Monocrystalline or Polycrystalline Solar Panels

Monocrystalline were typically more expensive and produced in larger numbers for a residential house or industrial applications. This is no longer the case and the costs aren't that different so consideration could be made regarding the purpose, site, installation, orientation to the sun etc for a year-round yield benefit. There are always differing opinions in this debate but if your panels aren't going to be mounted at 90 degrees to the sun then a wider sunlight collection method should be considered. In which case Monocrystalline may give a better year-round energy gain.

Polycrystalline, however, performs better in direct sunlight so if mounted at the correct angle facing directly north (if in the southern hemisphere) then your peak daylight yield will be greater. If this is matched to discharge cycles then performance could be measured in usable power during collection rather than stored energy which has to allow for electronic equipment conversions and losses and chemical conversion losses in turning DC energy into battery stored energy. Most small panels which are 36 cell under 200w are Polycrystalline so the decision of which is best suited to your installation might become a whole lot easier.

Most of what's discussed here is our own opinion as this topic has so many variables from manufacturing materials, cell connections, place in the world, installations, angles, colour, strength, quality, performance over years (25 year warranty on some panels) and rated output after 20 years.

Depth of Discharge explained.

Depth of Discharge is something that's relevant to all rechargeable batteries. This type of battery is specifically designed to perform and discharge before being recharged and is commonly referred to as a deep cycle battery.

Deep cycle batteries quite often don't advertise a CCA (cold cranking) rating as this is more typical with starting batteries. Dual-purpose batteries like some AGM batteries, however, have good deep cycle ability and a large surface area of active material which gives them high cranking output when compared to equivalent-sized starting batteries. Remember, the purpose of the battery is the most important consideration here.

Battery spec sheets of deep cycle batteries will show a cycle life that is expressed by a graph showing different depths of discharge with a corresponding life expectancy. When the depth of discharge is deeper the number of times that battery can cycle reduces. So general-purpose batteries might only be 50-70 cycles at 30% depth of discharge. These are sometimes referred to as Leisure batteries but in fact, are just standard typical starting batteries. 400 cycles at 50% D.O.D. is really where a purpose-built battery might be advertised as a deep cycle. This will extend to 80% D.O.D at 700-800 cycles before you get to the internationally recognised quality brands that might be as much as 1000-1200 cycles at 50% which is similar on the graph to the 80% at 700 cycles but shows the manufacturers intent of the battery to be longer-lasting over 1200 cycles than say once a day for 2 years until end of life.

State of Charge vs. Depth of Discharge

State of charge refers to how high a percentage of fully charged a battery is. An example would be if you were to discharge 25% of a batteries capacity the battery would be 75% S.O.C (state of charge). The same example would show a 25% depth of discharge.

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