need basic help getting started

jeffp · January 2013

I am new to solar power and posting to forums so I hope I am doing this right .I recently purchased 2-100 watt Renogy panels and I learned tonight that the connections are MC4 I have a cable with the connectors and the cable seems small the wire size calculator showed I need a #4 wire from the panels to the charge controler @ 12v 40' so does the #4 run from the combiner and how do I connect a wire that big to the charge controler? next question can I get MC4 connectors to put on the cable I have(#10solid copper)? I will have more questions later i am just trying to get the panel connections settled first.

niel · January 2013

Re: need basic help getting started

welcome jeff,
the mc4 connections you have to have only to satisfy the pv connections as cutting them can void the pv's warranty. what is normally done is to get a small cable with the mc4 connections on it like this one,
http://www.solar-electric.com/6fomc4so2exc.html
cutting it in half and putting the bare wire ends to the connections in the combiner while the mc4 part connects to the pvs. the wires can have wire spliced onto them if too short. if you have a combiner with mc4 connections then you need the full mc4 wires without cutting them. after the combiner the same splicing method can be employed to hook up other wires to it. (there are many ways to splice wires and may be too lengthy to get into right now) btw if the 2 pvs are being paralleled then possibly this type of an adapter may be used eliminating the need for a combiner box. http://www.solar-electric.com/mumc4colam.html

as far as the controller goes, here again is a splicing operation to go to the thickest wire the cc can accommodate. the spliced wire should not be excessively long as you want the majority to be in the thicker wire to reduce losses and the smaller wires are basically adapters. adapt the wires as close to the cc as possible, but do not try to put this internal to the cc or overcrowd a box because of this adaptation. make the adaptation neat and safe.

westbranch · January 2013

Re: need basic help getting started

to get you started here is a diagram of the basic components you may need done up by Midnite Solar.

http://www.midnitesolar.com/pdfs/offGrid.pdf

jeffp · February 2013

Re: need basic help getting started

Thanks for the info next question what type of circuit protection do I need and at what point in the line?

niel · February 2013

Re: need basic help getting started

technically with only 2 pvs you don't require a fuse or breaker from the pvs. if you plan on expanding the number of paralleled pvs (or strings of paralleled pv) to more than 2 then you need the fusing/breakers and it would be on each paralleled pv or paralleled string before being combined for the home run to the cc. many of us do put a breaker inline before and after the cc if not for protection when required then for a means of disconnect. the fuse/breaker from the cc to battery is required as is a means of disconnecting which a breaker can fulfill both requirements.

jeffp · February 2013

Re: need basic help getting started

So that being the case I will have a fuse/disconect between the cc and the batteries will a fused disconect like is used on a 120/240V AC unit work or do I need something else? I figure my 100 watt panels to be 8.33 amps each and I have a 30 Amp cc so do I size the fuse/disc. for the 30amps?

niel · February 2013

Re: need basic help getting started

you are fusing and switching dc, not ac. do not use ac rated components here as they must have a dc rating. you could go with some of the common automotive fuses on yours if you would like and as a disconnect you can either pull the fuse or go with a dc rated switch capable of the an excess of the current that will be passed.

jeffp · February 2013

Re: need basic help getting started

Ok I think I have it first my loads are 12v items are 61 amp hours per day, 110v items 13 amp hours @ 110v which if I understand correctly must be X 10 for 12v which gives me a total load of 191 amp hours per day . my system is two 100watt panels (12v output) #4 wire from panels to cc 30amp automotive fuse after the cc then #4 wire to the battery bank. the bb is four 6v golf car batteries @ 225 amp hours each connected to give me 450 amp hours of back-up at 12v from the battery I have #4 wire to a connection point for my 12v items and a #4 to the 750 watt inverter and from the inverter to a 6 position AC load center for the 110v items . I figurs it will take about 12 to 16 hours of good sun to supply the charge to replace a 24hour load which I think will be fine because this cabin is only used one day per week and not every week so it should have ample time to recharge . What do you guys think am I heading in the right direction? Thanks for all the help and advice with this.

BB. · February 2013

Re: need basic help getting started

Yep--It will do what you think... It is not great to let a battery bank do slow recharging over 2-4 days as it can sulftate faster and loose capacity over time.

Also, running 200 watts of panels on a 450 AH battery bank is on the light side for proper recharging. You should use a generator every so often to properly recharge the bank back to >80% before you leave.

Our normal rule of thumb for a battery bank being used is a 5% to 13%5 rate of charge--A 5% charge on a 450 AH 12 volt battery bank would be:

450 AH * 14.5 volts charging * 1/0.77 panel+controller derating * 0.05 rate of charge = 424 Watt Array minimum

Or a bit over 2x larger than the array you are proposing.

Your array is not really enough to properly recharge the battery bank at about 2.4% rate of charge. You may not get the full life out of the battery bank (around 3-7 years). However, I could not tell you if the bank will last 1-3 years, or more, or even less. It depends on your actual usage, amount of sun, temperature of battery bank, how deep you cycle, etc.).

To give you another way to look at power usage/available... Lets guess you are around Knoxville Tn, using PV Watts with fixed array/default settings, the hours of sun per day would be:

Month    Solar Radiation
(kWh/m 2/day)
1      3.23     
2      3.94     
3      4.83     
4      5.35     
5      5.29     
6      5.57     
7      5.57     
8      5.33     
9      4.96     
10      4.91     
11      3.65     
12      3.22     
Year      4.66

So, assuming a minimum of 3.22 hours of sun per day (deep winter), the amount of AC energy you would harvest (on average) per day would be:

200 watts * 0.52 system eff * 3.22 hour of sun (December) = 335 Watt*Hours per day (December)

Your AC loads would be:

13 Amp*Hours * 117 VAC = 1,521 Watt*Hours per day
1,521 WH per day Load / 335 WH per day December = 4.5 days to recharge under "average" conditions

It would probably take longer because of other losses--Such as self discharge from the battery bank -- Which gets worse as the battery bank ages.

So your choices are:

Run as planned--Replace battery bank every few years (guess)
Run with array use generator to recharge back >80% before heading home (and for 3 day weekends, etc.)
Install 424 watt to 1,100 watt array (rough numbers) to optimally recharge battery bank

-Bill

ZD7VC · April 2013

Re: need basic help getting started

I'm in the same boat as jeffp, having bought four Sanyo HIT 250w panels new (again the cart before the horse)! My situation is slightly different from most others in that I live on the tiny and very remote Island of St. Helena in the South Atlantic Ocean, no airfield and a supply ship every 4-6 weeks on average so it's a case of acquiring equipment piece by piece and doing the research. My wife & I have always been energy conscious but are going a step further now with cooking and heating water from a wood stove and eventually easing (altogether eventually) our reliance on the unreliable grid (two Caterpillar 1MW gensets).
I am also a Ham Radio Operator so would also like to be able to power the entire house from Solar although I realize that I will need more than 1KW of generation to possibly achieve this.
My initial question is which true sinewave Inverters (of the export type for 240V as used here just like the UK with the same socket as they use) are ham radio friendly meaning that they don't generate RFI, does anyone know?

I see that Morning Star, Midnite Solar & Xantrex indicate that their controllers are FCC B Class compliant.

westbranch · April 2013

Re: need basic help getting started

Welcome. I am not a ham so did not make note of the jist of a couple of threads on the FCC implications. I believe it was user "boB" either here or on the Midnite Solar forum http://midniteforum.com. Try a search for FCC on both and see what comes up.

hth

niel · April 2013

Re: need basic help getting started

welcome zd7vc,
as we tell most it is better to plan out something before you buy things as you can really get stuck or go down a bad path. knowing what you want to do with it as per your loads is important. i am wondering if the mini grid that is present there is going to be sufficiently big enough to maintain a grid tied setup at all times. it may be a safer bet to plan for off grid status on your solar or a remote possibly of gt with battery backup. there may be a lack of loads sufficient enough on that small grid system to act as a load sink for a full gt system.

as to rfi there is always a possibility of some no matter what it is you get. even getting led lights can throw some rfi. fan motors and even refrigerator compressors can throw tiny sparks that can generate rfi. even radio receivers can do this as some rf is generated internally on them and hence the fcc approval indications on some items we buy here. not too sure if they leave that on there for consumers in other countries or not. it is low level for most things, but there is always the possibility of a higher level of interference on a desired frequency or frequency band while still in compliance. go with the equipment that is certified, but in most cases i'd suspect it will be fine if properly installed as i doubt the interference would be sufficient enough to worry about in most cases even though possible. if interference should occur then your ham experience and knowledge should be a guide to its eliminate or reduction through shielding, filters, and traps, and even toroids and other ferrite materials that could attenuate rf.

need basic help getting started

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