Solar Utilisation

Seeing as we don’t get paid for any energy that we export to the grid, we’ve been on a mission to use all of the solar power our panels are generating. We’ve taken a step further towards this goal with the installation of a MyEnegri Eddi. This is a clever device that diverts surplus solar energy into our hot water tank.

Heating our Water

Prior to installation our hot water tank had two elements. The lower element heated the entire tank and was linked to our Economy 7 controlled circuit. This meant that it would heat the water up over night on cheap rate electricity (unless we switched it off!). The top element only heats the top of the tank and was manually controlled. This allowed us to heat up some water quickly should we run out of hot water at any point.

We don’t actually use much hot water so heating the full tank overnight even on cheap rate seemed like overkill and a waste of money to a certain extent. Every night the immersion heater would kick in, get the water up to temperature and then turn off. It would then kick in a few times for short periods of time during the night to keep it up to temperature.

You can see the electricity usage from the grid as it does just this overnight in the chart below.

Electricity Use by Immersion Heater

Even if we used no hot water at all from the tank it would do this as the temperature would drop during the day so would need warming up once cheap rate kicked in at night. All of which was a waste of energy and therefore money. It wasn’t huge amounts of power, usually just 2-3kWh but even small amounts every night soon mounts up.

Eddi to the Rescue


We have now taken the bottom element off the Economy 7 controlled circuit and added it to the main consumer board. This allows the bottom element to be activated at any time of day (both peak and off-peak). We have also added the Eddi into the mix. This means that during the day, if there is surplus solar energy it will be diverted to the immersion heater where it will heat the entire tank. In the summer that will probably be enough to keep the tank up to temperature and provide all the hot water we need.

The Eddi has boost timer functionality built into it as well. This allows us to set some timers either through the Eddi itself or through the MyEnergi app. These timers will activate a boost mode that will draw power from the grid to heat the water in the immersion tank. This will be useful in the winter when there isn’t enough surplus solar to heat the tank. We’ll then be able set a Boost period from say 5am to 6am where the tank will be heated from the grid so that we always start the day with a full tank of hot water.

We’re still playing with the various settings and things will change with the seasons but once we have the measure of it we should:

  • always have hot water
  • minimise draw from the grid to heat the water
  • use mainly solar power to heat the water
  • reduce our export to the grid
  • ultimately save money and save the planet!

Getting our Priorities Right

On an ideal day, when the sun is shining and the solar panels are doing their thing the solar energy will be used as follows.

First it will be used to power whatever is being used in the house (lights, computer, fridge, aquarium, oven etc etc). Once the needs of the house are satisfied anything extra will go next into the battery (which might become 2 batteries soon). Once the battery capacity is at 100% and fully charged the surplus will go into the car battery. Surplus going to the car battery relies on four criteria being met:

  1. The car is on the drive.
  2. The car is plugged in.
  3. The surplus energy is more than 1.4kw.
  4. The car battery is not fully charged.

If any of points 1 to 4 is not true then the surplus energy will go to the immersion heater via Eddi instead. This will actually happen fairly often. For a start the car isn’t always there as we do tend to drive it now and then! Even when it is on the drive and plugged in it will be a regular occurrence that point 3 is not satisfied. Quite often during the mornings, evenings, cloudy days, winter days or when we are using lots of things in the house the surplus solar power will be less than 1.4kw. This isn’t enough to start the car charging so until the Eddi was installed we were sending this back to the grid and getting nothing for it. Now when such conditions exist that surplus energy will go towards heating our water instead.

Here’s the MyEnergi App with the Eddi in action. When this was taken, the power coming from the solar panels was only 1kw. 0.4kw of that was being used to power things in the house and the rest was being sent to the immersion heater via Eddi.

Eddi in Action
Eddi in Action

We won’t quite be self sufficient even during the summer as high draw items such as the shower will still require some input from the grid. We will however be using as much of the solar power as we can.

What’s Next?

We are now thinking of adding a second battery. This will allow us to store even more of the solar energy we generate, which will improve the system in two ways. First it’ll mean we’re sending even less back to the grid and it will easily keep us going throughout the night during the summer months. In the winter months it’ll allow us to force charge more during off-peak times which will then keep us going throughout the day whatever the weather throws at us. It’ll allow for more solar storage in the summer and more rate-shifting in the winter. Perfect!

2 Responses

  1. Avatar forComment Author Steve Palmer says:

    Alan – Maybe time to consider a pumped hot water shower instead of an electric one?

    We have a similar arrangement but use a Solar iBoost+ to divert surplus power when our batteries are full.

    We have piping hot showers and no grid draw [except during off-peak boosts in the winter]

    I may have to look at the Eddi though. Could you blog more about the system?

    • Avatar forComment Author Alan Cole says:

      Yeah, we have though about such things – maybe next time the shower needs replacing, we just couldn’t do everything at once!

      The Eddi is good though – it just mops up the smaller bits of surplus solar and is most useful when the surplus is insufficient to charge the car (below 1.4kW). In that case the surplus goes to the hot water rather than being exported (we don’t get paid for any export so like to reduce export as much as possible!).

      I have blogged about it before:


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Alan Cole

Alan is a Freelance Website Designer, Sports & Exercise Science Lab Technician and full time Dad & husband with far too many hobbies: Triathlete, Swimming, Cycling, Running, MTBing, Surfing, Windsurfing, SUPing, Gardening, Photography.... The list goes on.

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