The 
Solar Generator is a Mekanism generator that makes up to 20 FE/t (50 J/t) from daylight, and the 
Advanced Solar Generator is the larger version which makes up to 120 FE/t. Neither of them needs fuel, but they’ll only run during the day and with open sky above them.
How much you’ll actually get depends on the biome, as cold and dry places give more than hot or humid ones, and rain cuts the output to a fifth. The Advanced Solar Generator has a second job as well, which is heating the Thermal Evaporation Plant.
How to Make It
Everything starts with the 
Solar Panel, which is 3 
Glass Panes over 2 
Redstone Dust and an 
Infused Alloy, with 3 
Osmium Ingots along the bottom. The panel doesn’t do anything when it’s placed or held, as it’s only used for crafting.
A Solar Generator takes 3 Solar Panels, 2 Infused Alloy, an 
Iron Ingot, 2 Osmium Ingots and an 
Energy Tablet. The Advanced Solar Generator is then made from 4 Solar Generators with 2 Infused Alloy and 3 Iron Ingots, so it’ll cost you 12 Solar Panels in total.
That’s a good trade, as you’re getting the output of six Solar Generators for the price of four. The advanced one is 3 blocks tall with a wide panel on top though, so it needs the block above its base and a 3×3 area above that to be empty when it’s placed.
How It Works
Both generators need three things before they’ll make any power, which are daytime, a dimension with a sky, and a clear view of that sky. Nothing is made at night or under a roof, and they shouldn’t work in the Nether or the End either.
The output follows the sun through the day, so it starts low in the morning, peaks at noon and drops away again as evening comes. The 20 and 120 FE/t figures are the noon peak, which means the average over a whole day is quite a bit lower.
A Solar Generator only pushes its power out of the bottom, so the cable or machine has to go underneath it. The Advanced Solar Generator sends power out of both the front and the bottom of its base, which makes it a little easier to wire up.
The Advanced Solar Generator panel
The advanced version checks all nine blocks of its panel, and it’ll run as long as more than four of them are able to see the sky. Its output is the average of the nine though, so every covered block takes a ninth off what you’d get otherwise.
Output by Biome
Each generator works out a multiplier from the biome it’s standing in, and this is where most of the difference comes from. Colder biomes push it up and hotter ones pull it down, and in biomes where it’s able to rain or snow, the wetter they are the less you’ll get.
| Biome | Solar Generator | Advanced Solar Generator |
|---|---|---|
| Snowy Taiga | 25.2 FE/t | 152.4 FE/t |
| Snowy Plains | 21.6 FE/t | 130.8 FE/t |
| Plains | 17.6 FE/t | 105.6 FE/t |
| Jungle | 13.6 FE/t | 82 FE/t |
| Desert, Savanna or Badlands | 12.8 FE/t | 76.8 FE/t |
So the snowy biomes will actually beat the listed maximum, whereas a Desert gives about half of what a Snowy Taiga does. These are worked out from each biome’s base temperature, and since it gets colder higher up, you might see slightly more on a mountain.
Rain and snow cut the output to a fifth while they last, on top of the darker sky. The one upside of a Desert is that it never rains there, so its low number at least stays steady through a storm.
Solar or Wind
A 
Wind Generator at sea level makes about 48 FE/t day and night, which is more than twice a Solar Generator at noon in Plains, so it’s the one to build first. The Advanced Solar Generator is where solar gets useful, at over 100 FE/t in a mild biome. You’ll need four of them for a Thermal Evaporation Plant anyway, and they’ll keep making power while they heat it.
Upgrades and Automation
Only the 
Muffling Upgrade fits in either generator, as none of Mekanism’s generators accept Speed or 
Energy Upgrades. They each have a redstone control setting and a slot that charges an item from the buffer, like an Energy Tablet.
The Solar Generator holds 38,400 FE and the advanced one holds 80,000 FE, which is a couple of minutes of output at most, so they won’t carry you through the night on their own. An Energy Cube is what you’ll want for that, or a 
Bio-Generator that runs off a crop farm whenever the sun is down.
FAQ
A Solar Generator peaks at 20 FE/t and an Advanced Solar Generator at 120 FE/t, before the biome is taken into account. In Plains that works out at about 17.6 and 105.6 FE/t at noon, whereas snowy biomes give more and a Desert gives less. Both drop to nothing at night.
It needs daytime and open sky directly above, so a roof, a tree or a block placed over it will stop it. Remember that power only comes out of the bottom of a Solar Generator as well, which means a cable against its side won’t be given anything.
It makes six times the output of a Solar Generator for four of them plus a little Infused Alloy and Iron, so it’s the better use of your Solar Panels. It’s also the only one that will heat a Thermal Evaporation Plant, which needs up to four of them.
They’ll still run, but at a fifth of their usual output for as long as the rain or snow lasts. Biomes with no rain at all, like a Desert, aren’t affected by this, although they give less power in the first place as they’re so hot.
