WIP
My solar cell is now complete and fully functional. I'll do a bit of a writeup on it with pictures and links so that readers can easily understand what they need and where to get it. One of the goals of this project was to use power in it's native DC form as much as possible for maximum efficiency. 12v devices for Car, RV, and Boat and anything that runs off an external DC power adapter are my main targets. If you are patient many of these things frequently go on sale for below production cost although expensive 12v devices are readily available. Also one of my main targets: battery operated devices (use this point to get your g/f interested in the project). Battery operated devices such as cordless mice and remote controls have been optimized to use very little power so you can avoid wasting your precious solar power.
First, the parts list:
$35 Solar Panel -
5w (0.42a) noname
$54 Charge Controller -
Morningstar SunSaver p/n: SS-6L 6a 12v w/ LVD
$120 Battery -
Seavolt Deep Cycle 12v 75ah flooded lead-acid *
$3 Plug adapters - 12v automotive plug (link coming soon)
FREE DC plugs - just cut them off of old brick adapters
$40 AC Inverter -
RadioShack.com 160w 12v auto plug **
$25 DC converter -
RadioShack.com Universal car 12/9/7.5/6/4.5/3 volt **
$11 USB charger -
RadioShack.com 5v car adapter for USB-powered devices **
$15 AA/AAA Battery charger -
RadioShack.com Ni-MH car charger ***
Total: $303
*I actually used the smaller and slightly more expensive $130 one but I had a $20 off coupon and didn't have to pay shipping. I highly recommend buying batteries locally as the shipping costs are quite high.
**I used one I had on hand. This one is comparable. You may find better deals.
***I used a nicer one that wasn't a "car" one but ran off an external 12v power adapter.
So, for less then the cost of a budget computer I have a fully functional solar cell with universal 12v, 9v, 7.5v, 6v, 4.5v, 3v plugs, a 120v outlet, and a 5v USB plug. Spiff, no?
Basic PV solar cell concepts
Photo voltaic solar cells convert light energy into electrical energy through a process I refer to as 'magic'. The only other things you really need to know about how they work is
1. that it is possible to run electricity backwards through a solar panel thusly wasting all your energy at night. A simple blocking diode or a charge controller takes care of this.
2. The most simple design of solar panels are made up of many smaller "cells" connected in series to reach the desired voltage range (which will vary quite a bit depending on how much light you have). If even a single cell breaks or is shaded the output of the entire panel drops to 0. If even a single cell is half shaded the output of the entire panel drops by half. So keep them clean and unshaded.
3. Bright sunlight shining directly onto the panel gives best results. So point your panel at the sun, duh. This means angling them towards the equator or getting a tracking system the readjusts the panel in real time throughout the day. The farther away from the equator you are the more valuable a tracking system becomes. The south pole can generate just as much power (on a yearly average) as the equator with a fully tracking system... except for weather and it kinda sucks that there's almost no usable sunlight for half the year. It's not that the equator gets more sunlight, it doesn't, it's that is much easier to use that sunlight as it's steady all year with better weather and you don't really need a tracking system.
4. PV works better when they are cool. So ventilation is your friend.
You should be pretty familiar with batteries. Flooded lead-acid are the cheapest and most reliable but they have many weaknesses. The most obvious ones being the lead and the acid both of which are poisonous. Other problems with lead-acid batteries are:
1. Charging them causes electrolysis (yes, just like what they use to make hydrogen for fuel cells) which destroys your water so you sometimes have to add more water.
2. Electrolysis also creates oxyhydrogen gas (a fancy name for gas that is 2parts hydrogen and 1part oxygen which is what you get if you don't seperate them during electrolysis. It's used in industry and also as a booster for combustion engines) which can be dangerous if allowed to build up as it is highly flamabe. Not really a problem for smaller battery packs in anything even slightly resembling a ventilated area.
3. The chemical reaction that powers the lead acid battery will eventually destroy it no matter what you do. Look for the "cycles" rating on the battery as it's the most important attribute of the battery.
4. DOD issues. This is where a lot of battery myths come from but basically it boils down to this: if you do not fully recharge the battery soon after having discharged it the battery will be ruined. My rough understanding of the process is as follows: When drawing power from the battery the lead plates become coated with sulfur oxide. When you charge the battery the sulfur oxide process is reversed (but not perfectly and you lose some lead). If you leave the sulfur oxide there for a long time it crystallizes and covers the lead preventing it from reacting with the acid (and the battery appears to be dead or no longer holds as much of a charge). You can remove these crystals (physically or with pulsed charging) but you lose all of that lead forever (you would have gotten some of it back if you hadn't let it crystallize). Another thing to note is that it's better to discharge 10% before fully recharging that to discharge 1% as with low levels of discharge and recharge the plates will not sulfurize evenly and thusly not wear evenly causing premature battery death. If you do not fully recharge you may not recharge evenly and can get crystallization on only part of the plates which is problematic in itself and also cause the plates to not wear evenly.
5. They are temperature sensitive. They can freeze breaking plates if not designed to handle freezing temperature. Lower temperature reduces capacity and amperage and increases the amount of voltage needed to charge but lowers self-discharge and increases battery lifespan. Higher temperatures increase capacity and amperage while decreasing charge voltage but decreases lifespan and increases self discharge.
6. Self discharge. Lead-acid batteries will discharge themselves losing power over time like a leaky cup losing water.
...more later.
Part Choices explained:
PV Panel - This solar panel gives some of the best watt/$ (one of the most important attributes of a PV panel. The other important one being watt/squaremeter) in the under $50 range. If you want your solar cell to be much more than a toy you'll want +200w worth of PVs but this 5w one is fully functional.
Charge Controller - A large PV array can damage a battery by overcharging it. A charge controller can also make sure the battery is being charged at the correct voltage for maximum efficiency. They also prevent the battery from discharging at night. Low Voltage Disconnect prevents you from accidentally fully discharging your battery (which breaks it). For my system a charge controller wasn't really necessary as the panel has a blocking diode in it but it gave me a lot of features to play with and my system is ready to have up to 6a (72w) of solar power connected to it.
Battery - Flooded lead-acid or AGM lead-acid batteries are best for solar systems. Flooded are cheaper. They need to be deep-cycle (not car, or marine, or dual-use) to get thick strong plates that won't break.
...more later
Future upgrades include: 2 12v sockts on the solar panel side to plug "car" solar panels into (will add 3w more power from panels I have on hand without having to permanently install them) and a
45w PV array
More details on component choices and explanations and some pictures later. Please ask any questions about this project or solar cells in general (I should know the answer and if I don't I'll remedy the situation immediately).
For a grid tie system you basically just get a beefier inverter and jump through some hoops to get the utility company to wire you into the grid. At that point you can skip the battery if you want to save money (but of course you also have no backup power in the event of a grid power outage).
Linear Mode
