The 82% self consumption over the entire month really is just a due to the circumstances combined with an extremely sunny month, but I have had higher such as 30th May which was a full on Sunny day with 98% consumption and 98% self consumption. I will return to this as an example shortly.
Firstly to start with here is May 2018 where the production was just short of May this year.
Back in 2018 you can see the unused green 33% of the production approx 200Kwh was exported unused. I purchased either evening or overnight 720Kwh, which could be reduced by 200Kwh if used more directly. Most of the self consumption was background house usage and a diverter to heat the hot water reducing the gas usage nearly to zero at summer, via the immersion element. I would try and run the dishwasher during a sunny morning and washing machine during the day. Cooking in the evening would consume more than the solar panels produced at that time. If the car was put on charge it would consume approx 7Kw at 32amp where as my solar maxes out in peak of a summer day about 3Kw so the other 4Kw would be consumed from the grid.
The electric cars back then where always charged overnight on economy 7 rate. The solar was mainly to cut down on the day rate consumption which is slightly more expensive than standard (approx double the night rate).
During 2018 I discovered that I could use the granny charger which is a 3 pin plug so charges the car at a safe limit of 10amp. I had an external socket connected which was connected via a relay such that once the hot water was full and there was excess it would turn on the granny car charger, but this although an improvement was hit and miss on changeable days.
Since then in 2019 I had a smart car charger fitted, this can be set to notify the car the available surplus from the solar to track, this had a higher priority than the immersion divertor so prioritises the more expensive car charging over the cheaper gas heating.
Late 2019 I had a small luxpower batter inverter with a 2.4Kwh pylontech battery fitted. My interest in this was to see if it was possible to prepare for the new smart tariffs should a smart meter be fitted, to store energy during the day for use to avoid the peak 4pm to 7pm slot used for cooking.
I discovered that this single battery however only had a peak output of 1.2Kw so although it removed general background usage such as fridge and TV etc. It made little effect on the oven which consumes 2.4 Kw.
A few months later I expanded with a larger us3000 pylontech module with approx 3.5Kwh capacity. With these two batteries the luxpower inverter can provide a peak of around 2.9Kw so can cover the oven or bulk of a kettle.
Interestingly I found that the battery although effectively a 5.9Kwh storage capacity can be partially used multiple times a day. I have in effect discharged over 10Kwh from this setup in a single day. An example shown shortly.
Other changes over the years are:
Gradual conversion of nearly all light bulbs to LED (I have about 3 old CFL left or flourescent tube for instance in garage and loft) even the halogen outside light has been replaced once it failed.
induction hob fitted in kitchen replacing gas hob.
TV upgraded to a larger LED model which gives off less heat and less power hungry than the prior smaller backlit LCD model.
When washing machine tumble broke last year, replaced for one with a delay timer.
when the dishwasher broke the other month, replaced for one with a delay timer.
The above means the battery needs to output less during the evening so lasts longer, the dishwasher and washing machine are set for overnight usage for most of the year.
When cooking in the evening I try to start with boiling kettle first when required and waiting for it to finish, only then turn oven on, thus lowering and spreading my load such that solar and battery have better chance of providing the demand.
Notably the induction hob at partial power the battery struggles to follow as it is a rapid fluctuating on/off demand every few seconds, whereas the oven fluctuates every few minutes.
I am happy this setup would cover the peak 4pm to 7pm for my usage with a little careful management. An extra battery module would improve its peak output to 3.5Kw and also increase its storage, but each increment does get less beneficial cost wise depending on your circumstances.
At this stage battery storage is not really much of a cost saving exercise - particularly for the short term, but it does help spread the load greatly for the grid and makes me feel better, and open up the possibility of moving to a more complex tariff once smart meters are available.
Now back to my example of 30th May 2020 which achieved 98% self consumption. Previous day was a very sunny day and the battery was nearly fully charged as I was charging car until just before 4pm.
I knew it was going to be an extremely sunny day and we had run out of washing, so nothing was on overnight and the car was nearly full so it was left on eco+ setting on the zappi to charge only when the solar was getting strong.
Afterwards we took the PHEV car out and returned, I put this car on fast charge it charges a max of 3.2Kw (16 amp)
The batteries which had been storing power during our absence provided the difference of what the solar was producing.
We went out shopping later and returned popping ut back on charge, then a short trip even later in afternoon and recharged. The car was effectively full before we started cooking for tea in early evening, this was mostly the HOB and you can see there was some limited purchase and export to the grid due to the fluctuating hob.
It’s only on these multiple occuring sunny days where for my own circumstances the battery is also powering me overnight. I aim to only import grid use overnight, yet ensure the PHEV is topped up to limit or avoid consumption of fuel on short journeys.
Nearly 18Kwh went via the zappi to the cars battery which would have provided about 65 miles purely by solar
Here is the battery monitoring showing its charge and discharge. You can clearly see the continuing fluctuation caused by the fridge.
The State of charge of the battery
Finally the Month of May 2020 to compare against the original 2018
Here you can see some days where the green blue and red are extremely close showing barely any import or export with plenty of consumption.
When the red is lots higher this was consumed overnight.
Today my leaf was recharged but as it has a larger battery this was mostly from travels undertaken a few days ago, we have had so many days of sunshine and rarely been out today that I have been recharging my leaf.
It must be noted that this has been an exceptionally sunny May with May June and July being the peak sunny months.
In December and January the solar production is very low such that 4 sunny days in summer is equivalent of that produced over January and December combined!