In an interview with Wired Magazine, Microsoft Founder Bill Gates talks about work being done to meet the world’s energy needs. The wide ranging talk covers the public safety issues of power generation (including coal and nuclear plants) as well as the economics and politics of energy.
Mr. Gates dismisses rooftop solar as “cute” – a deep insult in the nerd-world implying that it’s not a serious solution. He suggests that the only practical use of solar energy would be in large desert installations and points out that there’s a problem with generation during the nighttime periods:
I think people deeply underestimate what a huge problem this day-night issue is if you’re trying to design an energy system involving solar technology that’s more than just a hobby. You know, the sun shines during the day, and people turn their air conditioners on during the day, so you can catch some of that peaking load, particularly if you get enough subsidies. It’s cute, you know, it’s nice. But the economics are so, so far from making sense.
Again with the geek insults, in the tech world “hobby” is another cut saying it’s not a practical endeavor. In reality rooftop solar makes economic sense even now in parts of the world with expensive electricity like California and Japan. Because I saved money by installing my rooftop PV system myself, I’m already at “grid parity” (the cost to generate electricity is the same as the cost to buy it from the utility) so I’m not spending one extra dime to harness the sun’s power and reduce my carbon footprint.
Of course, Mr. Gates may be coming from a biased perspective: he’s a major investor in a company that’s promoting a new type of nuclear reactor. It’s a bit harder to be impartial about a race when you’ve got money riding on one of the horses.
In reality, there are currently two different solutions to the day/night problem with power generation. In large-scale desert solar installations, mirrors are used to focus the sun’s light onto a collector. Rather than create electricity directly as in a photovoltaic system, the power is used to heat a liquid in an enclosed system. That liquid (usually molten salt) is then used to heat water and spin turbines to produce electricity. To spread out the power generation over 24 hours, the molten salt can be stored in large tanks for use during the nighttime.
Another method for taking excess power generation and banking it for later use is gravitational storage. Also referred to as Pumped-storage Hydroelectricity, the system takes electrical power and uses it to pump water uphill into a holding pond. When more power is needed, the water is released downhill through a turbine generator. This works just like a hydroelectric dam except that instead of harnessing a river, water is actually pumped uphill to fill the reservoir. (Yes, it sounds odd but this technique is in use today to balance loads on the electrical grid)
While solar power is still improving, it’s already a practical means of electrical generation and one of the least harmful to the environment. Local rooftop microgeneration is a practical, reliable and cost effective way of meeting our increasing power needs while lowering our impact upon the environment.
In my area, even after you’ve hauled all the panels up onto the roof and connected them to the system wiring, there’s still more work to be done before you can throw the big red switch to the “ON” position. Before you connect your solar array to the grid the system it needs to be inspected (and approved) by three agencies:
The city fire inspector The fire department wants to make sure that you’ve followed their guidelines that allows safe access to the roof by emergency personnel if they need to respond to an emergency.
The city building inspector The city needs to inspect and approve of the quality of the mechanical work (roof mounting points and racking system) as well to ensure that the electrical work is up to code.
The utility company inspector The utility company also wants to look at the system’s electrical work and components to make sure there’s no potential of damaging the neighborhood’s grid.
Firefighters have a unique interest in the design and installation of a rooftop solar system. In the event of a structure fire the first responders will usually climb onto the roof to assess the situation and often cut large holes into the roof directly over the blaze to vent the heat. Solar installations that have wall-to-wall solar panels make access difficult or impossible. One fire official told me “At some point we may look at a roof (with an out-of-code installation) and declare the structure a loss because we can’t fight the fire. We’d hate if that happened”
Not only is physical access to the roof an issue but there’s also the matter of live wiring on or near the roof. If the fire happens during the daytime those panels will be generating electricity and the circuitry on the roof will be energized with potentially harmful voltages.
As a result, CalFire (the state fire agency better known for fighting wildfires during our dry summers) came up with a set of guidelines for designing “firefighter safe” solar installations. The city of Santa Rosa recently adopted those regulations and any new installation will need to conform to those rules. You can look at the local adaptation of the CalFire rules here
As I mentioned in the first video, the rules for access are straightforward: No panels within three feet from the ridge of the roof to allow ventilation and leave a three foot access pathway from the ground to the roof. This means no more wall-to-wall coverage with PV panels but that’s pretty easy to incorporate into any layout. Here’s my roof:
Leaving the three foot access path turned out to be pretty helpful during the installation; it gave us plenty of room to work when carrying those large panels. I can imagine a firefighter in full gear on the roof needing just as much room to maneuver. On the right is a picture of the ridge setback of the same array (click on the photo to see full size):
The electrical concerns are just as easily addressed. Any current solar system design will include a disconnect switch to remove the rooftop array from the household wiring. This is handy for keeping the system offline during installation and makes for easy disconnection for repairs or in an emergency. The codes call for clear labeling on the disconnect switch and a warning label on the main meter panel:
The last piece of code calls for specific labeling for the conduit. There are two reasons for this:
For single-inverter systems, even after the disconnect switch is thrown the DC wiring coming down off the roof is still energized. It’s no longer connected to the inverter and no current is flowing but the wires in that conduit are charged to hundreds of volts and any breach of the conduit with a firefighter’s chainsaw or axe will cause a massive short-circuit.
Conduit on the roof makes for a tripping hazard. For cooling purposes the standard construction technique calls for a standoff of an inch or more to keep the conduit up off of the surface of the roof. The fire code calls for reflective warning labels to be put on the raised tubing to reduce the possibility of tripping.
So there you have it – the rules are simple to understand and have a very important purpose: to make it easier for emergency personnel to safely protect your house if a fire should break out. Even if your local jurisdiction doesn’t have these setbacks and labeling requirements you may want to consider following them when designing your solar PV installation.
Yesterday we hauled the panels onto the roof and wired everything up – woo hoo!
While I’ve done nearly all of this project by myself, there are certain parts of a home solar installation that aren’t D.I.Y. – like hauling large panels around safely and efficiently. Everything else about this project I’ve done on my own: the measuring, planning, mounting the feet, hauling rails up to the roof, even the roof flashing – it’s all be a one-man operation. The only part of the project that was contracted out was the service panel replacement; that really needed a licensed professional. The very last step of the project is realistically a four-person operation: two on the ground and two on the roof. While they’re not unmanageably heavy the typical solar panels are quite ungainly for a single person to mount on the roof.
Fortunately I’ve got great neighbors; everyone was excited about the solar project and were eager to help out. The other “fix-it” types were interested to see how solar works and were quite surprised by how simple the whole process was.
I built a ladder hoist to get the panels up to the roof. It’s basically a frame that holds a solar panel which rides up a ladder. The inspiration came from an article in Home Power magazine. I modified the original design a bit by mounting an electric winch on the bottom of the ladder to do all the heavy lifting. I also added a latching system to keep the panel secured (you’ll see the “ears” lift once the hoist gets to the top of the ladder). Here’s a video of the hoist in action:
Total cost of the hoist was right around $100. Not bad compared to the price of one dropped panel (or a visit to the chiropractor after a day of heavy lifting). With two people on the ground loading up the hoist and two on the roof attaching the panels to the racking the job went quickly.
The first Solaricious video is now online! The series will take you through the process of designing and installing a solar PV system on your roof.
The first installment looks at how to take a survey of your roof so you can find the best configuration for your panels. It also looks at potential issues to keep an eye on and has some helpful tips on array placement.
More videos will follow to document every step of the process from buying the components to connecting to the utility grid!
Things have been hopping over here – the hardware has been arriving and I’ve spent more time climbing ladders than sitting at the keyboard. When I started my solar PV project I decided to make this website to both document the work I was doing and to help serve as a resource for other people thinking about a similar undertaking. In a sense I was turning one project into two!
Somewhere along the line I ended up turning two projects into three. I’m a visual learner; watching someone perform a task helps me understand much faster than reading about how to do a job. I’ve got a little bit of video experience and a camera that takes decent video so I decided to shoot a series about installing solar PV systems (and starting project #3…)
Now I’m working all three projects in at the same time – gathering resources for the website and taking video of the work while I’m actually doing the work! On the plus side, while I have to carry the camera equipment both up and down the ladder, all the PV hardware is only going in one direction – up!
The first video is finished (link to appear shortly), progress is being made on the roof (standoffs installed and flashed, rails next) and the panels arrive tomorrow (photos to follow, of course).
While the Australian rock band AC/DC are often described as “powerful” and “electric” they aren’t the topic of discussion today – instead we’re talking about the two common forms of electrical delivery and why they’re important to your solar photovoltaic installation. The band’s name does have an electrical origin though, they came up with the idea when they saw a label on the back of a sewing machine that said “AC/DC” meaning that it could operate from either alternating current or direct current.
So what is the difference between alternating current (AC) and direct current (DC)?
DC is the simpler form of electricity where there is a constant electrical potential (voltage) that moves electrons through a circuit in a linear fashion – much like water flowing through a pipe. DC voltage is found in batteries which commonly range from 1.5 volts (AA batteries) to 12 volts (automobile batteries). DC voltage can be generated in a battery through a chemical process, by a generator (like the alternator in your car) and by a photovoltaic cell. In a PV cell, photons knock electrons from one layer of a silicon semiconductor down to another, “pushing” them forward through the circuit.
AC works more like a wave, with electrons moving back and forth in the wire depending on the potential of that moment. The voltage driving the electrons continuously changes from positive to negative and back again; the frequency of the change is commonly measured in cycles per second (Hz). In the United States, the common line voltage is 120 volts cycled at 60 hertz (120V AC, 60 Hz) though some high power equipment is run at 240V AC. AC voltage is most often created using a rotating generator. Power plants (coal or nuclear) boil water to make steam that turns a turbine, hydroelectric and wind power also come from turning a generator using mechanical energy.
AC and DC power are not interchangeable. If you connect a device designed for AC usage to a DC power source (or the other way around) you will most likely have a front row seat to a display of smoke, sparks and melted components. If you’re lucky a fuse or circuit breaker will attempt to protect the device.
Most of the small devices in our modern life use DC power (cell phones, computers, flat screen TV’s) but the power that comes out of the wall socket is AC power. The solution is a power adapter – those bulky “wall warts” you plug into the wall convert the electricity from one form to another. In some instances like computers or televisions the adapter is built into the device and is usually referred to as a “power supply”. All of the parts inside your computer (PC or laptop) from CPU to memory to hard drive use DC power and need a power supply to translate the wall socket’s AC power into DC power. Many of the larger, “old school” devices in your home (toaster, air conditioner, washing machine) require more power and are designed to use the household AC directly.
Edison vs. Westinghouse
Why don’t we use DC power so we don’t need adapters and power supplies? Well, we almost did. The earliest form of DC electricity known is the Baghdad Battery, a simple chemical battery dating back to roughly 250 BC. In more (relatively) modern times, Thomas Edison built a network of DC electrical generating stations in the 1880s. The problem was that the voltage dropped off rather quickly as the current moved through the wires. The power plants needed to be less than a mile from the customer. Raising the voltage would solve the problem but it’s difficult to convert high DC voltages to low DC voltages – even more so in the nineteenth century! The answer to the transmission losses turned out to be high voltage AC power. Losing ten volts per mile isn’t a problem when you start out with a hundred thousand volts but it’s a deal breaker when you’re using 250 volts. Edison’s problem was that he owned the patents on DC power generation and distribution and stood to make a lot of money if the country adopted DC as the standard. George Westinghouse, his chief business rival, had bought the patents for AC power generation from Nikola Tesla and was lobbying for AC power. Edison fought against the AC system but eventually lost out to the more efficient way to transmit power from the generation stations to the home.
AC power can be converted from one voltage to another by using a simple transformer. Electricity is generated at the power plant, stepped up using a transformer to hundreds of thousands of volts AC for transmission across the country (via “the grid”), stepped back down again to low thousands of volts to distribute around neighborhoods and stepped down again using transformers on utility poles to 120 volts AC for delivery to your home. System wide the power loss is quite minimal, around 6%, even though you may live hundreds of miles from the nearest hydroelectric dam or coal-fired power plant.
What does this have to do with solar power? It all goes back to something I mentioned earlier – solar photovoltaic cells generate DC voltage. That doesn’t work so well when our house wiring uses AC voltage. That means if we want to use PV panels to run our homes, we need to change the power from DC to AC. Fortunately with modern electronics and circuitry we can efficiently convert from DC to AC using a device called an inverter. An inverter does what a cell phone’s power adapter does but in reverse, it takes the steady DC current coming from your solar panel and changes it to the regular alternating current used in your house. In general inverters are pretty efficient, losing only 1% to 5% of the power during the conversion.
Types of inverters
There are a number of different types of inverters depending on the intended application. The major types found in home installations are:
Off Grid Inverters – As the name suggests, off-grid systems aren’t attached to the local utility company; these are usually vacation homes or buildings in remote locations. Solar panels are used to charge up a bank of batteries and the inverter draws power out of the batteries to generate AC electricity. The battery storage system can come in pretty handy if the off-grid system is expected to be used at night.
Grid Tied Inverters – Here there are no batteries involved. The DC power from the array of solar panels is combined together and passed to the inverter. The output of the inverter is connected to the house wiring and, through the meter, the utility company. If the panels generate more power than the home is currently consuming the balance is sent to the grid; power flows “backwards” from the home to the utility where it is used to power other homes nearby.
Grid Tied Battery Backup Inverters – This is a hybrid of the two previous systems. The inverter is connected to the utility company but there are also batteries being charged by the solar cells. If the power company experiences a blackout the inverter will continue to provide power for the home until the main power is restored (or until the batteries run out)
Microinverters - A relatively new product, a microinverter is as the name suggests – a small inverter. While older solar installations had a single, large inverter (sometimes weighing hundreds of pounds) some newer setups use a small microinverter at each solar panel. The electricity is converted from DC to AC up on the roof and integrated into the household power using standard wiring. Generally microinverters are more efficient and easier to install than single, large inverters.
There will be more articles discussing inverters in the future. After the solar panels, the inverter is next largest piece of a solar installation and often represents 20% of the system cost (compared to 60% for the PV panels) Choosing the right inverter for your project is possibly the most important decision you’ll make during the design of the system.
When I went to Santa Rosa City Hall today to pick up my “Solar PV Rooftop Installation” permit, a plaque placed at the entrance caught my eye. It seems that Santa Rosa is one of 25 cities in the US that’s participating in the Department of Energy’s Solar America Communities project!
The DoE is coordinating with leaders at a local level to encourage the adoption of renewable solar energy across the country. Many of the 25 cities are much larger (most have NFL or NBA teams) but Santa Rosa and Sonoma County are doing their part to lead the way. According to the website, the city was placed at #5 in the nation’s top ten green cities in National Geographic’s Green Guide 2006.
To help encourage photovoltaic installations, the city has streamlined the permitting process and conducted special training for building inspectors to familiarize them with the technologies and applicable building codes. They’ve also established a Clean Energy Advocate to help homeowners with conservation measures including Solar PV and Solar hot water systems. The County of Sonoma has set up a special development fund to help homeowners make their homes more energy efficient.
Hopefully this program will spread to more cities across the country!
Many homeowners make the decision to go solar based on financial issues or environmental beliefs. Veteran Patrick Padilla’s experiences serving in Iraq convinced him that installing solar panels on his house would help the country’s move toward energy independence.
Solar costs are continuing to fall, as reported on Bloomberg News. Costs of industrial arrays are projected to continue falling to $1.45 a watt in the next ten years, prompting further growth in the industry. Manufacturing output continues to grow, which will only mean lower prices and more choices for consumers.
Today I went down to the city planning office to submit my application for a permit to install the solar system on our roof. I was more than a little surprised when they commented “Gee, you’re the first person to get an owner/builder (D.I.Y. without a licensed contractor) permit for a solar installation.” Really? I live in a pretty large city (150,000 residents here in Santa Rosa) and I see plenty of solar panels on neighboring rooftops. It seems like there are one or two houses on every block with a PV installation. Since you can’t install a solar power system without a permit (if you hook it up to the grid it has to be inspected by both the city and the utility) that means the hundreds of nearby installations were all done by contractors.
Is it really that difficult?
Well, yes and no. There are a number of skills required to install a rooftop solar system but we’re not talking about rocket science here. The rewards can be high if you do the job on your own. Besides the pride in doing the task yourself you’ll also save yourself quite a bit of money in the process. Here are some factors that you need to consider:
Home repair skills – If you’ve done other improvement projects around the house, regularly watch the D.I.Y. channel or HGTV and if you know you way around a couple of basic power tools, you probably have the skills to do most of the work yourself. While some of the wiring is best left to a licensed electrician, the bulk of the work requires nothing more sophisticated than a power drill and a ladder.
Project management skills - This job is going to require planning and paperwork. Lots and lots (and lots) of paperwork. Many cities are working to encourage renewable energy installations by cutting fees and permit requirements but you’re still going to need rudimentary drafting skills and you’re going to need to submit plenty of documentation about the installation to both the city and the utility.
Research skills – Unless you’re already a solar installer there’s a lot to learn about putting a bunch of panels up on your roof and plugging them into your power meter. From product selection to building codes you’ll end up doing a lot of homework before you ever climb a ladder. Fortunately there are plenty of helpful resources and I’ll be showing you where to find them.
Safety issues – More than likely you’ll be putting the solar panels on your roof. How steeply sloped is the ‘pitch’ of your roof? How high off the ground is the roof? If you’re working on a one story building with a gentle slope then you’re in luck. If you’re working on a multi-story building with a steeply sloped roof, unless you’re a mountain goat you may want to think about leaving the job to professionals.
Financing the project – Many contractors can also arrange financing for the project. If you can’t pay for the system out of pocket and if you don’t want to set up the financing yourself, hiring a contractor could still be an option. Believe it or not, there are now some companies that will actually lease your rooftop and install a solar system for free – the savings are much lower but there’s zero up front cost.
I’d describe a do it yourself solar setup as “straightforward but complicated.” When you break things down into individual parts, each step of the project will be pretty easy. When you put it all together there sure are a lot of individual pieces to figure out and keep track of. Knowing what the steps are and learning how to do them correctly is the name of the game here.
If you’ve made it this far through the article you’re probably still thinking of doing the job by yourself – good for you! This may be the most rewarding home improvement project you ever get involved in. You’ll be feeling good when you see how you’re helping the environment by installing a renewable source of energy and you’ll really feel good when you open up that electric bill and the utility company says “Hey! We owe youmoney this month!”