Starting off fresh

techcordtechcord Registered Users Posts: 15
I would like to run one 60w light build in my house using solar.
I would like a system that is expandable to some day run my whole house or most of it.
Suggestions for solar panels and charge controllers, even battery's and inverters would be great.
Thank you in advance!
Landon

Comments

  • CariboocootCariboocoot Banned Posts: 17,615 ✭✭
    Re: Starting off fresh

    Well the formula is pretty much the same for any off-grid type application:

    Watts * hours = Watt hours

    Watt hours / Voltage = Amp hours used

    Amp hours used * 2 = minimum battery bank size

    5% of minimum battery bank size = minimum peak charge current

    minimum peak charge current * panel Voltage at maximum power = array size with PWM type controller

    The devil is in the details of course.

    60 Watts * 12 hours = 720 Watt hours. If this is AC there is an efficiency conversion factor which is dependent on the the particular inverter. Say 90%; you're now at 800 Watt hours DC. The inverter will consume power too. Say it's a small one and uses 6 Watts for that same 12 hours: another 72 Watt hours for 872 total. This would be a 12 Volt system so that comes out to (872/12) 73 Amp hours for a minimum battery of 146 Amp hours @ 12 Volts. 5% peak charge current = 7.3 Amps, @ 17.5 Volts (Vmp for a "12 Volt" panel) = 128 Watts.

    But that is all minimal. If you want less DOD on the batteries you need to increase the Amp hours and the panel capacity. If you want faster charging, better charging in questionable weather, or power to use while charging you need to increase the peak charge current percent. Et cetera.
  • ggunnggunn Solar Expert Posts: 1,973 ✭✭✭
    Re: Starting off fresh
    techcord wrote: »
    I would like to run one 60w light build in my house using solar.
    I would like a system that is expandable to some day run my whole house or most of it.
    Suggestions for solar panels and charge controllers, even battery's and inverters would be great.
    Thank you in advance!
    Landon
    Just FYI, it's generally not a simple task to design a system that can be added to later.
  • techcordtechcord Registered Users Posts: 15
    Re: Starting off fresh

    Okay well scratch that then, lets do a system to run the one light 24 hours a day, can we do that?

    Thank you,
    Landon
  • CariboocootCariboocoot Banned Posts: 17,615 ✭✭
    Re: Starting off fresh
    techcord wrote: »
    Okay well scratch that then, lets do a system to run the one light 24 hours a day, can we do that?

    Thank you,
    Landon

    Yup. Although it seems a bit odd to run a light for 24 hours. The sun has to shine for some of that time or else the panels don't work. :D
  • techcordtechcord Registered Users Posts: 15
    Re: Starting off fresh

    Odd I might be,

    What panels and charge controller would I need?

    Thanks,
    Landon
  • CariboocootCariboocoot Banned Posts: 17,615 ✭✭
    Re: Starting off fresh

    What you start with is the batteries. They have to be able to supply the power.

    In this case 60 Watts * 24 hours = 720 Watt hours.
    Now if all you are going to run is that one light you can use quite a small inverter. In fact for just an incandescent bulb it doesn't even have to be pure sine. But this little Samlex would do it: http://www.solar-electric.com/sa150wa12vos.html
    If we look at the specs we see it is 85% efficient at peak, so your 720 Watt hours becomes 847 Watt hours on the DC side. Also it uses about 6 Watts itself, so that's another 72 Watt hours DC. Total: 919 Watt hours. On 12 Volts that's about 77 Amp hours, or a minimum 154 Amp hour battery at 50% depth of discharge maximum.

    Now you probably aren't going to find a battery of exactly those specifications. This is one of those numbers you want to round up on. So you might pick something like this Crown 185 Amp hour: http://www.solar-electric.com/cr185am12vod.html

    Then you plan the charging around that. Since the load will be on all the time you don't want to use the minimum rate as you have to compensate for the load (about 6-7 Amps continuous). You could go for 5% capacity plus load (16.25) or you can make it easy and go for 10% capacity (18.5 Amps). As you can see that adds in a little margin for error.

    Now if your using a standard PWM type controller you'd have to pick one capable of handling the full current. In this case something around 20 Amps like this: http://www.solar-electric.com/ss-20l.html
    Then you need to get enough panel by coming up with some whose combined Imp is around 18 Amps and whose Vmp is around 17 to 18. This will be in the neighbourhood of (18.5 * 17.5) 324 Watts.

    Strictly 12 Volt panels are somewhat limited in choice these days as sales (and thus production) favours higher Voltage GT type panels. Most 12 Volt panels are around 130 to 140 Watts and have an Imp of about 7. One example: http://www.solar-electric.com/sosp130wamum.html

    Now it's judgement call time. Three of those would have a current of (7.38 * 3) 22.14. This would max out the controller on sunny days, and provide a bit of extra power on not-so-sunny days. Two of them would have a current of 14.76, which would do for sunny days providing you didn't have the load on while charging.

    Inevitably in the design process you have to make that kind of decision. It is usually best to:
    1). reduce loads (and round up the amount)
    2). increase battery capacity (it will diminish over time no matter what)
    3). increase charge current (it is not always sunny)

    How much you push the numbers depends on how critical the load is and if there's any back-up power source available.
  • techcordtechcord Registered Users Posts: 15
    Re: Starting off fresh
    What you start with is the batteries. They have to be able to supply the power.

    In this case 60 Watts * 24 hours = 720 Watt hours.
    Now if all you are going to run is that one light you can use quite a small inverter. In fact for just an incandescent bulb it doesn't even have to be pure sine. But this little Samlex would do it: http://www.solar-electric.com/sa150wa12vos.html
    If we look at the specs we see it is 85% efficient at peak, so your 720 Watt hours becomes 847 Watt hours on the DC side. Also it uses about 6 Watts itself, so that's another 72 Watt hours DC. Total: 919 Watt hours. On 12 Volts that's about 77 Amp hours, or a minimum 154 Amp hour battery at 50% depth of discharge maximum.

    Now you probably aren't going to find a battery of exactly those specifications. This is one of those numbers you want to round up on. So you might pick something like this Crown 185 Amp hour: http://www.solar-electric.com/cr185am12vod.html

    Then you plan the charging around that. Since the load will be on all the time you don't want to use the minimum rate as you have to compensate for the load (about 6-7 Amps continuous). You could go for 5% capacity plus load (16.25) or you can make it easy and go for 10% capacity (18.5 Amps). As you can see that adds in a little margin for error.

    Now if your using a standard PWM type controller you'd have to pick one capable of handling the full current. In this case something around 20 Amps like this: http://www.solar-electric.com/ss-20l.html
    Then you need to get enough panel by coming up with some whose combined Imp is around 18 Amps and whose Vmp is around 17 to 18. This will be in the neighbourhood of (18.5 * 17.5) 324 Watts.

    Strictly 12 Volt panels are somewhat limited in choice these days as sales (and thus production) favours higher Voltage GT type panels. Most 12 Volt panels are around 130 to 140 Watts and have an Imp of about 7. One example: http://www.solar-electric.com/sosp130wamum.html

    Now it's judgement call time. Three of those would have a current of (7.38 * 3) 22.14. This would max out the controller on sunny days, and provide a bit of extra power on not-so-sunny days. Two of them would have a current of 14.76, which would do for sunny days providing you didn't have the load on while charging.

    Inevitably in the design process you have to make that kind of decision. It is usually best to:
    1). reduce loads (and round up the amount)
    2). increase battery capacity (it will diminish over time no matter what)
    3). increase charge current (it is not always sunny)

    How much you push the numbers depends on how critical the load is and if there's any back-up power source available.

    Thanks for the reply,

    There is something I am still not getting, your saying I would use around 77 amp hours. How will the 22.14 amps charge the battery's in the 5 average hours of sunlight I get a day. Do they put 22.14 amps back in to the battery's each hour?

    Should I be thinking bigger to start and get GT panels and charge controllers and battery's, I would love some day to be off grid.

    Thank you, Landon
  • BB.BB. Super Moderators, Administrators Posts: 29,698 admin
    Re: Starting off fresh
    techcord wrote: »
    There is something I am still not getting, your saying I would use around 77 amp hours. How will the 22.14 amps charge the battery's in the 5 average hours of sunlight I get a day. Do they put 22.14 amps back in to the battery's each hour?

    Short answer is yes.

    Amps is a "rate" (like gallons per hour). And Amp*Hours is an amount (like GPH * Hours of pumping = Gallons pumped).

    And don't forget the Voltage... Amps and Amp*Hours is always at "some voltage" for a complete discription of energy collected/used.

    Sort of like my Gallons Per Hour of pumping... We are missing "Pressure" in that example. A pump needs more energy to pump against a 100 PSI vs pumping against 10 PSI (pounds per square inch).

    And there are losses in any system... That is why you see us using 0.85, 0.77, 0.52 deratings all over the place... A GT system is around 77% efficient (when using panel "marketing specs.") and an off grid system is around 52% efficient (from panel specs to AC output from the AC inverter)--Yes about 50% efficient. That is always the problem with energy conversions and storage systems--A little loss at eac point multiplies out to a relatively large end to end set of losses.
    Should I be thinking bigger to start and get GT panels and charge controllers and battery's, I would love some day to be off grid.

    That is the $64,000 question... In general, it is very difficult to cost effectively expand a solar power system... Very few components will be transferable from a 1,000 Watt*Hour (1 kWH) per day system to a 3-10 kWH per day system (the rough range that many people fall in for an off grid small/energy efficient cabin/home system).

    Before going "off grid"--I would suggest measuring/studying the total power usage in your home. Then go on an extensive conservation project. From insulation, double pane windows, energy start appliances, using smaller appliances in place of present devices (i.e., laptop instead of a desktop computer, new TV that uses ~20 watts vs old TV that may use 150 Watts or more), etc...

    For many people who have never attempted conservation before, it is very possible to reduce power usage by 50% or even more.

    At that point, you could make the decision about how to proceed... After saving that much money, it is possible that you would not even need/want to consider solar power as your energy bill has been cut by 1/2.

    And if you still want solar, there are two major methods to use the sun. One is Grid Tied Solar (solar panels to GT Inverter to your main power panel). This will slow your meter down or even spin it backwards during the middle of the day. Basically, you are using your utility exactly as a giant AC Battery bank. Of course, this requires building permits and approval of your power company. And, there are many (typically smaller) utilities that do not allow/support Grid Tied power or give very little $$$ credit for generated power--Can be more complex to work through the utility billing requirements than the system design itself. GT Solar can actually save a person money over time. Lastly a GT Solar Power system does not provide emergency backup power.

    Then there is the Off Grid system, Solar panels-charge controller-battery bank-Off Grid AC Inverter. Costs a lot more to install and maintain (batteries are always an issue). And if you already have grid power, a battery based system will not usually save you any money. However, if you have long outages (weeks-months) because of ice storms and such, a solar powered Off Grid system can be a life saver (and you should have a backup genset and fuel).

    If you just want emergency power for a few days a couple times a year--Then a backup genset and fuel supply is usually the best answer.

    To make things a bit more complex, there are "hybrid" solar power systems... Uses batteries and a Hybrid inverter that can do GT when the utility is up, and Off Grid when the utility is down.

    Understanding your power needs (both in Watts and Watt*Hours, and in terms of outages/emergency or just "going off grid") will give you guidance on what size/type of system you need/want.

    Then we can help you do a paper design (or two) and figure out the costs before you lay out your first $$$$. Fewer surprises that way.

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • nielniel Solar Expert Posts: 10,300 ✭✭✭✭
    Re: Starting off fresh

    a better question is do you want to just offset the power used by a 60w bulb in a day? this is sending power back into the utility lines equal to that which you have used and bypasses controllers and batteries. these are generally needed for times when the grid goes down and this is either a hybrid system, which is a battery backed gt inverter system, or off grid with no selling to the grid at all. 60w x 24hrs = 1440watt hours. a gt system would need >374w stc in pv, which is 1440wh/77% (efficiency factor)=1870wh/5hrs full sun= 374w min. hope i figured this right as it's late.

    it is more difficult to generate the solar power and to then store it in batteries for later use and is less efficient than straight gt.
  • icarusicarus Solar Expert Posts: 5,345 ✭✭✭✭
    Re: Starting off fresh

    Why would you run a 60 watt bulb 24/7 wen you could run 4/15 watt CFLs or maybe 6 LEDs with the same power used for eye same light output?

    Tony
  • CariboocootCariboocoot Banned Posts: 17,615 ✭✭
    Re: Starting off fresh

    And the cheap answer is: replace the 60 Watt incandescent with a 13 Watt CFL. A lot less money, same effect on the utility bill.

    Good morning, Tony; I see you're up and at it (3 hours earlier on your side of the country!)
  • nielniel Solar Expert Posts: 10,300 ✭✭✭✭
    Re: Starting off fresh
    And the cheap answer is: replace the 60 Watt incandescent with a 13 Watt CFL. A lot less money, same effect on the utility bill.

    Good morning, Tony; I see you're up and at it (3 hours earlier on your side of the country!)

    no put in 4 of the 13w cfls and save even more by allowing 4 lights to operate instead of one for about the same 60w.
  • n1776n1776 Registered Users Posts: 6
    Re: Starting off fresh

    Yeah I would really get a energy-saving bulb.
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