There are a few different answers to this question, depending on what you are asking. I'll go over the main ones.
1. The Earth's axis is tilted in comparison to the Sun, so days get shorter in the winter months. This is due to less light, and therefore energy, hitting the Earth directly. Instead, that energy either misses entirely, or hits nearer to the Equator. This is why the poles have twenty-four hour days and nights depending on the season. (Night in the winter, day in the summer.)
2. In terms of the food chain, energy from the sun is converted to basic sugars by plants in a process known as photosynthesis, inside the plant's cloroplasts. Small animals such as mice and insects consume the plants, and the energy those plants converted from sunlight. This continues up the food chain until you get to apex-predators (tigers, bears, wolves, owls, etcetera).
3. In terms of electricity, solar panels are made of tons of 'solar cells' which tend to be lots of silicon atoms, which like to share electrons, and a conductive backing. (Pardon me if some of this section is incorrect, I only have a basic understanding of solar panels) When a photon (that is, a light particle) hits the silicon, it bumps off an electron, and the conductive backing catches it, resulting in a electrical current. This current is incredibly small per solar cell, so you need a ton of them to make any sort of useful power out of them. Solar panels do degrade over time, but incredibly slowly, there are some from the 1970's that still generate just as much power as they did originally (if not, only ever so slightly less).
I hope I answered what you needed to know! If you wanted a different answer, feel free to comment with some clarification and I would love to fill you in :)
Their progress and wealth is highly dependent on the harvests, and the price of grain. They probably have to import some industrial products and if they had a bad year (weather, other catastrophies, poor technology) they can't get the necessary amount of industrial products in exchange for their surplus e. g. in grain. There are so many standards and requirements about the quality of food production that no country can survive solely on agriculture without high quality technology (machines, unharmful fertilizers, research-based breeding, etc.).
