In the previous post I showed how electricity from my Powerspout is used in winter; in this I show how it's used in summer.
The seasons are quite different; winter sees generous hydro and little solar; summer is the opposite with lots of solar and little hydro.
There are other differences: in summer the fire in the house is not alight and the space (storage) heater for the priority 2 diversion load is switched off; together these differences create a quite different pattern for what happens to the electricity which is generated.
As with the previous post, I have taken data from one particular day, an unusually sunny day from the look of the solar generation record, to illustrate what happens in summer; the two plots below display the data.
Plot 1
Plot 2
Explanation of the plots
as before, the vertical axis of plot 1 is power in watts, of plot 2: watt hours, and the horizontal axis of both is the time of day.
the green line represents power being generated, - in the hours of darkness this is only the contribution from the Powerspout (283 W), but when the sun is up, it rises to 3000 W as the PV array adds its contribution; the PV comprises 12 panels, each rated at 275 W (ie 3.3 kW peak).
there being no input from a fire to give the house hot water in summer, the first priority for any spare power is for this purpose; the diverted power appears as intermittent blocks of red bars, intermittent because a washing machine, dish washer and bread maker are programmed to come on during the night; when they draw power, none is available for diversion, especially since the Powerspout is only producing 283 W;
from Plot 2, a total of 2 kWh can be seen to have been diverted to house hot water by 08:20, - little of it coming from the Powerspout and most coming from the PV in the first 1.5 hours after sunrise.
after house water is up to temperature, power is then seen to be sent to the second priority load, signified by blue bars, until that too reaches its thermostat setting;
the priority 2 load in summer is an immersion heater in the hot water tank of the annex; when both annex and house hot water are up to temperature, no diversion loads are available and excess power is fed back into the grid; there are just short duration top-ups to one or other diversion load from time to time.
the total energy exported to the grid on this day was ~ 14.7 kWh
imported energy from the grid was 2.7 kWh.
Conclusion
The big difference between summer and winter is the amount of energy which is spare; in summer, at least on a sunny day like the day studied, 14.7 kWh was put back into the grid, and to this can be added the 3 kWh which went to the priority 2 load because it is not usually necessary for us to have hot water in the annex;
in winter there is really none to spare; diversion to the annex which is optional in summer changes to being essential in winter; the 7 kWh which goes there is needed to take the chill off the rooms and stop water from freezing.
As I said in the previous blog post, the purpose behind analysing how our home generated electricity is used is to be able to make an informed decision about opting for home battery storage; I mentioned that one factor in that decision is what happens to the grid price of electricity.
This week I was notified of another increase !
On April 1st 2021 our off-peak energy moves up from 12.44p to 14.26p, standard day energy from 18.67 to 20.65 and the standing charge per day from 24.1p to 25p.
Now, I just need the price of batteries to come down !
