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Math formula for calculation of solar power?

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  • #16
    Wow!!!

    Yes, thick aluminum foil without gaps is a shielding method for the RFI/EMI that cause a buzz in phone lines and audio equipment. Some good Sinewave inverters have built in shielding that helps a lot. Back when I had dial up, it slowed down my internet connection speed by 3/4. I moved everything as far away as I could and use line filters. This is a real issue, not some loony tin foil hat garbage.
    Desulfators certainly help with lead acid battery life, along with monthly equalization and keeping the fluid levels up, etc. In reading the Battery Book, I found out that the biggest increase in deep cycle lead acid battery life is to limit drawdown to 20% (battery still 80% full), NOT the 50% recommended before. Sure they can handle a 90% discharge but lose a lot of life. An old timer near me had been on inverter/L-16 battery and generators for charging for 25 years and still had some good L-16s that old. He later mounted solar panels.
    Personally, now I would go for the nickel-iron---only because I'm not so broke!!
    It is said my system did not pay for itself in 6 years. Here is how that worked out; The total system cost for a full tracking 600 watt array, twin com linked DR2424s, charge control center, 8-L16s, wires, pole, conduit, through the wall as standard 220VAC to the 100Amp panel with breakers was $9,300 in 1997-8. Average local electric bills were $100/month from my numerous inquiries. The IREA wanted $4,975 to bring power to my house, with anyone on the way able to tap in free. No gov't subsidies in this area, and at that time, for solar. The local solar installer at that time wanted $25/hr. It took 200 hours, so I saved $5,000 in labor. Subtracting the amount that the coal fired power company wanted to bring in power from the original $9,300 is $4,325. That is roughly 43 months of bills. I added the mancon and desulfators for $250, so that makes it a 46 month to zero. Real Goods gave the energy of manufacture of the system as another 2 year penalty. So in 2004 the system had paid for itself in saved bills from the power company, with an unknown amount of CO2 saved from going into the atmosphere. Many tons.
    You are right in that not all solar installers are out to gouge the people, but many are. I saved roughly 53% by DIY. Others I have researched would save much more. I have also seen a 50% difference in price with shipping for panels and components that are the same, so it sure pays to shop around.
    It is also sadly true that the average person is just not like the pioneers that tamed the west. Schools have eliminated shop courses and mechanical drafting, lowered science and math requirements, with the dumbing down I have witnessed for the past 35 years. The average person is too dumb, ignorant, or lazy to do the research necessary and the hard work of DIY solar electric system installation or building their own house. Perhaps one out of 400 tradesmen is capable, maybe less. In my 31 years(23 as foreman/sup't) in the building business, masters and real multi-tradesmen with brains to design were a rarity. Only one out of 20 worked in the trades, if that. That was the second career I was forced into, even though a disabled decorated combat veteran. I was a pro pilot COM ASMEL, H, I, and CFI for all, and AGI for 7 years, but hit by affirmative action increased requirements for my sex and race. I wasn't supposed to heavy lift again, ever. I was shot down 1/14/70 N of Xuan Loc RVN flying a Dustoff unarmed medical evacuation helicopter (UH-1H). Transmission hit and crash which broke my 2 lumbar cartilages with compressional damage to my spine. I John Wayned it back to combat in 16 days. As a foreman my wages stagnated from the invasion, for 20 years. I had to do it myself from economic necessity, and have the skills, brains, and experience.
    I would like to think that many people, with determination, could do it themselves. Maybe many more could at least help to defray costs. That pioneer spirit that built this country must increase. It is a war to save the environment from that tundra methane self release tipping point, and a war for America, in America.

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    • #17
      Johnny - If you read posts on the site by Sunking and others 20% discharge is recommended with a maximum draw of 50% - to maintain battery life.

      I agree that the average person is a lazy type - hold their handout for others to do something for them.

      If someone is to lazy to learn about a product before they buy then they deserve what they get. Having said that I have zero interest in doing anything electrical - not my interest. I end up trouble shooting various systems (electric, automation, alarm, CCTV etc) in my home and detest the time spent. Mechanical or structural is OK - Electrical or electronics is in another world.

      The only thing wrong with your calculation is that you reference an 'average ' electric bill and compare it to your home which would use far less?

      Most of us respect the service rendered to our country by combat vets. I did my time in 65 to 69 but never in combat. No need to drag it out in a post such as this though.

      The good kids are still very good - the lazy-useless types are what drag things down.
      [SIGPIC][/SIGPIC]

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      • #18
        Originally posted by crisliu View Post
        Does anyone know if there are some mathematical formula for calculation of solar power? Or at least what parameters the electric energy depends on if produced by solar panel, like angle, days of sunny day, sunshine hour,latitude and longtitude,etc.?
        If you could get a hold of some hourly solar irradiance data (measured in the same plane that you intend to put the array) you could roughly estimate what kind of output you could expect from an array of X kW (DC) rating. You would have to take into account multiple inefficiencies as well. I think this would give you the most accurate estimate though, probably not the easiest to accomplish...

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        • #19
          Most weather stations offer a solar radiation reading as an option (requires optional pyranometer).

          In my Davis weather station radiation is measured as 'global solar radiation (GSR)' unless a project is specifically designed for other purposes. GSR includes all light hitting the meter. Measuring in the same plane has little meaning really.

          Easier to use the PV Watts calculator - a link is available on the forum page of the site. PV Watts takes into account factors that the casual user would never think of. The latest version is quite easy to use as well.

          PV Watts uses long term averages from NASA data so it is correct over a 10 or 20 year period - any year may be significantly higher or lower.

          If there is any shading, even from a power line, none of the calculators or even your weather station will accurately predict the potential production.

          NASA has a large quantity of historical weather data available on their site - not only for the US but around the world.

          Russ
          Last edited by russ; 07-15-2011, 03:03 PM. Reason: correction
          [SIGPIC][/SIGPIC]

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          • #20
            Electric bill per month

            Originally posted by russ View Post
            Johnny - If you read posts on the site by Sunking and others 20% discharge is recommended with a maximum draw of 50% - to maintain battery life.

            I agree that the average person is a lazy type - hold their handout for others to do something for them.

            If someone is to lazy to learn about a product before they buy then they deserve what they get. Having said that I have zero interest in doing anything electrical - not my interest. I end up trouble shooting various systems (electric, automation, alarm, CCTV etc) in my home and detest the time spent. Mechanical or structural is OK - Electrical or electronics is in another world.

            The only thing wrong with your calculation is that you reference an 'average ' electric bill and compare it to your home which would use far less?

            Most of us respect the service rendered to our country by combat vets. I did my time in 65 to 69 but never in combat. No need to drag it out in a post such as this though.

            The good kids are still very good - the lazy-useless types are what drag things down.
            I used the rough average of 100/mo. The actual I use with the rate, the monthly fees and taxes would now be 120/mo.(100Kw/hrs) I had used the map chart of min. winter sun hours in the sourcebook, and the electric use chart to find out my watt hours per day, multiplied by the 20% increase recommended for losses to get the 3000 watt hours per day. Divided by the 5 hours of winter sun to get a 600 watt array, full tracking or 40% more for fixed panels at the latitude angle. The roof of the shell I bought was at a 45* angle so I did not have the roof space. Also required at the time was the through the roof $600 DC GFI. So I decided on the full tracking pole mount well above the roof and braced to the inverter/battery split level shed and house barge rafter, 4' into the ground on 4" of concrete and set in 6" concrete all around.
            The next year I added the addition to the house and another 232 watts of solar panels increased to 296 shortly thereafter. My calculations for power had gone awry when I was required to have more power sucking devices and wanted more than I originally planned for. This computer for one!!
            When they saw I was not going to subsidize their lots by bringing in power lines, the 18K lot next to mine was offered at 11K. I refused. They could not sell to people who would either have to go to the expense of bringing in power or going to what they thought was expensive solar. The company folded and the county took the lot for back taxes owed. A guy bought it for 2500 and paid taxes the required 3 years. He realized he could not sell it either and offered it to me for 3,500. I bought it, erased the lot line and have 1.13 acre now. So part of my personal factor should include the savings on buying that lot!! I took advantage of people's ignorance of solar. I also got absolute water rights for 600' around my well, which meant that a number of lots would now need a cistern and could not put in a well without proving they would not affect my well--a nearly impossible hurdle. It should also be put in as a factor for getting the lot next door so cheap. This place was originally a ranch that was cut up into near 1/2 acre lots without regard to topography or drainage, and sold to people with a flat plan map. The county requires 35 acres to put in a well, but this land fraud area is grandfathered to where everyone can put a well on their lot, unless they are in a water right zone. The limit to building is a 30% (3 in 10) max slope, white water septic and well 100 feet from drainage and each other, or with regular septic 200". There are a great deal of un-buildable lots with insufficient water here. I let people know the codes and water situation whenever I can. That is my "community mindedness".
            The fact is that this area is great for solar power, yet few have it out of the general ignorance of its ease of DIY cost. 5 hours a day average of winter sun in the "banana belt of the Rockies", or anywhere, is very good.
            Last edited by Johnny Electriglide; 07-17-2011, 11:11 AM. Reason: Putting in land fraud facts for here

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            • #21
              A real community spirited type I see.
              [SIGPIC][/SIGPIC]

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