As soon as your utility approves your interconnection, an installation commonly lasts a single to a few days for residential rooftop; lengthier for ground mount. Regional Rebates and Incentives: Some area utilities and municipalities supply more rebates and incentives for solar installations. It’s really worth checking with your local utility https://www.slideshare.net/slideshow/how-solar-panel-installation-in-wa-can-reduce-your-electricity-bills/275722304