For the last year I’ve been researching a grid tied solar electric system with batteries for night and backup. Overall solar is affordable but the battery cost, nope, batteries will almost double the cost. I did find these awesome lithium batteries on ebay, they’re 12V and 40 amp hour, two of these in parallel would be fantastic. You can find them as cheap as $150 a battery. They’re used BUT a solar guru on YouTube tested two random ones and they were still above %90 capacity. Some batteries when you buy them brand new don’t have %90 capacity. the batteries are called Valence, they’re used in medical devices.