Additional Solar Panels Research

The current solar panel is a 250W, 24V panel. To upgrade the system correctly, we need one or more 24V panels. Around 750 additional Watts would be ideal. The current inverter's maximum continuous battery charger input is 3600VA. Monocrystalline solar cells are made from a single silicon crystal which makes them up to 20% efficient.

Monocrystalline Solar Panels - $ 192 - NEWPOWA 200W 24V MONOCRYSTALLINE HIGH EFFICIENCY SOLAR PANEL

Polycrystalline Solar Panels - $ 285 - Renogy 270 Watt 24 Volt Polycrystalline Solar Panel

Pricing

We can try to claim solar rebates, a tax refund, to lower our costs. North Carolina's solar incentives reach from property tax exemption to refunds per watt. Duke Energy offers a $0.60/Watt rebate for systems up to 10 kilowatts.

On solarize-nc.org, they mention the following about tax credits and deductions in North Carolina:

Unfortunately, the North Carolina solar tax credit (which paid back 35% of the installed cost of your system), expired on December 31, 2015, so it is too late to take advantage of that tax credit. (For those whose solar was installed before Dec. 31, 2015, your state credit can be used over five years, but can only account for 50% of your tax bill in any one year.) The Federal solar tax credit, which was scheduled to expire December 31, 2016, has now been extended through 2021 as part of the spending bill passed on Dec. 18, 2015. From now through 2019, it pays back 30% of the installed cost of your system (assuming you pay enough tax to use it up). The credit drops to 26% in 2020 and 22% in 2021. After Dec. 31, 2021, the Federal tax credit expires for residential customers and drops to 10% for commercial installations.