Is this plan a good idea

[dablack]

Ok guys. I'm still learning about solar. I would like to use solar for a long term food storage solution. I'm building my house right now and here is the plan. I'm going to put an extra plug behind the two fridges and the deep freeze. These "extra" plugs will go to a seperate breaker box that will eventually be powered by solar. I'm thinking to size it correctly, I will need to know how much power each of those things will use in a day. I believe there is a plug in device that I can use to get an actual reading. Then with that info I can figure out how many watts of panels I will need as well as battery capacity.

1. To save on battery wear, can't I just flip the breaker off at night. If I do it before I go to bed and then turn the breaker back on when the sun is shining, as long as the doors aren't openned too many times, the stuff in the fridges and freezer should stay very cool/frozen. Basically, they wouldn't have power for maybe 12 hours.

2. Just a very rough estimate on cost. From another older post I've figured out that to split the difference between summer and winter that I should have the panels mounted at 30 degrees. I'm putting on a 7/12 roof so that will give me that. My house faces dirrectly solar south and is a two story. I shouldn't have much of a problem with shading. I have NO idea how much a typical fridge or deep freezer uses. These are fridges and freezer that are 2008 or newer. What is your best guess on cost with me doing the install? I'm in east TX.

thoughts?

thanks
Austin

[ecomodded]

My 2007 fridge uses 135 to 120 watts varied which could easily be powered by solar and batteries full time with no need for grid power, I would do it this way and skip using the grid to power my fridge or freezer.
There has be a website or program you can use too calculated your needed solar panel area and battery storage requirements, your yearly sunny days will play a crucial part in sizing / pricing a system.

[dablack]

Sorry if this is a dumb question, but is that per hour average over a day?

I'm quessing that w two fridges and a freezer I'm looking at around 175 watts per hour but I'm going to have to wait and measure it.

I looked up the hours of sun and somewhere I read I have the equivalent to 4-5 hours of sun a day.

So, if I use 175 watts per hour for my refrigeration, that is 4.2kW/day.

So to supply that much power (or more), and assuming I get about 4 hours of usable sun a day, I need about 1000 watts? Is that right?

Am I anywhere close to calculating this correctly?

[philb]

Instead of putting in separate plugs, just split the circuits you want to power at the breaker box. Any electrician should be able to do that. That way you've saved a lot of expensive copper wire. You can use a transfer switch like this one.

There are many ways you could do this. Grid tie PV is probably the easiest way to go.

I have a separate system with solar panels, charge controller, inverter and the transfer switch because I don't want to deal with the electric company and their rules and regs. They will allow me to put electricity into the grid until my bill equals zero. Any electricity in excess, they won't pay me for it. I said no thanks!
You can also get 30% of the system costs on your federal taxes. Texas also has some incentives.

As soon as I learn how to post, I have a story about my system.

[NiHaoMike]

You can use a small solar panel to switch a small relay that enables and disables the inverter via the remote control terminals, with some manual switches to override it.

[philb]

you might check out this site. TheBackShed.com - System Design It should answer a few more questions.

[dablack]

Thanks guys. I'm the electrician, and I know how to wire up most things but two different sources of power is out of my comfort zone right now. I will keep researching and check out that link.
What I had in my head was two breaker boxes side by side. I would have grid powering one breaker box and solar powering the other. The only things that would have a solar plug and a grid plug would be the two fridges and the deep freeze. Once I got my solar system up and running, I would plug into the solar plugs for those three items. If I found that I didn't have enough batteries or enough panels, I could easily just plug them back into grid plugs until I got more panels and batteries. Then once those three things are running well, I can add more panels and batteries and then slowly move more circuits over from the grid breaker box to the solar breaker box.

thanks
Austin

[philb]

As your batteries age, they won't store as much power like when they were new. That's also the heart of your system and its downfall.

Check out these sites:
MidNite Solar Inc. Renewable Energy System Electrical Components and E-Panels
Solar Electric Power Discussion Forum by Northern Arizona Wind & Sun
BuildItSolar: Solar energy projects for Do It Yourselfers to save money and reduce pollution
Fieldlines.com: The Otherpower discussion board - Index

Lots of information.

[ecomodded]

Originally Posted by dablack

Sorry if this is a dumb question, but is that per hour average over a day?

I'm quessing that w two fridges and a freezer I'm looking at around 175 watts per hour but I'm going to have to wait and measure it.

I looked up the hours of sun and somewhere I read I have the equivalent to 4-5 hours of sun a day.

So, if I use 175 watts per hour for my refrigeration, that is 4.2kW/day.

So to supply that much power (or more), and assuming I get about 4 hours of usable sun a day, I need about 1000 watts? Is that right?

Am I anywhere close to calculating this correctly?

Your calculations are off, if your refrigeration is consuming about 135w each (aprox) that would be for three fridges, around 400w @ 3-5 minutes per hour , on average.
You need to find the yearly consumption of your fridge / freezers then size a solar system to support it, according to the needed sunlight hours.

[ecomodded]

You know, your pretty close with your guess of a 1000w in panels, it"sounds" about right with my guesstimate as well.. My fridge runs every couple of hours for 10-15 minutes but I live alone, I would double my earlier run time estimate after thinking more about it.. so off hand I would factor in 15 minutes of run time every hour, which is 5 3/4 hours of run time per 24hrs. at how many watts combined you are using.

edit to add:

in a perfect world , if you get your 4 hours of sunlight equivalent per day x 1000w pv panels and a drain of 400w every 15 min. you would fail by about 25% to make enough power but @ 1500w you will make it with 25% to spare - My seat of the pants math may well be flawed .. apply with caution !