In ‘Batteries’ Category

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Going hybrid: Adding batteries to grid-connected solar

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Going off-grid may not be for everyone; a better route may be to ‘go hybrid’, by adding batteries to grid-connected solar. Andrew Reddaway explores the options.

The solar battery industry is on the verge of disruptive change. Traditionally, large batteries were only seen in houses at off-grid locations such as Moora Moora (see box on the solar hybrid training course held there, which I attended earlier this year and which provided input to this article).

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For off-grid systems, reliability is crucial; failure prompts an emergency call to the solar installer, so such systems have been designed conservatively using proven lead-acid batteries.

Meanwhile, in towns and cities, grid-connected solar systems have gone mainstream. As feed-in tariffs for solar export have dropped far below the rates paid for grid electricity, householders are looking for ways to cut bills by making better use of their excess solar generation. One answer is to add batteries to create a hybrid system: a grid-connected solar system with batteries either for backup or load-shifting.

This article gives an overview of current hybrid technology and the options available for adding batteries to an existing grid-connected solar system.

Different batteries for hybrid
A hybrid solar system is tough on batteries. Unlike an off-grid system that may store enough energy to last multiple days, a hybrid system’s entire usable capacity will be charged and discharged daily. This requires a battery that can handle fast discharge rates at high levels of efficiency. Lithium batteries fit the bill, and have already become dominant in consumer electronics, power tools and electric cars. Compared to lead-acid, they are also smaller, lighter, don’t require monthly maintenance and don’t emit hydrogen gas. The only things holding them back in the solar market are unfamiliarity and price.

The recently announced lithium Powerwall battery from Tesla is priced well below previous products and has a 10-year warranty. Traditional lead-acid batteries cannot compete with this new benchmark, so it’s expected that systems will start to move away from them. Hybrid systems are now expected to become viable on pure economics in a few years or less. Early adopters are already installing lithium hybrid systems, as are some who value maintaining power during a blackout.

Read the full article in ReNew 132.

14-11-30 3 Batt charger inverter

Going off-grid slowly: a DIY project

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Stan Baker dreams of ditching his energy company and going off-grid. He explains how he aims to achieve this, one step at a time.

The well-documented ‘gold plating’ of the poles and wires networks has meant rising service fees for consumers despite falling demand for delivered energy. My own electricity bills reflected this and caused me to seriously consider leaving the grid altogether. A further consideration was the increasingly disruptive weather being experienced around the country resulting in power outages caused by high winds and electrical storms. When attempting to be energy independent, however, the problem is the high cost of the batteries and other equipment necessary to generate and deliver electricity.

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Being something of a DIY type, I considered what bits I had sitting around in my garage and what expertise I might have that could be relevant. A passion over the years for converting hybrid cars to plug-in hybrids meant I had a reasonable understanding of lithium batteries, including the management electronics needed to ensure their longevity. I also had a 1.5 kW, 12 VDC Latronics inverter acquired years earlier for some long-forgotten project. Naturally, I had the usual nerdy stuff such as miscellaneous electronic parts as well as some understanding of microcontrollers.

In effect, I had much of what was needed to deliver 240 VAC off-grid, but with one question unanswered: where was the input energy to come from?

First attempts

My house has a flexible pricing plan from Origin that provides cheaper electricity between 11 pm and 7am. This meant I had a lower cost source of electricity for charging the batteries, at least for initial trialling. So, about six months ago I put together a simple system using lithium iron phosphate (LiFePO4) batteries from an electric vehicle conversion that were down to around 50% of their original capacity and therefore unsuited for vehicular use.

The battery charger was a simple linear unit that used toroidal transformers. I had my fuse box modified so that the lights in the house could be powered either from the inverter or directly from the mains.

The original system was not particularly efficient and I estimated I was losing around 50% of the incoming energy, mainly due to the battery charger. However, it did keep my lights going during most nights and encouraged me to consider a more sophisticated battery storage system.

Read the full article in ReNew 131.