system plan sound reasonable? (new to solar)

edbee · July 2012

Hi,
Planning my first PV system. It is for an off-grid cabin where we will be spending a fair bit of time (30%) over the next year or so and eventually building a house and living there full-time. I figure our short term (first year or so) needs will be about Total Avg. Daily AC & DC WH = 1800.

I want to build the system so it will be expandable for when we have a full size house (family of 4) and workshop so it might seem like a bit overkill for now but that is the rationale for going with 48V battery bank and big inverter at the moment. We live in the Pacific Northwest.

Does this sound like a workable selection of components?

-1 string of 3 315 watt panels (Kyocera KD315GX-LP)
-Midnite Solar Classic 200 charge controller (it is about 75 feet from array to controller)
-Magnum 48V 4400W 120/240 volt inverter (need to power a 240 volt well pump)
-8 6V 240 Amp-hour renewable energy batteries (thinking US brand – do they have a good reputation?)

The panels will be in a spot with full sun all day long for most of the year (well, minus the clouds, at least no appreciable other shade).
Will soon need a 48V to either 12 or 24 volt converter to run a SunDanzer freezer too. (recommendations on convertor welcome).
Likely get one of those propane Generac EcoGen generators as well as soon as I can make that happen. Are they really worth the extra money over Generac‘s other propane generators?

Long term plan currently includes multiple strings of those 315 watt panels (4 strings of 3? the Classic 200 could accomodate that) and switching to L16 batteries.

For me, the solar power part of this project is one of the most exiting pieces of leaving the big city behind.

Hopefully I have included enough information to make my questions answerable. I have researched things quite a bit but being new to all of this just want to make sure I am not overlooking something obvious.

Thanks in advance.
Ed

PS - plan to get a Midnite Solar prewired system and work with the electrical inspector to make sure I do things in a safe manner.

BB. · July 2012

Re: system plan sound reasonable? (new to solar)

Before I go down the road with a bunch of math... Roughly, where will the cabin/home site be located?

If you are around the Marine Layer (such as Vancouver BC), solar is tough because of the cloudy weather and needs a fairly big array to make up for the poor sunshine.

However, we have a few people that live in the mountains up your way, and other than during bad weather, they are living quite well with pure solar and genset for winter backup.

-Bill

Regarding the inspector--Make sure you have a basic understanding of solar / off grid power systems (we will help you with that here). It has happened that inspectors and even licensed electricians have made some spectacular "oopses". Many folks are familiar with the requirements for AC power--But really have never thought about the issues of wiring up "low voltage/high current" DC systems.

Cariboocoot · July 2012

Re: system plan sound reasonable? (new to solar)

Welcome to the forum.

Let's have a look at your numbers and see how they stack up.

1800 Watt hours per day? Sounds quite low for a family of four. We use 2400 to 2800 Watt hours per day with just two of us.

What can you get from three 315 Watt panels? About: 945 Watts * 4 hours * 0.52 efficiency = 1965 Watt hours AC. That's cutting it rather close for 1800 Watt hours of load.

240 Amp hours @ 48 Volts: up to about 5kW hours (50% DOD). To recharge that much battery you'd want more like 1500 Watts of array: 24 Amps peak current @ 48 Volts = 1152 / 0.77 efficiency = 1496 Watt array.

Skip the SunDanzer.

(Short answer - running under T-storms here.)

icarus · July 2012

Re: system plan sound reasonable? (new to solar)

Let me chime in as a long time off gridder. We assume at the outset that you have no grid power semi easily available,, because even it it is expensive to bring grid power in, grid power is going to be way cheaper per KWH in the long run.

Now, There are a number of rules of thumb that I use when making suggestions. First, load always grow with time so figure long, and then add in a significant growth factor. Second, people almost always underestimate their loads, while at the same time they over estimate the amount of solar power they can actuall harvest on a daily/weekly/monthly basis. Combine the two and most people come up short.

My rule of thumb for battery based systems is this.. Take the name plate rating of the PV, and divide that number in half to cover all cumulative system losses, including, basic PV ef, charge controller losses, basic battery charging ef (~20 right off the bat!) Then, take that number and multiply that number by 4 to account for the AVERAGE hours of good sun one can reasonably expect, per day over the course of the year. You can fudge that number a bit especcially n the summer if you are fairly high latitude, but full time I wouldn't fudge it much unless you live in a 300 days of sun climate. So, for example, 1000 watts of PV might look like this: 1000/2=500*4=2000 watt/hours/day.

Please remember that all calculations start and end with the loads. Define the loads carefully and the other element will define themselves. PV needs to be sized for battery bank size, battery bank size needs to be designed to estimated loading (plus however many days of autonomy that you desire, inverters need to be sized to the loads, both peak and average, and in some cases multiple inverters are a good idea if you have large peak loading, but small average loads.

So, to avoid the biggest single (most expensive) error that people make, is avoid Ready, Fire Aim! Before you buy anything,start with a clean slate, and fill in the blanks accordingly. The mistake that folks make is buying hardware because it is a "good deal" but it turns out to be a square peg, and they then spend other money to try to make that peg round.

A couple of notes about usage. We use 500-800 wh/day, and that is very, small! We use a propane fridge which saves KWHs but costs propane. Propane makes sense if you are only going to use the place occasionally, but the curve bends toward a convention fridge the closer to full time it is going to be used. If you take my case, it would raise my loading to ~1.5 kwh. We use no resistance heating,(except the heated mattress pads!) at all. No toaster, no hot plate, no hair dryer etc. We even have a propane toaster! We use a cell phone ISP/voip system, lap tops. We also have no TV, although we do watch movies on the lap top. All our lighting is CFL or LEDs (More LEDs now!) and we seldom have a more than a couple on at any one time. We also have a couple of paddle fans, fridge fans, the radio. We heat with wood, with no ancillary electric cost, have demand hot water with standing pilot light. (most new demand water heaters now use ~5 watts in stand by and ~40 in use!)

I would suggest that your estimate is quite low, assuming you are going to use a conventional fridge. Spend some time logging your essential loads, and see where you can cut, but also see what you will really use. Welcome to the forum, keep in touch and I am sure you will have more questions. The folks here are really quite smart, and experienced (myself not included in the former!) and are more than willing to help. Many, and you will soon learn who they are, have learned more about PV than most of us will know, and in general have very good advise. Good luck and keep in touch,

Tony

edbee · July 2012

Re: system plan sound reasonable? (new to solar)

Wow, what a great board! Thanks for the speedy and helpful replies! I’ll answer questions and supply more detail the best I can, and ask more questions…

Where exactly: Salt Spring Island which is close to the American San Juan Islands and Victoria, BC. Yes, not the sunniest part of the planet but at least Salt Spring gets 1/3 the rain of where I presently live (North Vancouver, BC – about 40 inches/year as opposed to 120). The site in question has great southern exposure.

Grid: a grid connection is possible although would cost about $20,000 - $25,000. (loooong driveway) Here in BC electric power rates are forecast to climb dramatically in the fairly near future.

Underestimating loads: yes, my estimate of 1800 WH per day is not much. We plan to build a house and workshop in the next few years and the house/shop will have very different load requirements than the short term estimate of 1800 WH/day. The short term estimate is really just to have enough electricity to light a few LED lights (currently run those off a 15 watt panel and an old RV battery just fine), run the well pump periodically (right now runs off a 10 HP 240V overgrown lawnmower engine generator (came with the cabin and I suspect could almost be heard in Washington state on a quiet evening) , a laptop and modem (cabin does have high speed internet) and possibly a Sun Danzer freezer, could go propane I suppose. Right now when we go there we use a Honda EU2000i (also came with the cabin) to power the modem. Cabin has wood stove for only source of heat, gravity feed water system (use well pump to fill tank), tankless water heater with no electrical requirements other than 2 ‘D’ cell batteries (no pilot light either, has electronic ignition) and we cook on a Coleman propane “stove” and we have a propane toaster oven although haven’t tried it yet. Certainly won’t have any electric heating loads. We have no TV. Current situation is sort of like going camping so just trying to improve upon that somewhat until the house can be built.

Yes, likely I have underestimated number of panels required as there is a good chance we will find some additional uses for electricity as we start staying there more than just the odd trip. (not to mention lack of sun except during summer) I work from home so with a way to power the modem/laptop I will be able to stay there longer than the current set up where to be there on a work day would require running the Honda for many hours per day.)

Batteries: So, the whole battery question (number of amp hours required) is still quite a puzzle to me. I tried to work that out (and array sizing too) based on articles in Home Power magazine. What I came up with was this formula: Total Avg. Daily AC WH, divide invertor efficiency, add Total Avg. Daily DC WH, equals Avg. Daily Load (Wh/day), divide DC System Volts, equals Avg. Ah per day, multiply battery temp. multiplier, multiple days of autonomy, divide DOD, equals total system Ah which lead me to (with a bit of fudging the days of autonomy requirement) to about 240 amp hours. I then saw something about the “C-rate” for charging being less than 20 and calculated mine to be about 12.3 with the 945 watts worth of panels. Now I think about this I suspect I screwed up that calculation as I see I didn’t have anything about hours of sun per day in there, or charger efficiency.

Ready, Fire Aim: well , somewhat guilty as charged, some components already ordered (good deal :-) ) but not all. So, sounds like maybe I should plan for 2 strings of 3 of the 315 panels but what about the batteries, does it sound like I will be able to get by with these meager load requirements with 240 AH at 48V if I go with 1.8 kW of panels? I don’t want to chronically undercharge the batteries or rely on the generator daily. I was thinking about 2 ¼ days of autonomy. I know I will need to use a generator in the cloudy winter periods (make that fall/winter/spring around here).

Oh yes, in the long term I plan for something along the lines of a Generac EcoGen 6 kW (http://www.generac.com/Residential/EcoGen_Series/Product/6kW/) generator but for now would the Honda EU2000i I already have be of any use charging the proposed 240 AH @48 volt battery setup? (I plan to get rid of the existing 240V well pump generator ASAP as it is so terribly noisy and stinks badly, a really foul piece of equipment.)

Thanks again for the input, much appreciated!
Ed

PS – general consensus on Sun Danzer freezers? Thinking it has to be a step up from the Coleman cooler and block ice we are using now when we go there.

Ralph Day · July 2012

Re: system plan sound reasonable? (new to solar)

Hi Ed

If you plan correctly, the Honda should fill your needs. I have an overkill 10kw diesel genset. Overkill because once you get past the bulk phase of charge your load on the generator drops off...the batteries need charge, but how much laundry can you do to use the power output from the genset? IIHTDO (if I had to do over) I'd go for an inverter genset instead of a big diesel.

Will your shop loads require a large genset? Something to think about. Could you lose the 240v well pump and get something like a Grundfos 120v with a soft start? Xantrex and Outback both make autotransformers for 120 - 240 / 240 - 120 conversion. I have 2, one going 240-120 and one 120 - 240 to run my heat pump. The tare load is about 9 watts when they're running (both on breakers...only on when needed).

With everything, loads will creep up as time goes on.

Ralph

vtmaps · July 2012

Re: system plan sound reasonable? (new to solar)

two thoughts:
1. put your panels in strings of two. your controller will run cooler and more efficiently.

2. no sundanzer, get an energystar conventional and use the money you save to buy another panel or two. BTW, I have a sundanzer and am happy with it. For a variety of reasons (at the time) it was worth it to me to run on DC (I have 24 volts). In your case you would also need a 48-->24 converter to run a sundanzer.

--vtMaps

icarus · July 2012

Re: system plan sound reasonable? (new to solar)

Do the long term math,, and spend the $20 k on the grid! Your going to spend that much on a viable off grid system big enough to being to run a shop. While BC Hydro Rates probably will go up going forward, but so will most everything else,, like batteries!

Remember, roughly half the cost of a off grid system is the battery bank, with a united life, 5-10 years. (and PV is getting cheaper, batteries are becoming a greater percentage of the cost. So a 2 kw system might cost $5-8/watt all in, perhaps a bit more, say $15k. hat is 75% of your grid cost right away, but the batteries, are going to cost you nearly $1000/year replacement cost, amortized over 10 years. (not to mention that most newbie off grinders kill a set or two before they learn how to drive, so to speak.

Consider a grid tie system to potentially off set your hydro bill, and to reduce costs going forward, as well as to be free. Bottom line, battery based PV is neither cost efficient, energy efficient or green. (do realize that a battery based system will produce ~1/2 as much power as a grid tie system in the net, at about twice the cost, leading to a kwh cost of 4 times as much.)

Good luck, and keep in touch Salt Spring is the Riviera of Canada. I've known a number of folks over the years who have planted there.

Tony

Cariboocoot · July 2012

Re: system plan sound reasonable? (new to solar)

Salt Spring Island! Still printing your own money?

BC Hydro rates would have to quadruple before solar power starts to make economic sense. And since there's no incentive to go grid-tie either, you really have to check the numbers carefully. As you know, British Columbia's motto is "It's More Expensive In BC!" and that goes for solar too.

In general, the trick with off-grid is to reduce power consumption to an absolute minimum. Running a workshop doesn't really fall into that "minimum" category. The power comes with a very high cost. I have it because the grid connection is just plain not possible here, even for $25 million. As it is my 2.4 kW hour per day (when the sun shines) system cost $8,000 installed by me. In order to negate the viability of the grid even at $25,000 install cost you are going to have to do some serious number crunching, starting with getting an absolute kW hour usage figure. And since that will vary (and be unpredictable with the workshop) and go up over time ...

One possibility: plan a small, "essential" power system for back-up should those long Hydro lines go down in one of the storms. See how it works for you. If it's not enough, you could either go with the utility hook-up or add a second power system. We'd be glad to help you figure this out too.

Forget the Sun Danzer. If you're going to have grid or an inverter, just get a conventional refrigerator/freezer. They are efficient these days, and cheaper per cu. ft. by far.

mtdoc · July 2012

Re: system plan sound reasonable? (new to solar)

Hi Ed,

Salt Spring Island is a beautiful place. I live close by, near Port Angeles, WA. My wife and kids and i just did a ferry/bicycle tour from PA to your island 3 weeks ago. Spent 4 days just outside of Ganges -a great trip.

I agree with vtmaps - it would be better to run 2 stings of 2 of those Kyocera panels - if you can afford to buy 4. With 2 strings of 2 of those panels and a distance of 75' from array to controller you can use a Classic 150. That will give you plenty of headroom and allow you more room to expand your array in the future. It will also give you more PV for those cloudy PNW days.

I also agree that you may be able to get by with the Honda eu2000i genset. You can get a tri fuel conversion kit from Central Maine Diesel if you want to run it on propane. If you later increase your loads and battery bank and need more generator power you can buy a second eu2000i and parallel it. The advantage of this approach is redundancy and the ability to run just one, very fuel efficient generator when loads or battery charging needs are not high. The main advantage I see with the Ecogen is that it would allow automatic generator start.

westbranch · July 2012

Re: system plan sound reasonable? (new to solar)

when you are putting in the electrical wiring, have 'essential' loads come from a separate Circuit breaker box and add a Transfer switch so that the Eu2000 can power these.

edbee · July 2012

Re: system plan sound reasonable? (new to solar)

Thanks for the feedback, very helpful and interesting.

Grid or Off-Grid : one of the first things I did after acquiring the property was have a trench dug the 250 metre length of the driveway and have 2 plastic ‘pipes’ installed: one 2” diameter teleduct which now houses a Shaw internet cable (could provide phone and TV too but phone requires a 60 watt always on modem, not interested in TV) The other is a currently empty 3” diameter ‘pipe’ that could be used for hydro connection in the future. Although I was/am planning to make my own power with solar (and possibly micro-hydro which could be viable for 4, maybe 5 months per year) I was hedging my bets (didn’t want to ever have to dig that trench again).
My plan at the moment (after reading your thoughts) is to go with the PV electrical system for now (phase one when we are just there part time) and evaluate how that all goes and then make a ‘final’ decision on 'to grid' or 'not to grid' after having some experience with being responsible for creating my own power.

Strings of 2 versus strings of 3 (panels are 315 watt, Voc = 49.2 Volts DC) : I had originally planned to have 2 modules per string (one string for my initial phase and then 6 strings later on) and a Classic 150 could handle that. I then spoke with the tech support guy at Midnite Solar and he said that with a 75 foot run from the panels to the charge controller I would be better of going with strings of 3 using a Classic 200 controller so that way I could use #6 wire instead of #4 from the combiner box to the controller. He is certainly far more knowledgeable than I on these things and his logic made sense to me. I still haven’t done the calculations for % voltage drop or ampacity but will have to start thinking about those details fairly soon.

Fridge: Any recommendations as to which brand of conventional fridge/freezers are most efficient and well built? It would be nice to just run it off the inverter rather than have to buy a 48V to 24V or 48V to 12V converter as well.

Honda EU2000i: I’ll see how this works out for battery charging through the inverter/charger. It certainly does seem to be a nicely designed and built unit and I like the idea of twinning it as neccessary. Anyone have experience with the mentioned multi-fuel kit from Central Maine Diesel? Does it perform well? I have converted 2 cars to propane so I imagine converting the little generator should be fairly simple.

Shop Loads: The shop will be a hobby shop where I wouldn’t ever be running more than one thing at a time. It will have tools like table saw, band saw, drill press, jointer, compressor and a small welder. I figured as it would only be used periodically I could just fire up the generator if I have a bunch of work to do which would require shop tools.

Well Pump: the pump is at the bottom of the well (200 and something feet ) and I don’t want to start monkeying with changing that at this point. I’ll see how it goes running it off the Magnum 4448 inverter for now.

Salt Spring Money: I have heard of Salt Spring Dollars but haven’t seen any yet. http://saltspringdollars.com/faq/

Thanks again for the feedback!

vtmaps · July 2012

Re: system plan sound reasonable? (new to solar)

edbee wrote: »

he said that with a 75 foot run from the panels to the charge controller I would be better of going with strings of 3 using a Classic 200 controller so that way I could use #6 wire instead of #4 from the combiner box to the controller.
<snip>
I still haven’t done the calculations for % voltage drop or ampacity but will have to start thinking about those details fairly soon.

Use strings of two. Buy heavier wire and a Classic 150. The Classic 150 has a higher power capacity (for future expansion). I have done the calculations: http://forum.solar-electric.com/showthread.php?15907
Your Classic will run cooler and more efficiently with a lower Vmp input.

--vtMaps

SolarMusher · July 2012

Re: system plan sound reasonable? (new to solar)

I’ll see how it goes running it off the Magnum 4448 inverter for now.

A magnum 4448PAE 240VAC on E-Panel would be your best choice, don't forget that you can run easily any 240VAC portable generator without 120/240 VAC transformer (Outback or Xantrex) at full power/amps...
You can also find 240VAC Grunfoss pumps (SQ serie 700W) which are a better choice than a 120VAC only with a very soft start.
You'd better choose a DC fridge as it will keep your inverter at rest (8A) in the night time and save you 22A x 8/10 hours. You can find very good 12.6 Cu feet DC fridge or freezer 10 Cu feet in Canada (Quebec) far less expensive than in US. I run both on my system.
Good luck.
Erik

SolarMusher · July 2012

Re: system plan sound reasonable? (new to solar)

A little Solarconverter 48/24 10A could run both fridge and freezer without problem.

mtdoc · July 2012

Re: system plan sound reasonable? (new to solar)

edbee wrote: »

I then spoke with the tech support guy at Midnite Solar and he said that with a 75 foot run from the panels to the charge controller I would be better of going with strings of 3 using a Classic 200 controller so that way I could use #6 wire instead of #4 from the combiner box to the controller.

Consider placing your combiner close to your controller and using the Classic 150. You could then run 10 AWG from each string to the combiner and only need a very short run of heavier gauge wire to the controller. The run from the array to the controller is in conduit, correct? If so (not direct burial) you could use 10 AWG stranded THHN wire. You should be able to get 2 x 500 ft rolls of this for about $200 total. You could pull 6 or 7 pairs through your conduit to combiner located near controller and be all set for future expansion of your array.

Anyone have experience with the mentioned multi-fuel kit from Central Maine Diesel? Does it perform well?

Yes, 1 of my 2 eu2000is has a trifuel kit from CMD and runs well on propane (or gasonline!). I plan to convert the second soon.
If you do get a second eu2000i to parallel with your first, get the eu2000i "Companion" model which has a 30amp plug to allow you full output of both generators without buying the more expensive parallel conversion kit. You can order a Companion model with trifuel kit already installed from CMD.

With the Magnum 4448 inverter you will not need a 240 V generator since you will be running any 240 V loads through the inverter. You could also do the same with a 120V output only inverter and an autotransformer. This is how I run my septic pump when in "off grid mode"

vtmaps · July 2012

Re: system plan sound reasonable? (new to solar)

mtdoc wrote: »

Consider placing your combiner close to your controller and using the Classic 150. You could then run 10 AWG from each string to the combiner and only need a very short run of heavier gauge wire to the controller.

If you run each panel through 75 ft (one way) of #10 AWG you will lose 9.6 watts from each panel.
If you run three panels (after combiner) through 75 ft (one way) of #4 AWG you will lose 21.9 watts total.

--vtMaps

Cariboocoot · July 2012

Re: system plan sound reasonable? (new to solar)

vtmaps wrote: »

If you run each panel through 75 ft (one way) of #10 AWG you will lose 9.6 watts from each panel.
If you run three panels (after combiner) through 75 ft (one way) of #4 AWG you will lose 21.9 watts total.

--vtMaps

However it's not as though 4 AWG and 10 AWG are interchangeable. Sometimes you have to sacrifice a little power in order to make the wiring easier and/or cheaper.

SolarMusher · July 2012

Re: system plan sound reasonable? (new to solar)

With the Magnum 4448 inverter you will not need a 240 V generator since you will be running any 240 V loads through the inverter

Sorry, it's a Magnum PAE 240VAC, not an Outback 120VAC, if you want to have 60ADC full output to charge a 48V battery bank, you'll need a 240V generator. With a Honda eu2000i 120V you will have only half the ouput of the Magnum charger (17.5AAC). A Honda 2000i is not the best choice to match a Magnum 4448PAE. Edbee is in BC, so I think he will have to use his gen/charger several times a year. If your Outback inverter allows you to charge a steady 45A on a Dual Honda 2000i, it's not the case here...
Just my opinion, I could be wrong.
Erik

mtdoc · July 2012

Re: system plan sound reasonable? (new to solar)

vtmaps wrote: »

If you run each panel through 75 ft (one way) of #10 AWG you will lose 9.6 watts from each panel.
If you run three panels (after combiner) through 75 ft (one way) of #4 AWG you will lose 21.9 watts total.

--vtMaps

vtMaps - Did you mean 9.6 watts per string? By my calcs (could be wrong:roll:), with 10 AWG i'm getting a 1.57% Vdrop for a string of 2 of his panels. This equates to 9.6 watts per string or 4.8 watts per panel. This would be the same per panel drop as he expands his system. With 3 panel strings, combiner at array and a home run with 6 AWG (what Midnight advised) -with expansion to 4 strings (12 panel array) I get a Vdrop of 1.77% which equates to 5.6 watts per panel. if you went to 4AWG it would be less (but much more expensive).

mtdoc · July 2012

Re: system plan sound reasonable? (new to solar)

SolarMusher wrote: »

Sorry, it's a Magnum PAE 240VAC, not an Outback 120VAC, if you want to have 60ADC full output to charge a 48V battery bank, you'll need a 240V generator. With a Honda eu2000i 120V you will have only half the ouput of the Magnum charger (17.5AAC). A Honda 2000i is not the best choice to match a Magnum 4448PAE. Edbee is in BC, so I think he will have to use his gen/charger several times a year. If your Outback inverter allows you to charge a steady 45A on a Dual Honda 2000i, it's not the case here...
Just my opinion, I could be wrong.
Erik

Thanks Erik - good point - I did not realize that limitation of 120V charging with the Magnum Inverter. Still - 17.5 AAC (at 120V) = 35 amps DC (at 60volts) which would be more than adequate for his initial battery bank and probably adequate for any battery bank matched to that inverter.

FWIW the Outback GVFX3648's charger using AC input has a max input of 20 AAC (at 120V) = 40amps DC output (at 60V).

Cariboocoot · July 2012

Re: system plan sound reasonable? (new to solar)

mtdoc wrote: »

FWIW the Outback GVFX3648's charger using AC input has a max input of 20 AAC (at 120V) = 40amps DC output (at 60V).

Actually its AC in is limited to 60 Amps and the charger's maximum is 45.
This is quite normal for a grid-tie inverter of 3.6 kW as there's really not much point having a battery bank any bigger than 450 Amp hours. Its application being mainly to "sell to grid" it can't put out more than 3.6 kW which limits the maximum array size and in turn limits the battery capacity.
Mind you, being an Outback you can always stack them in interesting ways and increase the Voltage, current, or both.

GVFX3648 specs: http://lib.store.yahoo.net/lib/wind-sun/GTFX-GVFX.pdf

SolarMusher · July 2012

Re: system plan sound reasonable? (new to solar)

Hi mtdoc,
I had (and still have) a VFX3648 and I thought it was a 45ADC charger. Used it with two transformers, one for feeding the VFX and the other one to power a 240VAC pump. Not an efficient system... Or buy another VFX! Oups! I couldn't afford that. That's why I don't like Outback inverters, they had just forget that people like us (off-grid) are using 240VAC portable generators most of the time. Magnum has done it right from 4kw to 9kw for most of us.
My system now include a 4448PAE with Midnite stuff.
Just my opinion,
Erik
Erik

mtdoc · July 2012

Re: system plan sound reasonable? (new to solar)

I know the Outback specs list the DC charger limit as 45 amps, but in practice the AC charging limit is 20 Amps (you can adjust the AC charging limit with the Mate and 20Amps is the max you can set it) which at 60Volts DC = 40 amps if my math is right. I've actually measured it putting out 43 amps at 54.4 volts which is a little better ( and shows that the PF is actually very good at this level!) Obviously at lower voltages it could put out 45 amps DC.

The whole AC charging input limit of 20 amps confused me at first since the specs say AC Input Current Maximum is 60 amps - but that refers to the total AC input - Grid or Generator (for pass through + charging) not the AC input to the charger itself. At least that's my understanding from Outback - perhaps wrong? If there's a way to increase the AC charging input limit beyond 20 amps - I'd love to know about it!

Erik, I believe off griders with high demand for 240V loads generally stack 2 Outback inverters. This aspect of Outbacks system is a bonus I believe since it adds redundancy.

On the other hand you're right that for those with smaller loads but who need 240V the Magnum 4448 seems like a good option. I'm considering installing one eventually for a second system to power my garage/shop.

Cariboocoot · July 2012

Re: system plan sound reasonable? (new to solar)

The Volts don't actually work that way. In OB's reasoning 120 Volts is 2.5 times 48 Volts, so 20 Amps AC for the charger is 50 Amps on the DC side. Adjust for charger efficiency and you get 45 Amps max. The DC Voltage isn't relevant: the current is limited to 45 regardless of where the Voltage is at (and the current will be max at the lowest Voltage, not at the highest).

Yeah, it's a confusing way to do it.

mtdoc · July 2012

Re: system plan sound reasonable? (new to solar)

Yes, thanks for clarifying. I understand and agree with what you say. I was just using 60V for the easy math 8). In practice with a 20 Amp AC input limit to the charger the real max (if 100% efficient) at 60 Volts would be 40 amps. Correct? Personally, I've never been able to get it to put out 45 amps - but then again I've never tried to charge with my batteries below 48V!

Cariboocoot · July 2012

Re: system plan sound reasonable? (new to solar)

If you want to look at it from a Watts In/Watts Out conversion it's something like:
20 Amps AC * 120 VAC = 2400 Watts In * efficiency (90%?) = 2160 Watts Out.
2160 / 48 Volts = 45 Amps, 2160 /60 Volts = 36 Amps.

I'm not entirely certain there is a Watt limitation on it, though. You'd have to ask Outback for the actual performance specs (I'm leery of that calculated efficiency as mine seems lower than that but it is a different model and can do 80 Amps DC).

mtdoc · July 2012

Re: system plan sound reasonable? (new to solar)

Yes, I agree with your math. There are several angles to come at it from. Regardless, the equations in your sig will always be true!

As far as efficiency - as mentioned I have measured (via FNDC and using Mate/Wattplot) the charger putting out 43 amps at 54.4 Volts (corrected initial typo). The AC input voltage at the time was 122 V so this comes out to 96% efficiency if those numbers and the AC charger input limit of 20 amps is to be believed. Despite the lack of PF correction the Outback charger at high output can be pretty good by my experience (and others as reported on the Outback forum). At lower output efficiency would undoubtably be worse

The PF corrected charger on the Magnums is an advantage.

Getting back to the OPs questions, would you say a single eu2000i would be adequate to charge his initial battery bank through the magnum. Assuming expansion in the future and a battery bank of say 450 AH would 2 Hondas feeding 17.5 amps to the charger be adequate? Perhaps at that point instead of buying a second Honda to parallel, a 240V genset would make sense?

Cariboocoot · July 2012

Re: system plan sound reasonable? (new to solar)

mtdoc wrote: »

Getting back to the OPs questions, would you say a single eu2000i would be adequate to charge his initial battery bank through the magnum. Assuming expansion in the future and a battery bank of say 450 AH would 2 Hondas feeding 17.5 amps to the charger be adequate? Perhaps at that point instead of buying a second Honda to parallel, a 240V genset would make sense?

I'm wrestling with this exact question on my own system and future expansion plans. It's driving me nuts.
One EU2000i can drive 13 Amps @ 120 Volts. Two of them can put out double that (30 Amp outlet). So that's 1560 Watts & 3120 respectively.
45 Amps on a 48 Volt system is roughly 2400 Watts on the gen peak, but it won't stay at peak the whole time. So do you run two gens until the power demand goes down and then shut one off (this requires a total shut down of both gens and a restart of one) or do you go for the 3000 model and let it idle back as needed? Without the demand on it, the bigger gen will burn more fuel than one of the smaller ones but less than two of the smaller ones. With the load on it will probably burn less fuel than the two smaller ones (because of not having to supply energy to keep twice the mass operating).

If it were an "occasionally I need more power" thing pairing two 2000's would probably be the answer. Otherwise the one 3000 is likely better. A 240 Volt gen is even better, but I don't know of any inverter types with that output. Generators do not always play well with transformers either, although the inverter types should be fine.

The expected load have to be considered too. This is what is tangling me up, because if I double the battery bank size I can still use one 2000 gen but have to limit my loads as the charge demands would go to 9 Amps AC leaving a very small amount for loads.

That sure didn't help, did it?

vtmaps · July 2012

Re: system plan sound reasonable? (new to solar)

Cariboocoot wrote: »

A 240 Volt gen is even better, but I don't know of any inverter types with that output.

You set your sights too low.... Honda eu6500 has switch to choose between 120 and 240 volt output.

You can get the full output from its 240 volt outlet.

If you switch it to 120 volts you can still get the full output, but not out of a single outlet. The 120 volt outlets (30 amp and the two 20 amp) are all in parallel, they are not 'legs' of a 240 volt output.

--vtMaps

Cariboocoot · July 2012

Re: system plan sound reasonable? (new to solar)

The 6500 is too big for me, so I've never looked at it. But it might be right for the OP or anyone else who needs 240 VAC gen.

My 2000 is getting near the 5,000 hour mark, thanks to this wet Summer.

It may surpass the 1000's 6,000+ hours.

system plan sound reasonable? (new to solar)

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