Planning a solar install for a local off grid cabin

[ericfx1984]

I was recently contacted by a person in my community who has a small lake cabin that he has ran off of a generator for many years

Apparently word has gotten around my small lake community that I don't have a power pole, and that generally speaking I don't use a generator

I got to speaking with a gentleman and he's interested in having a small off-grid solar power installation done

He wants to be able to run a coffee pot and a fridge slash freezer as well as some 110 volt LED lights... In fact all the loads will be 110 volt

I explained to him that we could skin this cat a few different ways

One option, which I really would not recommend would be a 12 volt system

I explain that we could do an absolute maximum of 3000 watts but that you would pretty much be at the limit of a 12 volt install... Now I know that we can actually build bigger 12 volt systems... But with him having very little experience in this area and not being interested in really learning about it I think a 12 volt system would be foolish...


Furthermore I can't really find any decent 12 volt all in one systems that have inverter, solar charge controller, 110v to DC charger built in

And the fact that without adding multiple charge controllers you're pretty well limited to about 600 Watts of panels makes this seem like it's not a very good option

However... 24 volts opens up several all in one systems, 3000 watt inverter, 60a solar charge controller, 40 amp battery charger. Many of them for less than $500

This would allow 1,500+ watts of panels

And realistically even if I went 12 volts on this build I would likely have a pair of lifepo4 battteries as it would be necessary for the amount of current that he would be likely to draw at times

It seems like the cost of a 24 volt and a 12 volt system would be fairly close... But much more limited on the 12 volt side

Furthermore going up to 48 volts it seems that there are many options for an all-in-one system with only a marginal increase in cost

The only real increase after that is of course the increase in battery

But with this increase in battery cost comes other benefits, one of the most obvious ones being the increase in total battery capacity measured in kilowatt hours

Should I simply tell him, no I will not even plan out a 12 volt system for you... Or should I lay it out and explain that the 12 volt system will likely be about the same cost as the 24 volt system while losing the built-in battery charger and only being able to handle about half of the solar panels

Everybody wants to save a buck I know... But I fear if I build him a 12 volt system it's going to become a maintenance pit where I'm constantly having to monitor it and worse than that he'll be unhappy with the results

Another thing I should mention is he has mentioned that at some point he would like to expand the system to be able to run his 30 amp RV... I suggested that if he went 48 volts... It would be very easy to install another inverter that is dedicated to operating his RV and then it would simply be a matter of installing a pedestal outside of his cabin with the correct hookup

I'd love to hear your guys's thoughts on this... The good news is he didn't even bat an eye when I suggested buying a pallet of 250 w panels from Santan (despite the fact that he likely would not end up using anywhere near all of them)

 

[Mattb4]

If he eventually plans to run the 30a RV my suggestion is to use that as a baseline. 30a at 120v = 3600w In order to reliably produce 3600w and cover most startup surge he would want to be planning a 5000w supply. I do not think you can find a 5000w AIO that is not 48v.

Now that said it always depends on loads. You could have a 30a service that you never load to that level.

I would say that a good look at present and future loads needs to be done.

 

[740GLE]

You can lead a horse to drink . . .

I guess I’d give some recommendations (a nice 24v system should work) but if he wants more than that it’d be best to lay out expectations before hand.

Any well designed system should be relatively maintenance free, there are ways to make it idiot proof, but if the guys is looking for a turn key project plus support after commissioning, it might be best to place that responsibility to a contractor.

 

[Rocketman]

Show him your post here - you explained perfectly why he would not want a 12v system.

I would think he would not need another inverter to run his 30a RV. As long as he does not turn everything on at once in it. Just wire the 30a plug in.

Also , point him to several inverters that will do the job and let him pick out the equipment he wants. Be sure and include tier1 equipment on the list. He will need to maintain it in the future,

Good Luck with helping the right amount (not too much or too little).

 

[ericfx1984]

Any well designed system should be relatively maintenance free, there are ways to make it idiot proof

Right I totally agree A well designed system will be maintenance-free... But that also requires that the person using the well design system is operating it within its design parameters

I don't think he's wanting me to constantly be maintenancing the system for him... But my fear is if the system is not idiot proof that it may turn into something where I'm constantly doing maintenance and upkeep for him... Based on that, I feel it would be important to overbuild the system

 

[ericfx1984]

Also to help break it down I explained to him that I'm building a 10,000 w system for my house... It's completely off-grid and will be, at least starting out running on about 35 kW hours of lithium iron phosphate batteries

But... I'm not 300 square feet, I'm 1800 square feet... I pointed this out to him and explained, you would be undoubtedly, happy with a huge system that is way bigger than you really need

But your wallet would not be happy

He says that he's an extremely conservative guy when it comes to power usage, explaining that his parents grew up in the Great depression, and as such "you turned off the damn light" ... I got a laugh out of that one

 

[ericfx1984]

would think he would not need another inverter to run his 30a RV. As long as he does not turn everything on at once in it. Just wire the 30a plug in.

The all-in-one unit I'm looking at for 48 volts is a 5000 w inverter from sungold power

Which I believe is a manufacturer for Aims power

And it's relatively affordable at less than $800 granted it is only a high frequency inverter... But they tend to be a little more energy efficient than their low frequency brethren and I know for certain that a 30 amp RV will run just fine on as little as 3,000 Watts

I'm currently living in a 30 amp RV and using an AIMS power 3000 watt low frequency inverter... Granted it can spike at up to 9,000 watts

But I would imagine based on that that the high frequency 5000 watt inverter should easily be able to handle a spike of twice it's rated wattage... Meaning it would be a great option for the RV and having its own dedicated line

The other advantage to having multiple inverters in my experience is that if one inverter goes down and needs service or repair, I can offload those loads to a different inverter

This is definitely how my house build will be and also how I have ran my RV

I tend to operate on the "two is one, one is none" mentality

 

[740GLE]

And that’s where cost will probably shock him, and the few gallons of fuel he burns may seem more reasonable.

 

[Steve_S]

120V X 30A = 3600W to keep it simple.
I assume as this is his cabin, that it is part-time use.
- Will he be leaving or taking the batteries ?
If leaving, will he want the SCC to maintain them ?
- What amount of parasitic power use is acceptable for a period of time without any charge input ?

AIO's are attractive for many reasons but there are pro's & con's like with everything else. In a "Part Time" use case the trade offs need considerations. If you build a component based system with SCC, Inverter/Charger you can totally shutdown the Inverter and leave the SCC to maintain and you have no parasitic losses. With an AIO (pending make/model) it's either on or off including SCC & Inverter. Most can leave the inverter in an Eco/Sleep mode that wakes up the inverter when a demand is sensed, which cuts the standby power used.

My personal suggestion:
48V System if static (not trekking back n forth) 24V if trekking, battery packs in parallel.
SCC: I would be to look for an SCC capable of 85A + Charge @ 48V, which can be linked in parallel. Many good ones are capable of doing so with 2000W +/- arrays.
Inverter/Charger: A good quality 5000W (120V/41.6A uncorrected) Inverter with an efficiency over 90% for 120V can supply his needs including RV is he doesn't go nuts. He could go 240V Split Phase which still gives him all the 120 he wants but now gives the 240V options for current & future use. The gotcha with 240, is you'd have to up the wattage to increase the deliverable amps on the 120 rails, probably to 7000W. There generally isn't an appreciable difference in power consumption between quality inverters when operating below their upper power ratings. * Be careful when checking the efficiency ratings of inverters and their types, there are High & Low Efficiency in BOTH Low/High Frequency models, be aware that there is a price to pay with low efficiency in wasted power and often sadly in MTBF (mean time between failure). High Efficiency devices often have higher quality components and better programming as well.
There are many inverter/chargers which can be linked in parallel with communications/interaction as well.

Last Points of consideration.
How is his insurance about DIY ?
Do they need certified equipment or not for coverage ?
Will they want an inspection ?

Panel mounting also makes a huge difference whether it is roof or ground mount as maximizing what the array can & will generate when most important which for PT Occupied places are not the same as regular FT homes. Not to mention often affects the amount of panels needed to deliver the required amount of energy.

Hope it helps, Good Luck