How do I start sizing an off-grid solar system?

Start with a load list, not a panel package. For each appliance, estimate its watts and how many hours it runs in a day. Watts multiplied by hours gives watt-hours. Add those up for a daily total, then divide by 1,000 for kilowatt-hours.

Also note which things run at the same time. That helps size the inverter, which has to handle the combined power draw and any brief startup surge from equipment like motors. Your daily energy total and your peak power need are related, but they are not the same number.

The part people often underestimate is the season. A system that works well on sunny summer days may come up short in winter, so size the panels using the location’s weaker solar season rather than an annual average. Shading, panel direction, and conversion losses matter too.

For batteries, work from your daily use and decide how many low-sun days you want to cover. Check the usable capacity, not just the battery’s advertised total capacity. More storage can help through cloudy stretches, but it cannot keep the system going indefinitely without enough energy coming in.

A kit can make the component matching less confusing, especially for the inverter, battery voltage, and charge controller. But a package is only a good fit if it was sized around your actual loads and local conditions. A large-looking panel or battery count by itself doesn’t tell you whether the whole system fits.

I’d get a written design with the expected daily energy use, winter production assumptions, battery usable capacity, inverter rating, and backup plan. Then you can compare that with individual components or another package. If you plan to install it yourself, make sure the design also addresses electrical protection and local requirements.

Decide what happens during a run of poor weather before you buy batteries. You might choose to conserve power, use a generator to recharge, or pay for enough storage and panels to reduce how often backup is needed. Those choices change the price a lot.

Also look for ways to lower the load first. Efficient appliances and avoiding electric heating or cooking where practical can reduce the size of the system you need. A careful load estimate is much more useful than picking a system based on a generic house-size rule.