Author Topic: Where do I start with solar?  (Read 355 times)

0 Members and 1 Guest are viewing this topic.

Offline paulca

  • Frequent Contributor
  • **
  • Posts: 286
  • Country: gb
Where do I start with solar?
« on: December 13, 2017, 05:57:18 AM »
I've been thinking about having a go at solar, just initially as a play thing, but I have to start somewhere.

I have been tempted to just go for a cheap chinese panel, but I've done that road before and it often ends up with a repurchase of a more proper item.

I don't really have anywhere outdoors to put a panel.  I have a sky light and in calm weather I could put it out that for a while, but most likely any small panel I get will end up in my man cave room window.  The curtains are 99% of the time closed, so there is definately room for a 1m square panel behind the curtains.  It's south facing, and I expect I won't get very high efficiency behind double glazing.  But it is what it is.

It seems that most of the "kits" out there immediately assume a lead acid 12V battery.  Do I really need to go down that route primarily?  Or can I start with something else?  Maybe 18650s or something less arcaic, expensive, heavy and unreliable than an LA.

I'm not looking to spend a fortune, I'd think £50 for a first end-to-end set up and is it too optimistic to expect 20-50W from that money?

Just a first foot on the ladder type thing.  If I can charge my USB devices and battery devices etc. from it that would be enough to play with.

I hope to be moving house next autumn to somewhere with a garden, probably a garage and maybe a shed, but right now I'm in an appartment with no outdoor space (except my car parking space).
"What could possibly go wrong?"
 

Offline Belrmar

  • Contributor
  • Posts: 18
  • Country: es
Re: Where do I start with solar?
« Reply #1 on: December 13, 2017, 09:46:13 AM »
i would recommend you to use a lead acid battery , yes is not as energy dense as a li-ion battery but they are cheap AF and eviromentally speaking they are much better (basically almost 100% recyclable). also using a lead acid battery grants you the opportunity of only having to use a cheap pwm charger from ebay instead of a complex battery balancer.

Talking about the energy you wold get....expect the worse  as the windows of your house are no low iron and the ammount of light comming from a window is greatly reduced but for testing is good enough
 

Offline metrologist

  • Frequent Contributor
  • **
  • Posts: 881
  • Country: 00
Re: Where do I start with solar?
« Reply #2 on: December 13, 2017, 10:34:23 AM »
I got a 100W Chinese panel for $96 USD shipped and it works great!

I also bought one of those Li-ION solar charge controllers (you'll find the black or white plastic with blue labeling) and tried it with a 96WHr Li-ION laptop battery pack and it sucked. Maybe I could power a few USB devices, but I really did not have much else that would work well enough off the nominal voltage. I also found that the SCC would not dump the full power from the panel into my load.

I bought the exact same controller for LA battery and it works great! It will dump the full juice into my load and I currently use it with a 12V - 120V inverter to run my 42V Li-ION ebike charger and to charge other USB devices.

Adam Welch did a review of a MPPT SCC that had a programable setting and he said it worked great! I am considering that one so I can charge my ebike batteries direct from the SCC.
 

Offline paulca

  • Frequent Contributor
  • **
  • Posts: 286
  • Country: gb
« Last Edit: December 14, 2017, 07:04:07 PM by paulca »
"What could possibly go wrong?"
 

Offline metrologist

  • Frequent Contributor
  • **
  • Posts: 881
  • Country: 00
Re: Where do I start with solar?
« Reply #4 on: Yesterday at 04:11:13 AM »
the 20W system has the same kind of controller that I am using. Both of these are for lead acid battery technology. Polycrystalline panels are the second tier common panel with decent efficiency. Monocrystalline panels are superior. I have the former from Newpowa.

You should look into your region solar rating and figure out how much energy to expect, and then work out which battery will work with your system and needs.
 

Offline paulca

  • Frequent Contributor
  • **
  • Posts: 286
  • Country: gb
Re: Where do I start with solar?
« Reply #5 on: Yesterday at 07:11:45 AM »
the 20W system has the same kind of controller that I am using. Both of these are for lead acid battery technology. Polycrystalline panels are the second tier common panel with decent efficiency. Monocrystalline panels are superior. I have the former from Newpowa.

You should look into your region solar rating and figure out how much energy to expect, and then work out which battery will work with your system and needs.

I was going to ask about the battery size.  Lead Acids are not in any way cheap here.  £60 gets me a 40Ah car battery.

If the battery was too big, does it not just mean it won't get fully charged during the day or is there more to it?
"What could possibly go wrong?"
 

Offline Seekonk

  • Super Contributor
  • ***
  • Posts: 1581
  • Country: us
Re: Where do I start with solar?
« Reply #6 on: Yesterday at 07:47:15 AM »
C/10 is generally suggested.  Since this is an electronics board I would think you would want to build something.  I have 2KW of panels and I control them with an arduino. Total elecrtronics cost in my setup is only about $20.  I usually tell people who want to use a 100W panel to just give up and wait becuse there is not much you can do with that much power.  It sounds like 20W is really your limit space wise and I would use a couple old lap top batteries with a BMS board.  Grab a couple 2596 regulators for your USB and Li pack.  These can be made into power point controllers with just the addition of a few parts.  Lead acid batteries suck.  If you use one, just buy a new one for your car and use the old one for solar.
 

Offline metrologist

  • Frequent Contributor
  • **
  • Posts: 881
  • Country: 00
Re: Where do I start with solar?
« Reply #7 on: Yesterday at 09:11:43 AM »
This is just my thought process on a small solar system.

You would rather pick a sealed lead acid battery unless you put them outside (and you will need a deep cycle battery). The controllers you linked will not work with Lithium cells.

Generally start with what power demands will be on the solar system. If just wanting USB power to charge a phone, for example, that is probably just about 10Wh per day (assuming 2.5Ah cell battery @ 3.7 nominal volts).

Then, figure about 5 days storage capacity and introduce efficiency factors/system losses, and a battery margin, so about 80% efficient and ~20% margin. I'm getting about 78Wh/day. A 12V 7Ah SLA battery would work (and so would a quality laptop battery, with the right solar charge controller).

Now determine the insolation rating to ensure enough panel to charge the battery in a day, including charging efficiency. Let's just pick a nice round number like 2. Take 78Wh/2, divide by 85% charging efficiency, so a 50W panel should work.

I'm using a 15AH lead acid motorcycle battery with my 100W panel, because that is what I had. I should be able to use a 40Ah SLA at some point (my average insolation is 5.5), or I'll get a boost MPPT solar charger for my e-bike batteries.
 

Offline paulca

  • Frequent Contributor
  • **
  • Posts: 286
  • Country: gb
Re: Where do I start with solar?
« Reply #8 on: Yesterday at 07:18:22 PM »
C/10 is generally suggested.  Since this is an electronics board I would think you would want to build something.  I have 2KW of panels and I control them with an arduino. Total elecrtronics cost in my setup is only about $20.  I usually tell people who want to use a 100W panel to just give up and wait becuse there is not much you can do with that much power.  It sounds like 20W is really your limit space wise and I would use a couple old lap top batteries with a BMS board.  Grab a couple 2596 regulators for your USB and Li pack.  These can be made into power point controllers with just the addition of a few parts.  Lead acid batteries suck.  If you use one, just buy a new one for your car and use the old one for solar.

Thanks.  I like this approach.  I only just discovered that 18650 cells are expensive, but brand new laptop batteries are not and contain 6 18650s.  They may not be top of the range regards peak current etc, but I'm not sure I care yet.  £8 for a 6 cell Toshiba battery.  So I have an experimental 3s2p setup including balance lead, in the post.

For charging it, I could just use the Accucel 6 directly connected to the solar, it will take 11-18V on input, then buck or boost for the battery.  The downside is it requires attention, in that it won't auto start charging without you pressing buttons.  I have seen people using them on Youtube.  I'm not too sure how suitable they are regarding MPPT and what not, but it seems comfortable with a whole range of voltages regardless of what it's charging.  I charged two 3s lipo batteries in series (25.2V) from an 11.6V supply for example.

It might give me "Iteration 1" though.  I'm starting to apply methodologies we use in software in work to my hobby projects to prevent scope creep meaning things never get finished and there is always something else to order.  "Iteration 1" would be successful if I can charge my phone from a solar panel charged battery, for example.  Iteration 2 would advance based on feedback from Iteration 1 as to what is most important to do next.  Most likely an automatic interaction free charger.

I have an off the shelf regulator with a USB outlet and while it gets hot charging an eCigarette at 1.6Amps it works.  (I think it's s dicky little surface mount regulator, I'm probably torturing it, but hey, it was about £2).  Runs off a standard XT60 LiPo plug and while they are not everyone's cup of tea they are great up to 60A and what I will be fitting to my 18650 pack.

On space.  It's a BIG window.  Probably about 6 foot square.  So even a 1m square or 1x1.5m panel.   There are cupboards and fridges across the front of it anyway, so blocking the lower half of it with a solar panel is perfectly acceptable and the panel can lean back against those cupboards.
"What could possibly go wrong?"
 

Offline Seekonk

  • Super Contributor
  • ***
  • Posts: 1581
  • Country: us
Re: Where do I start with solar?
« Reply #9 on: Today at 06:54:50 AM »
It is fairly easy to modify any buck converter into a pseudo MPPT controller with just a few added common parts. Technically it is called MPPC (constant panel voltage).  Power point only changes with temperature and since inside that won't change much.  Many of the MPPT chips are actually MPPC with a temperature sensor.  BMS boards take care of all the charging requirements.
 

Offline metrologist

  • Frequent Contributor
  • **
  • Posts: 881
  • Country: 00
Re: Where do I start with solar?
« Reply #10 on: Today at 07:00:02 AM »
Thanks! I had not come across MPPC.

http://www.linear.com/solutions/4545
 

Offline fourtytwo42

  • Frequent Contributor
  • **
  • Posts: 279
  • Country: gb
  • Interested in all things green/ECO
Re: Where do I start with solar?
« Reply #11 on: Today at 07:51:41 PM »
Technically it is called MPPC (constant panel voltage).  Power point only changes with temperature and since inside that won't change much.
While this may be true enough for very small systems it is not true of large array's (several hundred watts up) because the MPP also varies with power output and shading, considerable loss of efficiency would be incured by trying to operate the array at a fixed voltage even if temperature compansated.
 


Share me

Digg  Facebook  SlashDot  Delicious  Technorati  Twitter  Google  Yahoo
Smf