Indoor solar panel testing / suggestions needed

Hi everyone,

This will be my first test posting so be gentle on me. Trying my best to do stuff myself but I tend to be lazy and let other people who know about this stuff better than me tell me what to do. So here it goes.

My idea is to make a backup solar indoor system at my current rental situation. I have 2 windows with the massive size of 40 cm by 80 cm. Since they are place on both sides of the building only one will be directly lighted in the morning the other in the evening. My idea is to either buy one 40x80 panel or 2 40x40 panels. Can anyone suggest any panel from their own experience or which they are interested in(it is a test). I will be doing as much test results as possible and post them here. As it is a backup system it will be needed to supply as much as possible for a decent price(requirements all posted below in a easy list). Also trying to use as much as possible what people generally would have in a 1st world householding situation(fancy way of saying I am broke and don't want to spend money). I have several power converters and a whole bunch of power chargers. Pretty much everything to do soldering and cabling.(except knowledge). Also have some normal car batteries in pretty decent charge state stored somewhere.Currently I would love to be able to charge/keep powered my laptop/refridgerator/lighting/internet modem/phone.

The List(specifications will be added/deleted)

What I have:
Soldering equipment(bought one of those 50+ all in one electricity kits)
Cheap volt/amp meter (include in above kit)
230 volt to 12 volt converter
2x 12 volt to 320 volt converter (max 150 watt)
whole bunch of phone/laptop chargers
some decent charge car batteries

What I need:
Kill a watt/other metering device
2x 40cm by 40cm indoor solar panel or
1x 40cm by 80cm indoor solar panel
some sort of power converter/charger for it all
maybe a better battery type/pack

Willing to spend about 200 to 300 euro on making this all work. Would love to hear from you all if this is doable.

Hi Bryan,

I would suggest you go ahead and get a kill-a-watt or equiv. Mine tend to die fairly promptly, which is annoying, but I haven't found anything comparable to use instead, and they're pretty handy.

A solar panel this size will not be powering your fridge... If you find a panel that fits the full window, it might be rated at 40W peak output. Your actual output will be lower; among other things, you will be limited in your angle options, and the glass will take a bit of a toll. Beware of shading the panel, it can take a disproportionate toll on output.

If the fridge is key, you might consider a larger battery bank than your solar panel can reasonably recharge; charge the bank off of an AC-powered charger when AC is available, then use the solar to maintain the bank until needed, and to slow the draining of the bank. Recharge when power comes back.

You can likely power your laptop/phone/modem and some basic lighting, preferably 12V, from even cheap car batteries, although you shouldn't expect very long life or runtimes from this sort of battery. Figure out the total combined wattage you need for these items, and determine if your current 12V-230V converters are adequate. I would only ever advise use of a quality pure sine inverter, but you can experiment with modified sine/step wave units if you aren't overly attached to your devices. Decide if you want to accommodate the fridge before buying...

The 'some sort of power converter/charger for it all' you mention is a solar charge controller. Readily available in all sorts of prices and quality levels. An 'MPPT' controller will get you a bit more power out of your panel vs a 'PWM' controller. Again, I'm not a fan of the cheaper options, but they sure are cheap.

For the solar panel itself, for your situation getting the best possible fit for the window is pretty much the primary concern here.

I'd suggest getting everything up and running with the best of the batteries you have, and upgrade the batteries after that.

1) You're on a budget
2) You're got some soldering kit
3) You've got special requirements regards matching panel size to window size
4) You're indoors so don't need professionally made weather hardened solar panels

So.. buy some solar cells from ebay, which will cost you about a third of the price per watt compared to a ready made panel, and custom make your own panel(s).
The main thing as you learn is to be very very careful how you handle the solar cells, they are extremely fragile. If you handle them carefully when moving, soldering and securing to a backing panel, then you will be OK.

On the batteries, technically yes you can use car batteries for light use but don't let them discharge more than 10%. ie keep them at 90% charged or higher, otherwise you will kill them.
However, don't use car batteries indoors because when you are charging they give off hydrogen gas and in certain circumstances lead and sulphur compounds. Maybe you have a balcony or roof space which can house a battery enclosure?
For any given power, Voltage is inversely proportional to current. And higher current gives higher losses in the cabling. So at low voltages eg 12, 24V, losses in cables are high. Keep your cable runs as short as possible and use good thick cables for any runs that have to be longer than a few metres.

Post some pics on here and let us know how you get on.

Dillon Nichols wrote:Hi Bryan,

I would suggest you go ahead and get a kill-a-watt or equiv. Mine tend to die fairly promptly, which is annoying, but I haven't found anything comparable to use instead, and they're pretty handy.

A solar panel this size will not be powering your fridge... If you find a panel that fits the full window, it might be rated at 40W peak output. Your actual output will be lower; among other things, you will be limited in your angle options, and the glass will take a bit of a toll. Beware of shading the panel, it can take a disproportionate toll on output.

If the fridge is key, you might consider a larger battery bank than your solar panel can reasonably recharge; charge the bank off of an AC-powered charger when AC is available, then use the solar to maintain the bank until needed, and to slow the draining of the bank. Recharge when power comes back.

You can likely power your laptop/phone/modem and some basic lighting, preferably 12V, from even cheap car batteries, although you shouldn't expect very long life or runtimes from this sort of battery. Figure out the total combined wattage you need for these items, and determine if your current 12V-230V converters are adequate. I would only ever advise use of a quality pure sine inverter, but you can experiment with modified sine/step wave units if you aren't overly attached to your devices. Decide if you want to accommodate the fridge before buying...

The 'some sort of power converter/charger for it all' you mention is a solar charge controller. Readily available in all sorts of prices and quality levels. An 'MPPT' controller will get you a bit more power out of your panel vs a 'PWM' controller. Again, I'm not a fan of the cheaper options, but they sure are cheap.

For the solar panel itself, for your situation getting the best possible fit for the window is pretty much the primary concern here.

I'd suggest getting everything up and running with the best of the batteries you have, and upgrade the batteries after that.

Can you tell me some of the reasons why yours tend to die? It is cheaper learning from your mistakes than buying and making them myself.

The fridge is not key atm, but will be in the future. Looking into either a small camper model on 12v or something similar that provides enough room to fill my one person needs.

Can you tell me which MPPT controller you have experiences with(or tell me if I can read your experiences somewhere here on the forum?)?

Thanks for the tips so far, will a whole bunch of small li-po batteries work? I have about 50 of them. They are really cute and tiny though. All from small rc stuff. Or things like phone batteries? I know there is a point where the gain/overall left power/whatever you techies call it. But willing to try anything and want to learn about it.

Steve Farmer wrote:1) You're on a budget
2) You're got some soldering kit
3) You've got special requirements regards matching panel size to window size
4) You're indoors so don't need professionally made weather hardened solar panels

So.. buy some solar cells from ebay, which will cost you about a third of the price per watt compared to a ready made panel, and custom make your own panel(s).
The main thing as you learn is to be very very careful how you handle the solar cells, they are extremely fragile. If you handle them carefully when moving, soldering and securing to a backing panel, then you will be OK.

On the batteries, technically yes you can use car batteries for light use but don't let them discharge more than 10%. ie keep them at 90% charged or higher, otherwise you will kill them.
However, don't use car batteries indoors because when you are charging they give off hydrogen gas and in certain circumstances lead and sulphur compounds. Maybe you have a balcony or roof space which can house a battery enclosure?
For any given power, Voltage is inversely proportional to current. And higher current gives higher losses in the cabling. So at low voltages eg 12, 24V, losses in cables are high. Keep your cable runs as short as possible and use good thick cables for any runs that have to be longer than a few metres.

Post some pics on here and let us know how you get on.

I am very interested in doing what you suggest, making my own panel. Not for the general bragging rights alone. Would love to be able to create my own custom solar panels for every situation there is. Also saw a youtube video once from a guy who does this. One of his tips was to got to manufacturers of panels and ask for broken/discarded solar panels. They pretty much still work, just need to be handled with more care when soldered into place. And kept in place better.

What kind of cell would you suggest? I already learnt that is easier to have cells with the strips which connect the cells together to have them presoldered on. But hey, if the price is right. I will do it myself.

Also for lighting I have bought one of those cheap ass solar charged garden light rail sets(80 leds). Primarily to use it as a cheap and effective not at home/someone at home light. Cost me 5 euro and I never had to switch it on or off. Just hung it over my existing lights which are mounted on the walls. Will buy one more so I have more than decent lighting at home. For no extra (money) charge. The battery inside is a simple rechargeable AA type battery. On a average day the lights will stay on for about 4/5 hours, recently had some really nice summer days in which the lights keep on all night.

One died while monitoring some pretty heavy loads a couple months after I bought it; another when I'd had it a year and had only used it a handful of times... I am assuming the deaths are down to crappy manufacturing/QC, but a brief postmortem showed no terribly obvious causes of failure beyond that.

So, unfortunately not really anything to learn here except 'cheap chinese gadget is built to cheap chinese quality standards'... Last time I looked there really wasn't much in the way of alternatives though.

You can possibly save a bit by using broken pieces of cells but to be honest the near perfect cells are so cheap that you might save $10 with the limited window area, but without regular shaped cells you will lose the ability to maximise that area. Cells should all be the same size, if you have irregular cells, then the whole panel will act as if all cells are the same size as the smallest cell. Broken bits can go into other projects like maybe you will break a couple of cells and end up turning them into a mobile phone charger to use outside.

The reliability and longevity of home brew PV panels is pretty poor. There are exceptions of course.

What really put the damper on do-it-yourself PV panels is the drastically lower cost of commercial panels with a warranty. Often less than a dollar a watt.

If you count your time as worth even five bucks an hour, you just can't beat this:

http://sunelec.com/solar-panels



Of course, there are lots of factors besides just cost, like learning a new skill, or having a panel you could open and repair (with the few extra cells you bought) as two examples.


Just as a quick and dirty estimation method, if you have 40 watts of panels with good sun exposure/hours, you might reasonably run 10 watts of appliance regularly every day. So with poor orientation, yeah maybe 5 watts. If you're not sure how to calculate watt-hours, just ask.

For occasional blackout purposes, that more depends on how big your battery bank is. Automotive starting batteries are about the least desirable kind of battery because deep discharge cycles will kill them in a very few months.

Hope that helps.

Okay that clears up a lot for my plans so far. No car batteries for a permanent solution, will be trying it for test/experience. As I am located in the middle of Europe, the US prices won't help me regarding the parts for solarcell/completed solar panel. So as stubborn as I am, will be looking into making my own and buying one probably.

Met a guy recently who has a campervan rental company. He uses old diesel bastards, cleans them out, and pretty much just makes them into a theme campervan. He uses a solar panel/charger/batteries system. And his vans rarely need to be put on extra power. Was talking to him about my idea. He will get me some of his data from his sets. As he said it would fit my personal profile atm. He also would be interested in hooking me up with a set when he orders a couple next time. He has a 12v refridgerator/freezer unit in his campers too. And regarding the current state of my fridge(pretty neat) I can still sell it or trade it.

I will be looking into what prices a completed set cost now and the solar panels/cells itself. Will keep everyone updated this. And if anyone has suggestions, please post them!!!

Dillon Nichols wrote:One died while monitoring some pretty heavy loads a couple months after I bought it; another when I'd had it a year and had only used it a handful of times... I am assuming the deaths are down to crappy manufacturing/QC, but a brief postmortem showed no terribly obvious causes of failure beyond that.

So, unfortunately not really anything to learn here except 'cheap chinese gadget is built to cheap chinese quality standards'... Last time I looked there really wasn't much in the way of alternatives though.

Regarding the breaking of Chinese quality stuff. A Chinese manufacturer once said, the only reason why Made In China breaks so quickly is because your production requirements make them do it. Or something in the line of that. This is true in my opinion. Once had a batch of these tiny car-key look a like camera's and they would come in the same packaging and all. But inside some had a full hd1080p camera. While others had your first blurry picture camera in them. Kinda like the vendor at see with a binocular around his neck. And a whole bunch boxed in his stall for sale. You get to try his one and be amazed by how good it magnifies and clear the image is. But he sells you a boxed in. Which is just near the quality difference that you won't see it directly/think it is a dirty lens/whatever tricks your mind.

My dad said he had some useful stuff for me, will be visiting him soon for some consumption metering equipment. Will post here what kind of goodies I will be using. And to get your uncorrupted opinion about them.