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Why We Can’t Size Solar Batteries Like The Aussies Do Most kiwis want solar to reduce their power bills, and mostly – their winter power bills. And most Kiwis tell us – “We want a solar system that charges up the batteries during the day so that we can heat our home at night.” News flash: Yeah........... Sorry - that’s not going happen aye. Here’s why. Everything You’ve Heard About Sizing Solar & Batteries Is Probably Wrong (For NZ) When you jump online and search about solar, you’ll find information from Bloggers and YouTubers in parts of the world with entirely different energy demand patterns. Think about Australia for a second. 99% of homes in Aussie use tons of power in summer, which is conveniently when they generate the most solar. Our clients often come to us with the idea that solar + battery means very little grid use with the potential for 'off-grid in the city'. In Aussie, that's almost possible! But not here, because most kiwi homes use more power in winter, than in summer - which is inconveniently when solar systems produce ~50 to ~70% less. We’re left with two conundrums: in summer, you can’t make the most of a big battery… and in winter, you can’t charge one. Batteries Should Be Sized According To Your Spare Winter Solar This is the main point. Read the rest of the blog for more insight. ‘Nuf Said. You Won’t Discharge A ‘Uge Battery In Summer Let’s say your solar system generates ~40kWh per day in summer – (typical for a 20 panels system). But your home uses ~25kWh per day. There’s a 15kWh difference between what your home uses, and what you’re generating. So if you don’t need that spare energy, what’s the point in storing it? * Whether you have a huge battery or not, if your home doesn't use the spare solar, you'll be selling that 15kWh for about 17c per unit, which adds a $2.55 credit to your power bill EVERY day. You Don’t Need Much Storage In Summer If your home uses ~25kWh on a typical summer day, the question is: how much of that energy demand occurs after the sun goes down? ‘Cos the reality is – most homes don’t use much at all. After 8pm in summer: … You’ve done the cooking … Used a bit of aircon in the arvo … Your hot water’s steaming … The beers are cold … And your TV uses 100w So on a 25kWh day, your home might only pull ~10kWh between 8pm & 8am. … So, with these rough summer calcs, with 20 panels, most people can only make the most of a ~10kWh battery. C’mon – Surely It Makes Sense To Have A Big Battery In Winter? Yeah, I know that’s what you’re thinking. Everyone thinks that. You get home from work... Crank the heating till 11pm, and then ‘sip’ the heating until everyone leaves the next morning. So of course, you need a big battery to power all that heating. But wait… Solar Sucks In Winter - Sorry ‘bout it. That system we spoke about, those 20 panels; they’ll generate about 40kWh on a typical summer day. But in winter, you’ll be lucky to get 30kWh. But most homes don’t have a 35 degree north facing roof. So 20 panels generate closer to 20kWh per day. And this hypothetical home we’ve been talking about (that uses 25kWh per day in summer), probably pulls 50kWh per day in winter. And of that 50kWh, 15kWh is probably pulled during the 9 – 5. Fridge, freezer, hot water heating, maybe a spa – whatever it is – even with nobody home, there’s still power use during the day. So, shit – of the ~20kWh these 20 panels are spitting out, more than half of it is chewed up by the homes base loads. The difference goes into the battery. And what’s the difference here? ‘Bout 10kWh, if you’re lucky. … So even though the house uses 50kWh per day in winter, there’s no point having a battery bigger than ~10kWh. It simply won’t get charged. You’re The Worst Salespeople Ever No, we’re not. We’re just saying it like it is. In summer, you couldn’t possibly use all of your solar. And in winter, you couldn’t possibly charge a huge battery. But you can still save a shit ton with solar. And the good news is, you don’t even need a battery to eliminate most of your summer bills. Read this . And this . And watch this. But if you want to reduce your winter bills, you’re going to need a battery. If it adds a year or two to your solar-system payback period, it’s nothing in the scheme of things. Especially when you consider the blackout experience. (Its awesome these days)! So, What Do I Do? Prioritize north, if you can. A north roof with a pitch of 15 to 45 degrees is ideal. North produces the most energy in winter, which gives you the best hope of charging a battery. If your roof has some north, and a bit of something else – prioritise north AND west. We love west, because west produces energy until the summer sunset, which is when you might want to cool your home. If your roof is East and West; look very closely at the winter production estimates, because most east-west systems struggle to charge even the smallest batteries in the 3 coldest months of the year. You Didn’t Answer My Question – How Much Storage Do I need? … Sorry, here’s the framework. Subtract your winter day time energy use from your winter solar production. The answer reflects the size of battery you should consider. You could buy a little more, but again – consider your summer evening loads, and ask yourself – do you want to spend a few grand extra (or more); just for it to be a pretty box on the wall providing little financial benefit? Does Equity Solar Brokers Support Solar Batteries? Heck yes we do! We love seeing our clients get batteries. About one third of them get batteries with their solar purchase. We’re not against batteries. We are obsessed with helping kiwis get a great return on their investment. We achieve that through smart solar system design and anonymous quote procurement, which is our leverage to getting sharp solar quotes. Everyone has a different solar objective - and we're all ears. Can't wait to hear yours. In a time of rising power prices and grid instability, batteries are awesome. And guess what – we’ve never had a client regret buying a battery. One client called to tell us they had a 2-day powercut, but only found out when the neighbors swung by. Priceless. Need a hand with system design? That’s what we do best. And we’ll get you the best quotes in the market while holding your hand every step of the way. Chuck your deets below, and lets do this.