I’ve been lurking around looking at solar panels to buy for the past few months… with a limited budget, I can’t really splurge and buy a 2kw array right away (wishful thinking), but I finally got some extra money to buy a few panels. I am planning to add to these over time, and hopefully grow them into something much more useful.
I did take the plunge and bought two panels last week… finally! In the process of doing so, I’ve come up with my list of the 5 top things you probably want to know about the solar panels you are buying.. I am sharing these in the hope this helps in your search too!
I placed this first I guess because if you’re like me with a limited amount of finances, you want to get the best bang for your watt… at the time of this writing, the cheapest prices i’ve found were about $1.76/watt+shipping at SunElec (see my previous posting on where to buy solar panels for more info) but these were pretty large wattage and size for me (usually 200 watts or so for the best prices).
I did decide on two new 12 volt, 85 watt panels that came out to be $2.21/watt including shipping that I found on Ebay. Not bad really since smaller panels cost a bit more per watt than large ones.
This is an important one if you decide to mount your panels on your house in the future since it seems you really need your panels to be UL certified to be even considered “legal” to install. (I am not totally sure of this last statement but a lot of the forums and talks about DIY solar installation recommend UL certified panels).
A lot of cheaper panels on the market don’t have UL certifications and only come with CEC or ISO or TUV or some other certifications. I believe those are good to have too but I guess they are not up to par to having UL certification (ISO/TUV are manufacturing standards that have to do with the process of creating the product but don’t really ‘test’ the product itself in demanding ways like UL). Again, I am not 100% sure about these, feel free to clarify if you know more.
Finally, if you want to get the 30% federal tax credit (and state credits) for your solar installation, you probably would need to have UL certified panels.
3. Voltage (Nominal Voltage)
Somehow, having MPPT charge controllers have made this less of an issue but if you have the normal PWM controllers or just want to charge 12 volt car batteries, this could become important for you. The important voltage to look at is your Vmp .. or maximum voltage the panel can produce as this will determine if it would work properly with your charge controller. (i.e. Charge controllers have a maximum DC input limit… be sure not to go over this, especially when connecting multiple solar panels together).
I planned to have at least a minimum of 24 volts running through the wiring (to lower cost of wiring compared to 12 volts) so I was either looking for a single panel of 24 volts or 2 panels of 12 volts (which can be placed in series to have the same 24 volts). I decided to go the second way because it seemed more flexible for me at this time.. For example, I could use a single panel (or 2 panels in parallel) to have 12 volt output, or use them in series for 24 volts. I could also do some more experiments with the panels and if I somehow damage one *evil smile*, i still have another one as backup.
4. Material Type
Amorphous, Polycrystalline, or monocrystalline? These are the main types of panels out there today and I won’t go into the details of each as there are a lot more knowledgeable websites on this topic.
Main take on these is that Amorphous is an ‘older’ technology that is less efficient (need more space to have same amount of output power) but does have some advantages in partial sun/shade and is cheaper in cost. Polycrystalline and monocrystalline are more efficient and newer.. monocrystalline being the more expensive one and probably a tad more efficient (and expensive) due to its structure being more cohesive.
If you have the space on your roof or land and want to save some money, then go amorphous. Otherwise, get the other ones.
5. Connectors/Cables and Mounting
It seems that solar panels, for the most part, have standardized the connectors that stick out of the back of the panels. I believe the most common one being used now is the MC4 connector which is pretty much rated for outdoor use and is available almost anywhere. I’m not sure why MC4 connectors are a bit on the expensive side though and crimpers are expensive too and cost anywhere from $50 to $150. (If you plan on wiring/crimping yourself). Other connectors are MC3 and Helios.
I did buy one with the MC4 connector to be on the safe side… with about 3 feet of cable for the positive and negative connections. This is a good thing to be aware of as some panels for sale don’t have this cable but just the junction box so you’ll need to spend a bit more money and time just to be able to connect your panels together (or to your charge controller).
A quick tip: Buy a male-to-female connector cable at least twice as long as the distance from your panel to your charge controller. That way, when you want to install them, just cut that cable in half. Connect the side with the connectors to the panels (positive and negative), then connect the ones without the connectors (from where you made the cut) to your charge controller. That way, you don’t have to remove the connector(s) from your solar panel and possibly void your warranty.
As for mounting, I believe most panels have mounting holes on their frames but the ones I got had free mounting screws and z-shaped brackets to be able to mount on a flat surface. Those add up to the cost per panel too.
So, that’s it! My top five things to check when buying a solar panel. I’m pretty sure there are others that you need to check too and your mileage may vary. Please feel free to leave any comments or suggestions or other important things that you think I left out (I just hope I don’t smack my head after reading your comment!).