eevBLAB 128 - Why Dont I Go OFF-GRID Solar/Battery? - Page 1
Forum section: electronics / general

author: EEVblog
author_rank: Unknown
timestamp: May 23, 2025, 02:11:54 am
content: A lot of people ask me why I don't go off-grid with my big solar and battery system, here is why.

author: EEVblog
author_rank: Unknown
timestamp: May 23, 2025, 02:13:31 am
content: FYI, I just switched from AGL to OVO energy who give me a free 3 hour window every day from 11am to 2pm. So can charge the EV and battery and heat pump during these time for free regardless of what the local solar is doing.

author: brucehoult
author_rank: Super Contributor
timestamp: May 23, 2025, 03:10:06 am
content: If you were for some reason off-grid -- which can include involuntary off-grid due to storms ... I just had 2 days off-grid last month due to Cyclone Tam and four days in February 2023 due to Gabrielle -- then no you would not put in 100kWh or 150kWh of batteries.Eyeballing your graphs it looks like your average load is around 800W and the slope of the battery discharge from 90% to 20% indicates about the same. So an AU$800 2kW petrol generator would get you through bad weather of any length. That's a heck of a lot lower capital expense than having an extra 100kWh of batteries and extra panels and MPPTs etc to charge them.That's more expensive per kWh than grid power, for sure. A small generator like that generates about 1.5kWh from 1l of fuel, so at $2/l in Sydney right now that's $1.33/kWh. Bigger generators are more efficient, but you don't need one, especially if you're not going to be using it a lot. I don't know what plan you're on there, but you might be paying 40c to 60c per kWh at peak times and half that off-peak.Primarily because I'm sick of outages where I am I just ordered an all-in-one 3kWh battery / MPPT / 240V charger / inverter unit and a 2200W generator, total cost US$3500. I might add a 2nd 3kWh battery, but the built in one is enough to power my whole house for 5-6 hours, or the essentials for 15-16 hours. Just purely charging it with cheap power before 7 AM to get through the 7-9 peak power prices period, and then topping it up before 5 PM to get through the 5-9PM peak looks like its on the verge of paying for itself without even considering the outages that are the main reason to have it.I'm estimating I'll need to generate around 50kWh of power a year from the generator ... 25-30 hours of running, and around AU$70 of fuel (more here in NZ, but lets look at AU prices since you're there).100kWh of extra batteries would cost $50k+. Maybe a bit less if you made those ones lead/acid on the basis that you're usually not going to put cycles on them. That's a hell of a lot of years of fuel.OK, if I was totally off-grid rather than just an unreliable grid, and I put in solar and enough battery to get through nights in good weather (12-15 kWh/day, maybe 8-10kWh needing to be stored) then there would be weeks in winter (or even summer sometimes) with a lot of generator use. Let's say a month a year, 400kWh, $500 or $600 of petrol. Those 2kW generators have 100 hour or 12 month service intervals, so that amount of use would just be getting it from time-based servicing to usage-based i.e. using it how it's designed to be used.Yes, you don't want to have a generator running at all hours in suburban Sydney, except in actual power outages when neighbours will understand. And your grid is a lot more reliable than mine in the middle of nowhere. My nearest neighbours are 300m away, and even then there's a small hill between us.But anyway, my point is that there aren't any circumstances where getting an extra 100kWh of batteries makes sense for extended bad weather. A generator makes sense. Or grid power, if it's available to you and still working.Btw, I find it weird than when your battery is empty you're making no attempt to charge it with off-peak power to use at peak times, but just letting it sit empty for days and days. For me, time-shifting is going to be the primary use of the battery, with a kind of "since it's already there I might as well throw a couple of solar panels on the lawn when the weather is nice". I'm thinking about 1230W (two panels) facing NE and two more NNW. I see the sun right from official sunrise (at 065º today), but lose it behind bamboo by 3 PM or so, well before the 295º sunset.

author: brucehoult
author_rank: Super Contributor
timestamp: May 23, 2025, 03:14:35 am
content: Quote from: EEVblog on May 23, 2025, 02:13:31 amThree hours? Nice. ElectricKiwi give 1 hour, and I get all my dishwashing and clothes washing and most of my hot water heating in that time. And warming the house at 9 AM on particularly cold winter mornings when the fire went out overnight. It's not a fixed time ... I have up to 23:59 each day to decide which hour that day I want to be free (starting and ending on half-hours outside 7-9AM and 5-9PM). Usually of course I change it in the app just after I switch everything on.Of course nothing is really free ... but if your supplier has such a thing then you know it's built into their other prices to compensate, so you should use it to the max.

author: EEVblog
author_rank: Unknown
timestamp: May 23, 2025, 03:32:38 am
content: Quote from: brucehoult on May 23, 2025, 03:10:06 amYes, but that's not the point.QuoteJust a bigger solar array makes sense. If you have a big property with a lot of space.But as always, it depends on your circumstances.My situation for example, I have lived in Sydney my entire life, and have no had a single full days grid power outage, ever.QuoteI literally don't have an off-peak period, it's a fixed tariff.Just this morning I switch one the only provider that has a free power period.

author: EEVblog
author_rank: Unknown
timestamp: May 23, 2025, 03:35:27 am
content: Quote from: brucehoult on May 23, 2025, 03:14:35 amYes, the daily supply charge it higher, the peak rate is higher etc.Will now set my timers to charge the battery at full 5kW, the hot water heat pump, maybe an aircon or dryer is needed, and the EV at fast charge if we need it, all during that 3 hour window.

author: brucehoult
author_rank: Super Contributor
timestamp: May 23, 2025, 04:14:22 am
content: Quote from: EEVblog on May 23, 2025, 03:32:38 amIf you don't mind them being under-utilised in good weather, yes.Just the panels themselves are now under a 1 year payback if you can use all the energy they generate over a year to substitute for power you would otherwise have paid good money for. That gets longer of course once you count mounting and cables and controllers, but probably still under 2 years. Which is a lot better than the rest of the setup, so a little inefficiency there is ok.Exporting power is just a waste of time, certainly as a plan rather than an incidental. Here they're paying 8c wile I pay 30c at night, 61c peak (6 hours a day), and 36c the rest of the time. So there's a 4:1 factor between the economics generating power you can use and installing extra capacity to sell.Wholesale power at my local substation is usually around 3c to 3.5c. I think the trend over the next 5 to 10 years will be for home exported power to approach that.The days of netting off imports and exports 1:1 always made zero economic sense and were just because they didn't have electronic meters with data comms that could measure both independently, and simpler (including mechanical) meters just naturally net it off.p.s. the site is dodgy at the moment.. Had to retry a couple of times.

author: EEVblog
author_rank: Unknown
timestamp: May 23, 2025, 04:52:16 am
content: Quote from: brucehoult on May 23, 2025, 04:14:22 amIf you don't mind them being under-utilised in good weather, yes.Cheaper than a bigger underutilised battery.

author: gf
author_rank: Super Contributor
timestamp: May 23, 2025, 05:55:40 am
content: Quote from: EEVblog on May 23, 2025, 04:52:16 amCompared to other countries, achieving autarky seems relatively easy in Australia. Attached is a screenshot of an examplePVGISoffgrid calculation for Sidney. A peak power of only 3x daily consumption and a battery for only 1x daily consumption seems sufficient to empty the batteries on only 0.1% of days (on average). Here in Germany, much more panels and batteries would be required to achieve the same.

author: brucehoult
author_rank: Super Contributor
timestamp: May 23, 2025, 09:46:06 am
content: Quote from: gf on May 23, 2025, 05:55:40 amTrap for new players. It's hard to see it with such over-panelling, but you'll get much better results with 180 azimuth instead of 0 :-) :-)Try reducing solar peak power to idk 3000W or something (which might be a sensible level with grid power available) and you'll see, but it does make a difference at your 30000W level too.With the correct azimuth 10000W is enough to get down to 1% of days that the battery gets empty -- presumably for just a short time usually. Seems fine. Excessive if you do have grid available. Or a generator even.

author: paulca
author_rank: Super Contributor
timestamp: May 23, 2025, 10:16:11 am
content: Going fully off-grid requires stupid money or a life style change to minimalist.For normal people there is a phase aligned transfer switch. If the grid power is "available" the inverter pilot wave is synced to it. If it's not, well, it isn't. If the grid comes back and it's out of phase, the transfer switch will not close until it is.I attach my custom data logs for my DIY system. Based around a Victron "camper van" inverter, 800VA only. 16x105Ah AliExpress specials LFP w/ JKBMS. 3x330W panels, 3xMPPT controllers. Raspberry PI inverter controller (Victron software image). ESP32 BMS monitor - send the 50 odd metrics from the BMS to MQTT.The graph shows a rather "bespoke" feature. You probably wont find in a commercial house battery. A tapering top of charge. The reason you wont see it in a commercial inverter is it requires hardware and software you would otherwise not need, bridging protocols between different manufacturers eco-systems... and all to get an extra 1% of charge.The battery cells get over ~3.4Vpc and begin "hockey sticking" upwards. The control loop steps in and begins asking the MPPT controllers to back off based on primarily the cell delta, but secondarily on max cell voltage. Only 2 of them will listen, so it can only really limit the power to 1/3rd or around 350W. So far the BMS and additional capacitor bank balancer have with held the parameters and not tripped the BMS.The yellow shaded area on the MPPT Power chart is the limiter. One control loop monitors the battery cells and publishes the target power. Normally it is pinned at 1kW and no action is taken. However if at any point the panels are generating more a second control loop will begin decrementing the "Amps" setting on the 2 victron controllers to meet that power limit. Both are "blind unanchored tracking" algos. Neither have a concept of what they are doing, they only know "up" or "down". Much like an MPPT algo.In confirmation to Dave's point however. There are weeks over December where the total off-grid power is measured as NEGATIVE Whs. Thankfully not kWh. The Wh's are consumed by the battery and it's BMS and the inverter is topping it up once a day or so to remain at my "RESERVE". Running the BMS, a capacitor balancer and an ESP32 is ultimately where those few dozen watt hours a week goes. The load is 100% on grid, though I still have my few kWh of UPS reserve power if the grid goes off.When storm Euoan or whatever they called it was coming through I changed the "Reserve" power setting to 100% charge for 3 days until the power cut risk passed. In the event of a local grid fault I would have 5kWh of mains power on at least one extension lead.

author: gf
author_rank: Super Contributor
timestamp: May 23, 2025, 10:48:00 am
content: Quote from: brucehoult on May 23, 2025, 09:46:06 amYou are right, of course -- wrong hemisphere

author: Fflint
author_rank: Frequent Contributor
timestamp: May 23, 2025, 12:22:48 pm
content: It is good to have grid as backup even if you do have "stupidly large battery" :-)Imagine your inverter has to be switched off for maintenance. You can switch to the grid.Also, regarding rural properties, it now costs the same or more for the ground mount for solar panels as much as panels itself. I got quoted many ridiculous prices for a 24 panel mount for Jinko 575W bifacial panels (29 of these cost me ~2500EUR last year). So I ended up building DIY legs made with concreted, galvanised fencing posts for those aluminium rails used for rooftop mounts.I'm much further up north than Sydney is south. I have 14KWp of solar (5 panels spare now) in the battery system and 65kWh of battery. I could disconnect from the grid 10 months in a year. I also have a diesel generator, but I haven't wired it in yet. The goal with building my system was a whole house ups. I think I have similar usage to Dave , minus the EV.The 14kWp array still makes about 1.5KW in a typical rainy weather. That drops to 700W if its really dark. I never saw it make less during daytime except under snow.Fun fact, I can't reach to the top to remove snow, but as long as I remove it from half of a panel it will melt the rest on its own. I only tested it in mild freezing weather (-10C tops). Don't expect it to work at -30C.

author: .RC.
author_rank: Frequent Contributor
timestamp: June 05, 2025, 09:12:08 am
content: This video to me sort of proves that these countries rushing headlong into generating their electrical requirements from wind and solar really have little idea of the full costs involved.It is not that it cannot be done. But it is going to cost a lot, for Australia I expect over a trillion dollars as you have to engineer for the absolute worst case scenario. If it costs a lot, then you standard of living you are currently accustomed to will drop as you are either paying more tax to subsidise the new electricity network that the government is funding, or you are paying through the nose for electricity, probably both.While some will say, oh you just have gas or diesel generators, well then you still have to build a massive capacity in them and have them fully maintained and ready to run at a moments notice.As for farms having more land area. Yes they do, but they also have a greater electrical requirement. They have to supply their own water, often have greater refrigeration requirements (I think a lot or urban people fail to take into account while they may use x amount of electricity at home, their actual energy usage is much higher once you take into consideration their use of supermarkets and other shops and their water requirements). Also farms may have a considerable workshop electrically powered and other electric motors on the farms powering things.In Western Australia a few years ago the electricity provider was giving farms a standalone electrical system complete with lots of solar panels a battery and a diesel generator. It was estimated the cost was $150 000 per farm.https://www.abc.net.au/news/2022-10-02/thousands-of-renewable-standalone-power-systems-to-be-rolled-out/101479136

author: brucehoult
author_rank: Super Contributor
timestamp: June 05, 2025, 09:55:59 am
content: Quote from: .RC. on June 05, 2025, 09:12:08 amAn extremely reasonable cost, considering that it is owned and operated by the electricity company and will be engineered to the max.People in rural areas are regularly charged $50k or $100k just to put in a few poles and a transformer to extend the electricity grid a few hundred meters to a new house.Heck, my uncle was recently charged close to $50k to get electricity to his new (relocated) retirement house that is 50m from the road and 60m from the farm house he built and had lived in since the late 80s. Across a perfectly flat paddock.

author: tszaboo
author_rank: Super Contributor
timestamp: June 05, 2025, 10:37:30 am
content: Quote from: brucehoult on June 05, 2025, 09:55:59 amIt's an issue of monopoly, and giving zero incentives for them to do it. Basically the electric company has monopoly, because nobody can touch their grid. They also have zero incentive to connect people in remote areas, so they give these ridiculous quotes for a hundred meter cables and some concrete. Realistically this is a few days of work to install it by a very small team, and cheap and readily available mass produced materials. And if you needed a power connection 60 years ago, they sent out some guys with a shovel and they did it in days.Now it's project planning, approvals, tax, tax on tax, local council bullshit, environmental studies if you need to cut down a tree.We wanted everyone to be connected to the grid, and just did it. And now it's a bunch of red tape and extra hoops to jump through. The solution is to stop treating utilities as cash cows.

author: paulca
author_rank: Super Contributor
timestamp: June 05, 2025, 11:10:35 am
content: Quote from: tszaboo on June 05, 2025, 10:37:30 amGreat series of videos from Diesel Creek on YouTube where the power company quoted him some ridiculous 5 figure sum for a 300 yard run and a transformer.... so he did the cabling, to their spec, the concrete wells, manholes and pads to their spec. Then paid the much less to just pull the cable and bolt the xformer in.

author: EEVblog
author_rank: Unknown
timestamp: June 05, 2025, 11:30:49 am
content: Quote from: paulca on June 05, 2025, 11:10:35 amAlthough I can't legally change a light switch in Australia, there is nothing against pulling cables and running conduit. As long as it's to spec, the electrician will wire it up.

author: themadhippy
author_rank: Super Contributor
timestamp: June 05, 2025, 12:43:10 pm
content: QuoteYea it was expensive,but it was more like 800 yards,and dont forget it was on the primary side so yer bog standard low voltage cable wont do and MV rated cable cost a bit more, they also had to replace a pole or 2.

author: indeterminate
author_rank: Regular Contributor
timestamp: June 06, 2025, 06:03:30 am
content: You need to remember that the grid is a very cheep backup power system.if you do not have the grid then you need a diesel generator and a fuel tank that can run for at least a week.if my inverter stopped working then i would need to run off generator 24/7 until i repaired it.if you have grid connectivity then its just a free phone call to get a truck out to fix your grid supply.

author: brucehoult
author_rank: Super Contributor
timestamp: June 06, 2025, 07:03:08 am
content: Quote from: indeterminate on June 06, 2025, 06:03:30 amIt's got to be a pretty serious situation if you can't drive somewhere to get more fuel every day or two. What usually happens here is that rural areas like me lose grid power for a day to four days (Feb 2023) but the city 35 km away has everything working again within hours.QuoteAverage power use is far lower than peak. If you only have a generator then you have to size that for the peak use. Even quite a small battery allows you to size your generator for average use -- or some small multiple of it, so you only have to run the generator intermittently.In my own case, average power to my essential things is ~200W, and full normal use with all the nice-to-haves is 500W-600W. Peak power ... I don't know ... between the hot water heater, aircon, electric kettle, toaster, oven, coffee machine, vacuum cleaner .. I guess I could get to 12 or 13 kW if I really really tried. But at the same time it's not hard to keep it down to maybe 4kW if I know I need to.I've got a 3kWh battery generator with 3600W continuous output, 7000W surge, arriving in about a week. And a 2200W (1800W continuous) generator arriving in 10 days.With just that, no solar, I'm expecting to have to run the generator around 50 hours a year, at a NZ$2/kWh cost vs $0.61 from the grid during peak hours.But I'll probably add around 2.5kW of solar later in the year. Once I have the battery and generator for resiliency already, the incremental cost of some panels and DIY ground mount is very low.QuoteNot when 80% of customers in your region are without electricity from three dozen separate faults, and the power company only has three repair crews. And the regions either side of you are in the same situation.This actually happened to me on April 17-19. They couldn't even repair anything on the 17th and 18th due to the ongoing storm, flooding etc. By the 19th the storm had abated and repair crews from all around the country had arrived, and they got most people back online by evening.In February 2023, as I said, there was a similar situation but it was four days before my power was restored.On these two occasions I simply suffered. I lost food in my fridge/freezer. Fortunately both happened in warm weather. I drove into the city to buy takeaway food and to take a shower at friends/relatives houses.Next time that happens, I'll have everything working except hot water and the oven.

author: tszaboo
author_rank: Super Contributor
timestamp: June 06, 2025, 02:06:21 pm
content: Quote from: brucehoult on June 06, 2025, 07:03:08 amYou think? Supply chain for fuel broke down in East Europe last time in 2022.The price went up, government set up a price limit to protect citizens. It was cheaper than neighboring countries, so people started coming over the border to fill up. Suddenly they set up a limit of 20L fill-up per day, some lower, only with a local license plate. This lasted months, and many many filling station just put up an empty sign. Because they were loosing money on the fill-up.It's a perishable goods, you can only store it for 6 months, and the supply chain goes all over the world. And you cannot just set up the refinery to buy the crude oil from somewhere else, because that's not how it works. The distillation column has a lead time of 2 years.

author: wilfred
author_rank: Super Contributor
timestamp: June 06, 2025, 02:17:22 pm
content: Quote from: paulca on June 05, 2025, 11:10:35 am$52000 if I recall correctly. But it was a long run of hundreds of meters and he had the earthmoving equipment. He was sore about it though.

author: brucehoult
author_rank: Super Contributor
timestamp: June 06, 2025, 03:50:55 pm
content: Quote from: tszaboo on June 06, 2025, 02:06:21 pmThat's an almost completely independent risk from weather knocking out the grid.QuoteThat is stupid. Prices exist for a reason -- to help limited resources go to those who most need/want them.Most months I use about 1-2 litre/day. And then some days I use 100+ litres.QuoteStupidity.What should I do? Stand in line for "my" 20l every day, and then sell it to someone who actually needs it?QuoteUtterly stupid government-created crisis.QuoteFortunately that's an incredibly unlikely scenario, and very far from the topic of this post.Ukraine and Russia have been in a hot war for more than three years, and doing their best to destroy each other's infrastructure, but you can still easily buy fuel for your car or generator in both countries.

author: tszaboo
author_rank: Super Contributor
timestamp: June 06, 2025, 04:22:04 pm
content: Quote from: brucehoult on June 06, 2025, 03:50:55 pmYes, governments make stupid decisions. Even yours. And there is absolutely nothing you can do about it, unless you can get some torches and pitchforks and overthrow it overnight. Short of that you are exposed to these risks from every government, and whatever fancy things work now (like money, or a petrol station) might not work tomorrow.