I not sure I'm doing it right

josephshaw
josephshaw Registered Users Posts: 7
My project is getting my house off the grid!
To start with I’m planning to build 7KW of panels. I’m going to place the panels on my roof. I have 5 panels built that should produce 94.5 watts each totaling 472.5 watts. I’m using a Power Jack 1200W Grid Tie inverter and measuring the output with a Kill-A-Watt meter. I find that when I should be generating 472.5 watts into the inverter my Kill-A-Watt meter is only showing 200 amps. I understand that the inverter is going to use 20% of the 472.5 watts or 94.5 watts. What is happening to the other 178 watts? Is this what I should expect, is there something wrong wrong/broken or I'm I measuring it wrong.

Thanks
Joseph Shaw


Peak Power 94.5 Watts ( 75% of below open circuit voltage and sort circuit current.)
Peak power voltage 36.2 V
Peak power current A

Open circuit Voltage 36 V
Short Circuit current 3.5 A
126 Watts

Comments

  • Cariboocoot
    Cariboocoot Banned Posts: 17,615 ✭✭✭
    Re: I not sure I'm doing it right

    Welcome to the forum.

    May I suggest you shut everything down now, before something horrible happens?

    Here's why I think it might:
    1). Homemade panels.
    2). PowerJack 1200 grid tie inverter. One of those "just plug it in" inverters? Not safe even with grid, shouldn't be producing anything without it.

    When you go off-grid you have an inverter powered by a battery bank. That battery bank is recharged by the solar panels through a charge controller. There is no other way to do it. In any case panels only produce power in response to a load: if you don't have 400+ Watts of load you don't see 400+ Watts on the K-A-W.

    This is a case where too little knowledge can be a very dangerous thing. But don't worry; we're here to impart knowledge! :D

    The first knowledge would be that going off-grid when you have grid available usually makes no economic sense whatsoever. So what are your reasons for doing this?
  • BB.
    BB. Super Moderators, Administrators Posts: 33,431 admin
    Re: I not sure I'm doing it right

    Regarding home made solar panels--Here are a set of black market panels (not even close in quality to UL/NRTL Listed panels--probably better than the average home made):

    Panel Fire Question

    I could not find out the information on the GT inverter (input/output voltage requirements)... But, usually the GT inverter requires some range of input DC voltage (50-100 vdc for one version of this GT inverter).

    But, from your specs... The Peak Power (Vmp) should be something like Open Circuit voltage (Voc)... Yours are almost the same at 36 volts.

    Kind of difficult to say which part of the system is not working correctly at the moment.

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • Vic
    Vic Solar Expert Posts: 3,208 ✭✭✭✭
    Re: I not sure I'm doing it right

    Hello josephshaw,

    While this Forum is a great place for many Solar Energy topics, we may not be the best place for this kind of info exchange. Perhaps only one or two percent of those here have the patience to DIY, or the specific knowledge about just how it is best for the DIYer to use those materials available to you folks.

    I am not trying to run you off, but, my personal BIAS is why would a person want to build many, many panels?? I am just a member here.

    Was just poking around on the net, using Google, and found this Forum and post. Perhaps it would be of some use to you, if you have not already looked here:
    http://www.solarpaneltalk.com/showthread.php?591-Are-DIY-Solar-Panels-Worth-it

    Just did a cursory look at this Forum, and hope that it is OK to post it, if not, Just Shoot Me.

    Wish you well with your project, I have trouble mustering the energy to just mount my commercial panels. Good Luck, Vic
    Off Grid - Two systems -- 4 SW+ 5548 Inverters, Surrette 4KS25 1280 AH X2@48V, 11.1 KW STC PV, 4X MidNite Classic 150 w/ WBjrs, Beta KID on S-530s, MX-60s, MN Bkrs/Boxes.  25 KVA Polyphase Kubota diesel,  Honda Eu6500isa,  Eu3000is-es, Eu2000,  Eu1000 gensets.  Thanks Wind-Sun for this great Forum.
  • josephshaw
    josephshaw Registered Users Posts: 7
    Re: I not sure I'm doing it right

    Thank you for the link I will check it out.
  • josephshaw
    josephshaw Registered Users Posts: 7
    Re: I not sure I'm doing it right

    Thanks for the information.
    The GT inverter is requires 28-55 volts. My panels are providing 36 Voc. When at the peek of the day the panels provide 36Voc and 3.5 Shorted current. The cell manufacture said that the peak wattage should be about 75% of the 36Voc X 3.5a Shorted Circuit. So with the 5 panels I get about 500 Watts. But when I measure voltage on the closed circuit connected to the GT inverter the voltage drops to 27.5 V under the spec of the inverter. Is that still in the range for the inverter or should I configure the panels to exceed the 28 volts when in a closed circuit?

    Thanks
  • josephshaw
    josephshaw Registered Users Posts: 7
    Re: I not sure I'm doing it right

    I have a very high power bill, I use 94KWH per day or over $400 per month. Also I live in a area the has a history with power outages and I have health issues and need power 24x7 for O2.

    I'm learning the "Off the Grid" is almost what I'm saying. I want to build a system that supplies me power when I have a power outage and I need a system to make O2 when it's down.

    The third reason is I'm changing most of my lighting to LED and 12 volt.
    I'm still in the testing phase and I have the panels in the driveway :)
  • Cariboocoot
    Cariboocoot Banned Posts: 17,615 ✭✭✭
    Re: I not sure I'm doing it right
    josephshaw wrote: »
    Thanks for the information.
    The GT inverter is requires 28-55 volts. My panels are providing 36 Voc. When at the peek of the day the panels provide 36Voc and 3.5 Shorted current. The cell manufacture said that the peak wattage should be about 75% of the 36Voc X 3.5a Shorted Circuit. So with the 5 panels I get about 500 Watts. But when I measure voltage on the closed circuit connected to the GT inverter the voltage drops to 27.5 V under the spec of the inverter. Is that still in the range for the inverter or should I configure the panels to exceed the 28 volts when in a closed circuit?

    Thanks

    Voc - Voltage open circuit - is not of much use for determining power potential. That's the Vmp number you want. Chances are it's about 8 Volts less than Voc on those panels, so your Vmp is just barely making enough to power the inverter. The inverter itself has a rather odd input range, if you ask me. Usually an inverter in that input Voltage range is a "one panel" design, like the Enphase. Most commercial "24 Volt" panels have a Vmp around 35 and a Voc of about 44.
  • Cariboocoot
    Cariboocoot Banned Posts: 17,615 ✭✭✭
    Re: I not sure I'm doing it right
    josephshaw wrote: »
    I have a very high power bill, I use 94KWH per day or over $400 per month. Also I live in a area the has a history with power outages and I have health issues and need power 24x7 for O2.

    I'm learning the "Off the Grid" is almost what I'm saying. I want to build a system that supplies me power when I have a power outage and I need a system to make O2 when it's down.

    The third reason is I'm changing most of my lighting to LED and 12 volt.
    I'm still in the testing phase and I have the panels in the driveway :)

    I think what you're really after is a "hybrid" system; it feeds the grid "surplus" power from the panels while maintaining a battery bank for emergency power. A couple of problems with that: they tend to be expensive and the utility will have a screaming fit if they find out you're back-feeding the grid without approval. You won't (shouldn't) get approval if using homemade panels, as they are not UL approved. Even if the utility and AHJ allow it, your insurance company won't like it. It gives them a ready excuse to deny any claim in case of fire, regardless of cause.

    A couple of points: neither grid-tie nor off-grid power is going to be cheaper than your utility. So it is a false economy to think this will save you money. You should first look in to reducing your consumption any way you can; much better return on the $. Take that K-A-W meter and start measuring.

    As for grid instability, you can use an off-grid inverter with batteries and no panels to power critical items. You simply recharge the batteries from the grid. In your case you could use your homemade panels to recharge and save a bit there. But darn it, the good off-grid inverters are expensive if your needs are for some serious Watts (like keeping refrigeration going).

    Any numbers for how much power you'll need when the grid goes down? Maximum Watts and total Watt hours?
  • fixer
    fixer Registered Users Posts: 12
    Re: I not sure I'm doing it right
    josephshaw wrote: »
    when I measure voltage on the closed circuit connected to the GT inverter the voltage drops to 27.5 V under the spec of the inverter.
    What the GTI will do is keep pulling amps and backing off, over and over, you may see this while you are measuring it.

    It will try to get the most power from your panel. It will charge it's internal capacitor and then draw that power over and over to try to get the best it can.

    When you built the panels were you aware that most open voltage "24V" panels are around 40V ?

    You may have shorted your 24V panels by a few cells. You may be able to make up for this by creating a small panel to "boost" the voltage for *each* panel.

    As for trying to be ready for a power outage, you have a lot of options, like running a charge controller along with your GTI so that when the batteries are charged then the GTI can pump power back into the grid or at least supplement the power you are using already.

    Depending on your technical skill level you have a lot of options. I would google for information on automatic transfer switches, UPSs, grid ties and solar stuff and just read up as much as you can.

    Sounds like you will have things going well as soon as you can add a few more cells.
  • BB.
    BB. Super Moderators, Administrators Posts: 33,431 admin
    Re: I not sure I'm doing it right
    josephshaw wrote: »
    I have a very high power bill, I use 94KWH per day or over $400 per month. Also I live in a area the has a history with power outages and I have health issues and need power 24x7 for O2.

    I'm learning the "Off the Grid" is almost what I'm saying. I want to build a system that supplies me power when I have a power outage and I need a system to make O2 when it's down.

    The third reason is I'm changing most of my lighting to LED and 12 volt.
    I'm still in the testing phase and I have the panels in the driveway :)
    Roughly:
    • $400 month bill / [94KWH per day * 30 days] = $0.14 per kWH
    For most people, if you take the total capital, battery replacement, and repair costs divided by 20 year system life/payback period (no taxes, no interest on loans, no present value/future worth calculations/no inflation)--you will be paying ~$1.00-$2.00+ per kWH for pure off grid power...

    Assuming $1.50 per kWH, your current $400 per month bill will be ~$4,000 +/- per month for 100% off grid power. And you will be prepaying at least 1/2 that cost up front and paying substantial costs everything you need to replace a battery bank (~8-15 years typically) and new electronics (charge controllers, inverters, etc.) every 10-15 years...

    So--if your electric rate was $1.40 per kWH (10x your current rate)--What would you change / do differently at your home?

    Even a Hybrid (GT/Off-Grid) system will cost you are ~$0.45 to $0.75 per kWH over 20 year average).

    To be honest, a good aim point for a "cost effective" off grid system that does not cost many arms and legs--Around 100 kWH per month or 3.3 kWH per day is a good aim point.

    In the end, power is a highly personal choice... Nobody here (including me) is trying to make the decisions for you--Just offering you information and different ways of looking at the problem.

    The best way to start... Measure your loads, spend time and money on conservation (insulation, new appliances, smaller appliances/laptop computers, efficient lighting, turn stuff off, etc.).

    Then review power use/needs and then look at alternative power options (solar, generators, etc.).

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • josephshaw
    josephshaw Registered Users Posts: 7
    Re: I not sure I'm doing it right

    I have reconfigured the panels to produce open voltage of 54 volts and the closed voltage drops to about 47 volts. I'm hoping this is a sweet spot. What do you think?

    BTW the cost per 194 (54 voc x 3.5 amp) watt panel is costing me about $150 each to build and they totally sealed and able to reopen for repair. Snow load testing is soon to happen.
    Thanks Joe
  • Cariboocoot
    Cariboocoot Banned Posts: 17,615 ✭✭✭
    Re: I not sure I'm doing it right
    josephshaw wrote: »
    I have reconfigured the panels to produce open voltage of 54 volts and the closed voltage drops to about 47 volts. I'm hoping this is a sweet spot. What do you think?

    BTW the cost per 194 (54 voc x 3.5 amp) watt panel is costing me about $150 each to build and they totally sealed and able to reopen for repair. Snow load testing is soon to happen.
    Thanks Joe

    That Vmp should work better based on the inverter specs.

    Don't count on panels being "totally sealed"; there have been instances of commercially made panels leaking inside. It's the most difficult part of building a panel; keeping the moisture out.

    As for snow load; panels are hunks of glass. They simply aren't meant to take loading. Usually in snow areas/season they get tilted up more so they shed the snow. You won't want the 72 degrees used up here, but it may be to your advantage to go for the maximum tilt possible to minimize any accumulation. Here's a good reference on angle vs. power production: http://www.macslab.com/optsolar.html

    At this point I have to point out you don't have any "off-grid" or back-up power potential as there are no batteries. It is not a good idea to try and run a GT inverter from a battery, as there's nothing to regulate the current draw. Panels are "self-regulating" in that they only produce so much current. A battery will try to provide full current all the time, meaning the inverter will draw to the max and deplete the battery in very short order.
  • fixer
    fixer Registered Users Posts: 12
    Re: I not sure I'm doing it right
    josephshaw wrote: »
    I have reconfigured the panels to produce open voltage of 54 volts and the closed voltage drops to about 47 volts. I'm hoping this is a sweet spot. What do you think?

    BTW the cost per 194 (54 voc x 3.5 amp) watt panel is costing me about $150 each to build and they totally sealed and able to reopen for repair. Snow load testing is soon to happen.
    Thanks Joe
    Those voltages look good but how did you measure them? Is the 47V in full good sun and with some sort of load? You also don't mention wire size and length.

    You DO NOT want to exceed 65 or so volts on that GTI, and on some days you may get the "cloud effect", clouds around the sun, where you produce a lot of voltage so be careful. The GTI will go "open" sometimes during the day when it's testing MPPT or possibly during a short grid outage. So just be aware of that.

    As I said before you can easily connect the GTI and a charge controller directly to the panels and have them both work together to keep your batteries charged and push the extra power to the grid. I think that's a great option for you.

    The grid tie would *not* run off the battery, they are both connected directly to the panels.

    So far it sounds like you spent $250 on the GTI and 5 * 150 = $750 so about $1000, is that about right? Not bad considering some "approved" system would have run you $4000 or more.

    So that's about 7142 KWh you need to produce for payback (at 14c).

    If you get 7 hours at about 300 Wh (conservative but good location) = 2.1 KWh / day, payback is 3400 days or 9.3 years (of good solar days of course).

    How much would that be at the "approved" price of $4000 ? 28,571 KWh payback?

    It would be hard to factor in that you have more GTI than you need right now, and can cheaply expand the system by just building more panels. That would further reduce the payback.

    It's really not worth talking about payback for any of this anyway, it's the principal of not being dependent on a power company, or any company for your existence. It's about reducing your carbon footprint. Screwing the oil companies, and all that.

    You can also picture it like insurance, power insurance.

    And since you are learning a good skill, you can easily grow your system at low expense and help others to go green too!

    For me, I like sticking my middle finger at the power company! Take that!

    Oh, and you better get this all working "before something horrible happens", like the power goes out for days!

    Walmart has some really good prices on batteries, they have a "Maxx" marine deep cycle battery, 125 Ah, for about $75 that is one hell of a battery for the price. 18 mo. free replacement. Don't forget a battery box and some decent cables to your (AC) inverter.
  • josephshaw
    josephshaw Registered Users Posts: 7
    Re: I not sure I'm doing it right
    I think what you're really after is a "hybrid" system; it feeds the grid "surplus" power from the panels while maintaining a battery bank for emergency power. A couple of problems with that: they tend to be expensive and the utility will have a screaming fit if they find out you're back-feeding the grid without approval. You won't (shouldn't) get approval if using homemade panels, as they are not UL approved. Even if the utility and AHJ allow it, your insurance company won't like it. It gives them a ready excuse to deny any claim in case of fire, regardless of cause.
    ....


    Any numbers for how much power you'll need when the grid goes down? Maximum Watts and total Watt hours?

    Yes I'm looking to build a "hybrid" system. I have talked to my power company , the local building department and my insurance company. All of them don't seem to have a problem with home built, but time will really tell!
    I'm not sure what the maximum KWH is going to be needed to maintain the basics. I'm hoping the conversion to 12v LED will reduce overall power usage.

    Joe
  • josephshaw
    josephshaw Registered Users Posts: 7
    Re: I not sure I'm doing it right

    I found my problem, purchase high quality crimp connectors. I tested my connections and found 68 ohms on one 10Gage wire. Bad crimping....
    Thanks for all of your help and it looks like I can build 100 Watt peek panels for for less than $120.00.
    I hope that is a good cost
  • HuckMeat
    HuckMeat Registered Users Posts: 24
    Re: I not sure I'm doing it right
    josephshaw wrote: »
    I have a very high power bill, I use 94KWH per day or over $400 per month. Also I live in a area the has a history with power outages and I have health issues and need power 24x7 for O2.

    I'm learning the "Off the Grid" is almost what I'm saying. I want to build a system that supplies me power when I have a power outage and I need a system to make O2 when it's down.

    The third reason is I'm changing most of my lighting to LED and 12 volt.
    I'm still in the testing phase and I have the panels in the driveway :)

    Building your own panels and mounting them on your roof, and using powerjack inverters is a fantastic way to burn down your house. Also, no utility will let you connect your panels to them in an intertie configuration.

    Replacing your energy usage via solar is going to take a lot more solar than you are building. You will need tens of thousands of dollars in batteries.