New to Solar--have a few questions!

Hi Jon,

I just installed a small PV system on my RV recently and encountered many of the same questions regarding system design.

1) Although many 180 watt panels offer an excellent $/watt ratio, they are physically quite large and therefore can be difficult to work with. You may also want to consider something in the 130 watt range to start off with such as this:

http://store.altenergystore.com/Solar-Panels/100-to-149-Watts-Solar-Panels/Kyocera-KC130TM-130W-12V-Solar-Panel-w-J-Box/p2403/

A great MPPT controller is the Blue Sky 2000e. It's a little more expensive than the non-MPPT controllers, but it is very efficient. It can handle up to 25 amps for future expansion of a small systems. If you plan on going totally off-grid in the near future, then you may want to consider something larger, but it would really be overkill at this point based on what you mentioned about your current needs.

2) To get the longest life out of your batteries, you should never discharge them more than 50% if possible. So the first thing you should do is calculate what you anticipate your total energy needs (in amps) will be per day. Then you can pick a battery that will provide sufficient capacity for your needs while taking into consideration the 50% rule.

Generally 6 volt flooded cell deep cycle batteries (wired in a series to produce 12v), provide the best value for the money. Sealed batteries are considerably more $ for the same capacity.

10/2 gauge wire will work great for your present needs and future expansion.

A baby box would work great for over-current protection. Circuit breakers should be sized based on the specs of your PV panel, controller, inverter and load needs.

http://store.altenergystore.com/Enclosures-Electrical-and-Safety/Electrical-Enclosures/DisconnectLoad-Enclosures/AC-andor-DC/Midnite-Solar-MNBabyBox-4-Slot-AC-or-DC-Breaker-Panel/p4480/

Check out the schematic here (click on the cabin image):
http://store.altenergystore.com/descfiles/kits2go/kitcabin1/cabin-170w.jpg
for an idea how to connect everything. In addition, most controllers will have instructions on how to wire everything up. Check out the PDF instruction manuals for those products available on this site.

4) Running your small appliances/electronics direct from DC will be a little more efficient than using an inverter as you loose some efficiency in the conversion process and the inverter also uses a small amount of energy. Many laptops, battery chargers, etc offer 12v car chargers that would work well in a PV system such as this. However, it may be more cost effective to just use an inverter, rather than buying new car cords for everything. One thing to consider regarding inverters is that some battery chargers (lithium batteries in particular) can not run from modified sine wave inverters. I am using a Samlex Pure Sine wave inverter and have been very happy with it.

http://store.altenergystore.com/Inverters/Off-Grid-No-Utility-Needs-Batteries/300-to-999-Watts/c600/

Hope that helps. Good luck with your project!

Bob

Thomas and Robert have already provided some good advice, but I would just like to add this:

You may want to start with a pure sine wave inverter instead of the MSW inverter you have in mind.  I started with a MSW inverter and wish that I hadn't wasted the money.  Motors ran at the wrong speed, making my timers useless.  I had noise in the audio of my radio.  I had streaks in the TV picture. I was always worried that I would damage something, so I seldom used the inverter. 

You might want to start with a 300-watt sine wave inverter instead, as your loads are fairly light.  Later, when you upgrade to a more powerful sine wave inverter, you'll still want to use the 300-watt unit at times because that will be more efficient than to use a big inverter for a small load.

Just MHO.
John