Buck converters as charge controllers

[stereotypo]

I would like to be able to harvest solar power by using as much of it as it is produced, e. g., running appliances like water heater, washer/dryer, refrigerator, etc., while the sun is up, with minimal battery storage, only in case the grid goes down. My question is, Can I tap dc to dc buck converters into the lines between the panels and the micro inverters and parallel them to a small battery storage and run an inverter from that? I realize that I would have to have my demand always less than the supply.

[chrisski]

I have not found for what you’re asking for.

I posted something similar a few months ago. I found how I could use a buck converter to run 12 Volt, 5 amp or 10 amp appliances directly off charge controllers without a battery, but nothing stronger than that. I found a company that made an inverter to run high wattage appliances off solar panels without batteries a few years ago, but they are not in business.

As best as I could tell, this wouldn’t work On large scale because if you don’t have enough batteries, you have way too many amps going into the battery and risk frying it, the electronics in some of the appliances won’t do well with being turned off many times a day as clouds go over, and these buck converters are wasteful of energy which I think means they bleed the unused energy off in heat.

I thought you could use a zener diode, but there’s no such thing as a 2000 watt zener diode to run your AC off. A DC rectifier could be built for a high enough wattage that could provide energy, but I’m not that smart and these are 2000 watt 12 volt DC rectifiers are not off the shelf technology. I really think there needs to be a balanced battery bank so that if its too small, then when the suns out, the battery is overcharged, and if it gets too dark, electricity is being pulled from the battery so quickly that it could harm the battery, shorten the battery life, or at the very least the 100 ah battery would not be able to power the 3000 watt inverter without the inverter faulting out.

I think it would be a great idea to run a 1700 watt electric kettle to boil water with off many solar panels without a battery, but that is not available commercially and I might be the only person in the world willing to set up 25 solar panels with this DC rectifier And no batteries to boil my water.

[bob-n]

stereotypo,

Your idea is theoretically possible but I don't know of one on the market.

Are you planning to build this buck converter? If you are planning to build it, then you can do whatever you like. You need a control method so the duty cycle is appropriate to split energy between the microinverter and the charger. You may want to sense energy going to the microinverter and use that in your control loop. You could monitor panel voltage to try to estimate energy available, but it will vary with the load on the microinverter.

In summary, it is an interesting challenge, but difficult.

[PNPmacnab]

Why only in case the grid goes down. Sooner or later every utility will start paying you not much at all for grid dump. I have this simple theory. If you have to ask, you probably can't. I do all of those except the dryer, but I know someone who runs the dryer heater element with PV. I run a large LG clothes washer off panels without a battery. Hot water of course directly off PV. I only have a car battery for running the entire house, just for surge currents. You have to be fairly technical to do this. If California keeps going the way they are there may be products in the future.

[chrisski]

Why only in case the grid goes down. Sooner or later every utility will start paying you not much at all for grid dump. I have this simple theory. If you have to ask, you probably can't. I do all of those except the dryer, but I know someone who runs the dryer heater element with PV. I run a large LG clothes washer off panels without a battery. Hot water of course directly off PV. I only have a car battery for running the entire house, just for surge currents. You have to be fairly technical to do this. If California keeps going the way they are there may be products in the future.

I'd like to know how you run a washer only off PV, if it is not a grid tied PV system. Reason I'm asking for not grid tied for me is because in my area, grid tied systems can't function in case of a power outage to prevent the 15KW solar panel system on the roof from going back into the grid when the power is out and electrocuting a lineman. So for me, this needs to operate completely separate from the grid.

For me the reason is a lot like what you're saying with the direction California is going and the more frequent power outages for customers in certain areas.

Running an electric washer off PV with no batteries not connected to the grid is basically what I'm looking for.