Storing Solar Power for Later

To make the most of your solar PV system, you’ll probably want to store some energy to use during the night. Learn about the two ways you can do this: Power diverters and batteries.

Sunset and dark horizon
Power diverters and batteries let you use solar energy right through the night

Power Diverters

Power diverters send surplus electricity from your solar panels to your immersion. Your immersion then uses this surplus power to make hot water. A typical hot water tank can store many hours worth of solar power in as hot water. This solar hot water can give you big savings because water heating adds a lot to the average electricity bill in Ireland. Another advantage of power diverters is that they’re very cost-effective. For these reasons I strongly recommend power diverters. To make the very most of your power diverter, try to use a pumped electric shower. This kind of shower lets you use your solar hot water for showering, which is one of the biggest uses of hot water in Irish households.

Batteries

Batteries today are way better than what was available a few years ago. Today, lithium-ion technology means that you can power your house all night with a battery the size of an old Dell computer tower. Better still, the battery can be installed out of your way in the garage or attic. What this all means in practice is a jump from around 50% savings without a battery to 70%+ savings with a battery. As an extra benefit, some batteries can also power your house during blackouts.

Can I have a battery and a power diverter?

Yes, batteries and power diverters can work together and complement each other very well. On one hand, batteries store energy in the most versatile form (electricity). On the other hand, power diverters allow you to store huge amounts of energy at a low cost. Good design maximises the benefits of both the battery and the power diverter. The way this works is that the battery gets priority: Power always goes to the battery first. Only when the battery is full will the power diverter kick in. Note that not all power diverters work well alongside batteries. In particular, the “zero export” types can cause problems. Talk to your solar PV installer to make sure you’re getting the kind of power diverter you need. The myenergi eddi is one model of a power diverter that works well alongside batteries.

Power Diverters and Heat Pumps

Heat pumps are becoming more and more popular as a way to provide space heating and hot water to Irish homes. In general though, heat pumps will only raise the temperature of the water in your tank to around 35 degrees C. Dangerous Legionella bacteria thrive at this temperature, so you must raise the temperature of the whole tank to above 65 degrees at least once per week to sanitize the tank. This is usually done with an immersion heater which is wired into the controller board of the heat pump. Unfortunately, you cannot connect a power diverter to the same immersion heater as the heat pump because this can damage the controller board of the heat pump. If you want to use a power diverter and a heat pump, then you will need to have two separate immersion heaters installed. So if you’re shopping for a hot water cylinder to go with your new heat pump then consider asking for one with two separate locations where an immersion heater can be installed.

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