Published: 28 March 2014
Category: Q&A
Colin asks this question, which concerns solar photovoltaic (solar PV) panels that are grid-tied, and how one has preference over the other at the right time. It has been answered by DIMPLEX (Theme – Energy Efficiency and Sustainability):
This Q & A is one of thousands posted in our Technical Expertise area, and answered on a daily basis by our Voltimum Experts.
Question: I’m just curious as to how the whole grid tied solar PV systems actually work…
I know that three electricity meters are required – for generation, import and export - and that any energy that is not used is fed back into the grid.
I have been told that solar PV power will have preference over grid power and that grid power will only be used when the solar PV system is generating less than what the demand is.
My question is, therefore, how does solar PV generated power have preference over grid power when there is a demand?
For example, if my solar PV system is generating (say) 3kW and I turn on a 1kW heater, as the two supplies are effectively connected in parallel, how can I be sure that I am using the solar PV power that I have generated, and not the more expensive grid power?
Answer: The electrical location of the different meters and the solar PV to grid connection point is the key here.
Photovoltaic grid tied energy may be shared by a residential or commercial building before, or after, the revenue measurement point (utility meter), the difference being whether the credited energy production is calculated independently of the customer's energy consumption (feed-in tariff) or only on the difference of energy (net metering).
In the UK only, the feed in tariff connection method is used - i.e. the photovoltaic generation meter and grid connection point is placed after the utility meter (revenue measurement point).
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