Solar Newbie With Panel/Controller/Wattage Questions

marsofold
marsofold Solar Expert Posts: 45 ✭✭
I'm a solar newbie with some existing backup equipment that I want to augment with solar panels and a controller and would like some feedback on my plans. Looking to Sun's site at their $1.74/watt panels and thinking of buying six "SUN ES-A-205-fa" with specs of 205 watts/22.8Voc/18.40 Vmp/11.15 Imp using connector MC-4. And a Xantrex XW-MPPT-60 controller for the low RF noise, since I like to listen to shortwave. My current backup setup which currently works well:

11kw Honda GX Propane Generator/500 Gallon Tank,
200Amp Connecticut Electric Panel/Manual Transfer Switch
75Amp IOTA DLS-75/IQ4 Battery Charger,
(6) 6.25v/220AH Johnson Controls Golf Cart Batteries,
6Kw continuous/12Kw Surge MSW Inverter, 12v/120v,
1.5Kw GE Transformer 120v/240v,
100Amp Manual Transfer Switch (to switch well power to batteries).
2-Gauge Switch-to-Starter cables for the 12v connections.

The batteries are wired in series for three 12.5v strings totaling 660AH.
At 60 amps out, I'd have a 9% charge rate. Want to have six panels to guarantee a full battery charge at the end of a cloudy day. At a 50% DOD, I'd need 330AH retained and with a 90% colombic efficiency would need 367AH/day outputted from the controller. Which equals 60amps out for at least 6 hours/day.

Do you think I could get that considering that the panels' totals equal around 35% extra power at peak? Do such panels come with leads already attached or do I have to solder them on? If I do have to, standard 63/37 solder or low-temp Indium solder? Thanks...

Comments

  • icarus
    icarus Solar Expert Posts: 5,436 ✭✭✭✭
    Re: Solar Newbie With Panel/Controller/Wattage Questions

    Marsofold,

    "Want to have six panels to guarantee a full battery charge at the end of a cloudy day. At a 50% DOD,"

    I'd like to be rich, but I have to settle for handsome instead!

    Please be advised that depending on how you define "cloudy day" you output might vary from 0% to ?%.

    In simple terms, if you take the name plate rating of a PV, de-rate 50% (53% is more accurate but 50% is easier to do quickly), multiply that number by the number of hours of good sun you could expect (seldom better than 4)and that is how much power you can draw out of a battery based, inverter system.

    Remember, you have inefficiencies throughout the system that you have to overcome, PV ef, wiring loss to the CC, CC eff, more wiring loss to the batteries, basic battery charging ef, more wiring loss to the inverter, and finally inverter ef. In simple numbers, you end up "wasting" ~50% of your potential. And very few places will give 6 hours of "ideal" sun day in and day out.

    So, in your case 1230 watts* .5=615*4=2460wh. Convert that to AH@ 12.6vdc and it would be in the neighborhood of ~195 ah

    Only you can guess in your particular situation whether that 4 hours is reasonable or not. Consider that haze, clouds, shadows will have a negative effect on output.

    Most people over estimate the amount of PV power they can actually get (especially with battery based systems) and they under estimate their loading. I suggest you get a very good handle on your loading, run a PV watts program (http://www.pvwatts.org/ ) with your location to see what reasonable yield might be.

    Tony

    PS Welcome to the forum, we hope we can help.

    PPS. Just for info, we live off grid. We have ~300 watts of PV and we draw ~.6 kwh/day out of 450ah of 12v batteries. We have 3 day reserve to before the batteries are draw down to ~70% SOC. We get fully charged nearly every day if there is good sun.
  • BB.
    BB. Super Moderators, Administrators Posts: 33,431 admin
    Re: Solar Newbie With Panel/Controller/Wattage Questions

    For your panels+MPPT charge controller--you really don't look at the Coulombic charge efficiency of 90+% but the Power efficiency, which for flooded cells can be down towards the 80% rate. Not a big deal--but I try to be conservative in predictions.

    Next, solar power output power--no matter what the advertising says--are pretty much proportional to the Watts per Sq. Meter / Foot of sunlight hitting the panel at any one time.

    For my Grid Tied system (GT can collect 100% of the available power, unlike off grid systems where, once the batteries are charged, you have no place to collect/store any additional power)--you would be lucky to capture roughly 50% of your daily available power with a light overcast vs a bright sunny day. And in deep winter with heavy dark clouds/rain, it is not unusual to collect only 10% or less of "normal".

    So--you are better off to design your system for "average" weather and use your nice generator backup system (and conservation for optional loads) for bad weather.

    Lets assume you are near Baltimore Maryland and using the PV Watts Website, we can see how much you could expect, on average, to capture. 6x205w=1.23kW of solar panels, assume derating of 0.52 (80% eff flooded cell and using 85% eff. inverter), fixed array:
    "Station Identification"
    "City:","Baltimore"
    "State:","Maryland"
    "Lat (deg N):", 39.18
    "Long (deg W):", 76.67
    "Elev (m): ", 47
    "PV System Specifications"
    "DC Rating:"," 1.2 kW"
    "DC to AC Derate Factor:"," 0.520"
    "AC Rating:"," 0.6 kW"
    "Array Type: Fixed Tilt"
    "Array Tilt:"," 39.2"
    "Array Azimuth:","180.0"

    "Energy Specifications"
    "Cost of Electricity:"," 7.8 cents/kWh"

    "Results"
    "Month", "Solar Radiation (kWh/m^2/day)", "AC Energy (kWh)", "Energy Value ($)"
    1, 3.47, 69, 5.38
    2, 4.40, 79, 6.16
    3, 4.79, 91, 7.10
    4, 5.12, 92, 7.18
    5, 5.28, 94, 7.33
    6, 5.70, 94, 7.33
    7, 5.61, 95, 7.41
    8, 5.28, 90, 7.02
    9, 4.95, 83, 6.47
    10, 4.90, 89, 6.94
    11, 3.58, 65, 5.07
    12, 2.85, 54, 4.21
    "Year", 4.66, 995, 77.61
    That gives you an average of 54 to 95 kWhrs per month or 1.8 kWhrs to 3.2 kWhrs per day--depending on season. There is a detail output in PV Watts that will give you the "average" output every hour over a 1 year average period.

    Generally, we size the battery bank and the solar panels to the planned load. So, for your question, roughly we are looking at for your 50% discharge of 330 AH and 12 volt bank, the power required to recharge would be:
    • 330 AH * 1/0.80 Batt Eff * 12 volt battery = 4,950 Whrs
    To figure out how many days to recharge, I will use the above solar data -- but I will have to back out the 80% battery losses and the 85% inverter losses (don't want to double count losses--bad enough already :roll: ):
    • 4,950 WH * 0.80 batt * 0.85 eff * 1/1,800 WH for December average = 1.87 days to recharge
    • 4,950 WH * 0.80 batt * 0.85 eff * 1/3,200 WH for December average = 1.05 days to recharge
    Regarding your genset load--you might be able to save some fuel costs/usage if you look at the average load on your genset... Typically, if your generator is roughly 2x your average load -- it will be fairly fuel efficient... If your genset is ~4x or more of your average load (i.e., the genset is running at 25% capacity or less on average)--then typically you have high fuel flow (typically 50% of rated load) and low power utilization (25% or less) which can cause you to consume 2x more fuel (at 25% loading) than a smaller genset would (hope that makes sense).

    In the cases where your average loading is low--then a second, smaller genset (like a used small RV unit) might be a nice investment (also provides mechanical backup too).

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • marsofold
    marsofold Solar Expert Posts: 45 ✭✭
    Re: Solar Newbie With Panel/Controller/Wattage Questions

    OK, I need more panels than I thought. How about the leads? Do the panels come with pre-attached leads or do I have to solder them on? 63/37 or Indium solder?
  • BB.
    BB. Super Moderators, Administrators Posts: 33,431 admin
    Re: Solar Newbie With Panel/Controller/Wattage Questions

    Most large panels today are designed for Grid Tied system which the NEC requires attached leads and an MC4 type locking connector...

    The simple way for a "non-professional" to connect the panels up is to purchase a male/female cable and cut in in half to hardware into the rest of your system (don't trim/cut cables on the panels--that may void your warranty).

    MC4 cables and MC4 disconnect tools

    Regarding your battery bank size... You have not said what your expected loads are... We have a rough rule of thumb that you have 3 days of storage and a maximum 50% discharge for optimum battery costs and life.

    Being able to recharge a bank in a day--may indicate that you have 1 day's worth of storage (50% maximum discharge) or that you are over-sizing your array.

    Neither a 1 day bank or over-sizing your array is wrong--but it can lead to questions... A 1 day bank may force you to use your genset more (cannot power system for more than 1 day of cloudy weather before firing up genset). Also, batteries tend to not last as long when cycled deeply/often. And batteries that have higher charge/discharge rates (faster than C/20 to C/10) tend to be a bit less efficient during charge/discharge (heavy current vs bank capacity).

    Over-sizing the array--mostly the issue is just expense of the array. If this is an emergency backup system rather than an Off Grid system--The arrays will be sitting and not making/saving you any money. And if you run your Grid Connected home on the PV backup system, you will be cycling the batteries and reducing their life (vs if you are just keeping them floating for standby use during storms, etc.).

    One option to think about--if you are looking at a lot of solar (say closer to 3kWatts or more), you may want to look at a Grid Tied Hybrid Inverter. You batteries will remain "floating" instead of cycling and you will be efficiently selling energy back to your utility (if your utility supports monthly or 1 year net metering or something similar).

    Also, in the past, there have been more energy rebates and tax credits for Grid Tied Systems vs Off-Grid/Backup systems (Feds = 30% credit and you can check here for state/local kickbacks).

    Anyway--just a few more things to think about.

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • a0128958
    a0128958 Solar Expert Posts: 316 ✭✭✭
    Re: Solar Newbie With Panel/Controller/Wattage Questions
    icarus wrote: »
    Marsofold,
    ... we live off grid. ... we draw ~.6 kwh/day ...

    I think this is incredibly impressive. Especially in comparison, we're averaging 62 kWh/day for this month for our family of 4 residing in a large metropolitan city - we have plenty of progress still to make.
  • icarus
    icarus Solar Expert Posts: 5,436 ✭✭✭✭
    Re: Solar Newbie With Panel/Controller/Wattage Questions

    Much as I would like to polish my halo, the reality is more complicated. We live in a very small house, use propane for fridge, hot water cooking etc, wood for heat and no cooling except for ceiling fans. We also use a generator to run the shops and have a gasoline powered washing machine.

    We use ~8-10 gallons of propane a month, and perhaps 15 gallons of gas per year for the shops.

    Net/net, we are still pretty frugal, but not quite what the .6 kwh/day suggests. That said , we use ~ twice as much electricity as we did 3 years ago.

    Tony
  • a0128958
    a0128958 Solar Expert Posts: 316 ✭✭✭
    Re: Solar Newbie With Panel/Controller/Wattage Questions

    Tony, thanks.

    Best regards,

    Bill
  • marsofold
    marsofold Solar Expert Posts: 45 ✭✭
    Re: Solar Newbie With Panel/Controller/Wattage Questions

    My intent is to prep for a possible TEOTWAWKI event. Originally, I had designed for 18 hours worth of storage so I could run the generator for 6 hours while keeping the battery bank charged and the freezer chilled. I could remove frozen food from the freezer at the beginning of the cycle, cook food in a crockpot, fill water jugs, wash clothes, and warm up the water heater so I could take a shower near the end of it. Then live on batteries for the next 18 hours. Since 8 of those hours would be during sleep when only the cube fridge would be on, then I could actually draw 350 watts when up and around. With 350 watts, I could get by quite comfortably. Even the well pump works on batteries (for short intervals). I spent...$7000.

    Now it looks like solar is NOT the inexpensive add-on I'd hoped. A 205 watt solar panel actually only outputs 187 watts peak in mid-USA. The controller only delivers about 168 watts of that. And the batteries only store about 138 watts. After conversion by the inverter, I might optimistically get 121 watts. And since the sun only makes practical power for 20% of the day, averaged over 24 hours a 205 watt panel actually delivers...24 watts. I'd need TEN $357 panels just to maintain my minimal 350watts/16hour level! And for a three day storage interval, I'd need TWENTYEIGHT $80 batteries! Unless I were willing to wire 14 battery pairs in parallel (I wouldn't), I'd need a new higher voltage inverter. With the controller I'd use and the new inverter, that would total to roughly...$7000. Hmmmm... 8)
  • icarus
    icarus Solar Expert Posts: 5,436 ✭✭✭✭
    Re: Solar Newbie With Panel/Controller/Wattage Questions

    Battery based solar is not generally considered a less expensive alternative to grid or generator power. In fact net/net it is ~4 times as expensive per kwh as grid tie, and grid tie is ~twice as expensive as grid.

    Tony
  • BB.
    BB. Super Moderators, Administrators Posts: 33,431 admin
    Re: Solar Newbie With Panel/Controller/Wattage Questions

    The best option for anything that assumes infrastructure goes kaput--Is conservation.

    You mention a "cube" fridge... Generally those draw close to 200 kWhrs per year for 1-3 cuft storage. You can get ~17 cuft fridges that are probably below 400 kWhrs per year for 10+x the storage area.

    People have also converted their 7+ cuft Chest Freezers into Refrigerators that run on less than 100 kWhrs per year:

    Chest freezer as a chest refrigerator

    So--if you have a large chest freezer, just get some sort of refrigerator range thermostat and you can run it at ~32-40F and very little power (use up the fresh food first, then as you run out of frozen--you can converter to fridge mode for the duration of the event).

    Anyway, don't give up on the plan just yet--really look at steps to reduce your fuel use, get a smaller genset (my guess)--A Honda eu2000i will run 400 watts on 1.1 gallons of fuel for almost 15 hours.

    Also, if you have heavy optional loads--for example water pumping--run those during the day when the sun is out (builds a storage tank if you don't have one). That will save you the 20% loss in the battery cycling and is a good place to expend your solar energy if you have excess that day, etc.

    For heating and cooling--insulation is pretty much the first suggestion there. More attic insulation, double pane windows, etc.

    There is a thread where we have collected a lot of information that spans a wide range of topics... I have not taken the time to re-write it--but there are lots of things for you to review and see what makes sense to you.

    Working Thread for Solar FAQ.

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • icarus
    icarus Solar Expert Posts: 5,436 ✭✭✭✭
    Re: Solar Newbie With Panel/Controller/Wattage Questions

    You got it about right. My rule of thumb is take the name plate rating of the PV, and by the time you draw power out of the inverter you are left with ~50%. multiply that number by 4 hours and that is what you can rely on under "normal" circumstances.

    So, in your case, 1200*.5=600*4=2400wh/day. You can fudge the numbers a bit up and down, but the net/net is going to be close.

    Tony
  • dwh
    dwh Solar Expert Posts: 1,341 ✭✭✭
    Re: Solar Newbie With Panel/Controller/Wattage Questions
    marsofold wrote: »
    My intent is to prep for a possible TEOTWAWKI event.

    If it comes to that then you'd be better off buying guns. It's harsh, but if you've got bullets, you can always get beans (or solar panels).
  • mike95490
    mike95490 Solar Expert Posts: 9,583 ✭✭✭✭✭
    Re: Solar Newbie With Panel/Controller/Wattage Questions
    dwh wrote: »
    If it comes to that then you'd be better off buying guns. It's harsh, but if you've got bullets, you can always get beans (or solar panels).

    Not quite, if you are polite. Better stated as , if you have guns & bullets, you get to keep your beans and panels. If TEOTWAWKI * happens, the only panels left are in transit..


    * The End Of The World As We Know It
    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 ,

  • icarus
    icarus Solar Expert Posts: 5,436 ✭✭✭✭
    Re: Solar Newbie With Panel/Controller/Wattage Questions

    If the end of the world as we know it comes,, I am not real interested in being around. Road Warrior/The Road all those other scenarios are not ones that I am interesting in living through. Without being too something about it, but IMHO there are somethings worse than being dead.

    Tony
  • Cariboocoot
    Cariboocoot Banned Posts: 17,615 ✭✭✭
    Re: Solar Newbie With Panel/Controller/Wattage Questions
    icarus wrote: »
    If the end of the world as we know it comes,, I am not real interested in being around. Road Warrior/The Road all those other scenarios are not ones that I am interesting in living through. Without being too something about it, but IMHO there are somethings worse than being dead.

    Tony

    This must be something about our generation, Tony! My 'apocalypse' plan is to paint a target on myself and hang a sign around my neck that says "SHOOT ME FIRST!" :p The only parts of civilization I don't like now are the uncivilized bits, and if it comes to that being all there is .... well I've lived long enough already anyhow.

    I realize some people may find that mindset hard to believe/comprehend.
  • BB.
    BB. Super Moderators, Administrators Posts: 33,431 admin
    Re: Solar Newbie With Panel/Controller/Wattage Questions

    I understand everyone's feelings and outlook on life---Just remember, we are not a survivalist forum. ;)

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • niel
    niel Solar Expert Posts: 10,300 ✭✭✭✭
    Re: Solar Newbie With Panel/Controller/Wattage Questions

    this might sound dumb, but if it's the end of the world did it really end because nobody was there to see or hear it end? (thinking along the falling tree in the forest scenario.)
  • Cariboocoot
    Cariboocoot Banned Posts: 17,615 ✭✭✭
    Re: Solar Newbie With Panel/Controller/Wattage Questions
    niel wrote: »
    this might sound dumb, but if it's the end of the world did it really end because nobody was there to see or hear it end? (thinking along the falling tree in the forest scenario.)

    Don't know about "end of the world noise" (opposite of "big bang"?) but I guarantee that when a tree falls in the forest it makes a sound even if nobody is there to hear it. I've been there, heard it, and I'm nobody. :p
  • russ
    russ Solar Expert Posts: 593 ✭✭
    Re: Solar Newbie With Panel/Controller/Wattage Questions

    İf such a time comes the last place İ want to be is around a bunch of the city guys with guns!

    A country boy probably knows how to use his gun but too many of the survival types have never lived in the country.
  • niel
    niel Solar Expert Posts: 10,300 ✭✭✭✭
    Re: Solar Newbie With Panel/Controller/Wattage Questions
    Don't know about "end of the world noise" (opposite of "big bang"?) but I guarantee that when a tree falls in the forest it makes a sound even if nobody is there to hear it. I've been there, heard it, and I'm nobody. :p

    actually the world does not end if people end and if the world itself does end the people will go with it. if people are still around it isn't the end in that respect either. it wasn't so much as to whether you could hear or see it, but the fact that if you can it didn't end.

    btw, it's the falling trees you didn't hear you need to watch out for.:p