Residential Solar Photovoltaics - a Primer
Residential Solar Photovoltaics - a Primer
As more municipalities, cities, states, and provinces get into the renewable energy stream, interest is growing. Time for a quick primer on residential sized photovoltaic (PV) systems.
What is Photovoltaic?
Solar can be used to heat water, or generate electricity. If you use solar to heat water, it’s called solar thermal. If you use solar to make electricity (directly from the sun), it’s called solar PV. Yes, it is possible to heat water with the sun and use the hot water to turn a generator and make electricity - but that is only done on large scale systems, not residential. So… photovoltaic is making electricity, directly from the sun, using solar modules. Most of these solar modules are made from silicon, though other chemicals are available.
Solar Modules
The solar modules or panels, are the devices that convert sunlight directly into electricity. This electricity is Direct Current (DC), not Alternating Current (AC), as used in your home. The panels come in various sizes and are rated by the amount of electricity they will produce per hour, measured in watts - 30 watts, 100 watts, 200 watts, etc. You string the panels together, in series or in parallel, to increase the amount of power you produce - just add the watts together - 5 panels of 200 watts each, would produce 1000 watts, or 1kW, of peak power (the maximum power).
Mounting Systems
For a residential system, most solar panels will be mounted on the roof of your home. The panels need to face the sun, thus they will be pointed south if you live in the northern hemisphere. Or north if you live “down under”. You also need to point the panels UP at the sun. As a general guideline, you till the panels up, at the same angle as your LATITUDE.
If you have the space, another option is to mount the panels on the ground. They can be static mounted (don’t move) or you can mount the panels on trackers. The trackers and be single axis (east-west) or dual axis (est-west and up-down). A dual axis tracker can increase your power output by 30% or more. Thus, though they may cost a little more to install, they usually more than pay for themselves.
Balance Of System
As mentioned, a PV panel will produce power as Direct Current. If you are charging Batteries, you’ll need a Controller to manage the charge on the batteries. You’ll also need an Inverter to change from DC to AC current, and a few other items. We’ll list some of the parts here:
Charge Controller
Manages the charge of your batteries, IF you have batteries. Cuts off the power from the PV panels, once the batteries are fully charged. Not that wind turbines work differently than PV panels and you need a different charge controller with a wind turbine…. one than transfers the power from a wind turbine into a DUMP load. PV panels don’t care if the load (batteries) just disappear, as they stop sending current if there is no load.
Batteries
Batteries are not always required. If you have a Grid-Tie system, your solar system will feed directly into the power grid. This saves you from purchasing batteries. However, if the grid goes down, your house will be black just like the rest of the neighbourhood. If you want power when the grid is down, you need batteries. You will also need a separate fuse panel for your battery serviced power. This will allow you to power a few important items - fridge, furnace fan, etc., when the grid is down.
Inverter
The inverter converts power from DC to AC. For grid-tie systems, the inverter usually includes a DC Disconnect and possibly some fuses.
DC Disconnect
This breaker switch allows your solar system to be isolated from the grid. If your electrical utility company needs to work on the lines, they will disconnect your system, so no unexpected voltage travels down the line.
Combiner Boxes, Fuses, Wire, Ground Lugs, misc items…
You’ll need to connect the system together. Thus you’ll likely need some combiner boxes to connect the panels together. These boxes often hold the lower voltage DC fuses as well. Your wiring will be selected to reduce overall electrical loses, based on voltages, distance travelled, etc. Each panel and most of the components will also be connect to Ground.
Put everything together and you have yourself a personal power system. Not only can you make electricity for your own use, but more and more states/provinces are coming out with Feed-in Tariffs (FiT). A FiT will pay you to produce electrical power and feed that power into the electrical grid. In Ontario for example, the FiT will pay a residential customer with up to 10kW of solar panels, 80.2 cents per kwh produced. Thus, your residential solar system, can also be a nice source of income!
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