The Call, Column 53 – Power From the Sun

12 11 2016

(August 14, 2016)

The Urban Farmer

Power From the Sun

Solar energy is hands down my favorite renewable energy. I find a simple beauty – not to mention the efficiency – in capturing the sun’s energy directly from the source. What’s more, solar energy systems need few moving parts, they are scalable from a single panel or residential rooftop to a large-scale solar farm, and have a really cool look to them that increases the value and curb appeal of a home.

Today, we’ll talk about the technologies that have been developed to directly capture solar energy – solar photovoltaic and solar thermal. I’ll give you a briefer on the science, and then discuss the current state of implementation and ways that we, as urban farmers, can get involved. Let’s begin!

What we call “light” – or more generally, electromagnetic radiation – is really a stream of little, condensed packets of wave energy called “photons”, which exist as particles in only the loosest definition of the word, but still contain lots of energy. The amount that a particular photon contains is inversely proportional to its wavelength, meaning that ultraviolet radiation contains more energy than visible light, which itself contains more than infrared radiation.

The sun outputs a very specific spectrum of light, which is a combination of visible (the rainbow) and non-visible (infrared, x-rays, ultraviolet, etc). That energy spreads away from the sun in all directions, and a small fraction of it gets directed at half of the outer layer of the Earth’s atmosphere (depending on the time of day). Some of this is filtered and dispersed by the atmosphere, and when all is said and done, roughly 1000 watts hit a one square meter area of ground in direct sunlight. Remember, a “watt” is a measure of the speed of energy transfer or usage, and your phone uses probably 3 or 4 watts while it is on. That 1000 watts/square meter is quite a lot!

The question we’ve been asking ourselves for thousands of years is: how do we make use of that energy? Agriculture was our species’ first big answer to that question, when we figured out how to deliberately capture the sun’s energy in a chemical form (“Calories”) that we could use to fuel our bodies, feed our animals, and heat our homes.

We’ve developed a variety of different technologies since that time, which have culminated with the two centrally important methods for capturing solar energy that I mentioned above: solar photovoltaic and solar thermal.

What’s known collectively as “solar thermal” is really a group of different technologies and building methods, unified by the underlying goal of capturing sunlight as usable heat energy. This idea is as old as human society, and is really easy to see in day-to-day life: leave a bottle of water out in the sun for a few minutes and observe the change in its temperature (don’t drink it after); or take note of which rooms in your house are the warmest when all heaters and air conditioners are shut off (hint: it’s the rooms with exterior walls with direct exposure to the sun).

There are a couple of basic types of solar thermal technology that are used all around the world. Solar architecture takes advantage of that “south-facing-room” effect, designing buildings that more effectively absorb the sun’s warmth in the winter, and do not absorb it in the summer. The knowledge that underlies this is as old as construction, but has recently made a comeback in the developed world.

Concentrated solar thermal is an up-and-coming technology, which utilizes mirrors and lenses in a variety of geometries. These concentrate sunlight into super-heated steam, which is most often used to drive a turbine and produce electricity. These require large areas and lots of direct sunlight, which makes them good candidates for desert development.

And of course, there is solar hot water. This is one I’ve mentioned before, when I visited Greece back in summer of 2014 and made note of the fact that nearly every house has a system of this type on its roof. This technology captures the sun’s energy by running water through a specially-designed (though easily made-at-home), dark-colored collector panel. The water heats up, and is stored for use throughout the day, either in a boiler or a separate tank that is often part of the standalone unit. These systems are hugely effective at producing large amounts of very hot water, which in turn is an effective way to store heat. There is a similar type of system that uses air instead, and which sometimes takes advantage of the way that air expands when it heats up.

Solar photovoltaic is a much more complex – but also more versatile – technology, which turns sunlight into electricity. Solar cells are thin sheets, usually made of silicon with small amounts of other elements deliberately added in, that turn light particles from the sun (photons) into electric current. When solar cells are connected together correctly, and then through output wires to some other electric circuitry, they form what are commonly known as solar panels.

Solar photovoltaic panels are the sleek, dark blue fixtures that I’ve been delighted to see popping up on houses in our area. The commercially-available ones are around 20% efficient – a similar fuel efficiency to the gasoline engine in your car – which means that, with an accompanying bank of batteries (so the energy can be stored) or a connection to the electric grid (so it can be sold back when it isn’t being used), the rooftop of a typical residence can supply 100% of that house’s electricity needs!

There are very few solar hot water fixtures in the United States, but I’ve started to see quite a few photovoltaic arrays on roofs in our area, and know of huge solar farms (fields of panels) that have been, or are being, built as I write this. We are  pretty far behind the energy-conscious folk of Europe, but the next few decades will be exciting as the solar industry in the United States grows by leaps and bounds. So what can we, as urban farmers, do to participate?

Passive solar architecture is probably the easiest way that we can take advantage of this amazing renewable resource. At its base, it’s as simple as knowing which curtains or blinds to open – and which to keep closed – depending on the season and outside temperature. There are retrofits that can be done to your house – adding insulation, changing your windows, sealing points where it’s open to the outside air – that increase its overall energy efficiency, partly by taking advantage of passive solar architectural design. And of course, if you’re in the process of building a new house, you’ll reap huge dividends by incorporating passive solar architecture into the design!

Solar thermal systems are another really good way for urban farmers to take advantage of free solar energy. They require a little more overhead – either having to buy the panel and water tank or building the system yourself, and then installing it – but when done right, they are capable of providing hot water even in the dead of a New England winter. There is a lot of information on the internet about building or buying these systems, and I encourage you to check it out.

And then, there are solar panels. It is my view that every new house should have solar panels installed on the roof – that’s how promising I think they are. There are quite a few companies that you can contract to install solar panels on your roof, which will allow you to pay them back simply by using the money you would otherwise have spent on your electric bill. In this way, your personal solar array is paid off in less than a decade (and is fully-functional for at least 25 years), without having any additional outlay of money. There are a variety of different financing programs, and

Climate change is one of the most serious threats that we face as a species, and solar energy is and will continue to play a pivotal role in solving it. These types of renewable energy systems really are one of the most democratized solutions to climate change. For a small investment of time and money, almost anyone can take advantage of this free, plentiful energy source, powering their lives while keeping fossil fuels in the ground.

My column appears every other Sunday in The Woonsocket Call (also in areas where The Pawtucket Times is available). The above article is the property of The Woonsocket Call and The Pawtucket Times, and is reprinted here with permission from these publications. These are excellent newspapers, covering important local news topics with voices out of our own communities, and skillfully addressing statewide and national news. Click these links to subscribe to The Woonsocket Call or to The Pawtucket Times. To subscribe to the online editions, click here for The Call and here for The Times. They can also be found on Twitter, @WoonsocketCall and @Pawtuckettimes.

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