utility meter response to triac control

Maybe this has been fully wrapped up by now, but I have some test data which may be useful confirmation for some people thinking of using "all" their PV power.

I have a normal grid & PV system, where I have fitted 3 conventional utility meters, for (1) Power used by house, (2) Power imported from Grid, (3) Power generated by PVs.  All three give 1000 pulse/kWh and I have built a (PIC based - sorry) system to read the pulses & display everything in the house.

Wanting to build an addition to use all my "spare" PV power to heat water, I was worried whether Grid meter might not see my "chopped" power going to the immersion heater, but may see "full power" of the applied heater.  I see there was some discussion here earlier in the year.

With a bread-boarded zero crossing cct driving a Triac in "integral cycle" mode, I put power through to a 1400W room heater in various multiples of full cycles ( 0, 4, 8, 16, 24 out of every 24 cycles)  Results are as follows : fully confirms that the Grid meter sees what I want it to see, and only imports the necessary power to make up my "reduced" load.  

It was a dull day, but the arithmetic pans out.

  cycles/24                         0              4                    8                       16                    24

Heater kW(assumed)           0           0 .23                0.47                    0.93                1.40

PV generated                  0.13         0.13                  0.13                    0.13                  0.13

House using                    0.37         0.63                  0.87                    1.36                  1.85             

Grid supplying                  0.24         0.50                 0.74                     1.23                  1.72


Hope this is useful





calypso_rae's picture

Re: utility meter response to triac control

I like your objective of using "all" of your surplus PV power to heat water.

Always good to hear that someone else has independently made the same observations. 

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