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Solar Diverters

Updated: Feb 16, 2021

In the previous article we discussed residential battery storage, however, battery storage is not the only option when it comes to storing the excess energy generated by solar PV. A solar diverter can also make use of excess electricity generation, diverters monitor the Solar PV generated power and the electricity demand in the home, if there is an excess generated, the Diverter will use that excess electricity to heat the water in the homes hot water cylinder. Provided you have a well-insulated cylinder this heat energy can be stored for many hours.

In the previous article we discussed a home in Cork with roof mounted solar PV, over 800 kWh of electricity was exported from this home during the first 8 months of 2020, about 44% of the total electricity generated by the solar PV. At €0.18/kWh this is the equivalent to €144, once this homeowner understood the amount of electricity they were exporting they made the decision to install a solar diverter. In the previous article we calculated that to cover the cost of this diverter, it needs to convert 2,222 kWh of electricity that would have otherwise been exported to the grid into useful energy.

The graph below is from a week day in October, it shows the electricity flow at the main incomer in red, values that are negative represent electricity that is being exported onto the grid. You can see that for the majority of the day this value was close to zero.

Electricity generated by the solar PV is shown in yellow, again we can see just how erratic this profile is, this is very common and is caused by clouds passing overhead.

Electricity flowing through the solar diverter is shown in blue, you can see how effective it is at reacting to the frequent changes in both generation and load.

When we reviewed the data, we found that between October 16th and December 16th, the diverter consumed a rather modest 23kWh, that would have otherwise been exported to the grid.

When compared with the same dates for 2019 it was found that 45kWh of electricity was exported. This difference was driven by the change in working arrangements brought about by COVID. Now that this homeowner is working from home it greatly increases the homes energy consumption during the day.

From this we can conclude that the payback period for the solar divert will probably by twice as long now that the house is occupied during the day, however it will be interesting to see if this changes as the year moves on, November and December are far from ideal months to be reviewing the performance of a solar diverter so we may review this at a later date.

What we can learn from this is that the successful application of technologies like solar PV, diverters and batteries are intrinsically linked to the behavior of the people who occupy the home. There is no one size all solution that will be a success in every home, only by analysing time series data and visualising the profiles within the premises can we make informed decisions around energy efficiency and review the performance these technologies once they have been installed.

DCSix and our Wattrics energy monitor have been helping clients all around Ireland gain a better understanding of their energy profiles and what energy efficiency technologies are most suitable for them, if you’d like to learn more about Wattrics and how it could benefit you please feel free to contact us at

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