Solar system

What panels really do

Panels produce changing DC power. A controller converts that power into the battery's required charging profile. Rated panel watts are laboratory output; roof heat, sun angle, clouds, dirt, cable/controller loss and shade reduce real energy.

Sun-hours

Daily solar is roughly array watts x peak-sun-hours x system factor. Example: 750 W x 4 h x 0.75 = 2.25 kWh/day. This is a planning estimate, not a promise. Use location- and season-specific solar data, then retain another charging source.

Series vs parallel

Series adds voltage and keeps string current; parallel keeps voltage and adds current. Series reduces cable current but one shaded panel can constrain a string. Parallel tolerates unequal shade better but needs more current capacity and often string fusing. Mixed orientations or panel types may need separate controllers.

MPPT sizing

Check four things against the exact controller data sheet: cold-corrected array Voc must stay below maximum input voltage; array short-circuit current must stay within the allowed limit; operating voltage must be high enough to start charging; controller output current must fit battery voltage and planned array power. Never use nominal panel voltage for the Voc check.

Installation

Use listed, compatible PV connectors and correct tooling; protect cables from UV, abrasion and sharp roof edges; make a serviceable, sealed cable entry. Provide disconnecting means as required. Fuse parallel strings when reverse current can exceed a conductor or panel rating. Do not open MC4-type connectors under load.

Rule of thumb

If you cannot state the expected current, full conductor length, protection rating and manufacturer limit for a circuit, the circuit is not ready to build.

CHAPTER CHECK

• I can explain the purpose of every component covered here. • I can identify the exact manufacturer limit that controls my design. • I have added the decision, rating or measurement to my schematic/worksheet.