Is there such a device that switches between solar and Wall outlet Automatically?

hmong2017 · January 2022

I will be setting up a small Solar Offgrid System for a Pond. But because of the high value to put into building it, I decided to go small.
My Pond lack Oxygen for my fishes in Summer. (as it is approaching fast) and it depend on a Water Pump to produce oxygen into the pond.
This Pump needs to be on 24 Hours, 7 days a week.

I live in California, and because of all the wildfires, our electricity is very expensive at around 40 cent per kWh.
This pump alone can cost me aproximately about $50-$70 or more a month. I would like to reduce this cost as MUCH as possible.

I just got a contractor to estimate to burry a cable from my Well to the pond. That will run 1026 Feet all the way to my pond.
He will install a Breaker Box with an outlet pole.

Now, I would like to be able to use my offgrid Solar system with this Outlet. I want a Device that is capable of Switching from full Solar when Solar is able to supply power, and automatically switches to Wall outlet when solar is low. Switches back to solar when solar is ready to use.

I hope such device exist. If there is, Please let me know the brand name or what this device is called. Thank you.

Photowhit · January 2022

Really hard to beat the grid.

I think the easiest would be to have an inverter which would switch back to the grid when the batteries reach a certain point. Understand this can leave your batteries low going into the overnight hours and use up the life span of your batteries.

BB. · January 2022

First--Wire AWG from pole box to pond. 1,026 Feet, assume 120 VAC for first pass. 250 Watts with 3% max voltage drop:

250 Watts / 120 VAC = 2.1 Amps nominal

Using a simple voltage drop calculator:

https://www.calculator.net/voltage-drop-calculator.html?necmaterial=copper&necwiresize=3&necconduit=pvc&necpf=1&material=copper&wiresize=0.4066&resistance=1.2&resistanceunit=okm&voltage=120&phase=ac&noofconductor=1&distance=1026&distanceunit=feet&amperes=2.1&x=31&y=38&ctype=nec

8 AWG @ 2.1 amps @ 1,026 feet @ 120 VAC:
Voltage drop: 3.36
Voltage drop percentage: 2.80%
Voltage at the end: 116.64

If you switch to 240 VAC and 1.05 Amps, you can use:
https://www.calculator.net/voltage-drop-calculator.html?necmaterial=copper&necwiresize=0&necconduit=pvc&necpf=1&material=copper&wiresize=0.4066&resistance=1.2&resistanceunit=okm&voltage=240&phase=ac&noofconductor=1&distance=1026&distanceunit=feet&amperes=1.05&x=64&y=20&ctype=nec

14 AWG @ 1.05 Amps @ 1,026 Feet @ 240 VAC:
Voltage drop: 6.70
Voltage drop percentage: 2.79%
Voltage at the end: 233.3

You can see here that just a simple change from 120 to 240 VAC version of pump--And you can use much cheaper cable to run the "same" 250 Watt load.

Next question... In general, the best bet is to go with Grid Tied (or Utility Interactive) solar power system. All you need are some solar panels, a GT Inverter, and wire that inverter to your home's (or other utility connection point).

This is the cheapest and more "reliable/least maintenance" solar power solution. You usually have to get permit(s), utility approval, and possibly add the utility as named insured to your home owner's liability policy.

There are some big, and small, installers out there that will do all the paperwork and installation for you... Last I read (a few years ago), $5 per 1 Watt of solar panels (or less?). There are programs where you pay everything (costs) up front. And others with a lease back from the installer/bank and they "guarantee" your utility payback.

From a technical point of view--GT Solar is the cat's meow. The GT Inverter takes 100% of the available solar power and converts it to 240
VAC power (morning/evenings, less power, middle of the day the most power). About the only way you can see it working (besides the inverter's status panel/software) is to watch your power meter. It will slow down (your home loads > solar power) or stop (home=solar power), or even spin backwards (home loads < solar power). The whole system is "transparent" to you--And depending on your utility's rate plan, they will calculate the savings/costs to you monthly (PG&E is 1 year net metering... In summer "money" credits to your account; In winter money debits your account. At the end of one year you pay the debit or the utility "zeros out" your account if positive credit--More or less, lots of details here).

Standard GT solar does not provide emergency/backup power--Utility pole hit by car, your power goes out until pole is fixed (there are some options here--For a little backup power when sun is shining--With some brands/models of GT inverters).

There are folks that do guerrilla "GT Solar" installs with small systems--But not usually legal and can run into safety issues (or even utility red tagging your home if they figure out what your are doing--maybe).

For more complex Hybrid Inverter systems... Use "local solar" when enough sun/battery capacity, and switch over to utility when battery/sun is low--Yes, there are hybrid inverters that do this--But not really a "cheap" solution--Mostly used as solar+backup power for homes--May not be cost effective for a pond.

Another possibility--Run your pump(s) on a timer... Turn off during summer Peak (and Partial Peak?) during $0.40 to $0.30 per kWH, and only run during $0.20 off peak periods (may run into "tiered pricing" costs).

GT Solar can easily save money ($0.15 or less per kWH) for your usage. Design/install system for whole home--And save money for all home power (my home electric bill near San Francisco Ca, is ~$10 per month usually).

Hybrid power (solar->charge controller->battery bank->AC inverter) can easily run $1.00 to $2.00+ per kWH (all up front hardware/installation costs, replacement electronics, battery bank, etc. every ~10+ years, etc.). Hybrid solar (really solar backup power for weeks/months of power outages at remote locations)--Does work. But if you design large enough system--Just go off grid completely (not really recommending if you already have utility power--Other issues around "loss of utility power to property" and reducing future sales price if utility pulls power pole, you get "old" and want to retire on utility power, etc.).

Classic Engineering Design Case... Look at "everything" (reduce energy usage, higher efficiency "appliances", cut power during high cost times, run several paper designs and look at costs and worth to you--Don't just focus on "one solution"--There are lots of options out there.

-Bill

Is there such a device that switches between solar and Wall outlet Automatically?

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