1,100 watts, probably slightly less than if powered by 120VAC. Not sure if there are any real benefits to this though.
Pro # 1. Would never draw from batteries. The way I have it set up now the inverter faithfully draws from the batteries to make the AC that runs the heater until the programmed delays run out.
Pro # 2. Less load on the inverter.
Con # 1. DC is harder to switch than AC.
This strategy has merit even where the sun shines brightly. Here in Puna where there are so many clouds, it almost doesn't matter where the panels are pointed as long as there is a clear line of sight to some part of the sky. I have been outside on a cloudy day when the brightest part of the sky was to the north simply because the clouds were thinnest there. On such days square footage of panels trumps everything else. With this setup the charge controller would never see the sum of all the attached panels because they are all generating at different times, except on cloudy days when the sky was uniformly gray. Those days are not a problem for other reasons.
I have a regular electric resistance 240 volt AC water heater as my diversion load. My charge controller turns it on when battery voltage is above 55 volts (float voltage) and off when it drops to 54 volts. I run it on 120 volts AC so it draws a little over 1,000 watts instead of the 4,500 watts listed on the nameplate. I could also run it on 55 VDC and get about 500 watts diversion load. I don't think that an electric resistance load cares about AC vs DC although the switch contacts would.
ETA: If this is a diversion load you could take the 95VDC coming directly from the panels before it goes through the charge controller and send it to the water heater. The resistance element wouldn't care what voltage it was getting. Wattage would be somewhere between 500 and 1,100 watts, probably slightly less than if powered by 120VAC. Not sure if there are any real benefits to this though.
Pro # 1. Would never draw from batteries. The way I have it set up now the inverter faithfully draws from the batteries to make the AC that runs the heater until the programmed delays run out.
Pro # 2. Less load on the inverter.
Con # 1. DC is harder to switch than AC.