Quote:
Originally Posted by psychobimbo
For those of you in the know, can you please tell me about one thing I'm interested in with respect to a battery-backed home solar system?
With just a roof-top solar system, anti-islanding requirements automatically isolates the inverter from the main switchboard in the event that power from the grid is lost. This is required to ensure the grid supply line is dead when isolations at either end of the supply line are activated so that workers are not at risk. In effect, this means that, when there is a power outage on the grid, your solar system is useless to you.
How is this managed if I were to add a battery back-up? I assume that there is an automatic switch of some type installed to allow the solar system to still function, ie supply the house, during a grid power outage.
And, if this can be done with a battery back-up, why can't it be done with a roof-top system without battery storage?
All of the above assumes the house is fed from two supplies; the roof-top solar and the grid.
I think I must be missing something.
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Hello PB,
Sorry about the long timescale regarding an answer.
I see that there has been no answer thus far, so perhaps I can help.
Your are quite correct in that an embeddeded generator must "obey" the anti-islanding requirements when the local distribution system (read local mains network) shuts down for whatever reason. The safety requirements are the primary reason, but it also protects the embedded generator as well. Trying to provide power to all of your neighbours could well cause a catastrophic fault condition on your local generator to your financial cost.
There are two ways (I believe) to ensure that the islanding requirements are met when there is a battery storage system in place and the mains system shuts down:
1. The battery backup system must also have anti islanding properties. This means that in the event of a power outage the house will be without power for the duration of the outage, or
2. There is equipment associated with the switchboard that isolates the property from the distribution system. This may be incorporated in the battery cabinet. In this event the solar Photo Voltaic system on the roof will continue to supply power into the property so long as the battery system is able to supply power within a quite "tight" specification. This involves both voltage levels and waveform frequency requirements. Where there is no solar power the battery system would operate on its stored energy capacity for so long as it lasts.
Now on the investigations that I have done, there is very little technical information available on the web, provided by the suppliers. This means some quite close questioning of supplier representatives about the matter. In my experience such details are outside of the representative's knowledge base.
As a side matter I remain to be convinced that Battery systems are at a cost level such that the guarantee period offered is sufficiently long to ensure that a battery storage system will endue for long enough to repay the purchaser for its cost.
Where the property is remote from a mains supply to make the connection costs prohibitive, my comments are not necessarily valid. In this case a more detailed analysis should be done.
Regards