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TESLA’S POWERWALL: A Game Changer? Purely by co-incidence, as we were reviewing and writing about the Tesla Model S, internet whispers started appearing about a secret new product being worked on by Tesla. Then came the official word: CEO Elon Musk would be hosting a major press launch on April 30 to reveal the big secret. By Ross Tester B y the time Elon Musk took to the stage, the whispers had become a roar – Tesla was about to release battery backup systems for home and industry. It was a natural progression from their work on the lithium-ion battery packs they’d developed for their electric vehicles but the detail was all that was left to reveal. As well as the “live” press launch, it was also beamed to the world as a webinar, so wherever you were, you could see the same message. And the message was pretty “cool”, at least as far as Tesla were concerned. For far too long, we’ve been saddled with lead-acid batteries as the main storage for, particularly, solar (PV) power systems. Lithium-ion batteries were simply too expensive. Of course, most installations (at least here in Australia) don’t have any storage; they’ve been grid-based systems which fed any excess power back into the electric power distribution grid. Those who got in early have been blessed with very high value feed-in Tesla CEO Elon Musk launching the PowerWall and PowerPack (for utilities), April 30 2015. siliconchip.com.au June 2015  25 One of Tesla’s 10kWh PowerWalls. Inside is 350-450V of lithium-ion cells and a DC/DC converter. It’s about 1300mm high, 860mm across, 180mm deep and weighs 100kg. rewards – as much as 66c per kWh. Those heady days have long gone but even today, you can put a solar power system in and reduce your electricity charges. But Tesla’s system is rather different to that. It is intended for either standalone (ie, not grid-connected) systems or hybrid systems, where there is battery backup as well as grid tie-in. Musk reasoned that everything about electricity production, usage and charges were out of step – the highest usage was in the morning, after most people had gone to work, and in the evening/night, after most people had come home. Either way, solar generation is minimal in the early morning and zero in the night, when you needed it most. You pay top dollar for power at these times too. What if the generation and storage of electricity could be “time shifted” - generate the power during the day when the sun was shining and use it 26  Silicon Chip during the peak periods mentioned above. All you would need would be a storage system capable of doing so! OK, that’s a bit of an over-simplification but you get the idea! immediately on announcement. (However the latest news [May 10] is that production through to the middle of 2016 is sold out – over 38,000 reservations had been received in that time)! Lead-acid battery disadvantages What’s in it? One of the major reasons for not using lead-acid batteries for storing electricity is the cost. Deep-cycle storage batteries are not cheap. Moreover, they need a lot of maintenance; they emit dangerous hydrogen gas when being charged; they sometimes leak (and their electrolyte, acid, is nasty stuff); they’re pretty temperamental about amount and depth of discharge; they don’t like being overcharged . . . and to top it all off, their life span can be pretty short (3-5 years is about average, 10 years exceptional; indeed, most deep cycle batteries only have a 2 year guarantee). Finally, when they have reached the end of their life, disposal is not as easy. They can’t be used in landfill, they can’t be destroyed and even many recycling centres that used to take plenty of lead-acid car batteries are becoming a bit reluctant to take them. Small wonder that most people with solar panels on their roofs stayed wellenough away from lead-acid batteries. Lithium-ion battery advantages While there are some parameters that need monitoring, for the most part lithium-ion batteries don’t suffer the disadvantages of lead-acids. They don’t need much maintenance at all, they’re much happier about charging and discharging (mainly because each cell is monitored and if necessary, equalised with other cells), they have a long lifespan (10 years would be minimum, possibly a lot more) and they don’t contain volatile materials so can even be disposed of in landfill. Or, as we reported in the earlier Tesla S85 story, they are looking at recycling as much as 90% of each cell in the future. Tesla’s PowerWall Two (related) products were announced on April 30, the PowerWall and the Tesla PowerPack. The latter is intended for large-scale applications. The first will start shipping shortly (within a couple of months) – in fact, Tesla Energy started taking orders The basic PowerWall comes in 10kWh “weekly cycle” and 7kWh, “daily cycle” models. Each contains enough lithium-ion cells to achieve a 350-450V supply. The PowerWall is designed to attach to a wall, inside or outside. Overall size of a single PowerWall unit is 1300mm high, 860mm wide and 180mm deep and weight is 100kg. Note that there is no DC-to-AC inverter built in but it does have a DC-DC converter, which means it should be compatible with solar panels (which generate DC). Up to nine PowerWalls can be interconnected to satisfy virtually all domestic demand. And the cost? The daily cyle (7kWh) PowerWall will sell in the US for $3000; the 10kWh weekly cycle for $3500. Let’s look at the more expensive one: in Australia, at current exchange rates and with GST that will probably sell for around $5000. For that, you get a ten year guarantee and minimal maintenance. Try buying, say, a 350V deep cycle lead-acid battery pack with anything like a 10kWh rating. Because you can only safely cycle down to, say, 40% you’ll need around 16kWh to be safe. At the moment, you’re looking at between $20,000 and $25,000. Invariably, that only gets you a 2-3 year guarantee and it also gets you all the trials and tribulations that go with large lead-acid battery installations, not the least of which is a total replacement after perhaps five years. Of course, prices are dropping . . . and Tesla’s PowerWall will have a lot to do with that! Other power sources One of the main reasons that Tesla’s PowerWall is likely to be a gamechanger is that for the first time, it makes economic time-shifting power demands. Solar panels are not the only means of charging batteries –wind and smallscale hydro are often mentioned. But the one which is often forgotten siliconchip.com.au PEAK SOLAR MORNING DEMAND EVENING DEMAND The average home uses more electricity in the morning and evening than during the day when solar energy is highest. Tesla’s Powerwall is designed to smooth out these curves. is the power grid itself. During peak periods, power charges are high. At “shoulder” times they’re lower and during off-peak times they can be quite low. Why not use cheap off-peak power to charge the batteries and either use it instead of expensive peak power. Or if you can get a reasonable feed-in tariff, sell it back to the power companies during peak times? We can already hear the screams: “you can’t get enough feed in tariff any more to make it worthwhile.” siliconchip.com.au Thinking big: Tesla also have plans for power generators and distributors to use very much larger battery banks to smooth out their own peak and trough cycles. Oh yeah? Go for a walk with Dr Google – you might be surprised to find that there are now companies in Australia (not the power companies!) who will buy stored power from you at much higher prices than the power companies offer. They on-sell it to match peak demand and therefore peak $$$ – and reward you with the proceeds (less their commission). If you think we’re talking cents per kWh, think again. It can be $/kWh! It is for all these reasons that we believe Tesla, and their $5000 lithium- ion battery, will be a game changer. Whether you’re using it to go completely off grid (now very much cheaper than it was), or putting in a hybrid system; whether you are looking at solar power or simply time-shifting cheap off-peak power into peak times, it’s a whole new ball game. And the best part? The game has only just begun! For more information, visit www.teslaenergy.com – or Google “Tesla Powerwall” and “Tesla Powerpack” sc June 2015  27