Just bought 49 panels (235w)... what is the best way to use them?

So I got a deal from my friend on 49 new panels. they are Yingli YL235P-29b panels and have the following specs:

STC Power Rating Pmp (W) 235
PTC Power Rating Pmpp (W) 211.2
PTC/STC Power Ratio 89.9%
Open Circuit Voltage Voc (V) 37.0
Short Circuit Current Isc (A) 8.54
Voltage at Maximim Power Vmp (V) 29.5
Current at Maximim Power Imp (A) 7.97
Panel Efficiency 14.4%
Fill Factor 74.4%
Power Tolerance -3.00% ~ 3.00%
Maximum System Voltage Vmax (V) 1000
Maximum Series Fuse Rating (A) 15

here is what im thinking... I'm making a place where my friends and I can hang out in the mountains. We all have rv's (well most of us) and I will want to distribute power to all of them. My plan is to build a clubhouse/casita which will have a kitchen, laundry, wellhouse, air conditioning and large dayroom with an entertainment center. I have no plans of using propane so everything will be electric.

electric stove and oven
hot water heater
satellite receiver
large tv (prolly 55" led)
jacuzzi (possibly)
well pump
lots of lighting (cfl and led)
a bunch of computers and laptops (lets say 4 of each for a small lan party)

5 rv's (sometimes more and sometimes less) with a 20amp circuit each

ok, couple of things... all of our rvs have generators and golf cart batteries (4 trojans) and the only reason for the 20a circuit to them is so they can fire up 1 a/c unit each. The only reason to run power to them is so I dont have to hear them run their gens :P

My spidey sense tells me (without doing ALL the math yet... cause I havent) that I will need to figure out my battery bank and then maybe add a couple of panels to size the array to my bank.

I would also like to have some redundancy since controllers and inverters can (and do) crap out. I am thinking minimum 2 controllers and 2 inverters in parallel so if 1 of each dies my food doesnt spoil or my bank doesnt die before I get back to find out.

The reason for no propane is that its a 3-400 mile drive round trip and propane means I have to drive my v-10 f350 to carry the bottles instead of the prius... over $100 fuel difference per trip (plus the cost of the propane)... 2 trips a month = $2400 a year... which is $25k for 10 years..., that buys a huge battery bank. Anyway, just my thinking.

for the array should I make my strings closer to 200-250v since I have the panels to do it? Also I am planning on using fork lift batteries but was wondering if I should do 2 or 3 banks in parallel or series to up the voltage (96 or 144v)? I assume the inverter choices would be the issue here.

so I guess what I am looking for is what will be the sweet spot for the amount of panels I am starting with... I can add a couple or subtract a couple if needed. I was looking at a couple of MidNite Solar Classic 250KS controller and it seems like some of these are good choices.

my location will be southern california in the mountains near Jacumba, ca...

Thnaks in advance for your help... sorry I am short on specifics as I have now are the panels and want to pencil out the rest before i start buying. Just looking at the best way of getting close to what I want out of what I got :)


  • BB.BB. Super Moderators, Administrators Posts: 32,741 admin
    Re: Just bought 49 panels (235w)... what is the best way to use them?

    Boy, you have bitten off a big project... OK, a "nominal system" would look like:

    We assume 5% to 13% rate of charge for a battery bank. In this case, I will use 10%--That is a good sized solar array for your battery bank:
    • 49 panels * 235 watts * 0.77 controller+panel derating * 1/0.10 rate of charge * 1/48 volt battery bank = 1,847 AH @ 48 volt battery bank

    Using PV Watts for a 11.515 kW (11,515 watt) fixed array (defaults) with a 0.52 end to end system efficiency:
    "Station Identification"
    "Lat (deg N):", 32.12
    "Long (deg W):", 110.93
    "Elev (m): ", 779
    "PV System Specifications"
    "DC Rating:"," 11.5 kW"
    "DC to AC Derate Factor:"," 0.520"
    "AC Rating:"," 6.0 kW"
    "Array Type: Fixed Tilt"
    "Array Tilt:"," 32.1"
    "Array Azimuth:","180.0"

    "Energy Specifications"
    "Cost of Electricity:"," 8.5 cents/kWh"

    "Month", "Solar Radiation (kWh/m^2/day)", "AC Energy (kWh)", "Energy Value ($)"
    1, 5.70, 982, 83.47
    2, 6.11, 927, 78.80
    3, 7.03, 1190, 101.15
    4, 7.50, 1199, 101.92
    5, 7.29, 1157, 98.34
    6, 7.15, 1083, 92.06
    7, 6.44, 999, 84.92
    8, 6.85, 1076, 91.46
    9, 7.06, 1098, 93.33
    10, 6.72, 1109, 94.27
    11, 5.99, 986, 83.81
    12, 5.27, 917, 77.95
    "Year", 6.59, 12723, 1081.45

    Of course, you should not plan on using 100% of your power every month--These are just long term averages and you should plan on using a maximum of 75% or so on average per month.

    The maximum average power you should pull from a generic lead acid battery bank is around C/8 rate of discharge (8 hours to battery dead):
    • 1,847 AH * 48 volt battery bank * 0.85 inverter efficiency * 1/8 rate of discharge = 9,418 Watts max 120 VAC continuous power draw

    You should only draw a battery down to 50% capacity on a daily basis for long battery life--so drawing 9,000 watts for a bit less than 4 hours would be the maximum recommended--But you would not draw that much in normal use. You would typically draw down a battery by 20-25% over night and recharge the next sunny day.

    • 1,847 AH * 48 volt battery bank * 0.25 discharge * 0.85 inverter efficiency = 18,839 WH per day = 18.8 kWH per day

    And during the summer, would would expect something like 1,000 kWH per month or:
    • 1,000 kWH per month / 30 days per month = 33 kWH per day during summer

    If I have your location approximately correct--You have a lot of sun and you could go with a 2x larger battery bank and still be OK (more storage, more power for several days of bad weather, more power available over night, even a larger inverter).

    Before we go into the details of the hardware--Really need to know what your daily power needs will be. This is a large off-grid system, and using electric power for A/C, Hot Water, etc. places a huge draw on the system. There are appliance selections that can help reduce power usage a lot and make going off-grid solar more practical.

    For example, Mini-Split A/C is very efficient can small enough you can "zone" your needs (only cool rooms that are occupied). And there are heat pump versions available that make it useful for heating/saving propane in winter too.

    Sanyo mini split
    AC (inverter/variable speed)

    For hot water--I would highly suggest installing solar thermal--But you can also look into Heat Pump type water heaters (GE makes a nice one). They are about 2x as efficient as a normal hot water heater--Plus they cool and dehumidify the room they are installed in. If you have a large system--there are A/C systems that can have hot water too.

    In the end--Your power usage needs to be very efficient. Normal window/roof A/C systems are not as efficient as mini-splits--plus they take a lot of surge current to start/operate vs a mini-split.

    Managing such a system is going to be a job in itself too... You are trying to manage 4+ independent RV's to use, in total, as much power as an average home in the US without A/C (~1,000 kWH per month). One person that uses more power than plan can toss your entire plan into the trash.

    Anyway--This is my guesstimate about what such a system would look like and how much power it would supply. Your thoughts/questions?

    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • CariboocootCariboocoot Banned Posts: 17,615 ✭✭✭
    Re: Just bought 49 panels (235w)... what is the best way to use them?

    Welcome to the forum.
    Let's look at one sentence in your post: "sorry I am short on specifics as I have now are the panels and want to pencil out the rest before i start buying."
    Except you already started buying by getting the panels. I hope you have a ton of money, because you're going to need it.
    Figure out what all that equipment you want to run is going to use in kilowatt hours, then have a good cry. Let me show you what I mean:
    Air conditioning; big power user with heavy start-up surge.
    Refrigerator; big power user with heavy start-up surge.
    Well pump; big power user with heavy start-up surge.
    Jacuzzi; big power user with heavy start-up surge.
    Electric water heater; big power user.
    Electric stove/oven; viciously big power user.
    Microwave; big power user.

    The rest of the stuff on the list will also come out to a need for a lot of Watt hours. Desktop computers, for example, will use about 100 Watts more than a laptop. Four of them used for eight hours is 3200 Watt hours, or more than I use for the whole cabin in a day. The 'frige will probably eat up around 1 kW hour, if it is efficient. More if it is not.

    Let's look at it from the other direction now. You've got forty-nine 235 Watt panels. That's 11,515 Watts in total, capable of approximately perhaps 12 kW hours per day AC (based on typical efficiency figures and 4 hours good sun). Turn the stove on for an hour and most of that could be gone (depending on the exact stove and how many burners you use with the oven).

    Some of what will be required to use those panels:
    MPPT type charge controllers, because the panels have an odd Vmp. Multiple because they only handle up to 80 Amps each and you have a current potential of about 240 Amps @ 48 Volts. So that's three controllers at least @ $600 or so.
    Battery bank of about 2400 Amp hours @ 48 Volts. This would be made up of 24 Crown 2550 Amp hour batteries @ $1,400 each = $33,600.
    Multiple inverters. Since the biggest are only capable of 8 kW and you have this want of far more than that. You'd need 12 kW just for the stove's potential appetite. That's two XW 6048's @ $3,000 each.

    Frankly this idea makes no economic sense whatsoever. For the kind of capital investment needed to utilize those panels and supply those load demands for occasional use you could put together a small system to run the "quiet time" loads, buy a big generator for the large loads, and still have "money left over" to haul in fuel with the truck instead of the Prius.

    If you all have RV's, why not use them? Adding solar to an RV is something frequently discussed around here.

    Rather than shell out something like $40,000+ to go all solar electric in a remote location used occasionally you'd be better off exploring other options. Don't worry; this forum is here to help with that.
  • mike95490mike95490 Solar Expert Posts: 9,583 ✭✭✭✭✭
    Re: Just bought 49 panels (235w)... what is the best way to use them?

    Using expensive solar PV electric, for cooking on an electric range, is very wasteful. If you HAVE to go with electric, look into an Induction Cooktop. At least they are 95% efficient, glo-coil is only about 40%. Induction needs IRON in the pan to work, there are some 3 layer pans, aluminum, S.S. that have a disc of iron i the middle to work with induction tops.

    And if you plan ahead, bring up a full tank of propane each trip into town, take the empties back. You can cook for a week with a 20# bottle, or 40 minutes from a days worth of electric.

    Build a covered shade structure to keep the RV's cool, don't run air conditioning. If you need AC, just stay in the city where the electric is cheap.

    Run a small circulation pump to a solar water heater for the hot tub. You can maybe raise the tub 10 degrees and then have dead batteries, heating with electric element.

    And read here and listen a lot. There is a LOT you need to learn first, before you start slinging 10's of thousands of dollars around.
    I think you can stack up to 3, XW-6048's for a total output of 18KW at 240V (from some huge battery bank). That in itself will be a major undertaking. Maintaining this will be a full time job for someone. watering batteries (distilled water) keeping panels clean, keeping rats out.....
    Powerfab top of pole PV mount | Listeroid 6/1 w/st5 gen head | XW6048 inverter/chgr | Iota 48V/15A charger | Morningstar 60A MPPT | 48V, 800A NiFe Battery (in series)| 15, Evergreen 205w "12V" PV array on pole | Midnight ePanel | Grundfos 10 SO5-9 with 3 wire Franklin Electric motor (1/2hp 240V 1ph ) on a timer for 3 hr noontime run - Runs off PV ||
    || Midnight Classic 200 | 10, Evergreen 200w in a 160VOC array ||
    || VEC1093 12V Charger | Maha C401 aa/aaa Charger | SureSine | Sunsaver MPPT 15A

    solar: http://tinyurl.com/LMR-Solar
    gen: http://tinyurl.com/LMR-Lister ,

  • Grim ShadyGrim Shady Registered Users Posts: 2
    Re: Just bought 49 panels (235w)... what is the best way to use them?

    yes, a big bite of a big project

    I guess I have to make some hard decisions about my must-haves and things I can live without. Solar water heater will probably have to be in the mix and I will look into the split A/C. The clubhouse will be just 1 big room (maybe 1000sqft or so) and pretty well insulated so hopefully the ac wont hit me TOO hard.

    I am thinking about budgeting in a 3rd 48v forklift battery pack to add some more reserve and then pull back my power requirements to fit what I can regenerate each day. I need to do some math on how many charge controllers I will max out with the array in my location and go from there. Cant think now though since I currently sleep during the day and its bedtime :)

    yeah I usually map out what I am going to do before I buy stuff but I got all 49 of them for $8000 with no shipping or tax so it seemed good enough deal for me to pull the trigger. I dont know about having "a ton of money" as I'm not rich but spending another $20k or so for this is expected and wont hurt me. My attitude is that its disposable income and its for spending on what I want... I have no debt and my bills are paid. I am sure it doesnt make sense to most people but I've done worse things (like racing) :)

    With that said I was figuring at least 2 controllers @ $800 each, about $6000 for a pair of inverters and a a pair of 48v forklift batteries for around $12k. With the wiring and cost of the panels I should come in around $30k. I have not looked at the crown batteries but I KNOW I need to think about which/what battery bank I want since I will have to stare at it for a very long time.

    as far as the generator suggestion goes keep in mind that although I will only spend maybe 8-10 days a month there it will be in constant use most likely by other people (friend and family). Most of us have solar and batteries on our rv's but this location is on the edge of the desert and their systems can not run their ac's without the generator and it will be hot. They need to run the ac for an hour or so to cool down in the evening as this is what we usually do before bed. I need to be able to soak up those surge loads after that its not TOO bad. The ac on my coach pulls 10amps @ 110vac so around 1000watts each. during the day we will be either outside or in the clubhouse so I dont expect the house ac and the rv ac's to be on at the same time so hopefully that will help.

    I live in yuma and spend 4 out of the 6 winter months camping in my rv by the sand dunes but cant sit still for the 6 months of summer and its too hot here to camp. So I promised myself that my summer place up the hill will be no hassles and lots of comfort. Im sick of eeking by on power in the rv so when I start fresh I am going to make sure I can play video games in comfort :)

    Thanks for the idea about induction stove i totally forgot about those. I used to have a house that had one and it worked fine... well not as good as gas but for electric it was great.

    as far as the propane goes I have 8 of the tall ones that I shuffle back and forth when I go to town from the dunes. I usually go into town and get 2 drums of fuel for the jeep and the bikes and 4-8 propane tanks depending on how much heater I run. Frankly I want to get away from that if I can... I may not but I hope I can. If my location has a propane delivery service available then I will go that route but I dont know yet... its pretty far off the beaten path.

    My plan with the jacuzzi was to cheat... I was going to heat it up with the gen and then maintain it with the solar bank. My old jacuzzi was electric and they store the heat pretty well after they are spooled up. But yeah... the cuzzi will prolly be on the chopping block or converted to solar. that was a great idea... I actually didnt think of that :)

    I hear ya on the maintenance thing. Im on my 4th year of my trojan bank and its a real pita to top em off in the rv... being in the desert sucks them up so fast its almost a monthly thing keeping the water filled.

    thanks everybody for your comments and help... im off to bed...
  • CariboocootCariboocoot Banned Posts: 17,615 ✭✭✭
    Re: Just bought 49 panels (235w)... what is the best way to use them?

    It isn't the Watts that will get you, it's the Watt hours. 10 Amps @ 120 VAC = 1200 Watts. Run for one hour is 1.2 kW hours. On a 48 Volt system that's roughly 25 Amp hours (not including efficiency losses) for one A/C run for one hour. That's a 100 Amp hour battery bank and 480 Watts of panel just to do that one little job. Multiply by four users. See how fast it adds up?

    Maybe you should look into installing some your 11kW of panels on a GT system at home where they would give you a greater potential payback, and scale down the remote site power demands as much as possible. Supplying big power off grid is very expensive. :cry:
  • icarusicarus Solar Expert Posts: 5,436 ✭✭✭✭
    Re: Just bought 49 panels (235w)... what is the best way to use them?

    Ditch the electric stove, electric water heater. Use Propne for the stove, and demand hot water..

    I can assure you that if you ease going to install a battery system that is "publicly used" you will destroy at least one set of batteries because your members will hve no clue how the system works and how quickly a toaster or hair dryer can draw even a big battery and doing this more than once will begin to degrade the life span of the battery bank, and speaking from expierence everyone does it,

    Get a 250-500 gallon bulk tank ns either hire the supplier to fill it once a year, or fork it onto a rented flatbed to fill it once a year. 250 gallons of propane weights ~1200# if memory serves. Still way cheaper than buying a huge battery bank for a stove, and hot water!

  • raydiasraydias Solar Expert Posts: 68 ✭✭✭✭
    Re: Just bought 49 panels (235w)... what is the best way to use them?

    Just a thought, any chance that you could have the utility power to the clubhouse? This could reduce the cost and while your not using the clubhouse you can be selling back to the utility. Just a thought.
  • techntrektechntrek Solar Expert Posts: 1,372 ✭✭✭
    Re: Just bought 49 panels (235w)... what is the best way to use them?

    I completely agree with the suggestion to leave your panels at home and look into a grid-tied system. Although many areas restrict the maximum size to a 10 kw system so you may still have ~1.5 kw of panels to play with elsewhere. A 10 kw system will give you about 45 kw per day on average year-round so you would get your best payback there.

    As for powering your outpost - you'll need a 15-20 kw generator just to power 5 RV A/Cs, not including anything else in the RVs or anything in your club house. To ensure nobody trips out the main breaker by also turning on their hair dryer and coffee makers you would need at least 25 kw to be safe. Again - just for the RVs. Add on loads from the club house and you'll be up to 30-35. There is no way you'll want to pay for - or maintain - a PV system that would be big enough to handle that kind of load. Think about spending an entire Saturday every 3 months just watering batteries. No thanks. Leave the PV at home where it will do you the most good.

    My suggestion is to leave the RVs out of the picture. People can spend their days in the club house if they want A/C, and run their own generator to cool things down in the evening before they go to bed. Focus on powering the club house - and definitely look at the Mitsubishi line of mini-split heat pumps (discussed later in the thread Bill posted above). With 1000 square feet with an open floor plan you might get away with using one larger one or two of the smallest (which get 26 SEER). Get a 6 kw Honda or Yamaha inverter-generator and stick it in a semi-buried open-ended bunker 100 feet from the club house and you'll never hear it. Put an extended tank on it, shut it down every night, and a remote start and you may only have to fiddle with it every couple of days. A lot less time than you'll spend maintaining a battery bank that is as big as a RV.

    Oh, and since you mentioned you have a Prius, if you can keep your loads below 3 kw continuous and 6 kw surge, take a look at the link in my signature.
    4.5 kw APC UPS powered by a Prius, 12 kw Generac, Honda EU3000is
  • westbranchwestbranch Solar Expert Posts: 5,183 ✭✭✭✭
    Re: Just bought 49 panels (235w)... what is the best way to use them?

    Tech has some good ideas.
    Does everyone else have 'their' spot? If so consider building a PV setup for each individual site and place the pv where it will shade the RVs??? Let your buddies supply their own CC at least add a setup to hookup their RV to the PV... Majority of PV goes to Casita. And YES get an inverter type genset at least fro boost charging as well as A/C.


    Add: for DHW or that Jacuzzi, you should be considering using at least a flat plate water heater or better yet an evacuated tube heater
    KID #51B  4s 140W to 24V 900Ah C&D AGM
    CL#29032 FW 2126/ 2073/ 2133 175A E-Panel WBjr, 3 x 4s 140W to 24V 900Ah C&D AGM 
    Cotek ST1500W 24V Inverter,OmniCharge 3024,
    2 x Cisco WRT54GL i/c DD-WRT Rtr & Bridge,
    Eu3/2/1000i Gens, 1680W & E-Panel/WBjr to come, CL #647 asleep
    West Chilcotin, BC, Canada
  • ggunnggunn Solar Expert Posts: 1,973 ✭✭✭
    Re: Just bought 49 panels (235w)... what is the best way to use them?
    Grim Shady wrote: »

    With that said I was figuring at least 2 controllers @ $800 each, about $6000 for a pair of inverters and a a pair of 48v forklift batteries for around $12k. With the wiring and cost of the panels I should come in around $30k. I have not looked at the crown batteries but I KNOW I need to think about which/what battery bank I want since I will have to stare at it for a very long time.

    An early PV experience for me was a real eye-opener. I was on a crew installing a solar with battery backup system, and they brought in this 48V 1000Ah lead acid forklift battery for the installation. It was the biggest battery I had ever seen and it weighed, I dunno, something on the order of 3000 lbs. That's a lot of electricity, right? Not really. 1000Ah @ 48V is 48000Wh, or 48kWh, which is only about $5 worth of power at grid charges. But wait, for most systems, a 50% DOD (depth of discharge) is the most you'd ever want to use, so it's really only $2.50. But wait, charging and discharging lead acid batteries is only about 75% efficient, so it's really only about a buck eighty five. Considering that lead acid is the most cost effective electrical storage medium that we have at the moment, that's pretty depressing.
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