How to Implement Solar Electricity
As discussed in Step 1, there are several different applications for PV systems. Which system is right for you depends on your particular situation and RE goals. Due to available incentive programs and the simplistic nature of batteryless grid-tied PV systems, they are the most common type of system installed in the United States today. Here is a checklist to see if this type of system might work for you:
If this describes your situation, then a batteryless grid-tied PV system could be the perfect fit. Compared to their off-grid counterparts, batteryless grid- tied systems are simple to understand and design, with only two primary components: PV modules and an inverter that feeds AC electricity back into the electrical system to offset some or all of the electricity otherwise purchased from the utility. These systems are cheaper, easier to install and maintain, and operate more efficiently than battery-based systems of comparable size. Their main drawback is that when the grid goes down, they cannot provide any energy for you to use. If the grid in your area is mostly reliable and outages are infrequent, these systems can offer the best payback for the least price.
The primary goal of a grid-tied PV system is to offset all or some of your electricity usage. Yet the first step in going solar is not sizing the PV system, but reducing electricity usage through conservation and efficiency measures. Once energy-efficiency and conservation measures have been implemented, you’re ready to size a PV system to offset the remaining energy usage. Annual energy use figures can be requested from your utility, and these values can be used to determine the PV array size. However, there are a few other considerations that will impact PV system size. In residential areas especially, a primary constraint to PV array sizing can be the size of the available shade-free mounting area. PV modules can be mounted on a roof, the ground, or a pole (which includes trackers). Regardless of which mounting method is used, the shade-free area, minus clearance needed for maintenance or roof setbacks required by local fire department guidelines, will limit how large the array can be. In the case of roof-mounted systems, typically 50% to 80% of a roof plane will be available for mounting PV modules. Often the most confining consideration is budget. Currently (early 2012), the cost per installed watt of residential PV systems ranges from $5 to $8, which includes everything—modules, inverter, disconnects, racking, wire, and conduit to taxes, shipping, installation labor, and permitting. Reducing the cost is the uncapped 30% federal tax credit. Additionally, many individual states, municipalities, and utilities offer rebates that can further offset a PV system’s cost. The Database of State Incentives for Renewables & Efficiency (DSIRE; www.dsireusa.org) organizes incentive programs by state and program type, making incentives easy to research.
Off-Grid Systems: Living off the grid is a romantic ambition for some; a practical necessity for others. But whatever your motivation for off-grid living, cutting the electrical umbilical cord from the utility shouldn’t be taken lightly. Before you pull out the calculator, size up the realities and challenges of living off the grid. Designing a stand-alone PV system differs substantially from designing a batteryless grid-direct system. Instead of meeting the home’s annual demand, a stand-alone system must be able to meet energy requirements every day of the year. Determining the home’s daily and seasonal energy usage, along with considering the daily and seasonal availability of the sun, allows designers to estimate the PV array and battery bank size, and charge controller and inverter specifications.