Batteries Aren’t The Only Way To Store Your Solar

Solar used to be simple; but in todays frenetic world, energy rates change by the hour, so managing your consumption is more important than ever.

Read on while we explain how you can make best use of different options for energy storage, and the smart technology to automate it.

Efficiency Is King

The cheapest kilowatt hour of energy is the one you never needed to buy in the first place. Making improvements such as better home insulation can slash your energy bills.

Self Consumption Is Simplest

I can’t stress it enough, the more solar you have on the roof, the more likely it is you’ll have your own energy available to use behind the retail meter.

At my house there’s 15kW of panels on the roof and about a third of them face what’s currently the brilliant afternoon sun. My electricity retailer has no idea the hot water service is energised and the dishwasher is running because at 3:45pm we still have around 5kW of solar yield.

While I could be exporting 5kW of solar, it’ll only pay 2cents/kWh, which is a small fraction of what you save from self-consumption instead of importing energy from the grid.

Many appliances have delay start timers built in. For instance, one keystroke on our Fisher and Paykel dishwasher turns it on, holding the button down enters delay start mode, pressing again advances the counter one hour at a time.

Hot Water As A Battery

Take these two different methods for storing energy using a resistive hot water service.

Using a variable type diverter, you can harvest every watt of available solar because it will follow yield dynamically. It’s even more refined when Fronius use a temperature sensor to give you and the system feedback from the tank.

Yellow shows electricity consumed in the house while the “excess” solar (in orange) is poured into the hot water. Once the tank is up to temperature, electricity is exported to the grid (in grey).

A more basic approach uses a contactor to simply switch the hot water service on and off. It’s not as refined, but not as expensive either.

The best results come from using a small element in the tank because you need a lot of solar to run a standard 3.6kW element. There will be more hours in the day with a surplus of 1.2kW or 2.4kW available, so you can switch the hot water on without needing to import electricity.

You can use a CatchControl device for the required signal and it will automate the most efficient operation.

Or utilise a relay output/dry contact which is built into better quality solar inverters as standard, the only catch is you may have to watch the monitoring and learn how to fettle the controls to best suit your situation.

Here we have a hot water tank which is switched on when export rises above 3kW and switched off when it drops below the nominal 2.4kW element rating. There is a rule for 25minutes minimum run time, so the contactor isn’t clunking on and off with every passing cloud, and in this instance it’s caused a small amount of grid import (shown in red).

Heat Pumps Are A Winner Too

It might be a deeply held belief, bordering on religious fanaticism if the comments section is anything to go by, but heat pump hot water is incredibly efficient. Though it’s mechanically and electrically complex compared to a standard hot water tank, the management is really simple.

A basic solar switching system is outright most efficient but all you really need to do is set a timer. 

Stick With A Single Manufacturer

As you can see in the header image, there’s 7 different components for your electrician to connect up with power and control wiring.

This is where having a single manufacturer ecosystem, a compatible CatchControl solution, or an integrated software system like ChargeHQ is essential. Once all these components can talk to each other, it becomes far simpler for the end user to set and forget.

This chart shows the full Fronius ecosystem at work, with the household loads being met with yellow solar energy, then hot water system soaking up solar in purple, plus an underlying green graph of energy being stored in a battery. Grey is electricity exported to the network, which could alternately be stored in an EV battery.

Choose Your Storage Options

Default programming will see your solar battery system begin charging up at sunrise, but this doesn’t always produce the best outcome. There are as many scenarios as there are customers but here’s how it could work:

1. Self consumption makes most sense, so morning toast and coffee powered with solar should be prioritised.
2. After that, you might charge the EV for whatever trip you’re making that day;
3. The hot water gets topped up after the car leaves.
4. Lastly, get the house battery charged before expensive evening peak period prices, whether using solar or cheap daytime electricity.

Your electrician may need to program which of these three storage devices to prioritise for which part of the day and which part of your retail plan.

However if your behaviour, retailer or seasonal yield changes, you’ll want to know how to adjust it yourself, so be sure the installer can explain it to you.

Home Assistants

If you have an appetite for much tighter control, and an aptitude for some basic computer coding, then using Home Assistant is a way to control any number of things in your house, without being forced to use the internet or surrendering your every private habit to Google, Apple or Amazon.

Bluetooth for white teeth? Why on earth would an electric toothbrush need data connectivity I hear you ask. Well one savvy user has written some rules because he knows a) when he’s leaving the house b) on a weekday, c) he picks up his toothbrush, and d) this activates his car’s climate control system. Hooray!

Image credit Chris Cathcart

Petrol Is Expensive

One of the major costs Australian households can minimise is fuel for transport. Given enough rooftop solar, many will be able to completely cover their energy needs without needing to import expensive fuels.

As federally incentivised home batteries are now much cheaper, they’re proving very popular. However they don’t suit every household, especially when a similar cost per kWh of capacity will buy you a very large battery and a free car.

If you can charge your car at work during the day, then bring it home and siphon a little electricity off overnight, it’s likely an economic no-brainer.

You can do it right now, using current V2L systems on many EVs. without any special network permission or solar compatibility. And it’s cheap.

If you’re looking to invest in a higher capacity, fully automatic, bi-directional charging solution, then the technology is now available, almost.

Makers like Sigenergy have a solution, only for Ausgrid customers who own a Ford F150 Lightning, but other networks and other car models are still coming down the pipeline, as are other V2G inverters.

This will be an interesting space to watch but full V2G will be made complex by network approvals and car warranty conditions. A simple V2L system may still be an elegant solution for those who just want a little backup and some nifty savings.

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