Harnessing solar power and optimising energy consumption are crucial steps towards sustainable living and reducing electricity costs. This post delves into my journey of data-driven observations and analysis to optimise my clevrHome, offering insights on maximising solar benefits, optimising water heating, and adapting energy use patterns across seasons.

“When performance is measured, performance improves. When performance is measured and reported back, the rate of improvement accelerates.”

Pearson’s Law

Time for exploration

Now that we have built a great dashboard, we can start analysing our energy consumption. The key thing here, and with many other data projects, is context. You need to know the context around the energy use to provide a good foundation for understanding and challenging it.

By understanding the context, such as when we manually switch things on/off, the habits of people in our home, and the energy ratings of our appliances, we can start to identify patterns and opportunities for optimisation. Remember, we need to optimise the energy system as a whole and not just individual components. Read the four steps to systematically reduce your energy consumption.

Getting value out of solar early on

Moving into a new home and working remotely, reliable electricity and internet become essential. As mentioned in previous posts, we are subject to loadshedding periodically, and 2023 was especially tough. Thus, having a solar system with battery backup from the start paid off well. For reference, the solar system is rated at 5kWp with 10.2kWh lithium battery storage.

What we didn’t expect was a massive storm that come through, causing havoc in large areas, especially on power networks. The result was that we had no grid power for about 7-days. Gratefully there were sunny skies, and we could continue our daily lives – lights, internet, making meals, etc. The only three things not on the inverter are the stove, hob and water heater.

The below trend shows the battery state-of-charge (blue), grid power (purple), solar generation (green) and home load (orange). The colours are used consistently across all the trends that follow.

We do have a solar water heater, so why no hot water you may ask? It turns out that the control system works off the same supply as the element, which is not connected on the inverter. That means the pump cannot circulate the water between the tank and the collector. This does not really make sense to me.

Zooming in in the last two day trends, you can clearly see when the grid power was restored, the 4kW hot water element kicking in. By that time the sun was getting low and the gird had to supplement about half of the power.

One can also see that a lot of solar energy is curtailed once the batteries are charged and there is no load to consume it. So, during the day would be ideal times to run dishwashers and clothes dryers. To avoid wasting it, exporting to the grid (where allowed) is another why to get more value out of the system.

Optimising water heating

To ensure getting maximum solar heating benefit, even during outages, the circulating pump, and thus the element, needed to be connected to the inverter. As it is only a 5kW inverter, having a large 4kW element could potentially cause an overload if there are any other large loads switched on or potentially even when the fridge compressor kicks in.

The element was replaced with a 2kW one so that it can run off the inverter comfortably and the circulating pump draws about 100W when it runs. The downside it that water heating will take longer, especially on rainy days. Water heating will also run off the batteries, so it is something to consider to manage battery health and capacity. But that is a worthwhile compromise and something we can plan for with timers and/or some automation.

From the trend below, you can see the 4kW element kicking in at 15:00 (for 50 minutes) to boost the temperature to the setpoint. It draws power from solar PV and supplements with the grid.

The next day, the 4kW element was replace with a 2kW element. It switched on at 16:00 (for 66 minutes) and drew less power from the grid even though it was an hour later. The key optimisation here was to give the solar water heater (thermal) more time to heat water (between 15:00 and 16:00). Then boost with the 2kW element with solar PV, catching the end of the solar generation bell curve. Thus, minimising grid power draw. The third day was hot and no additional boost was necessary at 16:00.

Optimising consumption

Let’s have a look at a warm sunny day in summer. Starting at midnight, only the residual loads are running and you can see the compressor of the fridge kicking in periodically. At 3:00 the hot water element kicks in feeding from the batteries until about 3:20 when it reaches the 40% threshold and switches to grid power.

Solar starts generating at around 6:00 and follows a linear pattern due to shading. That is why at around 8:00 the is a jump and then starts to follow the familiar bell shape. Consumption from the grid stops at about 6:30 when solar start to power the load first and then starts to change the battery. This was a setting on the inverter to ensure load is supplied first, otherwise all the energy would go to the batteries first and then consume more from the grid. There is more than enough time to charge the batteries throughout the day.

The solar generation started to curtail at about 9:00 already as batteries charge is limited to about 2kW and there was not much home load (about 600W). By 11:00 the batteries were fully charged. As it was a hot day, we used our two inverter aircons, one starting at 11:30 and the other at 13:30. As it was hot, there was no need to boost the hot water temperature with the element. You can also see we finished work at 16:30 and then went to the beach 🙂

We made dinner at 18:30 with the spike being the air fryer and induction hob. Some more cooling between 20:00 to 21:30 and then off to bed. You may be wondering why there was no grid power being consumed during this period? Well, the batteries are set to start discharging at 17:00 and utilise the stored solar energy. This is also means not paying for grid electricity and reducing the strain on the grid during the evening peak.

On a rainy winters day, the picture is quite different but we still get some solar energy benefit. You can clearly notice that the hot water element heating duration is almost the full two-hours that it is allowed to run with the Geyserwala timer.

As most energy goes to the load first, the batteries don’t charge much during the day. As a last resort, the batteries can charge from the grid between 15:00 and 17:00 to ensure there is full backup but also to discharge from 17:00. This is again to assist the national grid during the high winter evening peaks. And when you are on a time-of-use tariff, this period would also be the more expensive one and you would want to offset it anyway.

Conclusion

I shared the practical steps I have taken in my journey to optimise my energy consumption so far and effectively using solar systems for maximum benefit. It is important to consider the energy efficiency rating of appliances, especially when it is time to replace them.

Weather and season has a big impact on solar generation and needs to be considered when optimising your consumption and considering your backup needs. Another thing I discovered was that the solar generation during winter maxes out at about 3kWp due to the angle the panels were installed at. This was done to conform to the architectural guidelines and results in significantly less solar generation in winter.

From the data, you can clearly see behaviour patterns throughout the day in the consumption data. This is insightful in terms of when people use electricity to spot patterns and potentially adjust scheduling. One can also use the patterns of appliances to detect faults, e.g. when the fridge’s compressor stops working.