House battery backup - single vs three phase - Page 1
Forum section: electronics / general

author: Cuban
author_rank: Newbie
timestamp: February 14, 2024, 09:44:28 pm
content: When having battery backup for solar panels in a blackout, what does single vs three phase backup mean?Does it mean that the installer will only connect single phase circuits to operate in a blackout?What about if there is three phase circuit (32 amp), but it only 'ever' draws single phase (single phase mobile car charger)?I want to be able to charge my car in blackout, but want something more than the 15 or 10 amp single phase power points & hence be able to use the 32 amp three phase power point, using a 32 amp single phase mobile charger.

author: ejeffrey
author_rank: Super Contributor
timestamp: February 15, 2024, 02:19:08 am
content: Ask your insraller but I would guess you have to convert the three phase circuit to a single phase circuit (or three separate single phase circuits) normally it's not good to have one phase of a three phase circuit live, true three phase loads would not be happy.

author: Berni
author_rank: Super Contributor
timestamp: February 15, 2024, 06:30:57 am
content: Some houses don't have 3 phase power, so for those having a 3 phase inverter is pointless if they can only use one of the phases.You can also go the other way and install a single phase battery backup in a 3 phase wired house. If all your important loads happen to be on the same phase you could battery backup just that 1 phase. You can also rewire your electrical panel to have all the important loads grouped onto a dedicated input feed, then run only that feed trough the battery backup transfer switch. This way you can avoid having very large loads that are not quite essential in a blackout being backed up (might drain the battery or blow fuses if the inverter is not rated for enough power)Charging a electric car is a bad idea. The car likely has a pretty huge battery pack in it and charges at a pretty high rate, so it means you need a powerful inverter to handle it and unless you have an absolutely massive battery bank in your house, it will drain the emergency power very quickly. The car already has a battery built into it, just keep that battery charged up.For charging up the electric car a regular gas powered generator is a better idea (as ironic as that sounds). Storing hydrocarbon fuel in fuel canisters holds a lot of energy on the cheep. In a more extended blackout you can also use your car to go fill them up at a gas station and bring them home, then use the generator to charge your homes emergency battery back up. You still get a lot of benefit from the houses backup battery as the generator does not need to run all the time to have power, and when it does run to charge batteries, it runs at full load where it is the most efficient. (Keep in mind blackouts offten happen in bad weather, so solar might not be making much)

author: Siwastaja
author_rank: Super Contributor
timestamp: February 15, 2024, 02:41:58 pm
content: House batteries are usually quite small (maybe up to 10-20 kWh), unless you are a billionaire, so normally people want to do the exact opposite, power the house from the EV battery which is larger. If you are frequently having long outages, maybe an ICE car would be a great idea, or maybe a portable genset you can use to power the house and charge the EV.

author: NiHaoMike
author_rank: Super Contributor
timestamp: February 15, 2024, 02:55:49 pm
content: Quote from: Berni on February 15, 2024, 06:30:57 amGasoline is not good for something so rarely used, propane would be better.

author: schmitt trigger
author_rank: Super Contributor
timestamp: February 15, 2024, 03:10:22 pm
content: Or even better, a dual- fuel generator.

author: Cuban
author_rank: Newbie
timestamp: February 15, 2024, 08:27:31 pm
content: Quote from: Berni on February 15, 2024, 06:30:57 amThank you for addressing my post.I now understand that phase 'backup' means the circuits that can operate in a blackout - only the single phase circuits will operate & only those on the same single phase.My system will be 30kw solar panels, 15 kWh battery & will have 'islanding' to continue operating in a grid outage.I have since spoken to the installer & they are willing to connect the 3 phase power point circuit to the solar/battery, as I told them it only uses a single phase for the mobile car charger. It draws 7kWI might put a sign above the power point: DO NOT USE THREE PHASE EQUIPMENT IN A BLACKOUTOn a separate note, I also plan to have a bushfire (wildfire) sprinkler system using an electric pump (not diesel/petrol/gas). This will pump around 400l/min (24,000 litres/hour). As no one makes these stock, I'm in consultation with a couple of companies to custom manufacture. The power draw will be significant & in a severe bushfire the daytime sky turns black - so yes, solar production is very low.

author: nctnico
author_rank: Super Contributor
timestamp: February 15, 2024, 08:41:23 pm
content: Quote from: Cuban on February 15, 2024, 08:27:31 pmForget about the batteries and get a generator. When dealing with wildfires: get a car on gasoline or diesel. Your battery storage only has 60km of range for your electric car at most which is not enough to travel far enough to get out of danger.Also, water won't be enough to put out a wildfire. The air may even become so hot it will ignite your home (https://en.wikipedia.org/wiki/Firestorm). A better way is to plant trees / bushes which slow down a fire. As you seem to have plenty of water, you can install an irrigation system to keep these plants wet. This method is used in the NL to seperate patches of forrest which burn easely for decades.https://www.vintagetreecare.com/fire-resistant-trees-to-create-a-defensible-space

author: Siwastaja
author_rank: Super Contributor
timestamp: February 16, 2024, 07:13:39 am
content: For such large and expensive system, I would get a 3-phase backup inverter so that during outage, I could use whatever loads I want without special procedures. Then again, you want some automation to shut down unnecessary loads to avoid draining the battery excessively fast with unnecessary things. Remember that even if you fully discharge the 15kWh into the EV, and not use it for anything else, it would equal only some 100km / 60mi of range. The EV battery itself is much larger.

author: Berni
author_rank: Super Contributor
timestamp: February 16, 2024, 08:37:32 am
content: Sprinkling the house with water in a wildfire does help a lot, as long as all the outside surfaces are kept wet they will never get above 100°C and so never catch fire. But yeah there are limitations to how much it can handle, so cutting down all trees in a certain radius around the house is a big help. Tho that is not great in terms of providing shade, so in that case it might be easier to sprinkler the trees instead.The 15kWh is not all that much energy if it has to last you for a long period. To put things into perspective most hydrocarbon fuels have a energy density of around 33MJ per liter this is about 9kWh. The typical small internal combustion generator might have an efficiency of about 20% so that is about 1.8 kWh for every liter of fuel. You can easily store and transport 50 liters of fuel with containers so that would give you 90kWh of electrical energy out of the generator.There is no problems having 3 phase outlets. You can wire non essential loads onto a separate electrical panel that is not connected to the inverter transfer switch, so will loose power when the grid goes down. Just depends on how common power outages are in your area, if they happen often then it might be worth spending extra for running 100% of the house from battery, but if it is just for the rare emergency situation then it doesn't really matter if the non essential stuff stops working and you might have to run a extension cord here or there to get some non essential luxuries running.

author: Cuban
author_rank: Newbie
timestamp: February 17, 2024, 12:39:37 am
content: Quote from: nctnico on February 15, 2024, 08:41:23 pmThanks. I am well aware of bushfire/wildfire intensity, as I live in the worst country in the world for it - Australia. Not only that the worst state in Australia - Victoria.Our natives eucalypt trees are described as 'petrol on a stick'.There has been scientific research on the effectiveness of sprinkler systems & their design - I'm pretty up to date with it.