Need Suggestions For Common Solar Calculation Questions

rss2q
rss2q Solar Expert Posts: 75 ✭✭✭✭
Hi all,

For one of my computer science classes that is teaching us how to create iPhone/iPad apps, I decided for my first app I want to create a solar calculator based app that allows users to quickly gain needed information such as the following:

"Determine how long you can run something off a battery"
"Determine how many panels/batteries you need to run something 24/7"
"etc..."

I need help coming up with other popular questions, and then once I come up with a decent amount to start out with (8 or 10). Then I'll move on to generating some formulas that will allow me to start creating the app.

*I know there are some solar apps already out there, but I just wanted to create my own and maybe even add additional stuff other apps do not have that may be useful.

I also will be linking users to this forum within the app for additional support as several people here have really helped me with my solar projects which I really appreciate!

Thanks! :D

Comments

  • Cariboocoot
    Cariboocoot Banned Posts: 17,615 ✭✭✭
    Re: Need Suggestions For Common Solar Calculation Questions

    An interesting project.

    I shall steal this opportunity to mention that there's a difference in the accuracy of answers to any such question according to the amount of detail included. We always start out here with rule-of-thumb and "ballpark" calculations and it is a constant fret of mine that people think such initial calculations are equivalent to final system design.

    One suggestion: you might want to divide it up into off-grid calculations and grid-tie calculations, as the two types of system do have some fundamental differences.

    For off-grid, starting with determining peak Watts and total Watt hours is good, followed by battery bank capacity to handle same (and system Voltage to accommodate current flow). Then move on to the next step which would be determining array size.

    Of course the further you go the more complicated it gets, especially as theoretical calculations have to be adjusted along the way to accommodate commercially available equipment.
  • rss2q
    rss2q Solar Expert Posts: 75 ✭✭✭✭
    Re: Need Suggestions For Common Solar Calculation Questions
    An interesting project.

    I shall steal this opportunity to mention that there's a difference in the accuracy of answers to any such question according to the amount of detail included. We always start out here with rule-of-thumb and "ballpark" calculations and it is a constant fret of mine that people think such initial calculations are equivalent to final system design.

    One suggestion: you might want to divide it up into off-grid calculations and grid-tie calculations, as the two types of system do have some fundamental differences.

    For off-grid, starting with determining peak Watts and total Watt hours is good, followed by battery bank capacity to handle same (and system Voltage to accommodate current flow). Then move on to the next step which would be determining array size.

    Of course the further you go the more complicated it gets, especially as theoretical calculations have to be adjusted along the way to accommodate commercially available equipment.

    Yeah the reason I placed this in the Solar Beginners Corner is, I'm looking to start with the more simple questions, then as time progresses, I will move to the more advanced more detailed type questions. As I too need to understand what's required in order to get a "ball park" answer. However, probably as I'm giving the answer, I will link them to this forum & other sources so that they can get more detail information.

    I want to keep the app at first, as simple as possible, and like you said, just include "ball park" type solutions. I will not include grid-tie type questions just yet as I myself do not fully understand what is all needed. But for simple questions that comes with projects such as powering a small shed, or making a small solar power system is the questions I want to tackle first.

    So do you have some ideas from your experience here in this forum what "beginner" questions you see quite often concerning these "small" type solar projects?
  • mike95490
    mike95490 Solar Expert Posts: 9,583 ✭✭✭✭✭
    Re: Need Suggestions For Common Solar Calculation Questions
    rss2q wrote: »
    ... I will not include grid-tie type questions just yet as I myself do not fully understand what is all needed. But for simple questions that comes with projects such as powering a small shed, or making a small solar power system is the questions I want to tackle first. .........

    Grid Tie is MUCH simpler. Start there first. (no batteries required)

    Common to both:
    Location (Latitude)
    PV array angle (roof angle)
    Orientation (N, S, E or W, by degrees is better)
    [weather history] Scotland is different than Maine
    Shortest day of year & Longest day (maybe from a tide table)
    Electric bill : annual OK, monthly better

    Batteries add
    Attended or un-attended (how many days before you start the genset)
    Daily usage = battery size
    PV array size needed for 9 months or 12 months self sufficient.
    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 ,

  • rss2q
    rss2q Solar Expert Posts: 75 ✭✭✭✭
    Re: Need Suggestions For Common Solar Calculation Questions
    mike90045 wrote: »
    Grid Tie is MUCH simpler. Start there first. (no batteries required)

    Common to both:
    Location (Latitude)
    PV array angle (roof angle)
    Orientation (N, S, E or W, by degrees is better)
    [weather history] Scotland is different than Maine
    Shortest day of year & Longest day (maybe from a tide table)
    Electric bill : annual OK, monthly better

    Batteries add
    Attended or un-attended (how many days before you start the genset)
    Daily usage = battery size
    PV array size needed for 9 months or 12 months self sufficient.

    Oh okay. So what exactly would be the overall "question" for this information I'm requesting? Like what useful information are they getting by supplying this data? I haven't looked into grid-tie systems much myself so I'm not really sure right off the bat.
  • Cariboocoot
    Cariboocoot Banned Posts: 17,615 ✭✭✭
    Re: Need Suggestions For Common Solar Calculation Questions

    You see my signature line about having to ask the right questions? It's only partly a joke.

    Usually the first thing people ask is: "How much solar do I need to run my TV/air conditioner/refrigerator/toaster/curling iron/cyclotron?" That means you automatically have to go to how to figure out the power requirement of the device in question. Unfortunately referring to the manufacturer's specifications (tag on the power supply that says "1.2 Amps 125 VAC") is not accurate. Often it's not even good enough for a "ballpark" starting figure. I guess you'd have to set accuracy aside and assume the resulting Watts were correct. Not to mention the little problems like Power Factor and Start-up Surge and In-rush Current which will skew results. You can see why the number of disclaimers over the whole process is enormous, and it's real easy to miss out some. This gives certain people great delight when they get to point out the "mistakes". Me, I get tired of writing the caveats and exceptions to every part of the process in every post; it gives the nit-pickers something to do. :roll:

    Once you have a theoretical Wattage then you have to explain Watt hours. People get tripped up on that one very easily. Converting that number into Amp hours (another tricky term to understand) is a simple "divide by system Voltage", so long as you leave out all the efficiency losses.

    Then you have to bring up Depth Of Discharge and its reciprocal State Of Charge, and why you need at least twice as many Amp hours as you expect to use. As for explaining the intricacies of choosing one system Voltage over another ... is it any wonder we use rules-of-thumb like 1kW multiples?

    You could spend hours reading the Beginner's section and see what gets asked over and over. Similar questions will crop up in the General section and the Off-Grid section. But it almost always starts with "what do I need to run my ..."
  • rss2q
    rss2q Solar Expert Posts: 75 ✭✭✭✭
    Re: Need Suggestions For Common Solar Calculation Questions
    You see my signature line about having to ask the right questions? It's only partly a joke.

    Usually the first thing people ask is: "How much solar do I need to run my TV/air conditioner/refrigerator/toaster/curling iron/cyclotron?" That means you automatically have to go to how to figure out the power requirement of the device in question. Unfortunately referring to the manufacturer's specifications (tag on the power supply that says "1.2 Amps 125 VAC") is not accurate. Often it's not even good enough for a "ballpark" starting figure. I guess you'd have to set accuracy aside and assume the resulting Watts were correct. Not to mention the little problems like Power Factor and Start-up Surge and In-rush Current which will skew results. You can see why the number of disclaimers over the whole process is enormous, and it's real easy to miss out some. This gives certain people great delight when they get to point out the "mistakes". Me, I get tired of writing the caveats and exceptions to every part of the process in every post; it gives the nit-pickers something to do. :roll:

    Once you have a theoretical Wattage then you have to explain Watt hours. People get tripped up on that one very easily. Converting that number into Amp hours (another tricky term to understand) is a simple "divide by system Voltage", so long as you leave out all the efficiency losses.

    Then you have to bring up Depth Of Discharge and its reciprocal State Of Charge, and why you need at least twice as many Amp hours as you expect to use. As for explaining the intricacies of choosing one system Voltage over another ... is it any wonder we use rules-of-thumb like 1kW multiples?

    You could spend hours reading the Beginner's section and see what gets asked over and over. Similar questions will crop up in the General section and the Off-Grid section. But it almost always starts with "what do I need to run my ..."

    Exactly. My goal is to try to use averages mostly but again, state this within the app that the answers given are 'ball park" answers. So by basing the app around that prospective, I should be able to reduce my "base" equation down to just a few variables. Most would think the hard part is making the app, however, the hardest part in my personal case is going to be finding the right questions and generating a basic equation/formula from that question.

    A friend of mine actually works for a solar company and I may start with him since I'm not as advanced as you and several other moderators here, and that will help me speed up this first step. But I will try to scope through this forum and come up with several that I believer are good, and then once I get my equation, I'll confirm with you all if it's close enough for a ball park answer.
  • solar_dave
    solar_dave Solar Expert Posts: 2,397 ✭✭✭✭
    Re: Need Suggestions For Common Solar Calculation Questions

    Things like surge and inrush current are sort of moot points in a grid tie setup. Hence the easier place to start. The load side of the equation can be take from the users utility bill and entered since grid tie tends to average all that out. For grid tie you need to know the users billing scheme and that is probably the most daunting part of the equation, there are so many ways to get into the users wallet. Also if the utility offers any rebates, state rebates or credits ...
  • solar_dave
    solar_dave Solar Expert Posts: 2,397 ✭✭✭✭
    Re: Need Suggestions For Common Solar Calculation Questions

    Oh yeah, do not forget the users goal, reduced bill, net zero, greenie. Make it clear this is not a backup system, grid down equals solar off too. Figure the users ROI for justification purposes would be nice as well.
  • rss2q
    rss2q Solar Expert Posts: 75 ✭✭✭✭
    Re: Need Suggestions For Common Solar Calculation Questions
    solar_dave wrote: »
    Oh yeah, do not forget the users goal, reduced bill, net zero, greenie. Make it clear this is not a backup system, grid down equals solar off too. Figure the users ROI for justification purposes would be nice as well.

    Great, I'll bookmark this thread for sure and hopefully be able to implement some of the features suggested in the near future.
  • stephendv
    stephendv Solar Expert Posts: 1,571 ✭✭
    Re: Need Suggestions For Common Solar Calculation Questions

    Here is an excel spreadsheet dedicated to sizing an off-grid system from start to finish: http://www.solarweb.net/forosolar/downloads.php?do=file&id=6 ...unfortunately it's all in Spanish