Taking It To the Street– Grid-Tie Solar Pros and Cons

solar-meter-blog  The image is courtesy of ABCsolar.com, a commercial vendor, and it explains at a glance the appeal of solar electricity as it is practiced in many states with tax credits and rebate programs. Panels on the roof feed the grid, slowing the spin of that electrical cash register and sometimes even spinning it backward, selling power back to the grid at regionally mandated rates, sometimes identical to retail.

We’ve weighed in on the topic before, but the discussion, globally and blogospherically (is that a word?), is heating up (intentional pun, not funny but vitally important). Why are the systems set up this way? Here are five points, in descending order of priority, to explain the issues.

One. The grid needs help. Our electrical infrastructure is aging and stretched, and panels on America’s rooftops spell R-E-L-I-E-F for the power stations and the distribution network during peak usage hours, which happen to coincide with peak solar production hours.

Two. The math is simple this way. Since home-generated solar electricity can be used by the grid, the simplest calculation is to use the meter in two directions, in and out, and let lower power bills be the immediate reward for an investment in renewable energy for homeowners. Different utilities reward solar power sold to the grid at different rates, and some are capped as to yearly total power contributed from a single system. My local utility, Connecticut Light and Power, uses the Net Metering System, in which the meter simply registers resold power at retail rates. Even I can do that math.

Three. Grid tied systems are less costly. At quoted rates a nominal 5000 watt grid tie system costs the homeowner about $18,000 with all rebates calculated, and some quoted prices are higher. Similar systems involving storage batteries and charging and regulating equipment would cost considerably more, and payback formulas would be even longer than they are now (12-20 years, depending on who’s doing the math). The benefit of being able to use stored power at night and in bad weather is dearly bought on those terms. And remember, when the grid goes down, the panels are cut off, even in sunny weather, for safety reasons.

Four. The good news is the bad news. Most of us have very reliable local utilities who keep us well supplied with power, reducing our need for backup systems except in unusual circumstances (storms, blackouts, local line failure). Other countries have much less reliable utilities, and rolling blackouts are a part of life even in other developed countries. The incentive for grid independence, except among those in remote locations and cantankerous old hippies with long memories, is not compelling .

Five. Living with backup systems is a pain. Most Americans worship at the Church of Convenience, so to speak, and planning power usage to coincide with daylight hours while reserving battery power for small loads at night is too much thinking. Battery systems capable of running central air and electric ranges would be huge and expensive, and Americans who spend their days out of the house aren’t able to easily plan activities like clothes drying, cooking and water heating.

So—-  for now, this is what’s possible. Solar power with storage backup is too expensive for modest budgets, too slow on payback to be an attractive short-term investment, and too short on equipment life cycle to be an attractive long-term investment. But the numbers do work: solar power pays, eventually, modestly, reliably, efficiently, philosophically, politically. For those able, in these straitened economic times, to take advantage of it, it affords a chance to  be in on the ground floor of something that all of us will eventually join. For now, you might need that home equity as a safety net for your family. There are so many other energy measures that are very much within our reach. Let’s do those first things first.

It’s Not Rocket Science. Photovoltaic Cells Unmasked

photovoltaic-cell-blog      A faithful reader has commented on the DIY (do-it-yourself) potential of solar panel construction, and cited a source promising solar panel construction for extremely affordable sums. Here we are, not to debunk the claims of the “You Can Do It With My Special Video” entrepreneurs, but to give a framework of data to help you in your research.

A single solar cell consists of two wafers of highly engineered silicon, joined carefully by a conductive bond, fastened to a supporting backer, with electrical leads. That cell can typically generate .7 volts of direct current power. Connected in a cluster behind a clear glazing, the assembly, or “panel,” can be configured to deliver a maximum of 12, 24 or 48 volts direct current while sitting in the sun on your roof.

The catch, and there are a few, begins with efficiency. Silicon responds only to narrow frequencies of light, operates poorly at high temperatures, and seldom delivers, in many lower cost panels, more than 5% to 15% of the potential power of the sunlight falling on it.  Here’s a NASA link that explains some of the challenges and how they’re met. Optical reflectors, wafer stacking, and various cooling techniques can improve panel efficiency up to 20%. In my previous post, titled “3 kwh per square meter per day…” we did some math about the potential of any rooftop to deliver solar electricity, and this efficiency factor has to be part of that math. Even a well-constructed solar panel will only absorb and convert one watt in five in full sunlight.

Once the solar panel is on the roof and receiving sunlight, it needs to talk to a device that converts direct current to alternating current, which is the form of power distributed by utilities and used in your house. The Inverter, as it is called, massages that direct current of some lower voltage into alternating sine wave current at 120 or 240 volts for American homes to use. Voltage may vary by global region. The inverter operates at about 90% efficiency, depending upon a lot of factors, so use that in your calculations.

If your system will be tied to the grid, your panels and inverter will be specified and dictated by the utility. No home-brew systems that I’m aware of can be grid-tied with CL&P’s approval. The engineering of the specified inverters carefully matches grid voltage, among other things, and instantly shuts down the system if the grid loses power. This prevents the deaths of linepersons working during outages. It also prevents you from using your system, even if you manually disconnect it from the grid, during an outage.

As of this writing, photovoltaic panels can’t be bought at WalMart, except for specialty applications like charging lawnmower and car batteries, and powering tiny landscape lights. Solar panels are available through Home Depot in modest wattages, and they also subcontract installations in some regions. You cannot yet just fill up two shopping carts and be on the grid by sundown, at least not in Connecticut. In some ways the equipment is less complicated than the permits and inspections required by most utilities.

But we’re getting there. So, hats off to you DIY enthusiasts, I hope your time comes soon for affordability and regulatory friendliness. Meantime, you can do smaller projects at home, limited only by your purse and daring. Our time is coming, and your questions are always welcome.

Solar Power in CT– Can I Keep Some?

electric-meter-blog We mentioned last time that storage is a key issue in the advance of solar electric power as an energy source. In Connecticut the approved grid-tie system features no storage at all.

There are advantages: the installation is simpler and less expensive. The peak output of the panels coincides with Connecticut Light and Power’s peak usage during the business day, lightening the burden on the utility to meet peak demand. The relatively straightforward formula of retail power in, retail power out means that photovoltaic output defrays the cost of incoming power at the same price per unit, so the calculation is made right in your meter and on your bill.

Sadly, there’s nothing here for those interested in energy independence. You’re still tied to the grid, still paying your bill, still subject to rate hikes and only a tiny junior partner with CL&P in the business of powering the state, or your home. Storage is the problem.  Batteries are expensive, heavy, not at all maintenance-free, and not perfectly safe. If accidentally pierced, they stink and the contents are corrosive. Batteries are also not quite in the Star Trek category for capacity. For a bank of four batteries (in series, delivering 48 volts, an efficient output for power inverters) capable of powering your house for 14-16 hours at night, you would pay up to $2000; and forget about operating your electric range or air conditioning. Lights, television, refrigerator, computers is about the limit.

Other storage schemes are worth mentioning: hot water, both domestic and for heating, can be heated by solar electric power and stored. Hydronic panels can also be used for the purpose of charging a hydronic storage bank. Thermal mass built into your house can be used to store heat during the colder seasons, and to store “cold” during summer. More exotic applications like storing energy as compressed air or latent heat in a phase change compound are too expensive and complicated to be interesting to non-engineers.

Battery technology is being advanced rapidly by intrepid science jocks and inventors who want to revoltutionize home storage, hybrid cars and electronic gadgetry, and I wish them well. Beyond lead-acid batteries, Glass matt batteries, Nickel Cadmium, Nickel Metal Hydride and Lithium lie technologies that might put overnight storage within our modest collective reach. And utility companies might soften their stance on hybrid storage-grid systems to allow more off-grid independence.

The cruel catch, that rooftop panels cannot be used when the grid goes down, for safety reasons, is a bitter quibble. Imagine yourself sitting powerless under a roof full of potential, with no way to use the power. That’s the current state of the industry. Some accomodation between grid safety and home storage will arrive soon, I hope, and the whole enterprise will begin to make more sense for average people. Simply to partner with the utiliity in producing power and spinning your meter backwards is an idea of some appeal. To achieve emergency backup and the possibility of partial grid independence is a much better reason to hock the ranch and load up your roof with panels. I’m holding out for that.

3 KWH Per Square Meter Per Day — Absolutely Free


My roof, the southerly facing side, measures roughly 800 square feet. That’s about 75 square meters. According to the formula in the title, it calculates to 225 kilowatt hours per day.  And that’s a modest view of the potential of solar power on my rooftop, and yours, and everyone’s. Just in New England. In Florida and New Mexico it’s almost twice as much.

My house, one in which power is used moderately by American standards, consumes an average of 20 kilowatt hours per day. No electric heat, average range of appliances, lights used one or two rooms at a time, cooking done mostly with microwaves, air conditioning used very sparingly. Twenty kilowatt hours needed, 225 kilowatt hours potential from roof insolation. Twenty needed, 225 available. Twenty, two hundred twenty five. And your roof? And your neighbor’s? And a three-family apartment house? And a row of condominiums? Same figures, depending upon roof orientation. And more, usually, as you move south and west, outside New England and our famously changeable weather.

How, then, to collect it? And store it? And share it with other users in the vicinity who have changing needs? It costs about sixty thousand pre-rebate dollars to put panels on the roof, install an inverter and tie it to the grid. Your share would be app. 38,000 dollars, financeable via home equity, low interest loan, or cash if you deal drugs. Or have equity left in your house. Or if you qualify for a low-interest government-backed loan. And then only if you own your home. And the capacity of that expensive photovoltaic system will be only a fraction of the potential of your roof’s solar energy load, Less than half. And your daily contribution to the grid will be most of your home’s power usage. Only most.

It’s a dim picture, but not dark. The tax credits and rebates do not yet put photovoltaic power in the reach of average Americans of average means. And the contractors are charging princely sums for their systems, and the paperwork for the Clean Energy Fund’s credits is burdensome, and the systems tend to pay back at a rate that I, for one, won’t live to see, and the panels last thirty years in sunlight by a maximum estimate, twenty is a more conservative figure, and the grid doesn’t store the energy, it just distributes it among all connected customers.

So many things are not yet quite right about our approach to solar power. But we’ve begun. and demand does eventually affect supply, and the storage problem will be addressed, and there will be panels on most/every/many/your roof. Soon enough to save the planet? Sooner would be better, don’t you think? More next time.

2009 Clean Energy Bill — Cap and Trade and You


We seldom stray from the home front and the small picture. Today I’m a little excited by the likely passage tomorrow of the Clean Energy Bill. Warts and all, it is a small first step in a long political climb out of denial and into a clear-eyed accountability that will be difficult to reverse once it takes hold. For too long (well before Bush, so calm down GOP readers) we’ve denied that we might just possibly be fouling the nest. Now a strong Democratic majority is being joined by moderate and progressive Republicans to issue an IOU to the nation and the world on cleaner air and slower climate change.

Is the Waxman-Markey Bill a home run? No. Not even a sliding double. It’s a bunt toward first base that we can run out and hope that future administrations/generations will swing away and bring us around to home. The measures (17% reduction in targeted greenhouse gas emissions by 2020, 80% reduction by 2050) agreed upon after much compromise will not by themselves reverse the ominous predictions of scientists convinced that recent and future climate change on this planet is largely man-made. Glacial melt will continue, carbon dioxide levels will still increase, and coal power plant emissions will continue to blot out the heavens, as in the header photo. But the way America looks at industrial emissions will change forever.

 So much is missing from the bill. There is no scrutiny of the actual energy and climate cost of the ethanol and bio-fuel industries on which so many people have pinned their hopes. There are no real jaws to close upon persistent offenders: indeed, “cap and trade” means that dirtier industries will be purchasing “carbon credits” from cleaner industries not needing them, and the sale of these “pollution indulgences” will be mostly unregulated. Trouble brewing there, I’ll wager.

But, we and Al Gore are exhilarated by this first step, out of proportion to the actual impact of the bill. Due credit to Bush One for signing the U.S. into the Kyoto Protocols in the early 90s, but no piece of legislation since that one has had the same impact, for this one reason:  the cat is out of the bag, and, having admitted to ourselves that the job is before us, we are unlikely to retreat again into the darkness under the pillows.

Legislation is boring to read, and I’m only linking to a “talking points” discussion by the bill’s authors here. In order to give the bill a chance at passing, Waxman and Markey pulled back from the bold early drafts in order to court bipartisan support. In the event, only eight Republicans in the House voted for the bill, and all were promptly savaged by staunch conservatives, who favor increased investment in oil and gas for America’s energy future.

The Clean Energy Bill is touted by its supporters to be economically positive, creating jobs and provoking the kind of technological stampede for which Americans are famous when they get hold of an idea. I’m imagining home-brew CO2 sequestering devices being whipped up in garages, and complex climatic models coming out of college dorm rooms. Heaven knows, that’s how Hewlett and Packard and Gates and Allen, respectively, started out to change the world. The currency for which America has long been most famous is entrepreneurial innovation. The Waxman-Markey Bill is a big kick in the butt for inventors, venture capitalists and investors looking for reasons to come out of their economic bunkers and start generating life-changing ideas again.