Solar PV system with Tesla Powerwall, immersion heater controller and electric vehicle charging

When solar PV systems first started to become popular in the UK, the majority of installations consisted simply of some solar panels and an inverter. Nowadays there are some excellent products available to help the user get the most out of their investment.

Monitoring – your essential add-on

No solar PV system should be without some form of monitoring. Many people choose not to purchase a monitor and instead look at the readings on the generation meter. This is very limited as it only allows you to monitor system performance over a period of time (i.e. the time since you last checked the meter). It will not indicate if the system has been off for a period during that time.

Monitoring gives you the instantaneous figure, i.e. what your solar panels are generating right now. Good monitors also show you the house consumption, and can even show you what individual appliances are consuming.

Here is an example of a good mobile friendly monitoring system which shows solar production, import and export from the grid, battery power flow, heat pump power usage, house demand, electric vehicle charging, immersion heater and also a graph.

This is all live data, so if you’re reading this and it’s night time, don’t be surprised if there is no production from the solar panels.


Solar PV generation, Tesla Powerwall battery storage and automatic switching of electrical loads

Tip: This is live data! If you hover over the graph, you can zoom in or out, or scroll back in time so that you can see historic data.

Yellow: This represents the electricity being generated by the solar panels. Yields during the summer are much higher than in the winter.
Orange: This is electricity being used to charge the battery. Any surplus solar electricity will be diverted here. Between November and February when there is little surplus, the battery will charge overnight on cheap rate electricity that can then be used during the day. The state of charge of the battery is represented as a purple line.
Blue: During the summer the battery will often be fully charged by midday. Any excess electricity will then be taken up by the iBoost immersion heater controller for free hot water.
Red: This is the electric car being charged, which doesn’t happen every day. During the summer, the car will charge from surplus solar electricity. At other times charging usually happens overnight on cheap rate electricity, or in emergencies it can be charged at any time. This is achieved using a custom designed and built electric vehicle charger.

Footnotes: The monitoring is achieved using various electronic modules from the excellent open-source OpenEnergyMonitor project. The electric car charger is a custom built unit based on modules from the OEM project. As of May 2017 the car charger is an OpenEVSE unit. As of 2019 we’re using a MyEnergi Zappi EV charger. Their portal allows us to set price thresholds whereupon the car will charge on cheap (or even negative) rate electricity.

This page is a work in progress so things will be added or removed as time goes on, or it may just occasionally not work properly every now and then as I experiment with it.