Solar PV across different facing roofs
Posted by Chris Rudge on 3 September 2010 at 12:59 pm
Q: I'm thinking of installing solar PV panels on two roof aspects, one south facing the other east. Can you please explain in layman's language what is meant by 'series' and 'parallel'. Different installers are recommending one or the other or both!
A: Unlike battery charging PV systems, all grid connected systems need to have the solar modules connected in series which will provide a high voltage DC input to the inverter. This voltage is typically in the range of 150 to 500 volts.
For larger systems (over 3kWp), these series circuits (strings), will need to be divided into two or more as the total voltage will be too high for an inverter input. These separate strings will be connected in parallel into an inverter.
Another issue that is sometimes misunderstood, even by installers, is the problem of installing on roofs with variable or different aspects. As an example, if you have a double aspect roof, with one area facing south and the other east, both can have PV installed, but will need either two separate inverters, or a single special inverter with dual maximum power point tracking (MPP) inputs.
If both the South and East arrays were connected together to the same input, you would find the array with the higher output being pulled down to match the lower output array. It would emulate the whole system as never having any direct sun on it.
This can be likened to connecting a good car battery onto a poor battery, the poor battery will eventually make the good battery useless.
Photo by computerhotline
About the author: Chris Rudge is a qualified electrician who specialises in renewable energy.
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