Run appliances during the day, and switch to grid at night?

[twilliamsen]

It seems focus has been lost, and I will just unplug from the inverter back into the wall socket. All I wanted to do was emulate that action either on a time or triggered by a voltage drop.

[sensij]

Then buy a relay, as jflorey2 suggested.

[inetdog]

It seems focus has been lost, and I will just unplug from the inverter back into the wall socket. All I wanted to do was emulate that action either on a time or triggered by a voltage drop.

Probably the best choice for now.
It would not be too hard to get a standard time clock of some sort (of the kind used to turn plug-in lamps on when you are on vacation) and use the output of that to control a double pole/ double throw relay (DPDT, or Two Pole Form C contacts) to actually control the loads.
The most critical thing you need to do is use a single relay to make the transfer instead of opening one and closing another. That would not be a safe transfer operation and could sort your inverter to the grid, smoking it, if one of the relays failed.

[twilliamsen]

I think it is real clear what the OP wants.

He has equipment for a solar/battery system and wants to run his appliances on it during the day. He then wants to run those same appliances on the grid during the night or when the sun isn't shining.

Now what the OP doesn't understand is that the cost of electricity to run his appliances off the solar/battery system is probably 5 to 10 times the cost of running them off the grid during the daytime.

It is nothing more than what most people have been led to believe but really do no understand what the costs of an "off grid" system is. They think because the sun energy is "free" it will be less expensive to run their loads from it instead of the grid. That may be true for a "grid tie" system but is not true if you use a battery or "off grid" system.

My thoughts for the OP. If you do not care what it costs you to run your appliances from the solar/battery system during the daytime then you need to find a safe and electrical approved equipment to totally isolate your appliances from the grid when they are running from a battery power inverter. If you use something that is not UL listed you can run into issues with back feeding the grid or causing an electrical issue.

This is very true statement(s) but I need to know what is needed to reach my objective before splurging on thousands of dollars for $10/mo savings. If I need to add panels, batteries, expensive switches and inverters, etc. that is all part of the project costs. What if I just switch between solar/battery every other day? These are are questions that I am trying to weigh. All I need to know what is out there and what would you do. I have no intentions of hard wiring to the grid.

So to clarify, what would you do for as minimal amount of money to run a 24 cu. ft fridge and a 5cu ft chest freezer off of solar power?

Both of these appliances are in the basement and will be run at a constant temp as well as constant ambient temp.

One little fact, this initially started as a project for my 8 year old as she is learning about electricity and renewable resources.

[SunEagle]

This is very true statement(s) but I need to know what is needed to reach my objective before splurging on thousands of dollars for $10/mo savings. If I need to add panels, batteries, expensive switches and inverters, etc. that is all part of the project costs. What if I just switch between solar/battery every other day? These are are questions that I am trying to weigh. All I need to know what is out there and what would you do. I have no intentions of hard wiring to the grid.

So to clarify, what would you do for as minimal amount of money to run a 24 cu. ft fridge and a 5cu ft chest freezer off of solar power?

Both of these appliances are in the basement and will be run at a constant temp as well as constant ambient temp.

One little fact, this initially started as a project for my 8 year old as she is learning about electricity and renewable resources.

The cheapest way would be to plug and unplug the appliances between the battery inverter and grid power.

The next low expensive way would be to use a relay that will detect the battery voltage going down to a specific level and then switch over to the grid power. The problem is that you have not provided us with the current draw of either the fridge and freezer. That amp draw of your loads will determine the amp rating on the relay or probably in this case a Contactor that can "make & break" higher current flows.

Something else to figure would be a time delay between when you power down the fridge / freezer and then power them back up. The compressor motors inside those appliances do not like to start "under" a loaded condition so the compressor needs to equalize first before it is started again.

Oh. Last thing to think about. How did you determine you would save $10/month using a solar/battery system?

At this point you are already in the hole and will never recoup the money you spent on the batteries.

[ButchDeal]

So to clarify, what would you do for as minimal amount of money to run a 24 cu. ft fridge and a 5cu ft chest freezer off of solar power?

I would do a full self install of a grid tie system with permit, and interconnect.

BTW, I did a little more than that actually when I did mine mostly to get backup ability for the well pump, but for yours you could easily just do a small system of 1kw with enphase and be done with it. Skip the batteries. Teach your daughter about permits, interconnects, paperwork, electricity, and solar all in one project.

or you could get a loan and do a little more...

[twilliamsen]

The cheapest way would be to plug and unplug the appliances between the battery inverter and grid power.

The next low expensive way would be to use a relay that will detect the battery voltage going down to a specific level and then switch over to the grid power. The problem is that you have not provided us with the current draw of either the fridge and freezer. That amp draw of your loads will determine the amp rating on the relay or probably in this case a Contactor that can "make & break" higher current flows.

Something else to figure would be a time delay between when you power down the fridge / freezer and then power them back up. The compressor motors inside those appliances do not like to start "under" a loaded condition so the compressor needs to equalize first before it is started again.

Oh. Last thing to think about. How did you determine you would save $10/month using a solar/battery system?

At this point you are already in the hole and will never recoup the money you spent on the batteries.

Thanks... The fridge is rated at 11.5 amps, it seems that is not normal operating amp rating, but probably start up, the freezer was a lot less, at 5 amps.

The savings is rhetorical in stating minimal savings for maximum costs; i.e. ****ty ROI

[SunEagle]

Thanks... The fridge is rated at 11.5 amps, it seems that is not normal operating amp rating, but probably start up, the freezer was a lot less, at 5 amps.

The savings is rhetorical in stating minimal savings for maximum costs; i.e. ****ty ROI

I would look at your local electrical shop for a contactor that has two pairs of 15 to 20 amp contacts rated for your AC power voltage.

The other item would be a low voltage control that will sense a low battery voltage and make the contactor switch between the inverter output and the grid power.

[jflorey2]

This is very true statement(s) but I need to know what is needed to reach my objective before splurging on thousands of dollars for $10/mo savings.

What we are saying is that you are looking at two paths right now:
1) A path that will save you money in the long run (grid tie) vs.
2) A path that will cost you money in the long run (i.e. a battery backed system.)

Now, if you are OK spending the money for fun, no worries. But if your attitude is "I have some stuff and I want to make sure I use it to save me money" then you are going to be sorely disappointed.

If I need to add panels, batteries, expensive switches and inverters, etc. that is all part of the project costs.

If you are planning to spend money then it would be wisest to choose grid tie. Again, if you are OK with the expense of batteries, then that's not an issue.

So to clarify, what would you do for as minimal amount of money to run a 24 cu. ft fridge and a 5cu ft chest freezer off of solar power?

A 12V 20-30A DPDT relay. Specifically a T92S11D22-12 or equivalent.
A small 12V panel (5 watts should do it)
Some parts from Home Depot (outlets, box, power cord.)

[Sunking]

Why do you prefer to pay $1/Kwh for batteries, over 10 to 15 cents for the utility? Anything you take off-grid is going to cost you 5 to 10 times more than buying the power for the rest of your life. So if you intend to throw money away, have at it. But if you think you will save money is plain foolish.

[sensij]

One little fact, this initially started as a project for my 8 year old as she is learning about electricity and renewable resources.

This is really admirable. Not many 8 year olds get an opportunity to see renewable energy in practice. Unfortunately, what renewable energy *is* and *is not* often get misrepresented in the media, and your project here may be one of the most effective ways to convey the truth. Can you power a refrigerator with solar panels and a battery? Yes! Can you do it for less money than it would cost to power it from the grid? No. Are the long term costs of fossil fuels high enough that we should be willing to pay the premium for renewable energy now? Maybe.

Seems like as good a place to start as any.

[DanKegel]

This is really admirable. Not many 8 year olds get an opportunity to see renewable energy in practice. Unfortunately, what renewable energy *is* and *is not* often get misrepresented in the media, and your project here may be one of the most effective ways to convey the truth. Can you power a refrigerator with solar panels and a battery? Yes! Can you do it for less money than it would cost to power it from the grid? No. Are the long term costs of fossil fuels high enough that we should be willing to pay the premium for renewable energy now? Maybe.

Showing an eight-year-old how to measure energy usage might be a good start. A Kill-a-watt meter will run you $20; some public libraries even have ones you can check out for free.