looking for a way to connect a pv grid, the main grid, and the house wiring. - Page 1
Forum section: electronics / projects

author: kripton2035
author_rank: Super Contributor
timestamp: November 24, 2018, 05:12:58 pm
content: let's assume I have a 1kW PV array, and a grid subscription of 6kW.I'm looking for a device that would switch between the PV or the grid to the house wiringthe PV would be prioritary, so for all low power devices with less than a total 1kW the PV would feed.if I switch a more hungry device, the device would switch to the grid.there must be no interrupt time during the switch.bonus: the device could still feed the 1kW from the PV plus the kW needed from the grid when let's say a 2kW device comes on, the PV feeds 1kW and the grid 1kW.thanks for any hint.

author: kripton2035
author_rank: Super Contributor
timestamp: November 24, 2018, 05:14:49 pm
content: more bonus: the device should charge an expandable array of batteries.

author: Monkeh
author_rank: Super Contributor
timestamp: November 24, 2018, 05:18:58 pm
content: Your magic search terms are: Grid-tie inverter and battery backup.

author: station240
author_rank: Unknown
timestamp: November 26, 2018, 08:36:28 am
content: It's called a hybrid inverter.Takes say 48V input (batteries), PV input and AC input (main grid).Output is AC.Batteries can be charged by any of the 3 inputs.

author: kripton2035
author_rank: Super Contributor
timestamp: November 26, 2018, 05:26:45 pm
content: will it work with a very small battery (as it is the most expensive part of the system)I have very rarely power outage, I only want to use PV when there is sun or light, and grid otherwise.for a 5KWh system, a simple PV with controller is around $7000, and with the batteries it comes to some $15000...I could buy the PV+controller and small battery first, and then eventually later buy some batteries to have some spare energy.

author: electrodacus
author_rank: Super Contributor
timestamp: November 26, 2018, 06:46:17 pm
content: Quote from: kripton2035 on November 26, 2018, 05:26:45 pmYou do not need to ad any battery (that will not be economical). What you need is a grid connected PV array all of what you want will be done automatically.As long as the house needs more than PV array can provide it will use all the PV energy and take the difference from grid.Adding a battery to a grid connected house is just wasting money.

author: kripton2035
author_rank: Super Contributor
timestamp: November 26, 2018, 07:44:05 pm
content: I want a small battery to prevent power cut even some seconds when you switch prom PV to grid or grid to PV .isn't it necessary ?

author: Siwastaja
author_rank: Super Contributor
timestamp: November 26, 2018, 07:55:19 pm
content: Battery doesn't make sense for a second-scale energy storage. Due to the nature batteries deliver and accept currents (fairly low (dis)charge rates as a proportion to their capacity), you would need to design it to supply at least 10 minutes to half an hour, to satisfy the current spec; if you onlyneeda second, the rest is excess capacity.Supercapacitors are the choice for a few seconds, to about half a minute tops. In this range, they will be cheaper (but not much smaller) than buying a battery pack which is 100 times bigger capacity than needed.Traditional aluminium electrolytics may be the most economical below about one second, instead of supercaps.What you need is a grid-tie inverter. You are not going to be able to do it yourself, or come up with any really good alternative. Saving a bit by getting a traditional non-grid-tie inverter, then spending extra on a complex and potentially dangerous contactor system, then completely wastingallyour produced power (say 1000W) when the sun happens to be shining while you need 1001W, makes no sense.

author: electrodacus
author_rank: Super Contributor
timestamp: November 26, 2018, 08:33:02 pm
content: Quote from: kripton2035 on November 26, 2018, 07:44:05 pmA grid connected PV array consist of PV panels and a grid tie inverter. That inverter has just PV panels on the input and output is in parallel with the grid and synchronized with the grid.If your house uses 2000W and PV array generates 1000W then all those 1000W will be provided to the house and the difference of 1000W will come from the grid. No logic is needed to do that.Of course you need approval from your grid company to connect any source to the grid.