After PV system installation, power consumption went drastically UP - Page 1
Forum section: electronics / general

author: Goodi
author_rank: Newbie
timestamp: November 30, 2024, 09:27:47 pm
content: Hello,My parents-in-law had a PV system with battery installed in September.Before the PV system was installed, they had a power consumption of about 1500kWh to 2000kWh peryear.Afterwards they had a consumption of almost 800kWh in October alone. They are now already up to almost 2MWh since the installation.And that's not just what the inverter is showing, they also got a horrendous bill from the power company.I'm an EE engineer but my world is PCBs and high speed digital.My mind struggles to understand how the system can appear to work properly and still cause this sudden increase in power consumption.Any idea what could cause this?Thank you very much in advance!GreetingsStefan

author: coppice
author_rank: Super Contributor
timestamp: November 30, 2024, 09:41:02 pm
content: My guess is something has been reversed in measuring one of the current flows. Maybe a CT is clamped on a cable in a reversed manner, or two terminals have been swapped somewhere.

author: nctnico
author_rank: Super Contributor
timestamp: November 30, 2024, 09:43:39 pm
content: There is zero export! Likely a problem in the metering

author: Goodi
author_rank: Newbie
timestamp: November 30, 2024, 09:54:48 pm
content: As far as I know the system is not allowed to export power to the net. That's why.

author: coppice
author_rank: Super Contributor
timestamp: November 30, 2024, 09:57:41 pm
content: Quote from: nctnico on November 30, 2024, 09:43:39 pmWhy would they want to export anything, unless they have a massive surplus? There are batteries in the mix.

author: Goodi
author_rank: Newbie
timestamp: November 30, 2024, 09:58:34 pm
content: But as I said also the meter of the power company shows increased consumption, thus the increased electrical bill. And as far as I know nobody touched anything there. The system is also not allowed to export power.

author: coppice
author_rank: Super Contributor
timestamp: November 30, 2024, 10:01:47 pm
content: Quote from: Goodi on November 30, 2024, 09:58:34 pmCan you turn off the breaker from the PV panels for a couple of days, and see what that does to the numbers? If it doesn't restore the import to historic values it should tell you a lot.

author: KE5FX
author_rank: Super Contributor
timestamp: November 30, 2024, 10:04:55 pm
content: Or walk around with a thermal cam.

author: nctnico
author_rank: Super Contributor
timestamp: November 30, 2024, 10:26:31 pm
content: Quote from: coppice on November 30, 2024, 09:57:41 pmBut it is only a 5kWh battery by the looks of the daily charge capacity. That does nothing and it looks like this is a PV system somewhere between 5kWpeak to 10kWpeak which gives a massive surplus. My guess is the system is exporting (despite that it shouldn't do that) and the meter is adding imports and exports.Another problem can be with the PV / battery inverter and the loads connected making the meter measuring wrong. Smart meters can be prone to that. Putting a good old (passive) meter with a rotary disk in series with the smart meter can be very useful to detect whether the meter is working correctly or not.

author: rteodor
author_rank: Frequent Contributor
timestamp: November 30, 2024, 10:29:56 pm
content: If the meter is simple one without separate counters for import/export: follow the meter indication by hour and check if "consumption" increases while the sun is up compared to night time (or if the battery is empty). That should give a hint if there is an "unexpected export".A clamp meter could be useful too to check what's coming from the grid vs. actual house consumption.LE: But by the look of the daily variance, the "unintended export" is the most likely explanation.

author: Siwastaja
author_rank: Super Contributor
timestamp: December 01, 2024, 03:15:27 pm
content: First make sure you have proper contract with grid/energy company for export; selling them your excess energy. You must have done that, right? Sure at that point someone also checked that your utility meter is capable of metering the export, right?If that is taken care of, then make sure it works: get hourly metering data from the energy/grid company (sure it must be available online to you in year 2024 in Austria, yes?)This must mean two numbers, export and import. Compare both to what the inverter application says, to rule out energy metering error.Specifically check if there was any sunny day when you remember that battery was already showing 100% at some point in afternoon. Then there should be export. Verify that the export is recorded correctly both in the inverter and in the grid/energy company operator data.Batteries are nasty in that they totally destroy your energy consumption ifanythinggoes wrong with metering. In other words, the energy flow (direction and magnitude of power flow) the inverter seesMUSTmatch what is measured by utility meter, pretty closely - especially close to zero.And metering is not made easy by e.g. Chinese inverters having an overcomplicated system where a separate box is wired with RS485, then to that box is connected all three phase voltages and three CTs and the order of the phases must match as well as direction of CTs. Too many possibilities for installers to make a mistake, and mistake is hard to see, there is no intelligent diagnosis.It is also important to know what is thenetting periodyour grid company uses. This varies from milliseconds to a year depending on where you live and what kind of contract you have! And while of paramount importance, it can be nearly impossible toknowwhat it is, you need insider information. For example, Iknowthis is 15 minutes in most of Finland now, but I have no idea how I would Google that or where I would get that information as a consumer. Inverter net-zeroing feedback loop frequency response is somewhere around 0.1 - 0.5 Hz, so for netting periods shorter than a few minutes, extra cost is caused by timing mismatch. Also if phases are not netted together in a 3-phase system for billing (which was the case here still a few years ago!), it will totally ruin everything (inverter keeps total power at zero, which means some phases export while others import; if you are billed for the phases separately, you pay even at zero power).Also seehttps://www.eevblog.com/forum/renewable-energy/low-power-efficiency-regulation-of-battery-hybrid-inverters-(eu-and-otherwise)/- increased power consumption is to be expected.I would suggest not to get grid-tied battery inverter systems without third party management system (aware of hourly energy prices; maybe participating in reserve markets). For PV timeshift only, it is not worth the investment, and extra power draw negates large part of the effect.

author: Siwastaja
author_rank: Super Contributor
timestamp: December 01, 2024, 03:25:17 pm
content: Quote from: coppice on November 30, 2024, 09:57:41 pm"Typical" 6-10kWp PV system of today produces some 30-40kWh a day, while typical battery size is 5 to 10 kWh. So most still goes to export. This is why for example our control algorithm often chooses to export even at very poor price (say 1 cent/kWh), if it is known from weather and consumption forecasts that battery would become full anyway, and forced to export at even worse price (say 0).

author: brucehoult
author_rank: Super Contributor
timestamp: January 14, 2025, 11:13:39 am
content: Quote from: Goodi on November 30, 2024, 09:27:47 pmThat seems incredibly low! That's somewhere between 170W and 230W, on average. My computers, fridge, and Starlink together use about that much -- not even counting lightingDo they not use electricity for cooking or water heating? No heat pump, no heaters?QuoteThat's about 30% more than the average house here in NZ.I don't know what kind of place they live in, and you didn't provide any details, but I would find that more believable than 2000 kWh/year, unless they're living in a small apartment with gas cooking and hot water and heating provided by the apartment complex (and charged for separately).But if it's a hi-rise apartment complex then where didn't they put 9 kWh a day (in October!) worth of PV panels?

author: Zero999
author_rank: Super Contributor
timestamp: January 14, 2025, 11:52:38 am
content: Quote from: brucehoult on January 14, 2025, 11:13:39 amI dissagree. I wouldn't say it's incredibly low. Those figures are double mine.My annual energy usage: July 2021 to 2022I live in a small two bedroom property. I have gas heating and a gas stove. I also use a microwave, but it's not much.Gas is more commonly used for heating and cooking in Europe. Heat pumps are being pushed to cut pollution, but are still not that common.

author: Siwastaja
author_rank: Super Contributor
timestamp: January 14, 2025, 11:59:57 am
content: But the consumption is incredibly lowto buy PV let alone a battery system. That's the mistake here. These systems usually make sense in the 10MWh/year range and above. With so little consumption, PV goes mostly to export, so it only works in countries where special incentives for exporting are available; in most places this is not the case.And with so little consumption, battery would be mostly used to buy and sell energy on spot price markets, or act in frequency reserve markets. Which is something a "normal" hybrid inverter + battery simply does not do at all; there are specialized companies and products doing that.

author: nctnico
author_rank: Super Contributor
timestamp: January 14, 2025, 04:52:41 pm
content: Batteries are sold by many scammers nowadays. I came across this video which warns against these scams yesterday:It is an item from a TV show which deals with all kinds of consumer related items and scams. It is in Dutch; no idea whether Youtube can add subtitles in different languages or that it is even available outside the NL.People are pressured to buy a battery for nearly twice the price and borrow money through a 'zero interest' loan. They also need to buy the electricity from the same company in order to get to the promised ROI. The small print in the contract however says the complete opposite of the sales pitch.

author: Siwastaja
author_rank: Super Contributor
timestamp: January 14, 2025, 06:00:28 pm
content: Quote from: nctnico on January 14, 2025, 04:52:41 pmWe have interesting situation here as well; not something I would (at least publicly) call scammers, but let's say borderline scammers. These are supposedly "well known" "large" companies who push their stuff to random small "three electricians and a van" companies to sell it to the customers, especially the elderly (who also have money). Here the big buzzword at the time is frequency reserve markets. Which is a real market of course, but the size of it is 1/100th of e.g. spot price market and is rather quickly saturated with batteries.The market collapsed in Sweden a few years ago; initially, large paychecks (like 200 EUR/month) were promised and some actually got those for some months but then it melted to a level of maybe 10-20 EUR/month; the company doing it lost its reputation quite badly and the whole industry got a hit.We are doing battery control now but to make it non-insane one needs to combine optimization of own PV storage to using hourly spot energy markets and optimize the battery usage carefully as a whole. Even then the investment is large and payback is long. I used to say it never makes any sense to invest in batteries but after doing simulations of our optimization algorithm I can say that it's not completely stupid. And participating into reserve markets can addsomeearnings; if they dilute, no problem, because energy price variations during the day are not really going anywhere.You may want to take a look of my post about this with your preferred translation tool:https://www.enion.fi/artikkelit/enion-ohjaa-akkuja-lykksti-jo-tnn

author: nctnico
author_rank: Super Contributor
timestamp: January 14, 2025, 07:14:20 pm
content: IMHO it greatly depends on where you are located whether large price variations during the day will exist for a long time or not. Over here in the NL various companies are building large storage facilities using batteries and you can't beat their economy of scale as a tiny consumer. Especially not with a company in the middle as a broker / service provider getting part of the profit (which is probably similar to your solution; a paid for service to determine the best time to charge & discharge the battery). So I expect extreme price variations to be a thing of the past in a few years in the NL; at least it is not something I'd recommend basing in investment on with a projected ROI >3 years. Remember: the people getting very rich from mining are the ones selling the mining equipment.

author: Siwastaja
author_rank: Super Contributor
timestamp: January 14, 2025, 07:51:51 pm
content: It is indeed impossible to guarantee payback for a battery system. Though, if one is getting a batteryonlyfor PV timeshift - I can pretty much guarantee theimpossibilityof any payback. Being such expensive investment, one needs to utilize the battery in every possible way instead of letting it sit with light use.There are some benefits of distributing the batteries at consumer sites: while centralized sites require stronger grid infrastructure, consumer batteries have potential to do the opposite (reduce peak load) - although peak charge rate when everybody charges at the single cheapest hour might then again nullify this advantage (demonstrating the complexity of optimizingeverything). This also shows in money: if you are a consumer and use your own produced PV, you get more out of it compared to a centralized plant pushing electricity into grid. Details depend on country but for example here the bill is separated into energy and grid fee; by exporting you don't get paid for the grid fee; import price is bigger than export price. So with centralized solution grid is in use, and the consumerwillpay for it, in one way or another. Then there is also emotional side; people feel they are more self-sufficient, or that they are participating in the energy (r)evolution.But you are probably right that even with the mentioned benefits it is more cost-effective to do large-scale storage. And not only for getting the batteries and inverters cheaper per kWh, but also because large scale pretty much forces you to do things right. Home installations sit at poor utilization, or even worse, doing damage to the customer (e.g. by miswired/misconfigured energy meter). In my opinion grid-tied battery systems should not be sold at all without intelligent control becauseeven withthe control it's an iffy market.

author: brucehoult
author_rank: Super Contributor
timestamp: March 25, 2025, 01:04:37 am
content: Quote from: Siwastaja on January 14, 2025, 07:51:51 pmWell, that is an interesting question.I've been contemplating doing something, and am considering the questions of battery and PV cells independently.Battery seems to be the easiest to understand. All prices in NZD, currently worth 0.57 USD or 0.53 EUR.I consistently use 15% of my total electricity during peak hours (7-9 AM, 5-9 PM) when it costs 60.58 c/kWh vs 30.29 at night (11-7) and 36.34 during the day and evening 9-11. Most of that will be in the evening peak as I usually get up after 9 :-)I believe that's 15% of the total 4904 kWh I used in 2024 i.e. 735 kWh, but 18% of the 4002 kWh I actually paid for, as I schedule heavy intermittent uses such as water heating, clothes washing, dish washing, and (in the winter) electric heating in the morning (after 9) when the fire has gone out overnight during the "free hour".So a battery system could potentially allow me to replace 735 kWh/year (2 kWh/day, 333W average for those 6 hours a day) of 60.58c electricity with 30.29c or 36.34c electricity, a 24c or 30c saving, call it 26c average. That's potentially $190 a year saved, $950 over five years.What do I need to do this?It seems to me:1) 200 Ah of 12V battery, cost around $600. This part might be expendable over 5 years, if getting the cheapest batteries.2) an inverter. I don't know how much it is necessary to spend for this. Here's a 2000W "modified sine wave" one for $310. I don't know how horrible that is in terms of quality of output and efficiency.https://www.pbtech.co.nz/product/UCHDNX1627/Dynamix-TE6-1627S-2000W-Power-Inverter-DC-to-AC-InYou can pay almost twice that for another 1500W modified sine wave one. Or for "Pure Sine Wave" around $600 for 700W, $900 for 1500W, $1100 for 2000W.3) a battery charger. Looks like 50A would be about the minimum to both power the load and charge the battery in 8 hours or so. PBTech have one for $550.I can do my own microcontroller-based battery charge monitoring and turning the charger on and off based on both battery state and time of day easily enough, so don't strictly need to pay extra for that feature.So total cost for a very minimal battery-based time-shift system looks like $1500 which is an 8 year payback. Or, yeah, "never" if you're paying (or lose) 10% on the capital cost. The batteries might have less lifetime that that, but the charger and inverter should have much longer.There isn't an obvious big win there, but it doesn't seem like a huge loss either.The next step is whether it's worth adding 500W or 600W (actual, so say 2 kW rated) or so of PV to help power the load and charge the battery during the day. And better electronics. And finally maybe more battery to power things at night.I know people who've spent US$20k on a home solar system, and they're not even off-grid. I just can't see how that can possibly make any sense.Seems like I could do *something* that at least breaks even, roughly, for US$1k, and maybe expand that to US$3k. More just seems crazy.

author: Siwastaja
author_rank: Super Contributor
timestamp: March 25, 2025, 08:22:15 am
content: Quote from: brucehoult on March 25, 2025, 01:04:37 amDon't look into ghetto DIY with lead acid stuff. Efficiency losses (say, maybe 60% round-trip) alone significantly change the economy, and lifetime for this lead acid crap will be in range of 1-5 years. Premium lead acid exists but it's even more expensive.And remember to derate lead-acid capacity to 40-50%. 200Ah of 12V is just 1kWh.Instead, look into a hybrid inverter + HV battery solution. Plenty of manufacturers with decent track record: Solis, Sofarsolar, Growatt, Huawei etc. Now you have >90% round-trip efficiency, (hopefully) long battery life (possibly exceeding 10 years), possibility of adding PV directly to the inverter. And all controllable through modbus RS485 (or TCP on some inverters).It is a solution that actually works unlike a 12V ghetto system made out of chinesium. If you use that little energy then it might be a bit overkill, though. Your pricing differential is huge, but seeing your consumption is so small and most of it (dish/clothes washing, water heating) already being shifted to cheap hours, I would probably do nothing.

author: nctnico
author_rank: Super Contributor
timestamp: March 25, 2025, 11:27:11 pm
content: I think the first step would be to get a better idea of where most of the consumption is. Water heaters and washing machines are heavy loads but their duty cycle is very low. I think heating (and cooling) are where most of the energy usage is. If that is the case, better insulation / ventilation might be more worthwhile. For cooling two or three solar panels should be OK to run an AC from.One of my projects this year is to install a heat recovering ventilation system. I hope this lowers my heating bill considerably (besides making the indoor climate much more pleasant). The next step will be to replace all the glass in the windows with better insulated glazing. I noticed that about 2/3 of the energy I consume as heat (hot water + heating) goes towards heating.

author: brucehoult
author_rank: Super Contributor
timestamp: March 26, 2025, 03:40:34 am
content: Quote from: nctnico on March 25, 2025, 11:27:11 pmI know fairly precisely where the consumption goes. I've had a power meter on each of the different loads for anything from a week to a month each.- 2 kWh/day for M1 Mac Mini (6W idle, 26W compiling Linux kernel 4m35s) with 32" screen (26W), plus i9-13900HX laptop always running (Linux) with the lid closed (13W idle, 160W compiling, short burst at 210W, 1m15s to compile a Linux kernel), plus an assortment of Arm and RISC-V SBCs approx 5W each.- 1.5 kWh/day Starlink dish w/ WIFI router, plus 8 port switch, plus fr24 receiver- 0.8 kWh/day fridge- 0.3 kWh/day LED lightingWinter heating is mostly by wood fire, in which case neither of the below are needed (maybe a little)- 1.2 kWh/day dehumidifier (average, up to 2.5 in very rainy weather, 350W when running so 8 kWh/day would be possible).Code:01 Feb 1.33 kWh02 Feb 0.30 kWh03 Feb 1.94 kWh04 Feb 0.22 kWh05 Feb 0.37 kWh06 Feb 0.16 kWh07 Feb 0.79 kWh08 Feb 0.64 kWh09 Feb 0.58 kWh10 Feb 1.89 kWh11 Feb 1.14 kWh14 Feb 2.12 kWh (3 days)20 Feb 14.92 kWh (6 days)25 Feb 4.52 kWh (5 days)27 Feb 0.96 kWh (2 days)1 Mar 1.11 kWh (2 days)- 4.25 kWh/day mid summer Dimplex 4 kW portable air conditioner. 60W idle (fan), 1100W running. Typical use from 2 PM to 7 PM, conductive heating via roof and walls lags the sunSUMMER ONLYCode:13 Jan 2.60 kWh14 Jan 5.82 kWh15 Jan 2.45 kWh16 Jan 2.53 kWh17 Jan 0.55 kWh18 Jan 0.42 kWh19 Jan 2.05 kWh (heating!)20 Jan 2.50 kWh (heating!)21 Jan 7.23 kWh22 Jan 7.13 kWh23 Jan 6.78 kWh24 Jan 4.97 kWh25 Jan 8.42 kWh26 Jan 8.45 kWh27 Jan 2.99 kWh28 Jan 1.63 kWh29 Jan 3.82 kWh30 Jan 4.07 kWh31 Jan 6.12 kWhQuoteAlready handled in the "free hour of power".Other large loads such as electric kettle, toaster, microwave over, air frier, hair dryer, espresso machine are operated for only several minutes at a time and not worth worrying about. The same goes for lighting in other rooms such as bathroom, kitchen, bedroom. It's only used for a few minutes at a time and is already (mains powered) LED.QuoteThe bulk of winter heating is from about $150 worth of wood. There is some use of the portable air conditioner, but that's never going to be able to be covered by any reasonable amount of solar in winter.QuoteNot an option. Neither is installing a fixed heat pump, or connecting solar to the main house electricity switchboard, or exporting power.QuoteThat depends on panel size of course. Use of cooling correlates strongly with intense sunlight, though lagging by a few hours -- it's not needed until early afternoon, but needs to continue a little after sunset due to sun-heated roof and walls etc.I don't need something that powers 100% of everything all the time. The main idea is to gather the low-hanging and most profitable fruit. All of the continuous loads operate from 3-pin plugs, and all of them put together come to comfortably less than the 2400W that can be supplied from one socket. They are all also in the same open-plan area within a few metres of each other.I'd expect that a system large enough to power 4.5 kWh/day of electronics, fridge, and lighting (about 200W total, on average) in overcast winter conditions will pretty much automatically also be able to run 1100W of air conditioner in the peak sunlight summer hours (max 5-6 hours continuous, plus some intermittent, but most days less than that)The main thing, as I see it, is to get a good quality good efficiency combo (maybe) MPP PV controller / 3-pin plug battery charger / inverter with sufficient capacity at the outset, and then play around adding PV panels and/or batteries until a good balance is found.Latitude 35.5 S btw. Typical mid winter weather is light overcast. 2000 hours sunlight/year.Online calculator for my address:https://solarview.niwa.co.nz/Average kWh/m^2/day in each month.Code:With 12.0 tilt Jan 5.93 Mar 4.39 Jun 2.19 Sep 4.21With 35.5 tilt Jan 5.36 Mar 4.44 Jun 2.61 Sep 4.25With 59.0 tilt Jan 4.26 Mar 3.97 Jun 2.69 Sep 3.81Surprisingly small 2.2 ratio between Jan 12 deg tilt and Jun 59 deg tilt.So possibly 2 m^2 would on average do the job with 5.4 kWh generated in winter and 11.9 kWh in summer, even after some inefficiency.

author: Zucca
author_rank: Unknown
timestamp: March 26, 2025, 07:07:38 am
content: - check if your bidirectional meter is working.If it is set as common unidirectional (measure grid to house) the energy exported from home to grid is billed as the other way around.Yes, you pay for the energy you are exporting as you would use it.- what is the batteries charging strategy?Are the battery charged from the grid somehow?Finally use an current clamp meter to understand where the power is flowing.I would also phone up the company which installed the system...

author: Siwastaja
author_rank: Super Contributor
timestamp: March 26, 2025, 07:13:13 am
content: Quote from: brucehoult on March 26, 2025, 03:40:34 amLow-hanging fruit is probably still some time-shifting you can do with DIY home automation. Like running the dehumidifier only on cheap hours, etc.If you still want PV/battery: Usually popular / well-engineered solutions are good because of their economy of scales. In that case an obvious start would be some 6kW hybrid inverter and 4kWp or so worth of panels. You can then add the battery later if you so wish. Then again, a 5kWh LFP battery isn't that expensive anymore so might just get it from the start.Probably never pays for itself, but that's usually the case with most energy renovations, HVAC upgrades, PV/batteries/EVs and any other "green tech". The motivation usually is "I want this" and "this makes sense" and then picking the one which isclosestto paying back for itself (not making ahugeloss of money). If you get it to pay back and generate extra revenue, then that's an extra bonus.One thing you may want to verify is how exporting excess PV production back to grid is compensated where you live. That affects significantly what will be the optimal PV system size. If you get poor/no compensation, or even worse, back-feeding is prohibited or limited, you want a small enough system for your self-use% in the 70-100% range. If you are compensated well (subsidized), overly large systems, ignoring self-use% completely, may make sense. Most regions fall between these extremes and you'd usually want something like 50-60% self-use.

author: brucehoult
author_rank: Super Contributor
timestamp: March 26, 2025, 07:43:32 am
content: Quote from: Siwastaja on March 26, 2025, 07:13:13 amAlready do that. I turn the dehumidifier on at 11 PM or midnight or so (night rates start at 11) depending on whether it's starting to feel chilly inside (the 350W consumption also produces around 900W of heating) and it's stopped running (on "automatic" mode with a humidity sensor) before I wake up, and I turn it off completely then. Typically it's around 55% when I turn it on and 47% when I get up in the morning.As I write this the outside humidity is 82%. Anything from 70% to 100% is common, below 60% is unusual.QuoteThat all seems at least 2x oversized, except possibly the battery, which I think is flexibleThe maximum possible load with everything I'd every have attached to it is around 1800W continuous ... I guess a bit more when e.g. the A/C motor starts up. The average load is under 200W excluding A/C & dehumidifier. I need 0.75 kWh of battery to get me through the evening peak hours, half that for the morning peak. 3 kWh would get computers and fridge through from 5 PM to 9 AM, 4 kWh including the dehumidifier.It seems to me a 1 kWh battery would already do most of the trick. Fully charge it from night rate power before 7 AM, the 7-9 peak hours will use less than half of that. Solar will hopefully power everything during the day, and have the battery fully charged before 5 PM (2.7 kWh expected from 1 m^2 of panel in winter) -- use some shoulder rate power from 4-5 PM to make sure of that if needed.Being able to battery power through some or all of the night would be a bonus, but only if the incremental cost is small.2 m^2 of panel and 2-5 kWh of battery might make sense, but I think more than that would just very rapidly get to throwing power away most days.I don't care if I have to use grid power for a few days in really bad weather.QuoteAnother motivation is that I live in a very rural area and I'm literally the last house on the 2-wire 11kV line that winds its way 18 km through hills and farm land from Ruatangata East to Paiaka -- probably 30+ km wire length. The next house to the north/east is in a different administrative region with a different electricity distributor. I seldom go two months without some farmer driving equipment through the wires or a tree falling on them and losing power for 6+ hours. Heck it can take them 2+ hours just to find the damage. It would be good to have a high chance of at least 1 kWh in a battery when that happens.QuoteNo, that's completely off the table.The buyback rate is 12.5c/kWh. Maybe I've got a fighting chance of generating or time-shifting electricity for less than 30c/kWh, but 12.5c is ridiculous. You'd be stupid to oversize a system to aim for a lot of that. Sure, if you just accidentally sometimes have a bit of spare electricity on a sunny but not hot day.But ... to get that you have to hook your solar stuff into the house electrical system and then pay $170 to have an upgraded meter installed and you have to send the electricity company:- Certificate of Compliance (COC)- Record of Inspection (ROI)- Network (DG) approval letterNot to mention of course that you won't have those -- or be allowed to hook into the house electrical system -- without paying probably thousands to an electrician or professional installer.Just to get 12.5c/kWh buyback? In a rented house that I might well move out of in six months or two years?Forget that.I'm talking ONLY about an isolated stand-alone effectively off-grid system that gives me some 3-point sockets I can plug a few small appliances into, with the ability to charge the battery from a 240V 2400W socket (or generator) when needed.

author: Siwastaja
author_rank: Super Contributor
timestamp: March 26, 2025, 08:02:21 am
content: Quote from: brucehoult on March 26, 2025, 07:43:32 amIt's not that bad - it'ssomething. Actually quite lot of money. Probably not enough to warrant a sell-only system, but no one's suggesting that. "Oversizing" has one advantage - more production in cloudy weather and winter. Heck, people do that even when they have to prevent exporting and get zero compensation!With guaranteed buyback at 12.5c/kWh you can basically dimension your system for the worse-case conditions. Then in optimal conditions your oversized system might be producing 50kWh/day excess but that's $6/day!If the value of your self-use averages 40c/kWh (some of the production would coincide with morning peak hours), and you get 50% self-use, then your average value for PV would be 40c/kWh * 0.5 + 12.5 c/kWh * 0.5 = 26 c/kWh. That's excellent value for PV, you can possibly make it pay back for itself.Compare to that, my buy price averages to around 13 c/kWh and sell compensation to something around 4 c/kWh. Compensation is many times negative 0.5 cents or so, need to pay for exporting. In this kind of case maximizing self-use is pretty important and oversized PV system problematic. With guaranteed buyback at 12.5c/kWh, you don't have such problem, sizing of the system is not critical.Compare this to ghetto solutions of 12V systems, camping PV equipment etc.: the equipment still costs like 50% of a true solution, you waste 30-40% lot of your expensive energy into efficiency losses, you get paid zero for excess PV (instead of that 12.5c/kWh).A "real" system will be a bit overkill in size, but probably still offer the best payback. The other viable option is, do nothing.