J.u.t.a Solar

Re: J.u.t.a Solar

Emo,

Actually, it is sort of difficult to design and build an "expandable" system (at least starting small/cheap and reusing everything).

Small solar charge controllers have a limited output current/voltage they can support. You can add more charge controllers in parallel--but that does get a bit messy as you are adding more and more wiring/fuses/etc. to your system.

The next issue is batteries... Roughly, if you parallel a new battery with an old battery in the same bank--the new battery can quickly age down to where both the new and old battery may die around the same time. Normally, you want to keep battery banks as a set with the same brand/model and even date code batteries (if possible).

Inverters--a small 12 volt inverter is nice (find one that does not waste much power with small loads)... As you get bigger loads, you need a larger inverter. As you get a larger inverter, you need larger/more batteries. As the load+inverter gets even larger--you need to go from 12 volt battery bank to a 24 or 48 volt battery bank.

As you increase the size of the battery bank, you need more solar panels and charge controllers (or larger charge controller). As you increase battery bank voltage, you may need a new charge controller (depending on what you got before) and need to rewire your solar panels to support a higher voltage battery bank...

Etc., etc., etc...

For everyone, we usually recommend that you follow these steps:

1. Conservation: It is always cheaper to spend money/time/effort on conserving a Watt than it is to "generate" that Watt.

2. Know your loads: Define/measure your loads, and your expectations (by day, by season, generator backup or not, etc.).

3. Design your solar system: Now you have done 1-2, you can design a (hopefully) cost effective solution for your particular needs. Within reason, you can over design the battery/charger/wiring/inverter by a factor of 2x -- and add more solar panels if it turns out you need more power per day from the sun.

I can give you a few starting points to think about the system you want to start with...

Solar panels--If you can live with fairly large solar panels--look at mono or poly crystalline panels that are >100 watts... They tend to have the best pricing per watt. But they are large and not easy to transport (they are glass panels).

For Charge Controllers--Morning Star makes some very nice small PWM controllers. If you want the "best" small MPPT (Maximum Power Point Tracking) type controller--the Morning Star 15 amp MPPT is hard to beat... ~200+ Watts usable maximum of solar panels at 12 volts, or +~400 watts of panels on a 24 volt battery bank.

If you are looking at ~400 watt and larger systems, and 12, 24 or 48 Volt (and other voltages inbetween)--Xantrex XW MPPT 60 Amp charge controller is very good. Outback FM 60 and FM 80 are also very popular. These will control ~900+ watts of solar panels at 12 volts to ~3,600+ watts on a 48 volt battery bank.

Inverters--You pretty much need to size them for your loads. The Morning Star 300 watt (600 watt max) TSW Inverter is hard to beat at 12 volts... Xantrex makes a killer inverter at 6kWatts and 48 volts (can be used for Grid Tied, Off-Grid or Hybrid operations).

Battery wise--for your first set, look at "golf cart" type batteries. Most people kill their first set (aka "Training Batteries") and getting "good" flooded cell or very expensive AGM's can make a very expensive mistake.

Battery Monitor--once you get to larger battery banks (and especially AGM/Sealed batteries which you cannot measure specific gravity) a Battery Monitor can help prevent battery suicide or murder.

And read the FAQ's (frequently asked questions) that are on the NAWS website (by the way, I will point to products at NAWS--but you are more than welcome to shop around--NAWS funds this site and it is out of respect for their support of this forum--The Moderators here, Niel and I, are a volunteer spam patrol. Nobody here gets any commisions from sales at NAWS--Other than Windsun, the Admin from NAWS). Also, because NAWS stands behind their products and supports open discussions about any issues--they are a good first place to find good quality products at reasonable prices.

Of course, they don't stock one each of everything in the world there...

The links here are a lot to read--but try to go through them--they will answer many of your questions.

Northern Arizona Wind & Sun Home Page
Solar Panels
All About Charge Controllers
Solar Charge Controller PWM vs MPPT FAQ
Solar Charge Controllers
Inverter FAQ
Selecting Inverters for Pumping Water
MorningStar 300 watt TSW 12 volt inverter
Battery FAQ
Battery Monitors and Kill-A-Watt Meters

In the end, solar PV power is not cheap... For Grid Tied systems (solar panels + GT Inverter that ties to your utility meter) can be quite cost competitive with Tax Credits for areas with expensive power.

But Battery Backed / Off Grid systems will probably never be cheaper than Utility power for the near term. Basically, the batteries are expensive and must be replaced every 7-15 years (or less for "cheap" batteries on small systems).

Very roughly, the price per kWhr for various systems (as always, the numbers below are very rough estimates... You will have to design your own system on paper before you can get more accurate numbers):

$0.08-$0.30 per kWhr for Utility power
$0.10-$0.35 per kWhr for Grid Tied Solar power
$0.45-$0.75 per kWhr for Hybrid (GT/Off-Grid) Solar
$1.00-$2.00+ per kWhr for Off Grid Solar

-Bill