solar on/off grid installation

[dabedwe]

I just bought a nice pull behind camper and would like to install some solar panels on it to make it more self contained as well as tie the system into my home when it is just parked. I have tried to find a video online or even a diagram explaining how to wire this up, but all i can find is off grid installation information for campers and rv's. I want to be able to plug my camper into shore power and still run the solar set up when that is not available. Additionally, i would like to use the panels as a tie in grid system for my house when i am not on the road. I am not sure if i need to buy a separate inverter and install a switch that will cut the power to the camper when i plug the solar panels into my house outlet to feed my home system. I plan on buying an mppt charge controller and 400 to 500 watts of solar panels.

Can i just connect the load to the ac input in on my camper fuse box? i do have a free breaker slot available that i could connect the load to if that will work. If so, can I still plug the camper into shore power while the solar system is running? If i use the free breaker slot, i could just flip the breaker before i plug the camper into shore power if i need to. Additionally, if the breaker slot installation will work, can i use the existing shore plug to feed the power to my house or do i need to cut the feed (basic switch) going to the trailer charge controller from the solar panels, connect them to a second inverter, and then run a new plug from that inverter to plug into my home outlet for tie in use? If i can connect the load to a breaker in the camper fuse box, would i need a separate inverter or could i just run a second load wire with a plug from the charge controller to feed it back to the grid?

I realize there is a lot of questions here. depending on how i need to install this system may make some of them irrelevant. However, I would appreciate any advice on this.

[westend]

I forgot to add that i am buying an mppt charge controller for the camper. I thought that was in my first post. Really the important question i need answered is; Can i connect the load off the mppt charge controller directly to an ac breaker in my camper fuse box?

No, because the power is still DC. You need to invert it to AC, send the power through a transfer switch, and it can then be used through the RV's load center.

It will also be more practicable to store the solar power in batteries before inverting as there is a limit to the power produced and there is also the variability of solar output. IOW, what happens when the 500W modules are expected to supply power to a 1200W coffee maker and clouds intervene?

In my previous post I had tried to explain the characteristics of typical residential grid tie and the limits but deleted it after I looked at the length of my post. I'll post some of it again for clarity and continuity of the subject.

As Gavin noted, you can't connect 120V from a non-utility source (solar, wind, or hydro) directly to your utility supplied house system without an automatic relay that interrupts the alternative source in the event of utility outage. If you plan to install the complete residential system later, you could withstand the price of the switching gear and associated wiring, albeit there maybe need for additional interruption and wiring when installing the whole-house system.

Micro inverters are the new "sliced bread" for photovoltaic systems and there are certainly benefits as well as downsides. Upsides--power inverted at the module means less expensive wiring, output continually delivered from remainder of module string if only a few modules are shaded, and scaling if installing part system or upgrading is needed. Downsides---cost, possible durability issues, and the micro inverters are controlled through network based switching. The whole adds up to be a negative when applying to RV use.

I'd suggest, if embarking on solar power usage, to keep it simple. Design your initial solar as to the usage in the RV and design the residential system to it's own characteristics. While you are installing the residential system, you can keep in mind the output of the secondary output of a couple of modules and possibly integrate that into the house system. You will have connectivity to overcome when using the secondary source (parked RV to house distribution--you wouldn't want just a live 120V wire strung across the property). I think you would also find that the ROI for this secondary power addition to rule out it's use to grid tie.

Good luck with the solar, it's one of the better mods I've done for my RV.

[Shadow_Catcher]

I have a 185W high voltage panel intended for a grid tie system on our teardrop the situation and it requires an MPPT controller to work 12V. It could be used for your idea with the micro inverter wired separately.

[Gavin60]

dabedwe wrote:
I forgot to add that i am buying an mppt charge controller for the camper. I thought that was in my first post. Really the important question i need answered is; Can i connect the load off the mppt charge controller directly to an ac breaker in my camper fuse box?

I was just looking at cheap "inverters" on ebay for the connection to the house. I realize that you need to convert the dc current to ac. The "inverters" they are selling may actually be converters. they call them "grid tie inverters" in the ads. They state you can connect the panels directly to them and then just plug the "inverter" into a wall socket to feed the power. I did watch a guy who had a bank of 600w "grid tie inverters" in a camper that he had hooked to some kind transfer switch, but it was not automatic and he did not show how the system was connected directly to the fuse box in the camper. I am more concerned about the connection to my camper right now. I dont want to hook the charge controller up wrong and end up burning out part of my electrical system. The relay and double pole switch are both great ideas. I was thinking of having 2 switches, but there is always a possibility of both getting turned to the on position.

Do not use those inverters which plug into the wall socket!
They are not UL listed and can backfeed into the line....think of a power outage and a lineman outside grabbing a line and you are back feeding it! Someone gets hurt or killed, That kind of stuff is know as "Guerrilla power"
If you are going to grid tie you will probably have to pass a local inspection code, One thing about the enphase inverters is that they shut off when they realize the grid is down and sample the power in the grid every 5 mins until it is back up and running, think of it like an automatic transfer switch.
The only way to do your own thing with those type of backfeeding inverters is to be an "island" not connected to the grid.

The charge controller is on the DC side, between your panels and battery bank it just simply keeps you from ruining your batteries.

The inverter which takes the DC power and converts it to the AC power is the side you need to be concerned with in your camper if you are running off of AC power in your camper.
IF you are running off of DC power ( 12 volt system?) then your panels go from your charge controller to your battery bank.
I will be honest with you I have not seen an inverter ( AC side) which could stay on and on and on from constant usage without smoking itself other than an "Outback"...there might be others out there but I have not seen many last from constant usage...I guess those big box store/ebay inverters will do if you only use it on ocassions.

All the best!
Gavin

[Gavin60]

Hi I have a grid tie system of 22 220w panels, it can produce in the neighborhood of 700 KW-450 a month from spring through winter here in South Carolina,
IF you are going to grid tie I would seriously consider The Enphase micro inverters...one sits behind each panel and can be easily added on too as you grow your system. It will take the DC solar panel and convert it to AC, Thus as your system grows you will not have a large headache as with a central string inverter. You can find my output on the Enphase web site as "Gavin's system" On good days I make about 30 kw
The Enphase system is all plug and play.
OK, on your camper you will need a charge controller, between your batteries and your panels, it essentially dumps or disconnnets from the battery any excess power....excess power or overcharging is a bad thing on batteries it will make lead acid batteries boil themselves dry and ruin them, much less the hydrogen gas that will need venting.
The Lithium batteries will die dead flat from a overcharge, so a charge controller is very important.
Another couple of things to consider:
A good inverter back to AC.

With a standard string inverter, if one row of panels is shaded from an obstruction as the sun moves across the sky, it will knock the whole row of panels out of production, but with a micro inverter only that one panel is affected while the others keep on producing.

Another thing is....and I really hate to be a buzz killer here for you is, that unless you really conserve power or live alone or maybe with someone else who is real frugal with power, a few panels..maybe 2-4 wont make hardly a differance in your power bill.

The reason I put in my own panels is that my energy costs are high here in the neighborhood of 18-20 cents a kw, its an old Co-op from the 1930's and until recently they had crappy service and didnt give a******about the customer, they acted all smug about reaming the customer each month, but with panel prices falling I thought it would give them a reaming too.... they were oblivous to the panel prices dropping and told me the adventure would be too expensive yada yada yada. Now they are scrambling as more and more folks on the same grid are doing what I just did a few years ago.
The threshold of "cheap power" is in the neighborhood of 10 cents a kw
I didnt do it to be a hippie or be an over the top "Green Person", it instead just made pure economic sense to do so and the added benefit was beating those jackasses at their own game.
All the best!
Gavin

[dabedwe]

I forgot to add that i am buying an mppt charge controller for the camper. I thought that was in my first post. Really the important question i need answered is; Can i connect the load off the mppt charge controller directly to an ac breaker in my camper fuse box?

I was just looking at cheap "inverters" on ebay for the connection to the house. I realize that you need to convert the dc current to ac. The "inverters" they are selling may actually be converters. they call them "grid tie inverters" in the ads. They state you can connect the panels directly to them and then just plug the "inverter" into a wall socket to feed the power. I did watch a guy who had a bank of 600w "grid tie inverters" in a camper that he had hooked to some kind transfer switch, but it was not automatic and he did not show how the system was connected directly to the fuse box in the camper. I am more concerned about the connection to my camper right now. I dont want to hook the charge controller up wrong and end up burning out part of my electrical system. The relay and double pole switch are both great ideas. I was thinking of having 2 switches, but there is always a possibility of both getting turned to the on position.

[christopherglen]

You will need a charge controller for the off grid end of things. A grid tie inverter (here is what I am looking at) to take the panel output and convert it into 120/240 volt AC - and grid tie it. A simple inverter will blow if its output is attached to a live grid. The last thing you will need is a relay or double pole switch to either connect the panels to the charge controller, or the grid tie inverter. A relay with a 120 volt coil on the output of the inverter will do the job, and as soon as you unplug the panels - switch to off grid mode, plug back in and they switch to grid tie mode. Your onboard converter will keep the batteries charged when grid tied (and be powered off the grid tie inverter during the day), and the charge controller will charge them when off grid.

[dabedwe]

I realize the panels will not produce 120v. I was planning on having battery bank in the camper that is large enough to run lights, maybe charge a laptop, run a tv if possible, or a fan for a few days. I did not think about the power feeding back in the lines if there was a power failure if i use it as a tie in system. I was looking at purchasing a cheap 600 watt inverter to connect the solar system to my house outlet. I could put a switch to cut the panels from the camper and install a plug on the side of the camper, which could then send the 18v dc into an inverter and a relay in my garage. I am planning on buying an on/off grid system for my house within the next year, so buying some of the pieces now would not be a big deal. However, the system for my house will be around 5000 watts, so anything i buy now I will need to be able to handle a much larger system down the road. The tie in system could wait until i install the bigger system on my house, but I figured if the panels are working i might as well be using the power that is coming off of them, even if it is a small amount. Where i am located i can easily angle the panels true south with no obstructions. I appreciate the response and thanks for the link.

[westend]

RV solar is outfitted for the 12V system.With 400-500W of modules you won't be able to achieve +120V DC when connecting in series to grid tie to a conventional residential controller/inverter.

The main design failure is the assumption that solar modules are all capable of producing 120V AC. Typical solar modules output up to 35 V DC (although there are some rarities that output 70V DC).

Good reading here: Golden Rules of Solar