Photovoltaic (PV) Array Design
The price of photovoltaic (PV) systems have decreased significantly over the past decade, mostly due to the decline of PV panel costs. However, the costs associated with inverters, PV panel racking, installation, and other ‘balance of system’ expenses has not declined proportionally with PV panel costs. Therefore, these balance of system costs are now making up a larger share of the total installed cost for a PV System. To address these costs, NexusHaus will utilize a simplified panel racking system that can be quickly assembled and minimizes significant roof penetrations. This provides a number of benefits as it allows for easier and faster installation on-site (reducing install costs) and reduces the number of penetrations through the building’s skin (reducing thermal breaks and potential water barrier issues).
Positioning and Sizing the System
The positioning of the array – approximately 10 degrees – maximizes overall production for the available roof area by optimizing panel tilt and available panel spacing. While the system needs slightly more panel area to make up for the less-than-ideal angle, the idea is that the balance of system cost savings make up for the added panel expense.
In keeping with affordability as a goal, the system is sized to meet the electrical needs of the house rather than installing the largest system for the space available. In conjunction, mechanical equipment, lighting, and appliances have been chosen to reduce energy needs further reducing the overall energy consumption, and size of the PV array needed. Based on the team’s calculations, the right-sized array is approximately 8.1kW DC (approximately 7kW AC), which will provide sufficient energy for the year.
How the PV System Works
Micro-inverters take the direct current (DC) generated by the PV solar cells in the panels, and convert it to alternating current (AC) at the panel level rather than having a single inverter for the entire array. These integrated inverters allow each panel to operate independently, minimizing the impacts of partially shaded panels or arrays—important for a system that will ultimately be installed in a residential neighborhood. Additionally, using micro-inverters minimizes connection complexity and wiring costs, which in turn helps further reduce the overall installation time and costs.