system set up

System · August 2007

hi, i am new to the forum. i have the following equipment to install for a pv system.
90 hawker 2 volt cells @ 640 a/h ea.
4 sharp ND-208U1 (208 watt) solar panels
6 sunpower SPR-210-WHT (210 watt) solar panels
1 xantrex SW 4024 inverter
1 MX 60 charge controller
20K demand per day at $210.00 total bill at peak usage

i live in hawaii, we have 10 hours of sun in the summer and 8 in the winter.
i have all the switch gear and wiring for install, i am needing the optimum configuration to supply a 20K per month demand and cut my bill down. i got much of this equipment free, the 210 panels were cracked so i resurfaced them and they measure out. the batteries were also free and i bartered for the inverter and sold batteries to buy the 208 panels.

the watts and volts could overdrive my MX 60 so should i buy another one or set up the panels to come inder the 150 volt max ( 140 for flash event ) and 1600 watt max point. the series vs paralell will alter the parameters of the MX 60. with the amount of battery power availible i am thinking about recharge capability, any suggestions will be greatly appreciated.
jam

mike95490 · August 2007

Re: system set up

The ambient temperure controls the PV voltage, hotter it gets, the lower the voltage.

The edge of cloud events increase the Current from the PV's - not the voltage.

How did you "resurface" cracked panels ?

niel · August 2007

Re: system set up

jam,
generally speaking, i do think you will need another controller as that is too much pv for the mx60 at 24v output. the 24v is because you have a 24v xantrex inverter so this also means your batteries will be at 24v as well and of course the controller has to output that to charge the batteries.
as to the voltage configuration of the pvs i think you'll have to go with 48v(2 pvs in series) because you have 4 of the sharp pvs. had you had 6 of those it would've been possible to have 3 in series and parallel them. that of course would've been a 72v input and i advise against the 4 of them in series. even if you did have all 4 sharps in series it doesn't work out right with 6 of the sunpower pvs as you'd have needed 2 more to have 2 series strings of 4.
got any more of those pvs available as i might be interested(if yes, please pm me with this info) and how did you fix the glass on them?

crewzer · August 2007

Re: system set up

Jam,

You won’t get 8-10 hours of full Sun in HI. Check here for insolation data for sites in HI: http://rredc.nrel.gov/solar/old_data/nsrdb/1961-1990/redbook/sum2/state.html

Your assortment of modules presents a bit of a challenge. The STC Vmp/Voc specs for the Sharp 208’s are 28.5 V / 36.1 V, and for the Sunpower 210’s the specs are 40.0 V / 47.7 V.

I think you’ll need two MX60 controllers. You could wire the four Sharp’s as an 832 W STC array in a 2 X 2 configuration for ~57 V in and 24 V nominal out via one MX60, and the six Sunpower modules (1,260 W STC) either as a 1 X 6 array (40 V in) or a 2 X 3 array (80 V in) to the other MX60. The outputs of the two MX60 controllers could be wired in parallel to the battery bank and inverter (via appropriate circuit breakers, of course).

Assuming five hours/day of full Sun and 67% overall system efficiency, your system could generate ~7 kWh/day, or 210 kWh/month. Are you presently using 20 kWh/month or 200 kWh/month? 20 kWh/month (~667 Wh/day) is rather low.

HTH,
Jim / crewzer

niel · August 2007

Re: system set up

jim,
i'll bet on 20kwh/day.
jam,
crewzer and i are both in agreement on the need for multiple controllers. did you test the short circuit amps on the pvs and how did they do?

System2 · August 2007

Re: system set up

hi, thanks for the come back. before i fixed the glass i checked the output according to the test prescribed in the current test on this forum, they spec out with the one brand new one of the 210 sharps i have. first i resurfaced the panels with clear epoxy resin. this is a aluzine epoxy system, two part epoxy made by fibreglass hawaii. i poured it onto the panels and spread it out. spraying would work better it you have the equipment. i then applied a UV coating but it peeled off, maybe spraying would work better for the thin film required or no UV coating at all. my panels are water tight after storm rains and six months exposure. i already wired my system for two MX 60s but thought i could get by with one while i got funds ready and i have. i use 20K a day. right now i have all my panels paralell to a combiner box and to my MX60 and switched thru a sw4024 inverter.
i can do better withyour series setup. this is my first technical reply and need to digest, my next reply will be more accurate with the numbers.
jam

System2 · August 2007

Re: system set up

hi niel, i got the 208 panels from wholesale solar, lisa worked with and directed me to direct power & water corp. in new mexico for shipping prep ( extra charge ). cris and eric packed the order and i forwarded the frieght thru DHX with lisa helping with the shipping. 2 per order is the min buy and i bought the 4 they had in stock in sep of 06. they panels were hard to find but the two companys worked together, the price total was 4300.00 to my doorstep in hawaii. the 210 panels were cracked from a windstorm here, they were free due to my emplyoment on a commercial job and knowing the boss. they were landfill otherwise. the 210s were not availible to the public at that time, i have since heard of new 300s being put up by my friend here. they are made for grid tie applications. the glass repairs were easy, multiple layers of fiberglass ( at least two and spraying would be best ) . panels get broke in many commercial jobs and most repairs can be made if the cells are not crushed, a simple crack is no problem. the key is to cover the entire surface, a spot repair would also work but i needed a full cover as most cracks spread across the full sheet of glass. tempered glass usually fans out to all corners when broken or cracked, a partial repair might not seal totally, this is new and have not extensive experience or long term results but resin layers last a long time on boat finishes and heat /expansion could affect the life of the repair. will keep you posted on the results. this could save a lot of panels, i urge all to try before replacing.
jam

crewzer · August 2007

Re: system set up

20 kWh/day energy use? The system above will supply a net of ~7 kWh/day, so it should cut you bill by ~1/3.

HTH,
Jim / crewzer

System2 · August 2007

Re: system set up

hi jim thanks for the help,my figures point to a poorly charged battery bank and a mix of some panels that are performing less than could be expected. is it better to keep a large bank to cover a daily need with a minimum of over volts or a smaller bank fully charged with less reserve overall? my charge is up to 24.8 volts and down to 23.5 volts at night. my battery bank is made up of 84 2 volt cells at 24 volt sets, thats 7 24 volt sets at 640 a/h ea. if the math is right my 7k should leave me 1k left after daily usage ( 6k is my non 220 volt usage ) for recharge, it takes 15360 watts to equal my bank capacity. this where i lose the thread,too many batteries (for sure) to charge? ( or more panels that work 100%). thanks for your patience.
jam

mike95490 · August 2007

Re: system set up

batteries that are chronically undercharged, will sulphate and die early. So either more charging power or fewer batteries. Otherwise all batteries will die early.

re:repaired panels - the fiberglass resin used in boats, does not normally see the "sun exposure" or heat, that will be seen on a PV panel. The resin is usually covered with a "gel coat" that also protects it from UV. Maybe resin, with a outer layer of glass laid on top (plain glass cuts UV by about 90%)
With the panel backing it, the glass could be very thin, or possibly in 2 sheets, with the seam between cells?

System2 · August 2007

Re: system set up

yes mike, i am reducing my bank to get optimum charge and reserve for the panels i have. i wanted to place glass on top of a resin layer to waterproof the damaged panels, the tempered glass was $108 ea. for 1/8'', not a bad deal for getting 6 210 panels for free
the problem is they were crushed and not flat, too uneven for the resin fill and glass cover. maybe an expert could do it. the surface crack ones are working but the very bent and deep cracked ones are performing poorly. they are all watertight though
jam

niel · August 2007

Re: system set up

mike is right in that you are undercharging your batteries. if you had new pvs rated to output 100% of their wattage and no system losses for charging or resistance, that would put the charge rate going to your batteries at between 1 and 2%. that alone is a red flag, but what your situation is is worse because you don't normally get full stc rated wattage from pvs and yours are most likely outputting less due to the increased resistance path the light travels to reach the cells due to your fixes adding to the resistance losses of the wires and charging losses means you've got a severe undercharge condition going for you. add to that any drawing of power from the batteries and you're spelling out the demise of those batteries.

solutions would be to charge in the 5-10% range (rough % with no loads) and there are a few ways to get that. 1> eliminate most of the batteries so as to get the right percent charge and that could mean alternating banks to be charged. 2> increase the amount of the charge by using more pvs and/or a utility powered charger be it from utility 120/240vac or from a generator. 3> combining degrees of solutions from 1 and 2.
in any case you need to get a full charge into those batteries real soon as the longer the intervals between full charges means the shorter the lifespan for the batteries with the near term death of them not impossible depending on the time that has already passed since a full charge and the general battery conditions to begin with. make sure it has a proper electrolyte level and add only distilled water to reach that level of course. clean up all battery surfaces to prevent loss paths and to keep wires/connections corrosion free. i recommend a damp cloth wiping and chemical resistant gloves and safety goggles keeping in mind that the wet outer casing, even from the wet rag, could pass currents. inspect all wires and connections too.
p.s. do know the glass on pvs is lead free as well as tempered to take impacts.

system set up

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