Solar Made Simple
We'll dig deeper into PV in a later post, but to keep things simple we often just describe our focus as solar electric products or systems. By focusing on PV, we exclude other types of solar energy applications like solar thermal (using the sun to heat water or other fluids circulating in pipes), concentrated solar (utility scale reflecting of sunlight to concentrate heat), wind power (which is really derived from the sun heating the Earth's atmosphere, which causes wind), etc.
This diagram boils solar electricity down to its core. Of course the devil is in the details for any particular use, but it really helps to understand these principles because they underly all solar projects.
This is solar made simple after all, but isn't starting with the sun a little too basic? Well maybe. But seeing solar panels mounted on a north-facing roof tends to change one's mind. There is a lot more to this topic, but to keep it simple, we need sun to make solar electricity. And we'll need collectors, which we'll cover in a minute. But first, the more direct sun on those collectors, the better.
- Sunny days. The more sunny days the better. Cloudy, rainy climates mean less sun to make energy.
- Longer days. The longer the sun is up, the more energy can be made. So places closer to the equator with longer days mean more solar energy. Same thing with summer days vs. winter days.
- Direction. Collectors need to face the sun. In the northern hemisphere, that mean pointing south. As close to south as possible. The more those collectors point other directions (southwest, west, etc) the less direct sun they receive, and the less energy they produce.
- Shade. Like clouds, shade is bad for solar energy production. Depending on the equipment chosen, a very small amount of shade may really reduce the amount of energy produced (like a chimney or a branch above a roof). But some equipment can really minimize these losses.
- Angle. The optimum angle for maximum energy production varies by latitude and season. It's more complicated than this, but think flat at the equator and steeper as you go north.
Sun and the Panel
The next step in the solar PV chain is to collect the sun's energy keeping the above points in mind. How do we do this? Solar panels of course! “Solar module” is the more correct term, but most people still call them solar panels. A solar panel is really a grouping of solar cells. Those cells are what make up the grid-like pattern you see on a solar panel. You may read or hear about 36, 60 or 72-cell solar panels. Usually, the more cells means a larger panel which produces more energy.
The PV effect creates electricity in each solar cell when the sun's rays contact the silicon in the cell. The electrical current flows through ribbon-like wires that connect the cells within the panel. Those wires exit the solar panel through wire “leads” connected to terminal inside a junction box on the rear of the panel.
There are different types of solar panels. Most commonly used for a multitude of applications are the rigid style made up of silicon solar cells covered by tempered glass with an aluminum frame and an insulating back sheet. There are also “thin-film” style panels that are semi-flexible, plastic-like material that may be glued to a roof or embedded in a device. The composition of the solar cells may also vary and will certainly continue to evolve, but the standard today is silicone-based material.
So thanks to the miraculous photovoltaic effect, electricity is birthed of sunlight and silicone. Solar made simple. Got it. So you can just plug a TV into the solar panel's outlet and you're good to go right? Not quite. First, the solar panels aren't usually next to a TV (or other appliances) since the best direct sun is often on top of a house or mounted on a pole or rack away from the house. So the electricity generated from that panel needs to be routed to where it can be used. That happens through conductors or “wire” that connects to the leads of each solar panel. Often there is more than one panel involved, which we call an “array” that need to be wired into groups called “strings” in order to match the voltage and current from the array with the right equipment downstream.
But not just any old wire will do. It has to be rated to carry DC current at certain levels at certain temperatures in certain environments (hot roofs vs underground). So what is DC current or electricity? DC is “direct current” electricity. It's direct because electrons flow in only one direction. It's also the form that batteries store. But it doesn't travel long distances well. On the other hand, AC current (“alternating current”) is a form of electricity where the electrons alternate directions and travels over long distances without the losses of DC current. Accordingly, utilities specialize in producing and supplying AC electricity to homes and businesses to power almost everything.
Storage or Work
Once produced and moved from the solar panel, DC electricity must either be stored or put to work. The options really boil down to these:
- Option 1: DC electricity directly connected to power a DC appliance (or “load”)
- Option 2: DC electricity stored in a battery to power a DC appliance later
- Option 3: DC electricity “inverted” or transformed into AC electricity to power AC loads
- Option 4: DC electricity inverted into AC electricity and “sold” back to the utility grid
- Option 5: DC electricity stored in a battery, then later inverted into AC electricity to power AC loads
Option 1 is the most simple, but of limited utility. “PV Direct” systems only supply power while the sun shines. And the loads must be able to handle variable power depending on the strength of the sunlight and shade. Well water pumps and attic fans are typical examples.
Option 2 is the typical system for RVs, boats, and other remote “off-grid” power needs (lighting, remote pumps, instruments, telecom, sensors, etc).
Option 3 & 4 happens in a typical “grid-tied” residential system. The house uses solar energy to power AC loads while the sun shines or sells it back to the grid if not needed.
Option 5 is the most complex scenario and is the system used for off-grid homes, or grid-tied homes with battery back-up systems (a/k/a hybrid systems).
Knowledge is Power
While the sun is certainly power, so is knowledge! Knowing the basics of solar electric systems, you can make better-informed plans and decisions about how to employ solar systems for your project. You can have more efficient phone discussions with us about what are looking to do. You can better evaluate a contractor's proposal. And frankly, you stand a better chance of being happy with the end result.
- Tags: Solar Basics
- Dan Baldwin