You may have heard of the term “solar farm”, which on the face of it may evoke visions of a farmer working a field of sheep. While a solar farm may very well have some sheep, it’s actually just a way to describe a solar power station – a large-scale implementation of solar panel technology to provide a large amount of electricity to local users.
I think one of the reasons we think of them as “farms” is because sunlight is effectively harvested. We aren’t generating power in the sense that a coal or nuclear station is. These power stations release energy that’s caught inside a fuel source, while solar farms capture energy that’s freely available. Whatever the reasons the term “farm” is used, that’s what everyone uses. So now we know something about the name for these power installations, but how do they actually work? Let’s start by looking at who actually owns and runs these farms.
Who Can Own a Solar Farm?
Most really large solar farms are owned by the government. They are used as a way to diversify the energy mix of a country – reducing the need for oil, coal, and nuclear power.
Obviously, private citizens can get together and pool their money to create their own solar farms. A large, centralized solar farm will generally provide more watts per dollar than multiple small home installations. These so-called “community” solar farms will take investment from anyone and then add or allocate power output in line with your investment.
For the individual who wants to shift to solar, but doesn’t care about true grid independence, a community solar farm represents a great way to get in on the action. It also means you don’t have to go through all of the hassle that comes with a home installation of solar energy. You don’t have to cut down trees, get zoning permission, or do anything, really. Just sign on the dotted line and take advantage of economies of scale. This is mass-produced solar for the people – at least in theory.
How Big Are Solar Farms?
While the definition of a solar farm says that it is a “large scale” implementation of solar power, just how big is that? I guess that’s like asking how long a piece of string is – the answer is that it depends. I’ve seen a ballpark range of between one and one hundred acres. Clearly a solar farm is going to take up more space than the average backyard has to offer. It will be a large, open piece of land. Rural farmland is often a great candidate for solar farm use. Obviously, you aren’t going to see solar farms in cities because there simply isn’t any space, other than on the roofs of buildings.
Solar farms can, however, be as big as you like. There are farms that are thousands of acres in size. It all depends on how much land there is, the cost of making power this way, and if anyone wants to buy that power.
How Much Power Can they Make?
How much power you can get out of a solar farm (per unit of covered landmass) depends on many factors; generally the same ones that matter for small home installations too. How much sun does that piece of land get? What sort of PV panels are being used? How hot does the environment get?
In a country like Britain, which isn’t exactly known for its sunny weather, solar farms have been a great success. In general you need about 25 acres of land to make five megawatts of power. That’s enough to power about 1500 homes, or so I have read. It sounds like a lot of space; compared to something like a nuclear power station, solar is many times less dense. However, one thing we have no shortage of in the world is wide open pieces of land; especially land which isn’t good for any other use like farming or construction.
How Much Does Solar Farm Power Cost?
The key number when it comes to how much solar energy costs is the price of one watt of energy. To give you some perspective, the cost of generating 1 watt of energy for a home installation is between two and four dollars. That’s the average cost in 2018, but by the time you read this it could be significantly lower.
In comparison, a solar farm can make one watt of energy for one dollar. So if you put the same money into a solar farm you get between two and four times the electricity out. You can see why communal solar farms are a better investment from a cost perspective!
Of course, if we take into consideration the actual upfront cost of building a solar farm, then you better hold on to your hat. We’re talking hundreds of thousands to many millions of dollars. You of course need all that industrial-grade solar equipment, but you also need expert people to install, test, and maintain that equipment. So you need a big upfront investment as well as people to actually buy the power from you in order to pay it all back. This is why solar farms are usually created through government investment.
What About Virtual Power Stations?
A virtual power station is a computer-controlled collection of many different power generation units. So, for example, you could tie everyone’s home solar installations into the grid and then redistribute any surplus energy to other people who need it. This is a smart way to use existing solar generation owned by people as whole in a more efficient way, but doesn’t come close to the scale cost savings a proper solar farm provides.
I mentioned rooftop solar in cities as a way to sort of make a solar farm. This is actually a thing that people refer to (predictably enough) as rooftop farms. However, the types of roofs that are being targeted are huge manufacturing plants and factories – big buildings that cover thousands of square meters. The rooftop solar installation can put power straight into the business, and any surplus power can be sold to the grid or stored in batteries.
Since the smallest solar farms are generally in the one acre range, it’s not far-fetched to refer to rooftop farms. Some large warehouses or factories are about that size, and many compounds will reach that sort of area if you add all the roofs together. This is one way to address the general criticism that solar farms spoil farmlands.
How Eco-Friendly Are They?
While solar farms are obviously more eco-friendly than a coal power station, that doesn’t mean it’s all milk and honey. One of the main criticisms of solar farms built on actual farmland is that it may be better to use that land to produce food instead. Many farmers may choose to put up a solar farm instead of growing crops because it’s a more consistent and reliable source of income. On top of this, some governments provide strong incentives to help bridge the initial cost of putting up a solar farm on your land.
The good news is that when it comes to farmland used for livestock grazing, the effects are negligible. Sheep and other similar animals can graze freely between the solar panels. So the land in question can do double duty. Nonetheless, whenever anyone wants to put up a solar farm there has to be a careful impact assessment to make sure that it won’t disrupt or damage the natural environment excessively.
We also have to keep in mind that there is also hidden environmental impact from the actual manufacture of solar panels. When they reach the end of their life, they also need to be recycled, but there will still be some waste. Some scientists even think that mass use of solar panels could have climate impacts of its own, such as lowering the local temperature and inducing rain in places that were dry up to then. Since we are only now starting to embrace solar power in a big way, there is still a lot to learn about how this technology will affect the environment. It’s still going to be a huge step up from fossil fuels, but that doesn’t mean we won’t have a new set of challenges.
How Do They Store Energy?
You should read my article on solar storage for a detailed discussion of solar energy storage, but since it is integral to understanding how solar farms work, I’ll have a brief discussion on it here.
When solar energy falls on the PV panels in the farm, electricity is generated. If you don’t use it, you lose it. So the electricity from the panels either has to go into the grid where its used, or stored somehow. Home solar installation makes use of various battery technologies to store solar power. This doesn’t necessarily scale well in terms of cost or practicality. The Tesla company has, however, put up massive lithium ion power storage facilities that help redistribute peak output at times when people need it rather than when it is generated.
At this scale there are, however, interesting and cool options for storing solar power. Mechanical storage, for example, uses massive flywheels built with almost no friction and enclosed in special cases. Electrical motors spin these up to thousands of RPM. They can then get this power back by making the flywheels release their energy into generators. It sounds crazy, but it works!
Another Breed of Solar Farm: Solar Thermal Power Plants
When most people think about solar farms, what comes to mind is a field of photovoltaic solar panels. That’s not, however, the only way to collect solar energy at scale. Another approach is something known as a solar thermal power station. This type of solar power setup uses an array of mirrors to concentrate and collect solar energy at a central point. It basically works like a solar oven, but instead of cooking food, the thermal energy is stored or used to drive a steam turbine. Storage can happen by heating molten salt, which is great at keeping the heat for use later; this enables power at night.
Solar thermal power stations don’t take up as much space as solar panels, and they are more efficient at turning solar energy into electricity, by which I mean that you get more electricity from the same amount of sunlight. Concentrated solar thermal stations can be as much as 30 or 40 percent efficient. Compare this to the 20+% efficiency of modern solar panels, and you can see why this is an attractive option.
The downside is that thermal solar power stations need much more maintenance, monitoring, and overall work. All those mirrors need maintenance and adjustment, and there are more safety risks. PV panels are less of a hassle, but in desert areas and other high heat zones solar thermal stations can be a great option. Photovoltaic panels don’t like high temperatures at all, so there is a place for a variety of solar technologies to coexist.
Harvesting the Sun
The cost of solar power keeps going down, while the efficiency of the various technologies improves bit by bit. This is one of the most exciting times in modern history, where a technology whose time has come may finally free us from energy sources that are very limited and definitely highly damaging in the short term.
Ancient cultures such as the Egyptians often worshiped the Sun as a god. They may not have understood what the sun actually was or how it worked, but they understood its central role in making life on Earth possible. As modern humans we can now fully appreciate the priceless resource our sun is and how it will literally and figuratively provide us with a long and bright future.