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  • OT:Solar power system questions

    I'm planning a new shop building for my woodworking hobby/business and one of the things I am paying out is the electrical system.

    Down south we have not much wind,but lots of sun so I am thinking about solar to at least run my lights.What I have in mind is a split electrical system.Basicaly two circuit breaker panels,one main for all the heavy current loads and one sub panel for all the lighting loads.The main will feed off the grid as normal and the sub panel can be fed either off the grid or off the solar system as need be.

    I figure I can use one of the power monitor outputs on the inverter to switch between grid or solar as need be all that is fairly simple.

    What I am having a time with is finding reliable information on designing the solar componet.What I have found on the net so far is conflicting information about how much panel is needed to provide x amount of power y amount of the time.

    Do I match the panel wattage total to the total wattage of the draw and size the storage capacity for a quick recovery.Or do I reduce the panel wattage total by a factor and increase the storage capacity?

    I am assuming there is a point where the cost/benifit equation comes into play at some form of balance.Do I spend more on panels or more on storage,that's the part that is confusning me.
    I just need one more tool,just one!

  • #2
    The answer of course is "That depends". It depends on the average hours of sunshine you have in the poorest month you want to use solar. It depends on how much you are willing to depend on grid power. Your cost per watt for solar must be factored against the projected cost per watt of the grid.

    Another thing to consider is if you intend to use compact fluorescent bulbs you need to determine what the power factor will be on the inverter you intend to use. If it isn't a pure sine wave inverter the power factor will differ and may require you to size up on the inverter. Even if it is sine wave you will have to pay close attention to the power factor of the lighting load. You can't just add up the label watts on non-resistive loads.

    It also depends on what type of batteries you use and don't forget to factor in a disposal fee even if it doesn't exist now. It probably will when they need to be replaced. 5 to 10% of the capital cost would be a start. I bought a lead acid battery the other day for $26. Problem is that after taxes and the eco fee it cost $40.

    It also depends on what type of panels you use. Not all panels are the same. They fall into three main types: Amorphous silicon, polycrystalline silicon and mono crystalline silicon with the cost and efficiency going up in that order. They have a life of about 20 years since putting a solar panel in the sun slowly destroys it.

    Consider the hail resistance of the panels. I am pretty sure you get hail down there. One good hailstorm could take out the entire lot.

    That's just a few things for now. There are more.
    Free software for calculating bolt circles and similar: Click Here

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    • #3
      Why not just use sky lights?
      Neil Peters

      When on the hunt, a broken part is better than no part at all.

      Comment


      • #4
        Originally posted by NAMPeters
        Why not just use sky lights?
        They work only during daylight hours.

        Comment


        • #5
          This is the future, sterling engines that make good clean power.

          http://www.stirlingenergy.com/solar_overview.htm

          Comment


          • #6
            Originally posted by dp
            They work only during daylight hours.
            Skylights would be an option during the day,but we see three to four months of 90+heat and 90+ humidity.Skylights make for an instant greenhouse,great for tomatos,not so good to work in.

            Some people here put them in the tops of the side walls which works for heat,but it makes the building vulnerable to hurricanes.My intention is to build a shop that will handle 170mph winds to avoid buying wind insurance which is something only Bill Gates can afford now.
            I just need one more tool,just one!

            Comment


            • #7
              here is a good video.

              http://www.youtube.com/watch?v=kYKOjnCwmG8&NR=1

              Comment


              • #8
                Originally posted by Evan
                The answer of course is "That depends". It depends on the average hours of sunshine you have in the poorest month you want to use solar. It depends on how much you are willing to depend on grid power. Your cost per watt for solar must be factored against the projected cost per watt of the grid.

                Another thing to consider is if you intend to use compact fluorescent bulbs you need to determine what the power factor will be on the inverter you intend to use. If it isn't a pure sine wave inverter the power factor will differ and may require you to size up on the inverter. Even if it is sine wave you will have to pay close attention to the power factor of the lighting load. You can't just add up the label watts on non-resistive loads.

                It also depends on what type of batteries you use and don't forget to factor in a disposal fee even if it doesn't exist now. It probably will when they need to be replaced. 5 to 10% of the capital cost would be a start. I bought a lead acid battery the other day for $26. Problem is that after taxes and the eco fee it cost $40.

                It also depends on what type of panels you use. Not all panels are the same. They fall into three main types: Amorphous silicon, polycrystalline silicon and mono crystalline silicon with the cost and efficiency going up in that order. They have a life of about 20 years since putting a solar panel in the sun slowly destroys it.

                Consider the hail resistance of the panels. I am pretty sure you get hail down there. One good hailstorm could take out the entire lot.

                That's just a few things for now. There are more.
                Yup there is a lot to it,a lot of things to consider.The battery situation looks to remain stable here for many years yet,the core programs work too good to scrap and the state has said so.Old batteries are still worth money $5-10 each so they don't end up in landfills or the local creek.Plus I get a %50 discount on Exide brand so that's working in my favor.

                Hail,we do get it,but it's very rare and very small,I remember 2 times in the past 10 years,but used commercial plate glass is easy enough to get and would easily handle the hail we get.

                Powerfactor,that's where it gets nebulous to say the least.I don't plan on using CF bulbs,MH low bay fixtures for primary and incandecent for task are whats in the plan.The humidity just kills CF here,you can figure on ballasts and bulb holders every few years.

                My main goal if it is feasible for the long run is to offset some of my grid demand so maybe I can afford some AC to at least knock the humidity down in the summer if not some actual cooling,the older I get the less I can stand in the way of heat.I plan the insulate the hell out of the building and reflect as much heat as possible.

                The lighting level I want should require around 1800watts to run full bore.There is a good possiblity that I will have 3~ 220vac service,but that will mean either a demand meter or a higher rate take my pick.1400 watts @ 110v continous draw isn't insignificant.
                I just need one more tool,just one!

                Comment


                • #9
                  Originally posted by wierdscience
                  Skylights would be an option during the day,but we see three to four months of 90+heat and 90+ humidity.Skylights make for an instant greenhouse,great for tomatos,not so good to work in.

                  Some people here put them in the tops of the side walls which works for heat,but it makes the building vulnerable to hurricanes.My intention is to build a shop that will handle 170mph winds to avoid buying wind insurance which is something only Bill Gates can afford now.
                  Heat traps (storage) would be much more valuable than skylights at least in this part of the world. In fact here in the Pacific Northwest where we have 25 hours of night time per day and maybe two minutes of daylight between rain squalls, it is common to have a cistern under the main building that is solar heated. Thousands of gallons of water is a good energy sink. This collected heat is used to warm the house and pre-heat water coming into the water heater, as an example. Other people might call them a swimming pool but we really know they're cisterns, eh. The savings can be used to run a lathe or a video game - your call

                  In the near eastern, almost central part of the state it is very windy and wind mills are especially useful for creating augmented energy sources for such purposes as charging batteries for electrified fences to keep your bbq stock from wandering, and for providing outdoor lighting power to confuse mosquitos. We have enough excess power from wind that we could restore the ozone layer if everyone would install a compact wind-powered ozone generator. If we exported our excess ozone to China it could even create a balance in trade. Sure beats hustling carbon credits so you can use that Lear jet on the weekends.

                  But Puget Sound is an energy parasite because of the endless drizzle and year round fall-like weather. Not enough sunlight and wind to light a candle, here. Most machinists here have to use treadle powered shapers, mills, and lathes, in fact, and that assumes any two pieces of metal in these machines are not rusted tight to one another.

                  Comment


                  • #10
                    Originally posted by dp
                    Heat traps (storage) would be much more valuable than skylights at least in this part of the world. In fact here in the Pacific Northwest where we have 25 hours of night time per day and maybe two minutes of daylight between rain squalls, it is common to have a cistern under the main building that is solar heated. Thousands of gallons of water is a good energy sink. This collected heat is used to warm the house and pre-heat water coming into the water heater, as an example. Other people might call them a swimming pool but we really know they're cisterns, eh. The savings can be used to run a lathe or a video game - your call

                    In the near eastern, almost central part of the state it is very windy and wind mills are especially useful for creating augmented energy sources for such purposes as charging batteries for electrified fences to keep your bbq stock from wandering, and for providing outdoor lighting power to confuse mosquitos. We have enough excess power from wind that we could restore the ozone layer if everyone would install a compact wind-powered ozone generator. If we exported our excess ozone to China it could even create a balance in trade. Sure beats hustling carbon credits so you can use that Lear jet on the weekends.

                    But Puget Sound is an energy parasite because of the endless drizzle and year round fall-like weather. Not enough sunlight and wind to light a candle, here. Most machinists here have to use treadle powered shapers, mills, and lathes, in fact, and that assumes any two pieces of metal in these machines are not rusted tight to one another.
                    Hmmm..I can see that a treddle powered 36x8" wood planer

                    Seriously though,hot water is a snap here,cool water is what's in demand right now.Roundtoit #24,125 is to do as my nieghbor did on his swimming pool heater.He had his driveway blacktopped,but before he did he laid in a 500' coil of poly tubing under it.It works even on a 30* day so long as there is sunlight.The hot water heater in my house could just disappear.

                    Not that I want to save the planet,I just want to save some of my money from the nutty granola crowd aka "Insane AL"
                    I just need one more tool,just one!

                    Comment


                    • #11
                      Originally posted by wierdscience
                      The hot water heater in my house could just disappear.
                      Heck, I don't even have a hot water heater. The cold water heater, I would miss.

                      Comment


                      • #12
                        Darin,

                        Instead of skylights look into sun tunnels. They cost a bit more but the payback is fast and they don't transmit the heat efficiently, just the light. They can even act as task lighting. They will pay back a heck of a lot faster than solar electric and are zero maintenance. They also don't compromise the structural integrity.

                        Here are some links:

                        http://www.ecotun.com/en/

                        http://www.solatube.com/

                        http://www.veluxusa.com/products/sunTunnels/
                        Free software for calculating bolt circles and similar: Click Here

                        Comment


                        • #13
                          I'm facing this issue with my travel trailer right now.

                          In my research I've found much debate on the old or new technology panels. I hear the old panels have more to offer this kind of service.
                          1. They produce better on cloudy days. Will even produce under street lights.
                          2. They are cheaper.
                          3. Don't have to be aimed at the sun constantly for rated output.
                          4. More durable.
                          5. Can be officiant mounted flat on the trailer roof.
                          The new style will produce more power but only when pointed directly at the sun. The old style degrade faster when new but if you check, you'll find out the fudge factor has been built into them. When they degrade, they will be left at specs. My trailer won't draw as much as your shop so I'll be able to watch a Sony 26" HDTV on Satellite! (this is the boomer new style of camping and not the old style younger kids do?) I'll have a charge controller to save my dual deep cycle batteries and an inverter to power the 130 watt TV.

                          If you do this, do it to stop the carnage that is being heaped on Mother Earth by evil mankind and not to realize any savings. (Bear in mind that one good belch from a volcano can ruin all your efforts!) By the time you are done with hardware you'll be lucky to break even. Completely built home made windmills are cheaper to accomplish but of course require wind that you don't have!

                          I have a kitchen porch that will one day be windowed in for Fall, Winter and Spring. The plan is to put slate tile floor to hold some of the heat in collected by the sun when the trees have shed their leaves in autumn. Should make it a comfortable place to sit and grow old.
                          Last edited by Your Old Dog; 09-08-2007, 09:41 AM.
                          - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
                          Thank you to our families of soldiers, many of whom have given so much more then the rest of us for the Freedom we enjoy.

                          It is true, there is nothing free about freedom, don't be so quick to give it away.

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                          • #14
                            There are a number of considerations.

                            The first thing is to characterize the load. How many watt-hours per day will you be using? A 100W load for 5 hours is a 500 watt-hour load.

                            You can then grossly size the battery pack to provide that power for the number of days without sun that you want. For instance you might select 3 days backup. Set that thought aside for the moment.

                            Figure the battery pack at 10 volts for a 12V system and losses will be roughly compensated. Then your 100W load will pull about 10 A from a 12V battery. (5A from a 24V battery)

                            So 500 watt-hours is 50 ampere-hours at the assumed 10V.

                            To keep up the system, you have to provide about 1.2 times that power (allowing for battery inefficiency). Therefore you need to provide about 60 ampere hours per day to avoid a steady discharge.

                            Providing that will require about a 10A charge rate for 6 hours per day, which just avoids a battery drain. That 10A charge rate will take a bit over 1 square meter of cells of the usual type.

                            if you cannot get 6 hours of sun per day, hang it up, and stay on-grid.

                            Since we figured that you might need a battery to provide 3 days backup, you would need to provide a battery that can supply 150 ampere hours without being drained lower than about 25% charge remaining. Therefore you need a battery of about 200 ampere hours. Common T105s are 220 ampere hours approx.

                            Now, to do a good job of CHARGING, you must supply the daily usage PLUS a reasonable net re-charge rate. Leaving the battery "down" too long allows "sulphation", which reduces capacity.

                            A minimum rate of recharge is probably a "C/20 rate" (not at all a fast recharge, it would take about 24 hours, or 4 days sun) . Since "C" is 200 ampere hours, a "C/20" rate is 200/20, or an ADDITIONAL 10 A OVER the daily recharge rate.

                            At about 10A per square meter of cells, you need about 2 square meters of cells, and a 200 AH battery, with suitable charge controller.

                            Batteries should be "real" deep cycle, such as Trojan T105 "mileage master" golf cart batteries at 6V per battery. "Marine deep cycle" are not very good, and will cost almost as much but fail much faster. "starting" type batteries are pretty hopeless if you drain the battery as much as 50% more than a couple times.

                            My T-105 setup is more than 12 years old and still going. Same with others I know.


                            The comments by YOD are correct.

                            OLD PV cells will produce MORE in bad conditions, but less in perfect conditions. I had a set of old cells originally from the Carrizo plant, about 48" x 48" of cells. They produced 5A in the sun, and 2.5A on cloudy days, and were a solid brown color. A tree smashed them last year, after about 30 years total service.

                            The NEW setup is about 15" x 48", and produces nearly 5A in bright sun. On a cloudy day it drops to 1 A. It is merely a matter of area. the old cells were less efficient, and needed more area. But they collected more energy due to that, and cloudy days still produced alright. The difference in area is about the difference in current with the new ones vs the old ones.
                            Last edited by J Tiers; 09-09-2007, 12:44 AM.
                            1601

                            Keep eye on ball.
                            Hashim Khan

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                            • #15
                              grid-tie solar

                              The only time to even consider using a battery tied solar system is if you are in an off-grid situation. The batteries are still the biggest problem - being expensive maintanence headache, safety and reliability issue, and significantly hurt the system efficiency. The way to go anymore (as long as you are on the grid) is a grid-tie inverter that can track the max power point of your panels and extract every precious watt out of them. You won't need a 2nd service panel, in fact most of the new inverters have integrated in the junction boxes etc. They use the solar panels strung together in series to produce several hundred volts which minimizes the wire losses and cost. Many states and/or utilities now have incentive programs that rebate you a big chunk of the total installed cost. Here in Arizona, it is $3 per watt of panels which is a 3rd to 1/2 the system cost. The new inverters are all designed to be grid friendly and the utilities usually only require an in-plain-sight disconnect box and some red tape to tie in. This still doesn't make the payback of a system much better than 10 years, but over the 25 year expected life of a system, the payback is generally 2 to 3 times its up front cost. The biggest factor is what your utility rates are. 12 cents/kWHr or less makes it real tough to justify solar. Places like California where they have graduated rates and sizable users get up above 30 cents/kWHr they make lots of sense. Grid-tie systems are virtually maintanence free, no hassle, the most efficient and cost effective way to go. Invest the money on panels, not spend it on batteries.
                              Email me if your interested in a quote, I became a dealer last year just to get myself better prices.

                              Greg C.

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