Questions to ask when buying property with existing off-grid solar

So, I'm going to look at properties to purchase this week, one has a rather extensive off-grid solar system. Other than the obvious, how old are the components, are there any other questions I should be asking?

Find out what kinds of appliances are being run from the system.  This will give you an idea of whether it will be adequate for you.  Pay special attention to the batteries...they are usually the weak link in any offgrid system.  Most batteries have a finite lifespan and need careful attention to maintenance in order to maximize this lifespan.  You should find out how old the batteries are and ideally, there should be a maintenance log, like for a vehicle, where you can see what has been done to them when.  Other things to check out....is there a generator?  If so check this out like you would any other engine-powered piece of equipment as to age, maintenance, frequency of use, etc.  How is water being handled and moved around the farm?  Using solar to power a conventional well pump is either profligate or impossible, depending....you will get much more yield for the investment with something like a dedicated stand-alone PV direct pump which fills a tank or cistern.

Hi here are the types of questions I would ask and those We ask people when they call...
1)Wattage of solar array
2)name and models of all equipment
3)age, size  and type of batteries and voltage the system operates at
4)is there a generator, manual or autostart
5)Is the inverter pure sine or modified sine wave
6)who installed it and are they still in business
7)did the system get inspected if required (important for insurance) despite what people think most jurisdictions insist on full permitting code compliance and inspection despite not being grid connected.
are there DC lights pumps etc in the system or is it all AC
That is what comes to mind right off the bat. Pictures are good they give me a good idea of the quality of the install and the component choice

David

My understanding is that everything on the property is run from the solar, some heating systems, hot water heaters, front gate, well. There is a backup generator, the owner said they spent $500 on fuel for it last year.

My impression is that the system is overkill, that they didn't want to have to conserve. If we end up buying that property, I will likely make some changes as that is not in line with my values, and I don't want everyone to get used to unlimited power, as I would never pay to keep it that way.

sounds like a large robust system then. That is good. having the option to use power and using it are two different things. Is it grid connected as well? Solar electric heating is unusual solar thermal maybe more so. Cheers and good luck.

I don't know if it makes a difference for your questions.  This sounds like it might be a "whole house system".

If it is tied into the grid, the electric company may be offering discounts. They route the excess power into the electric grid for compensation from the utility company.

Personally for me I don't mind if there are alot of solar panels.
What I worry about is battery.
Batteries have to be replaced every 5yrs.
So find out how much he has installed, then figure out how much it will cost you to get new ones every 5yrs. Next I would ask for a drawing of the electric system so that you or someone else can look at it and make changes easier. also an inventory of the stuff used (model number+date/year installed)

I might be a good idea to split the system into two separate part.
One to run/power the house how you like it.
And the other set just as a "backup/workshop/e-bike/etc" that you will just not maintain/upgrade later.
If you use alot of electricity after sunset you will need alot of battery. (washing machine/dryer/etc)

If you heat a 50/80gallon hot water tank during sunlight. You will not need batteries to store power.
You would have to set it up not to refill with cold water or something.

I am not too sure how your electric heating is done. But if it is radiant heating. Then you could store the heat in a water tank during the day and then use that to warm up the house during the night. The floor can also store some heat too.

If you can do your laundry during the day you will need less battery storage, even better if you can air dry.
Electric cooking does not take alot. Induction cooking, tabletop oven, microwave really cuts down so much on electric usage
Fridge a chest fridge helps and less visits to the fridge help.
LED lighting + Flat panel TV/Monitors, All in One Computers and tables and phones help too.
I have seen a SERR 42 Air Conditioning unit, changing over to that will help alot.

But to help us answer you better.
How much gas(heating) and electric do you currently use.
Once I have that I can convert that to a solar system, and see how much of the off-grid system you can get rid of.

I use about 3.3kWHr per day in electric (100kWHr/month alot less than the avg) but a ridiculous amount on gas/heating easily 10x (1,111kWHr/month which is the avg for my area)
https://www.mass.gov/info-details/household-heating-costs

It is not grid-tied.

Here are some pictures.

With a Monthly estimated usage of 3,000kWHr aka 100kWhr/day and 4hours of sunlight per day.
Installed Solar Panel = 25kW (daily usages/hours of sunalight =100/4)
Min Battery Storage = 100kWHr (one days worth of usage rated for 50% SOD)
Avg battery Storage = 300kWHr (three days worth of usage for when there is low sunlight/storm)

Battery Price = $200/kWHr
Min Battery Cost = $200 X 100 = $20,000 every 5yrs
Min Battery Cost = $200 X 100 * 5 = $100,000 over 25yrs

Solar Panel Price = $0.50/W
Solar Panel Cost = 25kW * 0.50/W = $12,500 every 25yrs

Controller+Inverter+Charger Price = 0.50/W
Controller+Inverter+Charger Cost = 25kW * 0.50/W = $12,500 every 12.5yrs
Controller+Inverter+Charger Cost = 25kW * 0.50/W = $25,000 over 25yrs


These are just my guestimates, I would be able to give better numbers once you get some more info.
Hopefully they have a way more optimized system vs this avg numbers that I am showing you.

very pretty... older. its the outback assembly but with xantrex inverters. Frank would be more familiar. 4 Flexmax charge controllers which are newer. That battery bank is huge but there are 4 array of up to 4 kW each if those are the fm80 controllers... Again,  very pretty and nice install

Sweet, way workable equipment zantrex XWs and aquion batteries, the biguns, like 32kWh each large module.

Its the good stuff, nobody did(does)it like outback with the backplate mounted power centers, the best (even without fx inverters)! Midnite battery combiners nice too.

How big is the array?

Aquions! I couldn't figure it out. That explains the huge bank. Frank 24 volts or 48 do you think? The 4 controllers is unusual unless its only a 24 volt system... or it has 16 kW of panels!
Wow

Id ask how long the system generally carries the house when nobodys home and while occupied, if they know. Other than that, ask if the equipment works now, and if it does look into a service person or into being the service person to give it a checkup and then dont worry about it until you see a major change or the light go out.

Its really a nice system and should provide many years of use.

David Baillie wrote:Aquions! I couldn't figure it out. That explains the huge bank. Frank 24 volts or 48 do you think? The 4 controllers is unusual unless its only a 24 volt system... or it has 16 kW of panels!
Wow

Hard to tell the battery voltage for sure, if i remember, you could get the kWh in several configurations. I was so excited about these. Come to find out, they can be as toxic as anything..... nice characteristics and operation though.

The inverters, it almost looks like SW4048 not sure there either. I doubt a system that big would have lower battery voltage than 48, just based on the layout and equipment selection, battery size, etc., still dont know the array size. I bet its awesome too.

They (Trace/Zantrex) SW were good reliable gear but had some had issues.

David Baillie wrote: The 4 controllers is unusual unless its only a 24 volt system... or it has 16 kW of panels!
Wow

Sometimes its a big array(s) and sometimes the string counts just work out that way.... sometimes its 24v!

$20,000-ish battery if i remember too..... 12k-16k apiece for the modules plus bms, the inverters were 2k-ish each, 2k$ into the ac and dc distribution center, probably has a balancing transformer-$250, 500-700$ plus for the battery combiner and bus/breakers, 2k$ worth of charge controls, genset looks milspec/telecom/aviation and is also integrated sweetly,

Hours of installation.....

These guys spent serious money and someone cared to select hardcore gear. The array expense was probably wild if it dates to or before the inverters. Expansion has likely been done on the arrays too.

Interesting to see.

So, the realtor says that if the solar system was purchased at today's prices, it would cost around $100,000. I will get specifications when we look at the property on Monday. It looks like it could be a good property for us, I just don't know a lot about off-grid solar. I've done some research, but really basic.
Here are some pictures of the array.

The arrays look older so wow that was some serious change to install. In groupings of 8 for the two most recent arrays which is odd for 48 volts... really serious system.

Solar hot water and space heat to boot! Nice place to enjoy, hope you get it, if you like it!

Looks like the previous owners enjoyed it greatly while using a different cooler for every chore!

Just got back from looking at properties, so I have more info about the solar on this place. It has two sets of 8 each Sharp 185 watt poly solar panels on Wattsun solar trackers (2960 watts) and two sets of 12 each Solarworld Sunmodule SW 255 watt mono black solar panels on Schletter fixed ground mounts (6120 watts) for a total of 9080 watts. Four Outback Flexmax 80 charge controllers all less than 5 years old. Batteries were installed in 2015 and they are two M100-L0829P Aquion, total storage capacity of 56 kWh. Two backup generators - primary backup Shawnee Power Permanent Magnet 48 volt, 8 KW (56Vdc, 143Amp output) diesel powered generator which directly charges the battery bank and a secondary propane generator if the solar is out. Two Trace inverters to provide normal 120/240v ac power to the houses. And another generator in the barn for its' needs. There is a solar water heater, and an air conditioner for the main house.

All in all, the system seems rather extensive. The owner did the installation himself, apparently he's something of a pro. I will have to look into finding someone that can help me with it, as I'm not particularly knowledgeable. But the property looks like a good fit, and we will likely make an offer on it.