New Off-grid house

tyagel

All,

This will be my first post. I was temped to post a few weeks ago with all my million questions but spent the last few trying to get a little up to speed...

So I'm in the process of closing on an existing off-grid 3br/3ba house in Vermont. It is currently powered entirely by a Kohler 6.5RMY propane generator.

We are certain that we will use more power than the prior owners (looking to replace propane fridge with electric, put in dishwasher and clothes washer, install microwave, etc.). We are not planning on AC for the summer however. So I did the best theoretical calculations I could make on power consumption and came up with the following.

Average 260kWHr/Mo Summer, 320kWHr/Mo Winter, Peak power consumption (toaster, hairdryer, microwave, etc all running) 10kW.

So in trying to plan out how much solar wattage I would need I did the following calculation.

260kWHr / 30 (days) / 2.8 (conservative daily sunlight winter hours) = 3.11KW Panels Needed
Multiplying by 2 gives 6.22KW Panels Needed (IS THIS TOO Conservative?)
Panels for this much power would seem to run me <= 5K... I've looked at a bunch of panels online, read some reviews, but would love to hear people thoughts...

The Next Piece that I started trying to figure out was the batteries required...
I did the calculation 6.22kW * 3 (days) * 2.5 (figuring not to let battery drop below 60%) = 46.65kW

Its seems the most efficient battery option is 48V (I remember from years of physics that higher voltage equals less loss to resistance).
So 46.65kW / 48V = 971Amp.
Trojan L16RE-2V 1110Amp batteries that seemed like they would do the trick. @$353/per * 24 batteries = ~$8500.
I have no idea if this is wildly over battery (they seem darn expensive) for the system. Also there seem to be plenty of issues around the temperature and losses due to that?

Which leaves the Inverter.
A Sunny Island 6000W inverter seems like its close to what's needed for the daily power (no idea if it could handle the peak demands...). This coming in at ~$4700.
Seems a little silly not to have inverter enough for fully solar wattage so not sure if I would do better finding a bigger inverter or two smaller ones?

Which leaves the generator and charge controller. Not sure if existing generator would be acceptable at first or need bigger one. And haven't really learned enough yet about charge controllers except that maybe it would be another $1000.

As you can tell I have done some basic calculations, but I really would love some guidance in terms of how to size out and fit all the pieces together on this... I can keep reading, but feedback and maybe some more rules of thumb for figuring this stuff out would be really helpful.

Thank you for any and all advice you can give to me!

Thomas

tyagel

Re: New Off-grid house

Oops. 260Winter 320Summer... Sorry for mixing that up.

NorthGuy

Re: New Off-grid house

I think your calculations are Ok. I have slightly more loads and I'm doing fine with array of your intended size and less batteries. My batteries can be discharged to 80% DoD, so it's about the same as yours.

Trojan 2V batteries are not real 2V single cell batteries. They consist of 3 cells conncted in parallel. Not only get you all the bad things that come with parallel connections, you now have 72 cells to water instead of 24. Surrette makes 2V single cell batteries in L16 shape, and some other companies have them too.

niel

Re: New Off-grid house

ok a few questions here. are you looking to eliminate the need of the generator altogether or do you intend to keep it as backup (recommended)? would it not also be better to go with the 320kwh worst case to base your pvs needed, noting that this may not matter as much with the generator being run occasionally?

it seems viable, but it may be better as an option to use a smaller inverter to keep high loads off of the batteries and this would help you to learn to spread out the loads. odds are you may want to up the number of pvs as most do expand their loads sooner or later anyway. this would also benefit the batteries by keeping high loads operational to times of good solar production by being more able to throw a charge into the batteries and handle the loads directly upping efficiency.

mike95490

Re: New Off-grid house

At the risk of being ridiculed for being wasteful, what about using the propane fridge in the winter ? It's heat would help the house heating budget, and relive some of the electrical load.

And generally, a house has a small "base load" that a 2 or 3KW generator could manage, and still put some charge into the batteries, without consuming a lot of fuel.

And for off-grid, you never, ever, run the toaster, hair dryer and microwave at the same time.

tyagel

Re: New Off-grid house

Thanks so much for replying already!

NIEL -- I definitely plan on keeping the generator. I would like to reduce batteries (but not be running generator too much) -- these things seem so expensive. I didn't use the 320kW number because with the low sun hours in the winter it seemed like that would be the driving number (2 * 320kW / 30 / 4 < 6.22K). Not 100% sure what you mean by using a smaller inverter and spreading out the loads...Are you saying use two inverters and distribute the batteries in some way between them? I know I'm showing lack of understanding here Also absolutely no problem power up higher than 6kW if that makes sense and means better battery life or fewer batteries...

NOrthguy -- Thanks for you reply on the batteries. I can definitely look at batteries other than the Trojans (and watering 72 seems unappealing). I see that you have 8 Trojan IND13-6V. What was the reason for choosing those? Why 6V over 2V? Would it be preferable for my system? I also noticed you were using two controllers. Is that generally preferable? I will try to do some research online, but I'm not yet familiar with how to appropriately size controller for system.

In general I am finding the batteries the most complicated (and expensive) part about thinking about this system. One of the pieces of this is that I read that you can't replace batteries with new ones if one fails. How do people deal with this? I would hate to replace a 1yr old 8000 dollar battery system because one battery failed...

Thanks again!

tyagel

Re: New Off-grid house

Mike, Point taken on the hair dryer, toaster, microwave not all being run at the same time! I definitely would not want to fork out tons of money to over build a system just to handle that.
Running propane fridge in winter is definitely a possibility -- although the idea for using a non-propane fridge is that its bigger & looks stylish (please don't laugh me off the forum...its the wife's requirement). With respect to the 2-3kW comment that seems like it means that we wouldn't need to get a bigger generator that the existing 6.5RMY. (We are also fortunate enough to be getting a lot of gals of propane in the tank with the purchase).

niel

Re: New Off-grid house

the 320kwh would be the worst case draw you figured you'd need and if you design low you will need to run the generator more often. in fact you can even cut it all in half if you want to and run the genny more in the day while the batteries charge up to handle night time loads. it's all in what you feel is ok to do.

as to a smaller inverter it would stop you from popping a large load to your batteries at one time forcing a bit of awareness of your loads. instead of using 6kw at one time you can use 4kw instead and lessen the impact on your batteries by that 2kw which represents about 41a at 48v. the other 2kw in loads you would use at another time when you aren't using as much power. besides the 4kw inverters are generally cheaper, but there are also 6kw inverters that are cheaper than that too. all up to you how you want to do things and which you would prefer, but i'm just throwing out possible options to lessen battery strain.

you could even supersize it and just about eliminate any need for the genny, but even then i'd hang onto it as mother nature throws curve balls.

vtmaps

Re: New Off-grid house

Welcome to the forum,

You seem to have a good grip on the basics.

Are you planning to do the install yourself? Have you thought about how to mount the panels (roof, pole, ground)? Where do you plan to put your batteries & electronics (power shed, utility room in house, garage, basement)? Do you have or plan to have a water pump (surface, submersible, booster)?

--vtMaps

P.S. What part of the state are you in? Do you need recommendations for an installer?

tyagel

Re: New Off-grid house

Vtmaps,
You raise a number of good questions that I haven't figured out...
- The house is in Vermont. Reading. Not too far from Ludlow.
- I would love solar installer recommendations. I'd love to do the project myself but time and experience will likely dictate that I work with someone for the project (I've done plenty of carpentry and wiring but nothing of this complexity and size) . How much do solar installer generally cost? I don't want to pay mark up prices on components but would be very interested in how it generally is priced.
- It wouldn't be a roof mount because of space. We have plenty of land so it could either be pole or ground rack. I'm not worried about theft vandalism but snow could be a factor so being able to rotate panels and have them off ground for snow would be great. Thoughts?
-In terms of buildings sheds etc I also need to understand this.. . I know temperature affect battery performance so should there be heating in she'd with batteries inverter etc? I already have she'd for generator but it's too small to add anything into. And it's also too loud but that's another issue.

vtmaps

Re: New Off-grid house

tyagel wrote: »

Vtmaps,
You raise a number of good questions that I haven't figured out...
- The house is in Vermont. Reading. Not too far from Ludlow.
- I would love solar installer recommendations. I'd love to do the project myself but time and experience will likely dictate that I work with someone for the project (I've done plenty of carpentry and wiring but nothing of this complexity and size) . How much do solar installer generally cost? I don't want to pay mark up prices on components but would be very interested in how it generally is priced.
<snip>
In terms of buildings sheds etc I also need to understand this.. . I know temperature affect battery performance so should there be heating in she'd with batteries inverter etc?

I was in Reading a couple of days ago. Your foliage should be nearly peaking:D

I will be happy to discuss installers with you by PM. First you need to figure out a bit more about what you want. Start with location of panels and type of mount. I have a top-of-pole mount and am very happy with it except for one thing: it doesn't go completely vertical. Vertical is very desirable when there is snow on the ground... the snow reflects light up onto the panels, and vertical panels shed snow very well.

Once you know your location for the panels, you need to think about how to get the power from the panels to your house... are you OK with digging a trench through your rose garden? I strongly recommend that you keep your batteries and electronics outside your house. Batteries make heat and if you put them in an insulated box in a earth-bermed power shed they will do just fine. They have less capacity when cold, but as long as you design for tat you will be OK. I keep my battery and electronics in a detached, lightly insulated garage/workshop. I have a woodstove in the garage and I light just enough fires to keep the temp above freezing. My batteries, in their box, never get below 50° F in that environment.

If you do decide to have your batteries and electronics in an outbuilding, be sure to run two conduits to the house... one for the power and one for monitoring and control wiring.

--vtMaps

tyagel

Re: New Off-grid house

Neil,

Having slept on it your points all make sense to me I believe.
- I was thinking only of the wattage of the array and not the batteries. The batteries need to be sized for summer even though there is more daily wattage coming of the array. So I'll redo the battery calculations with the 320 number.
- I also get the inverter point now. I was Sizing the inverter to the solar array. Your point is that a 4kw inverter will easily handle the average load with room to spare. It then just leaves the question of what max loads we want to plan for, right? With the same load does a larger inverter put any additional strain on battery over a smaller one?
- now another part of the equation also seems to be coming into focus... If I plan my array for what I am expecting to be daily usage with efficiency losses and accounting for winter sun (6kW array) then how do I recover without always having to run the generator to recharge? Do I plan for twice the array needed so I can pack in one extra battery day charge per day? Or maybe 50 percent over? Frequently the system will draw minimal power during the week but even stil 4 days to fully recover from 60 percent would seem reasonable. Thoughts?
- In terms of the batteries, is there a way to calculate the maximum number of watt / hour you can charge? Also is there a strain on the battery the faster you charge them?
- Ok so I'm still lost in terms of calculating the right batteries to use... 2 4 6 12v. There seems to be some serious cost trade offs... But I'm assuming there should be some economic benefits in Sizing the 'right' batter array. If any battery system I'm going to install will only last 5 years, I'd rather go with the lowest initial price tag... I'm sure someone has done these trade off calculations... I'd be very interested to know people's thoughts? (or a link since maybe it's been discussed)

Thanks again! This is truly great being able to discuss with such a knowledgeable group.

tyagel

Re: New Off-grid house

So sorry for misspelling name. Niel

NorthGuy

Re: New Off-grid house

tyagel wrote: »

Thanks NOrthguy -- Thanks for you reply on the batteries. I can definitely look at batteries other than the Trojans (and watering 72 seems unappealing). I see that you have 8 Trojan IND13-6V. What was the reason for choosing those? Why 6V over 2V? Would it be preferable for my system? I also noticed you were using two controllers. Is that generally preferable? I will try to do some research online, but I'm not yet familiar with how to appropriately size controller for system.

My batteries are weired. I bought them because they promised longer life and deeper discharges. Howere, the way they're designed is absolutely unsuitable for solar applications. I wouldn't recommend them to anyone. It was a mistake to buy them.

Usually 6V batteries consist of 3 2V cells connected in series, so you get the same thing as if you had 24 separate 2V cells, but in a different pakaging. I would prefer separate 2V cells. They are easier to move around or replace, but they require more wiring. Noone makes them as small as I needed, so I had to go with 6V.

About the controllers. A controller can only handle so much. Mine can do 3.5kW each, so I had to use two for 6kW array.

Dave Angelini

Re: New Off-grid house

I would also consider an XW system from Schneider Electric. The 5000 watt 600 volt solar charger is extremely easy to install. Also consider a Honda 6500i modified for propane. They are extremely reliable and the benchmark for quiet running. There are some pictures on my webpage. Did you have any problem closing on an offgrid property? Good luck

mike95490

Re: New Off-grid house

Also with inverter size, the internal AC charger size varys . The 4Kw inverter may have a 60A charger, the 6Kw may have a 100A charger.

Then you have to read the fine print on the Power Factor of the charger, which varys from .9 to .6 between different brands. That Power Factor affects your generator size and running costs.

Having 2 generators, one small and one large, gives you many more choices. I use a 30A 240V dryer cord to connect to my different generators, or you could use a utility box and interlocking switches for connecting. (outlets are mounted on the generator, plug & cord on the breaker box)

tyagel

Re: New Off-grid house

Dave I really hope we don't have any problems closing... Its this month. I will research the components you recommend! Thanks

tyagel

Re: New Off-grid house

Mike, on the inverter concepts you are discussing is it the case that one can charge batteries either from inverter or from charge controller? Or maybe what this means is that you need the inverter to go from generator AC to DC into the charge controller? Or do you go direct?

vtmaps

Re: New Off-grid house

tyagel wrote: »

Mike, on the inverter concepts you are discussing is it the case that one can charge batteries either from inverter or from charge controller? Or maybe what this means is that you need the inverter to go from generator AC to DC into the charge controller? Or do you go direct?

The charge controller sits between your panels and your batteries. It regulates the charging from the panels.

The inverter/charger is also connected to the batteries. When the generator is on it becomes a charger and charges your batteries independent of the charge controller and solar panels.

--vtMaps

niel

Re: New Off-grid house

tyagel wrote: »

Neil,

Having slept on it your points all make sense to me I believe.
- I was thinking only of the wattage of the array and not the batteries. The batteries need to be sized for summer even though there is more daily wattage coming of the array. So I'll redo the battery calculations with the 320 number.
- I also get the inverter point now. I was Sizing the inverter to the solar array. Your point is that a 4kw inverter will easily handle the average load with room to spare. It then just leaves the question of what max loads we want to plan for, right? With the same load does a larger inverter put any additional strain on battery over a smaller one?
- now another part of the equation also seems to be coming into focus... If I plan my array for what I am expecting to be daily usage with efficiency losses and accounting for winter sun (6kW array) then how do I recover without always having to run the generator to recharge? Do I plan for twice the array needed so I can pack in one extra battery day charge per day? Or maybe 50 percent over? Frequently the system will draw minimal power during the week but even stil 4 days to fully recover from 60 percent would seem reasonable. Thoughts?
- In terms of the batteries, is there a way to calculate the maximum number of watt / hour you can charge? Also is there a strain on the battery the faster you charge them?
- Ok so I'm still lost in terms of calculating the right batteries to use... 2 4 6 12v. There seems to be some serious cost trade offs... But I'm assuming there should be some economic benefits in Sizing the 'right' batter array. If any battery system I'm going to install will only last 5 years, I'd rather go with the lowest initial price tag... I'm sure someone has done these trade off calculations... I'd be very interested to know people's thoughts? (or a link since maybe it's been discussed)

Thanks again! This is truly great being able to discuss with such a knowledgeable group.

actually everything starts with your daily load requirements that determine your battery bank size and ultimately your pv size. a generator can be run daily if you wish to keep the costs down on what the solar array and batteries may cost as systems designed to handle full normal daily loads can run up the price quite high. to further this in attempting to eliminate the generator periodically could go super expensive as that would be very tough to achieve. most allow up to 3 days autonomy for battery backup, but this is 3x the size of a battery bank that is based on a day's usage that could be supplemented with the generator if the next day is too cloudy. most of us base everything on a day for loads and charging as a starting point and some opt to handle it with cloudy days on the genny. this may be more use of the genny than you may find acceptable and hence upping the battery capacity for each day of operation that solar may not be available for.

opting for higher autonomy does add to the basic charging requirements of a pv system to being able to supply said loads and charging the batteries back up after the autonomy period is up and you now have available sunshine. i have times where the sun is gone for weeks and that would be a ridiculously over sized battery bank. the over sized array can make the autonomy needs smaller by giving more power in less than optimal times and when the sun appears it can supply both load power and battery charge power.

as you can see it is basically simple, but with so many ins and outs it adds complexity.

as to the inverter wattage rating, that is basically the most power to be drawn at one time. it is possible with many higher power electric loads running in tandem with the many normal smaller loads to hit 6kw of draw and that can be a huge strain on a battery bank even though the instances of the loads hitting the 6kw point might be rarer. a simpler 1kw inverter, only as an example, if run for a day at max would be 24kwh and at a 48v battery voltage would be a 500ah draw for a 1000ah battery bank set to max recommended 50% depth of discharge (dod). that would obviously be too small for some of your all at once loads and nobody does that at max continuously, but if you figured every load on you could have to present to an inverter it could probably exceed the 6kw inverter too. it is not desirable to do without some loads that would be an on/off thing in duty cycle in having continuous loads, but it isn't necessary to go with the max total possible load you can put to it either as you can spread out the loads. instead of running the microwave while running the sweeper and washing machine/dryer combo at the same time, you could run them at different times or even at the time of receiving good solar power with an over sized pv system able to provide power to the loads while also providing power to the batteries for charging.

rather than keep you head spinning on all of this go with a 6kw inverter anyway if you figure you'll need it and if you wish to limit the wattage draw i believe you can do that even with a lower sized main breaker to pop off to remind you of your high draws. some may not like that option as it may pop at an inconvenient time. in fact go with the basic system you've figured and just add more pv to it and if necessary another mppt cc to handle it and most circumstances will be accounted for. it's the variables that can come into play that give one a headache. you can add to the pvs system later too if you like.

Dave Angelini

Re: New Off-grid house

If you do you can contact me or post here on the forum. There are different strategies for insuring and loan issues that are specific to offgrid that I have help others with.

tyagel wrote: »

Dave I really hope we don't have any problems closing... Its this month. I will research the components you recommend! Thanks

Dave Angelini

Re: New Off-grid house

You can charge from the inverter/charger with a generator, the solar charge controller, or both at the same time which is an excellent strategy in winter in your climate.

tyagel wrote: »

Mike, on the inverter concepts you are discussing is it the case that one can charge batteries either from inverter or from charge controller? Or maybe what this means is that you need the inverter to go from generator AC to DC into the charge controller? Or do you go direct?

zoneblue

Re: New Off-grid house

I remember being in your position vividly. While i considered myself suffciently smart, the whole process was a rapid learning curve akin to leaping off a cliff and absorbing absolutely as much as you could before you hit the bottom. At which point you write the check and hope you got it right.

I would summarise the state of the industy like this: Because of the recent changes in pricing of pv, lead, and copper we are currently in a transition period. Many of the old timers know and love small engines. Its a part of them, and generators are hence part of their world. But theres another paradigm probably at the far other end of a spectrum, thats as full of shades of grey as any other.

That paradigm says that pv is now cheap. Batterys are now expensive. Hence, the new model says that you use more pv, LOTS more. Less storage, just enough to get you through the night really, one grotty day maybe. I know a guy whos just installed a setup like this 10kW PV, small bank, small inverter. Obviously you can go too far, but you get the idea.

The inherently related thing is an attitude to demand management. If you want/need a no arguments lifestyle, well thats the modernist school. You just want what you want. In this world you need generators, big batterys, big inverters, and generator support. Prepare to get your hands dirty.

The progressives amongst us, would on the other hand, say: well, its rainy this week, so power isnt available, (and heck it wont dry anyway), so ill do the laundry next week, when its sunny. No big deal, its a part of living in tune with your environment. That way a power shortage isnt a crisis. Dont need a generator, can get away with a small bank. Can run a bunch of stuff off of DC directly, so small inverter.

Low idle losses, low storage losses. Fast and lite. Small bank equals fast charge so AGM comes into its own taking high C charges. Doesnt cost much, couple of grand, so replacing it isnt eye watering.

As far as installation, around here they charge about 1-2 dollars per installed watt. Its not rocket science, you seem to know what you are doing, id encourge you to give it a try. Sticky beaks that we are, we will probably help!

Have fun with it, there are few things more satisfying than making your own power.

Cariboocoot

Re: New Off-grid house

No matter how cheap PV gets it still won't work without sunshine.

zoneblue

Re: New Off-grid house

well i cant speak for where you live, but the sun shines ok here.

tyagel

Re: New Off-grid house

OK. Its amazing how much easier it is to think about this stuff when you are getting feedback.

- First off I think my battery calculations must have been off. Let's say my peak power requirements are 300kW/Mo (rounding down from original 320kW/Mo number). That's 10kW/Day. Multiplying by 3 days = 30kW. Multiplying by 2.5 for max drain of 40% = 75kWhr. Then you need to adjust for battery through inverter efficiency (85%?). So 75kWh * (1/.85) = 88kWh. Now I'm certain I am investing in batteries nowhere close to that number. Maybe best case i would invest in 40k or a little more to try to offset inverter inneficiency. I could do 43,200 with 16-450amp, 6V batteries... In any case it seems my original calculation were off (I was just looking at solar wattage). I'm calling this $6,500? Should i go for an even cheaper battery option?

- No I need to be able to at least replace one days battery usage with solar panels. This is where i used the winter hours and came up with a need for 3.11kW Panels. It seems that if I have a sunny day and I want to charge up I need to start with my losses through the charge controller and through the inverted? I was using 50% losses before but it seems less than that? Was i more correct in the first place to assume 50% losses? So anyway Lets say 75%. So 3.11/(1/.75) = 4.15kW. Doubling things up to 8.3kW lets you put a bunch of charge on the batteries the first sunny day you get. @$0.85/W thats about $7,000. Would I find good panels at that price by pallet or should I go up to $1/W+ panels?

- If I had two of the schneider electric 600V, 80Amp charge controllers can i put 8,300kW/hr onto the batteries (less efficiency losses for charge controller (and obviosly less any power I was pulling through inverter)? These run me $2,200. I guess whether i needed more charge controllers would depend on the specific panels?

- So then inverter which will come in 3-5k depending on whether i go 4kw or 5/6kw inverter...

What do i need to be considering in terms of monitoring the system? Can everything be programmed (when the generator turns on / off?). Can I monitor my system completely remotely?

niel

Re: New Off-grid house

you are making it seem just as complex as you probably perceived what i said it to be. generally from pv to cc to batteries to inverter and then to the loads is almost 50% in losses and is really listed as 48%. that means for a 1w load it needs 1w/.52=1.92w in pv to start. now this can vary considerably as one does have some say on the amount of losses that are experienced. bb. can elaborate more on the standards that derived the .52 efficiency factor as i do not have that link on this pc. my guess is still that your initial setup with a tad more in pv would probably work out well. it is often difficult to nail it down exactly in every case and even then it can change in a few years due to increases in loads and slight degradation in battery efficiencies as they age to any number of other smaller influences. if you want to get right down to it it is always best to err on the safe side by going a bit more on the high side of things and that even influenced my advice in staying with an inverter in the 6kw range. your instincts on what you need are probably very good and going with that and a bit more in pv power i think should work out very well for you and if not you would have time to upgrade your batteries, controllers, pvs, etc if need be. always think that the system you settle on may need to be expanded on and you will find yourself with less hair loss in the future.:p

tyagel

Re: New Off-grid house

Thanks again Niel.
The help from all of you is amazing! I'd love to pay it forward one day.

So I hear you on the overall average 52 percent loss. I was assuming though that there were two 'sets' of losses that I'd be concerned with how much do I loose of 1w from battery to ac plug (affecting how big size my battery) and how much I loose from 1w pv getting it into the battery.

Also was my understanding of the controller generally correct? Are there any other major components to the system that will contribute to the cost significantly that I have missed? Surge protection? Monitoring equipment? I know racks are another big decision but I haven't spent much time with that... (figured once all this is figured out I'll read a bunch of posts on that)

Blackcherry04

Re: New Off-grid house

Having played this off-grid for a long time, I'd add a extra 10 % to your capacity while your designing it. Over the years the 24/7 parasitic loads have gone crazy. Everything has a transformer and a remote these days and they all suck power. If you don't you'll drive yourself crazy looking for them, everything adds up and pretty soon you'll find yourself coming up short.

niel

Re: New Off-grid house

good point as phantom loads can be a royal pain at times. some loads you may want switchable with power strips and in some cases you could utilize a switched outlet.

as to the figures going from the battery to ac loads i don't have the link to the info as bb brought that link to that info onto the forum and you may find it somewhere here. we often have cited efficiencies going from the pvs to the batteries at roughly 77% so you may be able to extrapolate from that the info you want.

Cariboocoot

Re: New Off-grid house

The over-all loss factor is based on all power being stored to and used from batteries. Efficiency improves with an increase in the amount of power used "directly" from the panels (i.e. batteries charged; make use of panel power that otherwise would go unrealized).

It will also vary with local conditions of course. At 3200' elevation my panels are approximately 5% more efficient than typical, and the 16 hour Summer days give plenty of Watt hours. Trouble is they are offset by 6 hour Winter days which render the system unusable.

And of course it does rain here occasionally, which is why there is a generator. I've heard it never rains in southern California. Or New Zealand, apparently.