Solar and Shore Power Interface

[Texan]

A friend of mine bought 9kw of solar panels and 3 5kw inverters that are grid intertied and backfeed onto the grid. His electric bill is almost 0. I'm still considering a skoolie and would likely mount solar on the roof. Since my bus would be at home most of the time sitting at my house, I had the bright idea of my skoolie inverter actually using my solar panel output while it's parked at the house and backfeeding it into my house to lower my electric bill. Has anybody equipped their bus with this type of inverter? What are the downfalls. I can build it to be grid intertied, but I need it to also function as a stand alone. My buddy's system has no batteries and shuts down during a power outage.(disconnected from shore power)

I am considering moving and I'm putting off solar for the home until I decide whether or not I will be here. A bus solar system can move with me and provide a place to live while I build my next home.

It would drive me nuts to only use my bus 3-4 weeks /year on the road and see it sit for 11 months of inactivity for the expense of solar panels. I want to benefit from solar year round.

[JDOnTheGo]

Check with your local utility (electric). I have no experience but understand they only accept permanent installations and are VERY picky and require several inspections before they allow anything to be connected to their grid.

[skoontz]

I haven't done enough research to know for sure if this would work, but one idea that I have had about this is to use a generator transfer switch like this one:

https://www.lowes.com/pd/Reliance-30...Switch/4712891

Then I would run a cord from the bus inverter outlet to the input of the generator switch, and run some of the circuits in my house off of the bus inverter. This way the loads are powered off of solar, and there is no need to grid tie. If something fails you could flip a switch and be back on the grid.

[ACamper]

I people usually call them "transfer switches", the have basic switches that will disconnect and connect the entire system or circuit breakers to mange parts of the system. You would have to calculate the costs and complications to tie into/share with the electric utility provider and the ROI. Might take a couple of years to pay off.

I also wonder about the utilities company fees and rates at which they buy power and sell power. They seem to be very tricky with billing and selling, sell you a nickel for a dime and buy a dime for a nickel ?

[BeNimble]

You can buy an electric car and then use the bus solar to charge that and not involve the utility company. Or a plug-in hybrid like a volt given your in texas and might have long drives, but get 40 miles free via ev.

[ACamper]

This thread sparked my curiosity about electricity “buy backs”, so I did a bit of looking online about them.

It seems like different utility companies have different deals depending on where you live. The utility companies are getting federal subsidies to encourage the creation of them. Some you go thru utility company to buy and install the solar set up, others you buy your own set up. You sign into a “buy back” contract with them for the price they will pay, some pay “credits” many seem to advertise they will pay the same rate they they sell at.
You have to contact your local utility provider and ask them what deals they have.

A couple of my concerns would be what happens if the federal subsidies run out ? Will they still see it profitable ? They have to maintain a metering system to harvest the small amounts.

How much for the meter equipment install ? Do you have to have a licensed certified installer put it in on your dime ?

I am interested in more details if you find some on your search.

[o1marc]

I've always seen residential solar as profitable after about 15-20 years. Not many are in the buy back plan because you need to provide so much extra power for it to be beneficial, requiring a massive panel array. Pretty much all of it is on your dime until you throw the switch to the power company. Solar has changed so much that the original investments have gained is size with replacement costs during that 15 years. I see it similar to vegetable fuel, too much work for the ROI.

[Texan]

My friend installed his system on his home and had an electrician sign off on the installation for the tax break. He has $13.5k in it and will pay for the system in less than 3 years. He has no batteries and stores extra electricity using net metering with the power company. My plan is to do the same thing, but also install the solar and an inverter on the bus to complement the home system. The difference is that the bus will have batteries and I need to determine what happens during a power outage. I don't think the bus could support the entire house at that point. I would also need to have a system to disconnect the house from the grid to protect electrical workers.

[ACamper]

Originally Posted by Texan

My friend installed his system on his home and had an electrician sign off on the installation for the tax break. He has $13.5k in it and will pay for the system in less than 3 years. He has no batteries and stores extra electricity using net metering with the power company.

Math is not my cup of tea so please correct me if I am wrong.

The average cost of electricity in the US is .12 a kWh = This is what your average electric utility company will pay in a “buy back”.

Cost of neighbors system $13,500 / .12 = 112,500 it would take selling back 112,500 kWh to pay off the system.

You could probably get 4000 watt system installed for $13k that could produce 16 kWh a day .12x16= $1.92 a day if you sell all of it back. You could pay for the $13,500 system in about 19 years, if someone sold every single kWh back.

That is of course if the utility company is still buying back electricity after subsidies run out in a couple of years.

Another factor is life span of solar equipment, will it last 19 years ?

[o1marc]

Originally Posted by Texan

My friend installed his system on his home and had an electrician sign off on the installation for the tax break. He has $13.5k in it and will pay for the system in less than 3 years. He has no batteries and stores extra electricity using net metering with the power company. My plan is to do the same thing, but also install the solar and an inverter on the bus to complement the home system. The difference is that the bus will have batteries and I need to determine what happens during a power outage. I don't think the bus could support the entire house at that point. I would also need to have a system to disconnect the house from the grid to protect electrical workers.

$375 a month to pay off a $13.5K investment in 3 years. That's pretty optomistic.

[Texan]

After his first year with solar panels, he spent a total of $67 for electricity. He has a 2400 sf house, a 2400 sf air conditioned shop, and a pool pump running 8 hours a day. He doesn't cool the shop very often. He payed $13.5k for 9 kw array and inverters. We both work on solid state emergency power equipment for a living and he installed his own system. Texas has net metering.

[ACamper]

Originally Posted by Texan

After his first year with solar panels, he spent a total of $67 for electricity. He has a 2400 sf house, a 2400 sf air conditioned shop, and a pool pump running 8 hours a day. He doesn't cool the shop very often. He payed $13.5k for 9 kw array and inverters. We both work on solid state emergency power equipment for a living and he installed his own system. Texas has net metering.

$1.50 sqf is super cheap for a solar install. The going rate for panels alone is $1.00 watt The typical contracted install is $3-$5 a watt. I spend at least $2watt on my bus install doing all my own labor, but I put in quality stuff.

At 9000watts in great conditions you might see $5 a day back with full “buy back” rates. I seriously doubt your neighbor will pay of his system in 3yrs.

If the utility company buy back doesn't pan out maybe you could hook a bitcoin machine to your system.

[Booyah45828]

I agree. I don't see how he could save/make $13,500 producing his own electric(eliminating his bill) and having the utility company buy the excess back.

I mean, we don't pay 13,500 over 3 years in electric costs at the shop, and we go through what I would consider a lot of electric.

[Native]

Our house is on average billing. We have the thermostat at 81 degrees this summer. The bill is just under $300.00 per month. That would be $3,600.00 per year or $11,800.00 in electric paid in three years. So we would have to produce $25,300.00 in three years to pay for that system while also producing enough for our own needs.


If the goal is to only produce enough to cover useage, then we would need to produce just under $10.00 per day, every day. At $0.12 per KWH, that is a little over 83 KWH every day. This would require a large solar panel array.


I think we use too much electric energy!

[joeblack5]

Originally Posted by Texan

We both work on solid state emergency power equipment for a living .

Now I am curious, you seem to work in this field.



For the other people concerned with the financial aspect:


We have multiple solar panel and solar collector systems spread over several houses.
there is netmetering
there are tax credits
there is REC.. reneweble energy credits


and there is .. just one of the right things to do..
what is the payback of your granite counter top or your shiny oversized pick up truck??



why are people even putting solar on their bus, sure is not financially attractive compared to a generator and gas

.
people like quit and clean in their own environment, maybe some are socially responsible an do it for their camping neighbors.


i would think the same applies for home situation.. only the pollution is just outside you horizon .. there where the coal is being burnt and the earth being torn up.


Now coming back on the original question.


using your bus a a "mobile generator" while parked at your house.

It is a great idea and easy to implement.


If you have batteries and want them to be part of your emergency system then look into outback grid tie inverters like GVFX3648 or GVFX3524.
the gvfx3648. probably more complicated then you need to go.



for direct feedback you can use any of the micro grid tie inverters and wire them parallel to your solar panels before your charge controller, you might need to install a diode in series with your charge controller to prevent battery feedback thru the charge controller into the grid tie micro inverter when you are connected to the grid.



Then there are the inverters like this one..


https://www.amazon.com/Inverter-Limi...94429130&psc=1


All this stuff is is designed to work safely and shut off when the grid goes down to protect the lineman.
A smart lineman would short the wires anyhow while working on "dead lines" since induction can electrify them anyhow.


Of course , all above illegal without filling out proper filing work, as by the way also any electrical work on your bus is. that is why you have RIVIA.. haha


Johan


Oh and ACcamper is right , average install by an improved installer is $3 to $5 per watt. Mainly due to inflated labor price and complications the power company places on you to try you not to install it and affect their bottom line.


If you can install your own with $0.50 watt solar panels and $0.20/ watt inverter you should be able to get below $ 1/ installed watt.

[CharlesM99]

Originally Posted by ACamper

The going rate for panels alone is $1.00 watt The typical contracted install is $3-$5 a watt.

These numbers are outdated. The PV industry is very dynamic, and prices have been dropping drastically. I paid $0.58/W for my PV panels before credits.



And under $1.50/W installed is common after tax credits.


But back to the main point.
Yes, its totally possible to build a PV system for your bus and power your house electrical with it.


After you build the system for your bus, the simplest solution is to run an extension cord or two into the house and power some power strips.


The more complex solution is to get a transfer switch, they have Automatic ones (ATS) or manual ones (MTS). There are some transfer switches that have a space for breakers also.
The transfer switch will let you change power to the loads from your Bus system or the grid.



If you get a "Break before make" transfer switch you wouldn't even really need to get the Utility involved since the bus electrical would never interact with the grid.