Newbie Considering Battery Storage (No Solar) - Page 1
Forum section: electronics / general

author: ssashton
author_rank: Frequent Contributor
timestamp: October 19, 2022, 02:28:32 pm
content: Hi,So, I'm in the UK and we have crazy increasing electricity costs, but there are 'off-peak' deals where the price between say 1am and 7am is as much as 10x cheaper.Therefore I was considering what is involved in adding battery storage that charges during those cheap rate hours and powers my home during the day?My daily use is approx. 10KWh so that would be a nice target for battery capacity.I wonder if there is a good resource I could go to learn about this?My current questions are:1) How would an DC-AC inverter current share with the mains supply? I don't really want a hard switch between battery and mains. It would be nice should power draw exceed the inverters capability it makes up with the mains supply.2) What kind of charging and inverter system do I need to do this, bearing in mind I don't have solar. Are there keywords I should search for?3) Is it even a good idea? As electric cars become more common and people charge them at night, I guess the off-peak deals will become less attractive. Any opinions on this in the UK?

author: Marco
author_rank: Super Contributor
timestamp: October 19, 2022, 04:38:36 pm
content: Lets say you save 20p/kwh, so up to 2 pounds a day. Lets say you buy a commercial system for 4000 Pounds, 2000 day earn back time.It's a bit of a gamble whether that will ever be worth it, on the other hand if you get an inverter with islanding and there are rolling blackouts you'll be sitting pretty.

author: 50ShadesOfDirt
author_rank: Regular Contributor
timestamp: October 19, 2022, 06:39:18 pm
content: I'm off-grid, so I do have solar involved, but otherwise, I utilize what I think you are after. A whole-house inverter/battery-charger, LiFePO4 (LFP) batteries, and propane generator, in my case. This battery-bank (300ah@24v) gives my family of 4 a rough buffer of 12 hours, before needing refill by solar or generator; nothing in our house that can't be run by this system.You could add a combined inverter/battery-charger (one unit, 24v or 48v) and LFP battery-bank (two or more LFP batteries at 24v or 48v) into your on-grid mix, and have a similar buffer. You would gain the benefits of protection from power outages, some kind of offloading from peak times (run off of battery-bank during peak time, and flip back to grid for recharge), and so on.The higher-end inverter manufacturers, Magnum, Outback, and many others, all have integration guides on their sites. You'd be going the grid-integrated route, so you don't need solar (unless wanting to sell-back) and a generator is optional (to refill and/or keep running if numerous outages from your grid).The LFP battery options have gone up in capacity, and come down in prices. I think you would want to size a battery-bank for your desired buffer, and spec all components to either 24v or 48v (common/efficient voltage choices); the high-end inverter (from a vendor in your neck of the woods) will convert to your local power needs. This forum will help with the gory details:https: //diysolarforum.com/As you are on-grid, there will be blood (electricians, inspectors, red-tape, etc.). As you are in the UK (in an area with underground power lines?), you could have less of an outage issue than we have in the states, with our above-ground power lines (which are subject to all kinds of disruption). Over here, a car can take out the local power grid with one unforseen but well-placed hit.Does this help?

author: Faringdon
author_rank: Super Contributor
timestamp: October 19, 2022, 07:17:51 pm
content: QuoteYou could go to powervault website and try their youtube videos.

author: Marco
author_rank: Super Contributor
timestamp: October 19, 2022, 08:37:51 pm
content: Quote from: 50ShadesOfDirt on October 19, 2022, 06:39:18 pmThe land of the free to drown in codes and Australia are outliers.

author: richard.cs
author_rank: Super Contributor
timestamp: October 20, 2022, 09:44:15 am
content: Divide battery cost by expected total lifetime throughput (buried in the warranty small print) to get a measure of what it costs to store a kWh for later use. When I looked a few months back it was looking rather hard to justify battery storage for grid-connected properties in the UK. That may change from April if the unit rates go up as expected.

author: ssashton
author_rank: Frequent Contributor
timestamp: October 21, 2022, 12:54:53 pm
content: Wow thanks for the replies! Very helpful.So do the inverters somehow mix the battery power with the mains in terms of current sharing or do they just switch from one to the other?I found Victron brand parts seem popular and available here. The MultiPlus 24/1600/40 seems like it would do what I want in one box, right? 24Volt batteries / 1600watts output / 40amp chargehttps://www.victronenergy.com/upload/documents/Datasheet-MultiPlus-inverter-charger--800VA-5kVA-EN-.pdfOther than the electric kettle, oven or my woodwork shop tools it should handle all the daily usage at 1600watts.I'm a little confused that some people seem to have 'chargers' as well as 'charge controllers'. Why are these separate parts?EDIT: One more question - the LFP batteries seem to be a bunch of smaller cells inside but I don't see breakout for charge balance sense like you might see on a multi-cell lipo. Is it handled internally on the battery pack, or it's not a big issue with LFP?

author: NiHaoMike
author_rank: Super Contributor
timestamp: October 21, 2022, 01:06:25 pm
content: It would probably make more sense to set up some automation to run stuff at night.

author: ssashton
author_rank: Frequent Contributor
timestamp: October 21, 2022, 01:08:03 pm
content: Pretty much the only things I can run at night are washing machine and dishwasher. Everything else is for me to use at that moment or must be on all the time like refrigerator.Those of you not in the UK may not realise the insanity of electricity costs in the UK recently. Whether a battery system makes sense I think depends how this pans out. Right now Gov. has agreed to pay part of the electricity costs (guaranteeing the energy company profits using tax) but what happens after this is anybody's guess.I think one of the fastest ways to get money back would be to go for a used electric car and charge it at night. However I only have on-street parking so that is simply not possible.

author: Marco
author_rank: Super Contributor
timestamp: October 21, 2022, 04:06:47 pm
content: Can the solar inverters with battery and islanding capabilities not charge the battery from mains? Cause they are a lot cheaper than anything from Victron.

author: ssashton
author_rank: Frequent Contributor
timestamp: October 21, 2022, 04:10:28 pm
content: Can you give an example please?Having searched a little on the cost of LFP batteries, the idea of using a salvaged EV battery is quite appealing. Need to do more research!

author: gf
author_rank: Super Contributor
timestamp: October 21, 2022, 07:27:10 pm
content: Quote from: ssashton on October 21, 2022, 12:54:53 pmDepends on the model. Dumb battery inverters cannot switch at all. Off-grid inverter/chargers can onlyswitchthe load betweeen utility and inverter. But there exist also bybrid inverters which can operate both, either grid-tied, or off-grid, they can "mix" battery power with utility power, and even feed back to the grid (unless you prevent it). Multiplus is such a hybrid.QuoteCheck if the Multiplus can be legally connected to the grid in your country. At least in Germany, only the Multiplus-II models have the necessary certification, and the inverter/ESS still needs to be registered with the power grid operator. Regulations are different in each country, though.For 10kWh you need a couple of batteries in parallel anyway, so the battery power is likely sufficient for driving a 3kVA (or possibly even a 5kVA) inverter model. Then you could even power your kettle and a sbuset of your tools.I'd also go with 48V instead of 24V, and I'd prefer server rack battery packs (like Pylontech or similar) which can be easily stacked. But that's just my personal preference. If you a willing to build DIY battery packs, then things become significantly cheaper, of course.When you compare battery prices, then also look at the lifetime in charge cycles. At the end, the quantity of interest is price per kWh per charge cycle. Mostly, the charge cycles for 80% residual capacity are specified. But some manufactures specify charge cycles for 50% residual capacity - so take care, these numbers are not comparable.Btw, in order to run the Multiplus as ESS, you also need a GX device, either an external one, or you need a Multiplus model with built-in GX. Alternatively a Raspbery PI with Venus OS and suitable communication adapter can also serve as GX device.QuoteConsider them as synomyms. But you need to distinguish AC charge controllers (-> charge battery from AC), and DC (solar) charge controllers (-> charge battery from PV). Both can be either separate units, or built-in in the inverter (Multiplus for instance has a built-in AC charge controller, but no solar charge controller).QuoteItISa big issue. Those battery packs usualy have a built-in BMS. Depending on the battery model and the inverter model, the inverter may even be able to communicate with the BMS and retrieve e.g. charge and discharge voltages and current SOC directly from the BMS.EDIT:Example calculation: Retail price for 3 x Pylontech US3000C + MultiPlus-II GX 48/3000/35-32 is about 6300€ in Germany. I guess UK prices have a similar magnitude. US3000C has an expected lifetime of 6000 charge cycles. With 1 charge cycle per day, that's a cost of 1.05€ per day, over a lifetime of 16.7 years. So it is only worth the investment if you can save more than this amount of money per day. Also keep in mind that the ESS efficiency is not 100% and that the inverter has some self-consumption - you need to add an additional margin for this.

author: ssashton
author_rank: Frequent Contributor
timestamp: October 22, 2022, 12:30:59 am
content: Thanks for such a detailed reply!I do have a couple of electronics questions mostly general curiosity.How does the hybrid inverter manage to current share with utility mains? Does it PWM between them? If it just increased the inverter output voltage until the desired current flows from battery vs. mains supply then it could end up at a very high output voltage, right?I've seen people fitting 3rd party BMS to used cells. The BMS only has very thin wires to each cell (obviously for voltage monitoring). In this case how does it achieve cell balancing when charging? It surely does not pass any charge current down those thin wires. Do they just report the error and then it's up to the user to step in?

author: gf
author_rank: Super Contributor
timestamp: October 22, 2022, 02:23:58 am
content: Virtually all sine wave inverters today use PWM to form the sine wave and to control the amplitude. The major difference between a grid-tied feed-in inverter and a grid-forming off-grid inverter is the feedback loop (current vs voltage feedback). The former acts as AC current source, while the latter acts as AC voltage source.An off-grid inverter provides a constant voltage and the load determines the drawn current and power.OTOH, a grid-tie inverter pushes a constant current (and therefore a contant power) into the in-house grid. If the consumption in the house is lower than the production of the inverter, then (due to Kirchhoff's law) the difference happens to be fed into the public grid. If the consumption is higher, then both, inverter and utility will power the load. If you want to prevent grid feed-in, the production needs to be explicitly throttled in order not to exceed the in-house consumption, which requires an additional current or power sensor.A hybrid runs grid-tied when the grid is available. Upon detection of grid failure it disconnects (relay) from the grid and switches to off-grid mode where the inverter provides its own "island grid" at its output.The thin wires and only milli Amps of balancing current seem to be sufficient in order to fix the cell imbalance occuring during one discharge cycle. You certainly need to start with (almost) equally charged cells and they should have almost the same capacity. Balancing between completely full and empty cells is IMO far beyond the capability of such a BMS.

author: NiHaoMike
author_rank: Super Contributor
timestamp: October 22, 2022, 04:17:51 am
content: Quote from: ssashton on October 21, 2022, 01:08:03 pmHave you considered thermal storage for HVAC? Also, if you have a dedicated freezer, you could wire a relay to force it full cold at night so it would run less during the day.

author: jonpaul
author_rank: Super Contributor
timestamp: October 22, 2022, 06:21:07 am
content: Easy to schedule high consumptionElectric water heaters and frigerator retain temp for many hours.We heat water only off peak, and turn up frig temp or off during peak hours.Electric stove used off peak.Get a natural gas/ propane generator for long outages.battery energy densité is 5..10% of oil, gasJon

author: ssashton
author_rank: Frequent Contributor
timestamp: October 22, 2022, 12:16:01 pm
content: Quote from: NiHaoMike on October 22, 2022, 04:17:51 amThanks for the replies.FWIW we don't have HVAC (most don't in the UK). I have a gas powered hot water boiler that provides hot water for kitchen / bath / shower and also heats water that is pumped around the house for heating.It's pretty cheap compared to electricity, especially as the energy company have failed to bill me for any gas over the last 6 months despite me telling them 2 times!!Making the freezer colder over night is an interesting idea. I bet it uses more energy in the long run but as the energy at night is cheaper it might work out less expensive. I don't feel like I want to do this though, it might even burn out the compressor.Quote from: gf on October 22, 2022, 02:23:58 amThanks! It's great to get a better understanding how this tech works.My thought is that as utility mains is fixed around 240V the only way for a grid-tied inverter to provide the majority of the current to the load is by increasing voltage above the mains supply. As you know a current source is only a voltage source that adjusts voltage to achieve a desired current. If mains supply and inverter both have equal voltage then they would supply 50/50 current. How high will the inverter output become to supply 90% of the load current?

author: gf
author_rank: Super Contributor
timestamp: October 22, 2022, 02:06:34 pm
content: Quote from: ssashton on October 22, 2022, 12:16:01 pmIt is not possible to connect two (ideal) voltage sources with different voltages in parallel, as it would result in an infinite current. And even when the voltage were the same, the current ratio were undefined.Therefore a grid-tie inverter acts as current source (with ahighsource impedance), while the grid acts as a (lowimpedance) voltage source. Then the grid determines the voltage, and the inverter injects a particular amount of current into the junction which connects the inverter to the grid. And the load draws as much current as needed from this junction. The difference between injected current and load current is then either drawn from the grid (if the load current is higher than the injected current), or otherwise fed into the grid, according to Kirchhoff's current law.If the inverter is set to inject 90% of the current required by the load, then the remaining 10% will come from mains. If the load requires less current than injected by the inverter then the difference is fed into the grid (the excess current has to go somewhere).EDIT:Quote from: ssashton on October 22, 2022, 12:16:01 pmIn order to build a current source from a voltage source, you also need a series impedance (at least a small one) which turns the voltage difference (between voltage source and grid voltage) into a current. The control loop (which measures the current and adjusts the voltage) is then able to increase the apparent output impedance by keeping the current (almost) constant, independent of the exact grid voltage. The said series impedance is typically formed implicitly by the inductors of the LCL filter at the inverter output (which eliminates the PWM ripple).

author: ssashton
author_rank: Frequent Contributor
timestamp: October 22, 2022, 04:55:15 pm
content: Hmm.. so if I understand you, the voltage before the LCL filter (series impedance) of the inverter may be above that of the grid so that current is drawn primarily from there, but as the output of the series impedance is connected to the (low impedance) grid the voltage on that side is fixed at grid level, even though current will 'prefer' to flow from the inverter?If I want to understand better I think I'll need to play with a simulator!

author: gf
author_rank: Super Contributor
timestamp: October 22, 2022, 05:35:51 pm
content: Quote from: ssashton on October 22, 2022, 04:55:15 pmThere is a junction where three legs (grid, inverter output, and load) are tied together. And at the junction,Kirchhoff's current lawapplies. The current coming from the inverter is enforced by the inverter. The current to the load is enforced by the load (it draws as much as it needs, not more and not less). So the current entering the junction on the 3rd leg (-> grid) can only be the difference between load current and inverter current, otherwise Kirchhoff's current law were violated.Quote from: ssashton on October 22, 2022, 04:55:15 pmYes, and the voltage difference Vsrc- Vgridacross an impedance Z implies a current Iinverter= (Vsrc- Vgrid) / Z flowing through the impedance.

author: ssashton
author_rank: Frequent Contributor
timestamp: October 22, 2022, 09:46:53 pm
content: Again thanks very much for helping clear my thinking!

author: ssashton
author_rank: Frequent Contributor
timestamp: October 24, 2022, 10:36:57 am
content: I posted on diysolarforum.com but it seems like a ghost town.Can anyone suggest alternatives to the Victron MultiPlus-II hybrid inverter/chargers? It needs to have the suitable certificates for the UK.The MultiPlus-II is getting kind of expensive for me.

author: Marco
author_rank: Super Contributor
timestamp: October 24, 2022, 05:53:39 pm
content: How about the Growatt "off grid" solar inverters? The manual says it's able to charge the battery from the grid, so you'd think it would work without solar panels at all.Also lets you eventually add solar panels.

author: gf
author_rank: Super Contributor
timestamp: October 24, 2022, 06:42:55 pm
content: Quote from: Marco on October 24, 2022, 05:53:39 pmOP wants a hybrid (not just a pure off-grid one). That would be Growatt's SPH models. However, the price of an SPH3000 (3kVA) is not really cheap either (while some of the cheapest Chinese 5kVA hybrids aren't much more than half that price, also with an integrated solar charger. But of course without certification...)

author: Marco
author_rank: Super Contributor
timestamp: October 24, 2022, 07:02:05 pm
content: I was thinking the SPF 5000 ES, but I can't quickly find for what countries it's certified.

author: gf
author_rank: Super Contributor
timestamp: October 24, 2022, 08:31:08 pm
content: I may be mistaken, but my undestanding is that SPF models cannot operate grid-tied, but can only switch the output beween grid and inverter. OP wants the ability to power the load from grid and inverter power simultaneously.

author: Marco
author_rank: Super Contributor
timestamp: October 24, 2022, 09:18:53 pm
content: It can operate grid tied with solar, but it seems not as battery + utility. But it does have an overload bypass mode. So presumably if you used the following mode together with the Utility charging time and Overload bypass it would work.QuoteOnly question is how many amps the internal change over switch is.

author: gf
author_rank: Super Contributor
timestamp: October 24, 2022, 11:02:00 pm
content: This is not what the OP desires. In the fisrt post he wrote:QuoteThe SPF model is an off-grid inverter/charger with transfer switch. Its inverter ouput is at no time connected to the grid, therefore utility and inverter cannot power the load simultaneously. However, the SPH models can do that, and so do the Victron Multiplus models.EDIT:"Grid-tie" means that the inverter output is connected to the grid, so that the inverter has the opportunity to feed into the grid.

author: ssashton
author_rank: Frequent Contributor
timestamp: October 25, 2022, 01:35:00 pm
content: Presumably I must by law have an inverter/charger that is certified right?I mean it's pretty tempting to get one of the Chinese ones that are half the price. Also I think GF mentioned the older Multi-plus (not II) are not certified for the UK, but there seem to be some on sale here such as this -https://batterygroup.co.uk/Accessories/Chargers/10891/Victron-MultiPlus-24/1600/40-16-230V-VE.Bus-PMP242160000?number=69132&gclid=Cj0KCQjwkt6aBhDKARIsAAyeLJ3z1jZONvzFj_efeeCNmUqTXViagmsEd2y131v5x3gt3ScthDLmtOUaAqPDEALw_wcB

author: gf
author_rank: Super Contributor
timestamp: October 25, 2022, 07:09:45 pm
content: Quote from: ssashton on October 25, 2022, 01:35:00 pmDon't know UK regulations. Maybe someone familiar with UK regulations can answer this.If a missing certification does not violate law, then it may still violate the conditions of the contract with the grid operator, which need to be accepted in order to get the house connected to the grid (or to remain connected).QuoteLikethese ones(for instance)?Well, some people simply don't tell anybody... (but don't take this as an invitation).One issue with these Chinese ones is certainly the meager documentation and support, while there is plenty of documentation for Victron, also when it comes to interfacing with some 3rd party stuff, or customization of the behavior. I also can't assess their robustness and longevity, while Victrons are commonly known to be pretty robust.QuoteThey are surely not certified forGermany(and I think they can't be, due to lack of a redundant relay which is only available in the "II" models).I don't know UK regulations, but I'm afraid that the same may apply to UK as well.QuoteIt is not prohibited to sell them. They are offered in Germany, too.

author: Marco
author_rank: Super Contributor
timestamp: October 25, 2022, 09:18:29 pm
content: Quote from: gf on October 24, 2022, 11:02:00 pmIt can't load share, but it can bypass the mains to the output during overload, which is almost as good. Assuming for a moment the "hack" of the mode I mentioned + bypass + charging hours works, what would happen is that the max 32A output would feed the house during non charging hours. As long as the load stays below 5 kW (10 kW surge) the battery feeds the house, otherwise it bypasses the mains to the output.Less ideal than load sharing, like the Victron can do on its output, but not useless.QuoteGrid-tie need an external current sensor on the mains in this application. Grid tie converters connect in parallel with mains rather than with feed through like the Victron or the SPF, so they'd never know how much power to supply from battery otherwise.

author: gf
author_rank: Super Contributor
timestamp: October 25, 2022, 11:30:15 pm
content: Overload bypass unfortunately implies that particularly high load must becompletelypurchased from utility, even if the battery is full and could provide say 90% of the power.Yes, zero feed-in requires of course an external power or current sensor.SPF is "feed through", but the inverter in the Multiplus runs in parallel to the grid, and AC input and AC output are interconnected as long as utility power is available. I.e. the inverter can also feed back to loads connected to the AC input and feed into the grid. If utility power fails, it disconnects from the AC input and provides an island grid on the AC output only, for powering emergency loads.

author: NiHaoMike
author_rank: Super Contributor
timestamp: October 26, 2022, 04:43:47 am
content: I'm not aware of very many inverters that have both backup and zero export capability to loads on the input side by means of external sensors, Sol-Ark is one of the few that can do that. The Schneider XW series, for example, can only zero export to loads on the output side and there's no provision to connect sensors for zero exporting to the input side.

author: gf
author_rank: Super Contributor
timestamp: October 26, 2022, 06:11:54 am
content: "Zero export only to loads on the output" basically just implies that an internal current sensor at the AC input is used instead of an external one, as limiter for the feed-in. This is supported by the Multiplus, too.Edit: When AC input and AC output are interconnected in the pesence of utility power (in order to mix utility power and inverted battery power), then the inverter cannot selectively feed the input or output anyway, but it feeds into the junction, and at the end the location of the power or current sensor determines which power flow is limited to >=0 (either the power flow from grid into the house, or the power entering the AC input of the inverter/charger box).Yet another option for mixing utility and battery power is an off-grid inverter/charger with AC-DC-AC double conversion for the utility power. Here, mixing of utility and battery power happens at DC. This may be beneficial wrt. regulations (inverter does not operate grid-tied), but the inverter must be powerful enough to invert the full power of the AC loads connected to the output, otherwise it still can only fall back to overload bypass. Supplementing any loads at the AC input with battery power is of course not possible.

author: gf
author_rank: Super Contributor
timestamp: October 26, 2022, 07:22:21 am
content: Quote from: NiHaoMike on October 26, 2022, 04:43:47 amGrowatt SPH series, some Deye hybrid models, Voltronic Infinisiolar1), the ISolar models from EASunPower/Powland, and of course Victron Multiplus, EasySolar, Quattro also come into my mind.1)The name Voltronic almost never appers directly, however it is a big Taiwanese ODM/OEM company, and their inverters are re-branded or licensed and sold by dozens of other companies. Mostly just a different name is printed onto the enclosure, sometimes there also may be value-added features. Growatt models also seem to be at least derived from Voltronic designs. Don't know if they are also produced in a Voltronic factoty. I'm also unsure about EASunPower/Powland. Either they are also rebranded Voltronic ones, or clones? At least for a few ones, I don't find an obvious 1:1 equivalent in the Voltronic portfolio.

author: ssashton
author_rank: Frequent Contributor
timestamp: October 26, 2022, 11:15:59 am
content: Yet again thanks for loads of info!At this point I have actually decided not to proceed with a home battery. The main reason is that after looking at details of the various tariffs, the best ones are not available!Octopus Go which was intended for night time charging EVs, but which some people had used for water heater or battery storage now check if you have an EV and refuse access otherwiseAlso I know someone paying 5p/kwh and another at 7p/kwh but I think its now 12p.EonNext Drive is simply 'not available until further notice'. The basic night time economy tariffs have become far more expensive.. which means with my planned 2-3year ROI I do not have the budget even using salvaged batteries.The only option for interter would be a Chinese brand with no customer service or a very basic used one with no features.The good news is I now understand a lot better about this stuff and so I'm placed to reconsider this plan if things change.

author: NiHaoMike
author_rank: Super Contributor
timestamp: October 26, 2022, 01:16:50 pm
content: Quote from: gf on October 26, 2022, 07:22:21 amLooked up a few of those and they're for single phase, which is much easier to do. In the US, most residential uses split phase or (less common) a "2/3" phase system which substantially increases the complexity. A US reviewer of the Schneider XW mostly operates his in off grid mode even though he has a grid connection, since he doesn't like how it would export on the less loaded phase when presented with an unbalanced load, which some power meters may detect as an attempt to cheat the meter.

author: 2N2222A
author_rank: Regular Contributor
timestamp: October 26, 2022, 03:03:29 pm
content: Lots of good information in the replies!There are Chinese grid tie inverters that have an optional load sensor on the mains to prevent back feeding the grid. They're intended for use where the utility charges customers for electricity in both directions. The grid tie inverter will limit its output to what your house is using. Just hook that to the battery bank and have it scheduled to turn off when cheap hours start and have the battery charger set to turn on at the same time. The problem is I'm not sure what certifications the Chinese grid tie inverters have.

author: gf
author_rank: Super Contributor
timestamp: October 26, 2022, 06:06:22 pm
content: Quote from: NiHaoMike on October 26, 2022, 01:16:50 pmSome are also available as 3-phase models (e.g. Growatt, Deye), some others support combining 3 single-phase units for 3-phase. I think Victron also supports 120/180/240° split phase by combining two 120V units, and for 180° split phase, also a couple of different configurations with autotransformer.

author: 50ShadesOfDirt
author_rank: Regular Contributor
timestamp: October 29, 2022, 06:37:28 pm
content: Possible sidebar solution, depending on how "handy" you are ...If "electricians, inspectors, codes" involved, then cost/complexity goes way up. This includes the newer *requirements* for "listed equipment only" (UL/ETL). It's darn near getting impossible to DIY, if you follow codes & such. I don't, as I'm off-grid, self-insuring, etc., which doesn't apply to about 99.99% of everyone else.However, one way to change the dynamic of "everybody and their dog has a requirement" is to implement a "parallel" power system, wherein the grid powers your home as is, and no costs to keep using it the way it is (other than we want to shed loads at peak power cost times).The parallel part is a totally separate DIY (with off-the-shelf components) for inverter/charger & LiFePO4 batteries; hook the high-load things to it during peak times, and run them off of the batteries. Off-peak, swing them back to the grid, and use the grid to recharge the batteries.I leave it as a homework exercise to decide how to be safe, how much of it you want to DIY, etc.

author: Marco
author_rank: Super Contributor
timestamp: October 29, 2022, 07:00:04 pm
content: Nothing is required here, even by insurance. If I did something especially egregious they could take me to court to argue their case if something goes wrong, but I'm not required to have any electrical work certified or performed by a certified technician. What when I sell the house you ask? Caveat emptor.

author: NiHaoMike
author_rank: Super Contributor
timestamp: October 30, 2022, 12:06:28 am
content: Quote from: 50ShadesOfDirt on October 29, 2022, 06:37:28 pmOne could have a device that plugs into the wall and then the loads plug into the device, basically a UPS with additional functionality. As a plug in device, it would be an appliance rather than part of the building, therefore building codes would not apply. There would be the limitation of not being able to backfeed the building wiring if it's a shared circuit (since that could inject more current into the circuit than the wiring is rated for), but that shouldn't be a problem on a dedicated circuit.If one wants to build a grid tie inverter from scratch for the learning experience, using a low voltage transformer to couple the circuit to the grid would be a workaround as long as the transformer itself is UL listed. The isolated low voltage would make it far safer to tinker with the circuit. It just becomes increasingly impractical at higher power levels.