System Design

Sizing

Systems sizing starts with a load calculation. Light Energy made an initial estimate based on our utility bill. At this point it appeared that I was not going to have enough useable roof space to put a system big enough to offset our loads. At this point I started focusing on figuring out how to maximize the size of the system.


As I was doing more research I also learned that in general it is cheaper to reduce load than to produce PV power. Since we are grid connected we didn't need to go to extremes. I also didn't want to make any significant compromises. I did discover the joys dimmable compact fluorescents. I was pleasantly surprised by the dent it made to our power consumption.

Panel selection

First place for maximum power is to look for the most efficient panel. I compared different panels and looked for most power for a given area. I also decided that a smaller panel will probably allow more layout flexibility. The panel that best met this criteria was the BP-585. There was actually a BP-595, unfortunately it was not available in the US.

Maximum Power Point Tracking

To get all the power from the BP-585s, I matched them up with RV PowerProducts SB3048. A MPPT allows a battery backed up system to be more efficient. A MPPT is particularly good match for the BP-585, the maximum power point on the BP-585 is a little bit higher than other panels. The bay area climate is fairly mild so I expect to get a boost most of the time.

Inverters

For a battery backed up grid tied system there is only one choice. Trace SW series.
 

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