Grid tie panels or RV panels

[headgeek]

So - the cost per watt seems much nicer for 2 250 watt grid tie (37 volt) panels.  Is there any reason not to choose 2 of them over the more expensive 12 volt 100 watt panels?  I'm looking at about 500 dollars versus 1000 dollars here in Canada. I'm planning on putting them on my trailer's roof.

[TomW]

Hard to say from the limited information provided.

It is a good idea to provide a good overview of your system in order to get a useful answer.

Things like:

System voltage, intended system PV power, battery bank capacity, other equipment details. More info is better than less, as well.

I doubt the "12 volt" panels are generally a good match through a Kid controller. I suspect most systems would work better on the "grid Tie" panels as they are built to feed into higher voltage inverters.

Of course systems vary enough that any "rule of thumb" will not apply to some systems.

Fire off some more details and you will get good advice here.

Personally, I would buy the Grid Tie units and get twice as many rather than spend $1000 for the 12 volt units. It seems obviously a better use of the funds.

Tom

[headgeek]

Sorry.
System voltage will be 12.  Using two 6v golf cart batteries in series. I will have 228 ah.

Debating the expense of duracel versus rolls surrette. I was thinking of two panels of 250 watts for a total of 500 only because more is better, I have room on the roof, and perhaps I can avoid tilting although I will build in that ability for one panel. 

I live in central bc where I get limited sunlight in winter but lots in summer (many daylight hours - from 5 am till 10:30 pm. I'm going to use this to benchmark my expected results for a possible home based grid tie system.

So I'm going to try to run my rm3663 fridge off an inverter. It's about 4 amps on it's own. As well, a magic fan (still to be installed) and the normal lights and a radio, etc.

I'm a bit of a geek - so I plan on running a pi2 as a samba box with an attached hd for storage (for the kids to watch movies mostly.

Lastly I plan on running a usb wireless as an access point and running a pi camera as a backup camera on the back window. I'll access that via a webpage with zoneminder or via raspivid and vlc on my smart phone.  When I'm home I'll put the system into a client mode and just cronjob some variables like battery charge, etc. via email.

Does this help?

[ClassicCrazy]

Get the less expensive panels and use the Kid  MPPT controller to drop the voltage for your batteries.
You could also put them both in series and then run 24v battery system , but if you already have your inverter and other 12v devices then that is an extra cost.

Those other panels are useful if you wanted to use a less expensive PWM 12v controller. But you get a lot more monitoring and control capability using a Kid and that way you can use the less expensive panels too. Get the Whizbang and a shunt to go along with your Kid too.

Larry

[headgeek]

I've got a 600 watt 12 volt inverter in my truck I've thought of bringing over.

Right now all I've bought is the kid with the shunt and the whizzbangjr. From what I've read it is the one part that is the easiest to screw up on.

I've got two 12 volt batteries, one that came with it and an optima 48ah that I've had kicking around. I plan on getting new 6 v batteries soon.  From what I've read the only advantage of 24 volt is in longer cable runs?  I've got a 17 foot trailer.

[ClassicCrazy]

yes advantage to 24v is you can use smaller wire sizes. And closer to  your panel voltage series string , then the controller would be a bit more efficient .
If you have old batteries not too much to loose if you hook them up in parallel before you get your new batteries - not good to mix different aged batteries though. When you get your new batteries keep them matched . Series for batteries has advantages since all the current goes through all the cells. I think any of the 6volt golf cart batteries are pretty similar in specs so you might just shop based on price. East Penn Deka seems to have the best prices and they just put different stickers on their solar ( and other ) lines. Just make sure when you get them that you are getting fresh batteries that are less than 6 months old and they are the same month - stickers on side or stamped in date code .

And if the Kid doesn't come with the external temperature sensor get one of those too - it will adjust setpoints for batteries according to their temperature.

You won't mess anything up hooking up the shunt and Whizbang if you just follow the wiring diagrams. Basically you will have only one connection on one end of your shunt and that is the one going to the battery.  The other side will end up going to everything else. All you have to do is when you mount the Whizbang on the shunt is make sure you put the wire to the correct side of the shunt as it says in the instructions.

Larry

[PbdBlue]

I was thinking of two panels of 250 watts for a total of 500 only because more is better,

Can the Kid handle two 250 watt panels?

[tecnodave]

PdbBlue,

The kid can handle 2  250 watt panels in a typical installation even though 500 watts divided by 14.4 volts is over 34 amps. The Kid will limit the current to 30 amps in any case you will not get 500 watts out of 500 watts of panels ....more like 300-350 in your non-optimal orientation required for your RV.
No problem there,

I will run the BIG RED FLAG  about running that fridge on an inverter.....The RM3663 is a propane/electric absorbsion refrigerator.     They are horribly inefficient !   250-350 watts with a very high percentage run time......a real energy PIG!  You would need many more panels than that to do that!

Been there, Done that......don't even try.......you will end in frustration! .....with a failed solar experience!

There are much better refrigerators for low power situations. Even household refrigerator is way more efficient than an adsorption refrigerator.

Ok here is my real time experience there......I live in a 34 foot Class A motorhome/movable mountain cabin.......My Dometic refrigerator went to the scrap yard.........replaced by a DC powered "Digital inverter compressor " refrigerator.  It uses 45 watts with a vey low run time! Directly powered by the battery bank!  Total power use is a small fraction of the Dometic!  It will run on one panel alone!

This technology is new! There are a few companies making these.

The biggie is Sundanzer, mostly chest types, their upright is about $1400.00 USD.

Other players include EcoSolarCool. Upright referigerator/freezer $1200-1400.00 USD

And the new player......Grape Solar.  With the Glacier GS-5  $630 at Home Depot Online delivered free to your local Home Depot store.

I bought the GS-5 from Home Depot online last year and love it!  It is not as efficient as the Sundanzer but it saves lots of energy. The unit is sized to replace the Dometic at 24 " wide 20" deep and 48" high.....it will fit in the space where the Dometic was.

The Sundanzer is 30" tall 30" deep and 52-60 " long depending on model and not RV size friendly.

Yup $630 for a small 5 cu.ft. Frig is expensive but you will have more than $1000 in solar gear to run that Dometic!

Like I said...been there , done that......all my gas fridges are gone.....replaced by "digital inverter compressor" referigerators........way less hassle.

I've been using the GS-5 for a year and I did just replace it due to a defect in the freezer door installation. When I called Grape Solar I got a real person first ring....real service....a new fridge shipped Fed-Ex in a few days....no whimpering !  No cost to me except getting it back out of the Motorhome......it is a tight fit.

Hope this info will save you the grief of Dometic referigerators!

David



(Edit).   Amazon now carries the GS-5 for $581. USD with free delivery

[PbdBlue]

The kid can handle 2  250 watt panels in a typical installation even though 500 watts divided by 14.4 volts is over 34 amps. The Kid will limit the current to 30 amps in any case you will not get 500 watts out of 500 watts of panels ....more like 300-350 in your non-optimal orientation required for your RV.
No problem there,

Good to know. I'm currently running two 160 watt 12 volt panels in series but thinking of going to 2 x 250 residential panels in parallel. I'm guessing as you say in real life you will never see 30 amps from them.

[ClassicCrazy]

Thanks for that refrigerator info David .
I was looking at small 5 cu ft chest freezers last week for $150 and was wondering if it is possible to change the temperature controller and just use it as a fridge .
I will look up that refrigerator you mentioned.
Larry

[russ_drinkwater]

Just a suggestion.
Shop around a bit in regard to the panels.
There must be grid-tie solar system installers where you live.
Many people upgrade their panels over the years.
You may find 2nd hand panels cheap.
Here in australia you can buy 2nd hand panels up to 225 watts of various voltages for $50 each.
$1000 is a lot of money to fork out for panels, been there done that!
What you save can be put into another couple of batteries depending on the prices over there!