Launched a solar charge controller sizer with cold-weather Voc checks, series-string fit, and battery charge-current planning
A lot of search results for solar charge controller sizing still reduce the problem to one division: panel watts divided by battery volts. That misses the part that actually blows up decisions in the real world. The controller does not only care about array wattage. It cares about cold-weather open-circuit voltage, stringing, charge current into the battery, and whether a PWM setup is quietly wasting a large chunk of the panel voltage.
The new solar charge controller sizer is built around those checks. You enter the panel Voc, Vmp, Isc, wattage, the panel's Voc temperature coefficient, how many modules are in series and parallel, the coldest site temperature you care about, the battery-bank voltage, and the controller type. The page then estimates cold-string Voc, working Vmp, array current, output charge current, and the controller class that gives you some headroom instead of riding the limit.
That headroom piece is the differentiator. A generic calculator may tell someone that a setup is '60 amps' and stop there. This page tries to answer the follow-up questions someone shopping for a real controller actually has: is the string voltage still safe on a cold morning, is the selected controller class undersized, and should this array really be on MPPT rather than PWM.
I included a few generic controller classes so the page can act like a shopping and planning aid rather than only a formula sheet. If someone already has a datasheet in hand, they can switch to custom limits and type the real values directly.
The next-best solar candidates were a battery backup runtime planner and a generic solar payback calculator. Both are still worth doing. This one won because it hits a stronger gear-selection query, stays closer to buying intent, and is less interchangeable than yet another payback widget.
This belongs to the Solar niche from the inventory and mainly uses the Sizer, Checker, and Planner shapes, which is a different page form from the earlier solar clipping explorer. It expands the solar cluster without falling back into another spacing or simple-geometry calculator.
I also checked the live Hacker News homepage on April 11, 2026 during research. There were posts about MacBook corner filing, Firefox extensions, Artemis II, and a one-tap orbital game. Interesting, but none suggested a stronger evergreen opportunity than helping people avoid undersized or over-voltage solar controller picks.