Mixing mains.  Grid vs. Off grid. - Page 1
Forum section: electronics / general

author: paulca
author_rank: Super Contributor
timestamp: March 05, 2023, 11:08:56 pm
content: This is surprisingly hard to google. 99% of the answers are "Yes! Of course you can!", but not actually what I'm asking.Say I have my normal grid provided mains and I have an appliance or two running of a battery and a pure sine invertor. Fine right?Obvious any mistakes with "dual power" would cause, hopefully blown trips on both and not sparks and flames.If both invertor (and thus battery) are ground referenced to the same local ground (house earth), it should be fine for them to, say share signal grounds and floating DC connections. Could you power, say some PC monitors, PCs etc off an invertor while other equipment they are connected to are being powered by grid mains?It sounds dangerous. Can it be done? Surely this just becomes the same problem as multi-phase power in buildings, you just have to be careful they don't mix, right?I can obviously go grid tie invertor. But I don't want to connect the solar system to the grid. I'd rather have independant power supply. Grid tie invertor will cut out the instant the grid mains goes down. Partly for safety, but partly I don't think they function at all without a wave to push against/with.

author: uer166
author_rank: Super Contributor
timestamp: March 05, 2023, 11:25:13 pm
content: Nothing wrong in having a separate islanded "grid" sharing the PE/Ground of the real mains grid, as long as the phases/live conductors are 100% isolated.The issues you might run into are to do with building code if you ever attempt to run your own islanded grid over the building wiring. If it's all localized and using extension cords/IEC cables, there shouldn't be issues.

author: pqass
author_rank: Super Contributor
timestamp: March 06, 2023, 01:12:22 am
content: No issue with two devices (on isolated power sources) communicating since the connecting signal cable (rs232/ethernet/usb/hdmi/audio/whatever) carries a common return for all (single-ended) signals or each signal has its own complement (differential) return.So connecting them to the same PE isn't necessary for them to communicate, however, it is necessary for user safety if your connected device has a metal case.Were you planning to use the same house wiring (incl. breakers) for both grid and solar/battery sources? Or sharing the same panel with both? Typically, there's a separate sub-panel for high-priority circuits. If so, you're going to need an electrician or your insurer will walk away from the smoldering ruins.Instead of grid-tied, you can have a transfer switch (or interlock kit) selecting between grid or solar/battery/generator sources.

author: paulca
author_rank: Super Contributor
timestamp: March 07, 2023, 01:05:10 pm
content: How does this look?The 2 sockets. One may actually just be the upstairs 6mm^2 feed wire currently used for DC directly wired into the consumer unit. The second socket is for the garage beside the solar setup.Panels output 330W. The 8S1P pack, the wiring and the charge controller can handle 40A at ~30V, the invertor "claims" to handle more, but I overrated it. I'm aiming for 1kW max load on the invertor. 6 amp circuit fuses are quite rare considering a 13Amp plug socket, but I really don't want anything trying to pull more than 1kW, 2 absolute tops.There is also an earth lug on the charge controller. Earthing it will probably earth the panel - but that's fine.

author: kripton2035
author_rank: Super Contributor
timestamp: March 07, 2023, 01:43:50 pm
content: you should buy an hybrid inverter. it will balance the mains grid, the PV, the batteries, and the house charge the way you wantyou can set up priorities, from any source, use only the batteries, etcand it will not cut the power if the grid is down...

author: paulca
author_rank: Super Contributor
timestamp: March 07, 2023, 04:31:50 pm
content: Yes, I looked at hybrid invertors. The really, really sad thing is, most of them power off when the grid power goes down.Other than that,- they are all aimed and priced for full roof solar installs.- they will require a certified solar professional to install- they will require a micro-gen certificate from the electric company w/ inspection at my costWhen you add a certified transfer disconnect switch, you are looking at £2000, just for the hybrid invertor install + expenses on inspections etc. They don't make it impractical, but they do make it impractical at such a small scale.I have a few "5 year" financing options opening next year and it's a race between an actual official grid-tie hybrid solar system and reglazing the house. Until then I have now more solar power than I can use charging my phone and running some LED lights!

author: gf
author_rank: Super Contributor
timestamp: March 07, 2023, 04:47:24 pm
content: I'm rather careful with the term "hybrid", since it is not used consistently by different manufacturers.Usually they are multi-function devices, integrating an AC charger, inverter, transfer switch and a solar charger in a single box.Some of them can run grid-tied with fallback to off-grid operation upon grid failure. These models are usually able to power the load from the grid and from the inverter simultaneously. Others models just include an off-grid inverter with transfer switch, i.e. the output is either powered from the grid or from the inverter, but not from both simultaenously. There also exist dual-conversion models, which generally turn grid power to DC, and then back to AC with the inverter.

author: paulca
author_rank: Super Contributor
timestamp: March 07, 2023, 05:14:15 pm
content: For off grid you can get away with so much stuff. For example my old 100Ah lead acid solar battery made it till the start of december this year before cutting out in daily use. I had thing I wanted to use running off it, like my phone charger and my headphone amp. What to do. I took a bench PSU down to the garage and hooked it up to the lead acid battery set to 5Amps, 12V and left it there until after christmas when I realised it was wasting a load of power, fully charged the lead acid and put the PSU away.It's solar with mains backup. I was even going to implement an automated way to click in the charger when needed with a smart switch.

author: pqass
author_rank: Super Contributor
timestamp: March 07, 2023, 06:51:18 pm
content: Four methods to integrate two power sources (substitute the generator source with the output of your solar inverter):https://www.electricaltechnology.org/2013/11/how-to-connect-portable-generator-to-home-supply.html

author: kripton2035
author_rank: Super Contributor
timestamp: March 07, 2023, 07:13:18 pm
content: Quote from: pqass on March 07, 2023, 06:51:18 pmthere are so many ads on this page that you can't extract the real informations ...

author: pqass
author_rank: Super Contributor
timestamp: March 07, 2023, 08:07:13 pm
content: Quote from: kripton2035 on March 07, 2023, 07:13:18 pmReally?The ads are on the right and you don't have to go past the first article (tags, related articles, and comments links).Unfortunately, I can't attach it here since the printed PDF is greater than 4M.I suggest you issue File->Print; then Print to PDF, printing only the first 25 pages.My preference would be to separate high-priority circuits (furnace, fridge, emerg. lighting, comms) into their own subpanel then using a transfer switch or interlock to choose the source (grid or inverter). You can't really have two sources [simultaneously operating] in one panel; all circuits can only be switched to one source.

author: paulca
author_rank: Super Contributor
timestamp: March 07, 2023, 08:16:55 pm
content: Maybe a little OTT, all I hope to do is make a dent in this:Probably the just nes bus power feed from the invertor, when I manual choose to power it that way. I can just change the plug over between two sockets.

author: paulca
author_rank: Super Contributor
timestamp: March 07, 2023, 08:25:01 pm
content: .. and/or... a solar powered freezer.It's hard to find their instantaneous wattage but the average consumption is in the order of a few dozen kWh per year. You can work that out on your won in watt years.I figure a periodic load of maybe 200-300W. Short bursts of 5-10 minutes of the compressor at 200W + (maybe) 500W pulses of de-ice rails. A few dozen kWh per year has to mean once properly down to temp and left alone, closed, it shouldn't need to run the compressor that often, maybe a 1% duty cycle.If the fan and the shit combine more than 2020... I'm not prepping, but electricity is a life blood.

author: Red Squirrel
author_rank: Super Contributor
timestamp: March 15, 2023, 09:18:31 am
content: I basically have my house setup this way. My shed has a solar setup with a 3kw inverter feeding a 40a panel. There is a 40a feed to another panel inside the house. I have a few 15a circuits from that panel going to outlets in a few locations which I labeled as solar. I plan to expand this further as I'd like to cover the kitchen and server room, as well as furnace. My end goal is to have mini transfer switches that can switch loads between hydro and solar based on power availability. Once I design these I'll probably get PCBs made professionally and put it in a nice project box. It will have 2 power inputs and one output, indicator lights, a switch to manually transfer, and dry contacts so it can be controlled from another automation source.For grounding, I need to figure out what is the best approach but I imagine I should ground the solar setup to earth ground and then tie it with house. Right now it's floating.If sharing loads I would be careful that any communication cables between the loads (ex: HDMI) are isolated by nature. Ex: if PC is on hydro and monitor is on solar and grounds are different. I know ethernet has isolation as part of the spec but not sure about VGA, HDMI, etc.

author: Ice-Tea
author_rank: Super Contributor
timestamp: March 15, 2023, 09:28:30 am
content: If you share PE, isn't this essentially like a 3(2)-phase system? Don't see the problem...Re: hybrid inverters. They are required to kill themselves when the main mover goes away and for good reason. You don't want a grid fault, send out a maintenance crew and find the wires live even though the substation is switched off. Some/many/mine allow it to function as a UPS but only when installed with a hard switch that will disconnect the grid first.

author: kripton2035
author_rank: Super Contributor
timestamp: March 15, 2023, 01:01:05 pm
content: for me "hybrid" inverters are the one that do not cut the power when the grid is down, but do not send anything to the grid.so they are safe for grid maintenance crews.on an hybrid inverter you enter the grid, the solar panels, eventually a generator (wind or fuel), and it outpu!ts the availabler power to batteries or house.examples : wks evo circle, multisolar II, solax x1-x3 ...

author: Ice-Tea
author_rank: Super Contributor
timestamp: March 15, 2023, 01:33:31 pm
content: You still have to switchover somehow. Manual or auto.

author: kripton2035
author_rank: Super Contributor
timestamp: March 15, 2023, 03:02:22 pm
content: on the wks evo circle for example it's fully automatic.you define priority for solar, for battery, or for gridthe inverter does the rest automatically.you have manual bypass if you want, but no need to manually cut the grid in case of a power down.

author: NiHaoMike
author_rank: Super Contributor
timestamp: March 16, 2023, 04:39:02 am
content: Ideally, you'll want a "zero export" inverter with external sensors so that only the backup loads need to be rewired. Sol-Ark is one of the better known ones (pretty expensive) that has both zero export with external sensors and backup capability, but I think there now are a few other manufacturers offering that.

author: paulca
author_rank: Super Contributor
timestamp: March 27, 2023, 07:20:43 pm
content: As per other threads, been around the houses a few times and ended up with...Short story.Motorhomegarage invertor system. Explains it better as most people understand that kind of system.The grid is "Shore power" or "Generator power" or either/both depending on unit.Nobody needs to know any better. I'll promise to earth the panels when I install them on the roof. The "grid" will be a 13Amp fused plug.Longer story:Earthing IS covered under the regulations, even for "load only" grid tie/islands.It covers both the case of an exported earth (or neutral) becoming live and the case where you, as the island, lose the grid protective earth... or it becomes un-usable due to fault.After some back and forth with a helpful gentleman, I agreed to invest in a local spark to make that determination. It depends on your particular earthing scheme and the utilities as to whether you would or could export an earth or neutral AND if usually requires an earth rod is installed in addition to the utility earth to protect in both "grid earth fault" or "island earth fault" ... that both can terminate in a low ohm earth rod locally and "not export" or... import a ground fault from the grid! Didn't think of that.EDIT: There does exist an option. If the inverter is designed to run a single AC outlet and a single appliance and there is not requirement for those appliances to be earthed (2 core devices), then it's "fair game", under the stipulation that you can never have more than one device on that extension as it must remain completely isolated. No PE at all. Sounds DAF! No thanks. At the same time I don't want to create a stupid ass E-E or N-E fault with a few 100mA of E-E/N-E current between island and grid via an audio cable because the each have different "ground reference".As to actual RVs etc.? I don't know... when you hook up to shore power are you also required to ground the vehicle chassis in case of a shore power earth fault? What about boats? Does the salt water constitute enough of an earth?The schematic is WRONG! The island earth and mains earth should be bonded at the main earth terminal at the house consumer unit! (I'll leave that up to the spark). BOTH however need to exist independently.

author: Kim Christensen
author_rank: Super Contributor
timestamp: March 27, 2023, 07:55:48 pm
content: Quote from: paulca on March 07, 2023, 08:25:01 pmEver thought about an absorption freezer, but instead of powering it with propane, using concentrated sunlight?