Want  household solar panels to always be the preferred power source - Page 1
Forum section: electronics / general

author: Faringdon
author_rank: Super Contributor
timestamp: August 07, 2021, 02:38:17 pm
content: Hi,I have a 2kW solar farm on my roof. It feeds into a grid tied inverter, which then just dumps the electricity into the mains. Supposing i am using 1kW in the house.How can i be sure that absolutely all of this is being provided by my solar panels?I mean, maybe the electrician messed up the wiring of the solar system...., and the input resistance from the mains supply grid to my household electrical loads is lower...and maybe 500W of the 1kW load is still coming from the mains supply grid?As you know, there is no conveneint switch which switches out the mains supply grid when the entire household loading is within the load supply capability of the solar panels.As you know, electricity from the mains supply grid will cost me more than electricity from my panels.

author: NiHaoMike
author_rank: Super Contributor
timestamp: August 07, 2021, 02:46:16 pm
content: Install a sensor to detect whether you're importing or exporting.

author: Faringdon
author_rank: Super Contributor
timestamp: August 07, 2021, 04:28:36 pm
content: Thanks, thats a good idea.....but would the normal case be that 100% of the load comes from the solar panels when the solar can produce at least that much?...i mean, what are typical percentage supply situations in most domestic households?.....80% solar/20% grid....?

author: AndyC_772
author_rank: Super Contributor
timestamp: August 07, 2021, 04:38:44 pm
content: It's hugely variable, as clouds pass in front of the sun and as heavy loads are switched on and off.If you monitor your solar generation and power usage closely, you'll soon observe that there's no correlation at all between the two. It's one of the biggest problems facing the switchover to renewable energy.If you're using 1kW and your panels are producing 2kW, then you can be certain that the power you're consuming is indeed coming from the panels. You can't be both importing and exporting power through the same cable (ie. your grid connection to the mains) at the same time.We have a nominal 5.6kW system with battery storage, and for the last couple of months, on average, we've produced about the same total energy as we've used. However, we still import power from the grid between ~1am and dawn, and any time a heavy load coincides with a cloud. In the afternoons, after the battery is fully charged, we export the surplus.

author: NiHaoMike
author_rank: Super Contributor
timestamp: August 07, 2021, 04:53:53 pm
content: Quote from: AndyC_772 on August 07, 2021, 04:38:44 pmNot true in the US, you could be exporting on one phase and importing on the other phase.

author: bdunham7
author_rank: Super Contributor
timestamp: August 07, 2021, 04:59:02 pm
content: Quote from: NiHaoMike on August 07, 2021, 04:53:53 pmAlthough perhaps literally true, it hardly matters because your the meter will only give a net reading.

author: NiHaoMike
author_rank: Super Contributor
timestamp: August 07, 2021, 05:26:41 pm
content: Quote from: bdunham7 on August 07, 2021, 04:59:02 pmOne reviewer of the Schneider XW smart inverter took issue with that since its "zero export" mode exports on one phase while importing on another when dealing with an unbalanced load, which may cause certain smart meters to detect reverse power.

author: Faringdon
author_rank: Super Contributor
timestamp: August 07, 2021, 06:12:45 pm
content: QuoteThanks, yes i appreciate what you are saying...but is there ever a case whereby the solar panels "would be capable" of supplying 1kW...but they do not...and all the energy comes from the grid? (eg due to the wiring meaning the impedance seen from the grid to the loads is less than the impedance seen from the house's inverter to the loads?)Also, if its a bright sunny day and loads of people have solar in your neighbourhood, then may be the mains level gets high such that the GT inverter in your house wont start pumping power into the mains......and so even though your panels could supply the entire 1kw...they dont...and the 1kw unfortunately comes from the grid (costing you more)...can this happen?If its a really bright sunny day and loads of the neighbourhood have solar, then whose GT inverter gets priority to start working?...and whose GT inverter just wont activate because the mains level is too high due to your neighbours' GT inverter's supplying the power to the grid...(for which you pay a high rate for)I am surprised that people with battery stacks dont have an automatic switch on their mains grid electricity connection so that they can switch off the grid to their house when their battery is full...and then just power their house from their battery stack..............and then their inverter would not need the faff of grid tying?...Also, if you have a 1kW solar/inverter system (GT inverter), and your many close neighbours all have 7kW solar/inverter systems, then surely your inverter never gets to activate? (and you dont make/save any money from your solar panels)

author: bdunham7
author_rank: Super Contributor
timestamp: August 07, 2021, 06:27:22 pm
content: Quote from: NiHaoMike on August 07, 2021, 05:26:41 pmIs that observed or hypothetical? It 'could' report such a situation, but I know of none that do. In those jurisdictions that require you to sell all of your solar power at a feed-in tariff and then buy all your power at a retail rate, they use two meters. If you live in such a place and are trying to load-shave on the sly, then I suppose this could be an issue if the power company has programmed its meters to catch you. I those cases I think you can set up the Schneider inverters to work differently (isolated loads) if you use batteries, but you can't exactly zero out the usage.