If you can sell your power from the panels back to EDESur, then you could offset your costs. If not, then you need batteries. You still need a way to get the DC provided by the panels turned in to AC if you can indeed sell it back to CDEE. I am not sure if no batteries are needed, but those with more solar experience will chime in.
yeah, I did the deal where you sell your excess back to edenorte. And I'll never do that again. I had to have a special solar meter that cost 24,000 pesos and a special solar inverter hooked up to it, another bigger expense but I forget how much exactly, I think between $700 and $1000. What ends up happening with this equipment necessary to sell back to the grid is that they are able to spy on your total usage, and they do. First the bill starts out with your total usage. Then they make an adjustment on the bill after two weeks based on the numbers they get from your meter and the bill goes down, and then after a year you are supposed to get yet more credit in the form of a check. I have seen some people's checks so I am fairly sure they do that but it hasn't been a year for me yet. And they don't seem to be a windfall or anything, they aren't huge.
But when I ran the numbers between what I produced and what I used and what I paid, it seems they are still cheating me and making me pay for some of the power that I am producing myself. Granted, my bill is only about 1,200-1400 pesos or so, but they are cheats, nonetheless. It should have been half that. When you're on solar, your total usage is absolutely none of their business, you should be paying for what you use from them only, but they have this goofy setup where the office in Santiago is in charge of the meter in Sosua and nobody is capable of answering questions about it, in Santiago or Sosua. They conveniently pass the buck when it comes to questions and also play stupid when the questions get too specific. Okay, maybe they're not playing! But point is, it ****ed me off and I don't want them in my business ever again.
After this latest reaming I wised up and in my new house I am totally off grid. They will never know how much I use. Eventually, I will get a hookup for emergencies but for now I feel free at last. Edenorte has been the biggest pain in my ass of living here. Just know that if you sell to the grid they are spying on your total usage and charging you accordingly. Plus Santiago is extremely slow to come to Sosua to do anything to the meter. The local office won't touch it, says it's off limits to them, Santiago people only can touch it. If you have a problem with the meter, you are at their mercy and it could take weeks or months for them to come. If you are off grid you are only at the mercy of your local electrician.
If I knew all this beforehand I would never have agreed to it. I think maybe for huge systems it may be profitable to sell back to the grid but for us people with home systems it's not worth the exponentially higher degree of fuss.