“Going Solar” Affordably

April 13, 2010 by Richard Blake  
Filed under Solar Power

The focus of government programs encouraging the individual use of alternative energy sources focusing primarily on high end systems, particularly solar photovoltaic (PV) systems, although well-intentioned, may ultimately end up ineffective for the most part. Programs that result in significant numbers using at least some solar, geothermal or other alternative energy sources are infinitely more valuable than ones that are more expensive but are only utilized by a small “elite” of environmentally aware AND financially well off consumers.

While strong majorities of Americans believe that all new home construction ought to offer consumers a solar option, and most state that they would be willing to pay a premium of 10% more on a new home, very few Americans currently own solar home installations.

No doubt part of the reason for that lies in the fact that most people are only aware of PV and, to a somewhat lesser extent, solar hot water systems. PV systems are often out of reach for most Americans because of high initial costs. Solar hot water systems, while not as costly, are still out of the reach of a lot of consumers, and often have performance, maintenance and installation issues.

Fortunately there are a number of additional alternatives for “going solar,” all of which are significantly less costly than PV systems. Also many of these systems are passive and thus have no moving parts or major maintenance issues.

PV, Warts and All

None of this is intended to discourage anyone who really wants to invest in a PV system. After all, for systems to improve over time there need to be pioneers who are willing and able to make the investments and take the risks that will pay off for all of us over time. It is preferable, however, that those pioneers make that investment with their eyes wide open and not feel “duped.”

Moreover it does the renewable energy industry no good to obfuscate the facts concerning current PV costs. The National Renewable Energy Laboratory (NREL) bottom lines it thusly, “Although PV now costs less than 1% of what it did in the 1970s, the amortized price (of PV-produced electricity) is still about 25 cents per kilowatt hour. This is double to quadruple what most people pay for electricity from their utilities. A solar rebate program and net metering can make PV more affordable, but they can’t match today’s price for utility electricity in most cases.”

On the other hand, the fact that PV electricity is now at least in the same ballpark as other utility produced electricity and future utility price increases are unpredictable, other than they are very nearly a certainty, PV systems are beginning to look more and more like a good investment. The biggest problem has always been the initial costs of the system, something an increasingly smaller percentage of consumers are able to do given the current recessionary economic state.

According to NREL, small single panel PV systems that produce about 75 watts are usually priced around $900 or about $12 per watt. Unfortunately, most homes use significantly more than 75 watts on a daily basis. Indeed many individual light-bulbs consume that much energy in and of themselves. A 2000 watt system (two kilowatts) is usually priced at between $16,000 to $20,000, or $8-$10 per watt. A two kilowatt system generates sufficient electricity for an energy efficient home.

NREL has published a 20 page consumer guide to PV systems at http://www.nrel.gov/docs/fy04osti/35297.pdf (PDF file). The guide covers such issues as the science behind photovoltaics, incentives, system costs, choosing a PV provider, roof area needed for PV systems of various sizes, issues involved with connecting to the grid, i.e., insurance, permits, etc.

Sun Power Corporation publishes a “savings calculator,” which estimates energy bill savings over the life of one of their systems. In my case, using an estimated $100 per month electric bill, it estimated that I would save $37,421 over the life of the system (until 2034). Perhaps the best thing about the “calculator” is the attached graph which gives a better idea of when that savings begins to be realized, which is certainly not in the first couple of years, except perhaps from tax credits, rebates and other incentives.

Incentives include net metering, which is available in 35 states. When a PV system produces more electricity than is consumed in the home, the meter “runs backwords,” giving the homeowner a credit rather than a bill. Net metering provides that PV owners are credited with the retail price for electricity produced by their systems, rather than the usually much lower wholesale rate.

State incentives vary but a good source for information on the incentives in your state is the National Database of State Incentives for Renewable Energy, produced by the North Carolina Solar Center. California state incentives can be viewed at http://www.gosolarcalifornia.ca.gov/

Fortunately, there is good reason to hope that in the very near future research breakthroughs will lead to PV systems being directly competitive with, or even more cost effective than coal or natural gas produced electricity. One of the most interesting potential breakthroughs, “black silicon” was discovered at Harvard University.

Black silicon was discovered by accident when as assistant to Harvard physicist Eric Mazur “blasted” a silicon chip with a short, but very intense, focused laser beam. Due to its rough surface, black silicon is capable of absorbing significantly more light, including frequencies in the infra-red spectrum than conventional silicon wafers. Black silicon may potentially convert up to 40% of the sun’s energy into electricity, versus 8-20% for conventional silicon PV wafers.

New Forms of Solar Financing

In recognition of the fact that the initial cost of PV systems is a major factor hampering their widespread adoption, governments and others are introducing programs for financing PV and occasionally, other renewable systems. The most innovative of these is the CityFIRST program (City Financing Initiative for Renewable and Solar Technology) administered by Renewable Funding, LLC.

CityFIRST allows municipalities to issue loans to individual homeowners for solar and other renewable energy home improvements (usually energy efficiency upgrades). Renewable funding purchases CityFIRST bonds and transfers the proceeds to individual property owners on demand.

The program is made possible by a new California law that allows homeowners to finance renewable energy projects through a voluntary increase in their property tax bill. Cities and Counties provide funding for the program through the issuance of a bond that is repaid semi-annually through special taxes and assessments on the annual tax bill of the participating property owners. Additionally, Renewable Funding is also developing a program where the municipality may opt into a statewide clean energy financing program administered by the California Statewide Communities Development Authority (California Communities for short).

To date the City of Berkeley has been the only California municipality to institute a CityFIRST project. Depending on Berkeley’s experience, more municipalities both in California and other states may institute similar programs in the future. Eligible projects include PV, solar thermal (solar hot water and solar space heating) and major energy efficiency upgrades.

One question on the Renew Fund’s FAQ page which might be taken a couple of different ways is “Is a participant obligated to continue repaying if the solar system stops working,” to which the humorous response is that if that were the case it would be the least of the participant’s worries. Another looming problem, however, is far more serious. That is, it seems likely that the State of California’s current budget stresses, including issuing IOUs in lieu of payments due, will impact the growth of this otherwise very encouraging program.

Solar Hot Water Heating

Prior to the widespread use of energy efficient hot water heaters, home solar energy companies estimated that approximately one third of the average family’s heating bill went for hot water heating. That, and the fact that he initial installation costs of solar hot water heating systems versus solar photovoltaic systems are considerably less, are helping to make these systems increasingly attractive.

There are only two main parts to a solar hot water system, collector plate or plates, and a storage tank. While most solar hot water systems are active, in that they rely on pumps to circulate the water, there are designs for passive solar hot water systems that depend on gravity and the principle that water circulates as it is heated.

For do-it-yourselfers, there are a number of websites on building your own solar hot water system, some of which advertise that you can do so with an investment of under $1000.

For a passive solar hot water system, one site has put together a kit for around $500.

The Energy Guy.com put together an extensive webpage listing both the most common problems associated with solar hot water systems, as well as the associated estimates for repair, replacement and maintenance. While most reliability issues have known solutions or means of avoiding problems in the first place, the Energy Guy notes that the same problems tend to surface time and time again. The site lists a total of 27 major categories of problems with solar hot water heating systems, including pipes bursting from freezing, overheating, poor water quality (hard water can produce deposits that will ruin a system), fluid leakage and roof related problems as a solar hot water system can be quite heavy.

Passive Solar Heating Systems: The Trombe Wall

The two great advantages of passive vs. active solar heating systems are the much lower costs associated with installation in most cases, and the fact that with no moving parts, a lot fewer things can go wrong with a passive solar system. That is not to say that passive systems require no maintenance of any kind forever. A Trombe wall that is housed by dirty glass will be much less efficient than one with clean glass, and paint, wood, sealants and metal all can always deteriorate over time. The greatest disadvantage to passive vs. active systems is that many, if not most incentive programs do not finance or incentivize passive solar improvements. On the whole, however, the lower initial cost is a great equalizer.

One of the most famous, and in my opinion, at least, one of the best passive solar heating devices is known as the Trombe wall. Named for French solar scientist Felix Trombe, the primary force behind the world famous French solar facility at Odeillo in the French Pyrenees mountains, the concept of the Trombe wall is in fact much older. Indeed, as far back as the Greek and Roman civilizations of antiquity (not to mention ancient civilizations in the American southwest), whole cities were designed to take advantage of passive solar energy.

The basic idea behind using passive solar to heat is to allow solar heat in, and then insulate like crazy against allowing radiant heat to escape. In the northern hemisphere, of course, the source of solar energy is always to our south. Therefore, the Trombe wall needs to be built on a southern, or at least southeast or southwest facing wall. Conversely, insulation should be added, windows should be covered with storm windows or plastic and heat leaks caulked or covered on north facing walls intensively, and to a lesser extent on all walls not involved with the Trombe wall.

NREL has put out a paper that goes into a fair amount of detail about one Trombe wall design that has been used for buildings in Zion National Park as well as at the NREL site itself. The link is http://www.nrel.gov/docs/fy04osti/36277.pdf (PDF file). Mother Earth News has also featured what are essentially Trombe wall designs over the years although they are not always labeled as such.

The “Build it Solar” website shows a very simple Trombe wall built over an uninsulated south-facing masonry wall. The “Build it Solar” design does not include holes in the walls, which is usually incorporated in most Trombe wall designs. Instead the increased heat is absorbed by the wall and slowly radiates to within the structure. The disadvantage of that particular design is that it takes longer for the solar heat to work its way into the living space. An advantage is that even on cloudy or stormy days there is no heat loss as might occur with the hole design if the homeowner does not properly plug the holes on unsunny days. Wikipedia also provides a very good reference article on the Trombe Wall.

The basic concept behind the Trombe wall is relatively simple. The idea is to increase the thermal mass of your south facing wall and allow that heat to radiate into your living space. Thermal mass can be composed of rocks, bricks or blocks. The best thermal mass would be black either naturally (in the case the stone basalt incorporated into a rock wall) or painted black. The thermal mass is covered by a glazing, which is basically just a covering of glass or plastic. The wall can be covered by a glazing that is specifically for solar uses. Another innovative idea that has been suggested, is the use of one way mirrors which would allow light and heat in but not allow it to radiate out. The glazing should be as airtight as possible and cover the entire thermal mass plus an area just above and just below the mass to allow for vents.

To me the vents are the most ingenious part of the Trombe wall. Since hot air rises and hot air off of the thermal mass will rise to the top of the Trombe wall enclosure, the idea is to have a vent that will allow hot air to flow into the house, but not back out. Therefore a vent needs to be cut into the wall that contains a flap on the inside that will move for hot air to enter and close off hot air escaping. Conversely a vent or vents cut below the Trombe wall ought to allow cold air to leave the living space but not re-enter. Therefore a flap needs to be placed on the outside of the living space within the Trombe wall enclosure for that purpose.

When cutting the vents for the Trombe wall, save the cut-out areas and insulate them to the extent possible, creating vent blocks. That way during long periods of stormy or cloudy weather the vent blocks can be reinserted into the vents to prevent heat loss. A Boulder, Colorado resident who built a Trombe wall swears that it has practically eliminated his winter heating bill. Of course, Colorado has an unusual number of sunny, albeit often cold winter days. Also the Trombe wall needs to be under an overhanging roof so that while it is affected by the low sun of the winter, it is not so affected by the high sun of summer. When summer comes the vent blocks also ought to be inserted and, if necessary the glazing opened up for venting or one way mirrors turned around.

For a full range of ambitious and inventive passive solar heating and cooling techniques that are currently being used on a house at the 6000 foot elevation level in Utah, check out
http://www.allanstime.com/SolarHome/index.html. Besides a Trombe Wall, Allan uses a solarium, solar hot water panels, a eutectic salt chamber, berm insulation and, in the summer, passive solar air conditioning, using black painted chimneys that, pull hot air out of the house to be replaced by cooler air from a 50 foot tube in the lower northwest portion of his house that uses the principle of evaporative cooling.

Passive Solar Heating Systems: The Eutectic Salt Chamber

Allan considers the eutectic salt chamber the most efficient passive solar improvement he uses. The eutectic salt chamber uses Glauber’s salt, (sodium sulfate decahydrate) and works on the principle that while it takes energy to melt ice, the laws of physics state that therefore while ice is freezing energy is being given off. Allan refers to this as the “fusion principle,” and gives the practice of fruit orchards spraying their blossoms in their orchards with water when freezing threatens as an example of its utilization.

Water is, however, a relatively inefficient medium for fusion energy as it releases approximately one calorie of energy per gram as it freezes. Glauber’s salt releases over 80 times that amount. The salt in Allan’s chamber is stored in black tubes to absorb the daytime sun causing the salt to melt (Glauber’s salt has a melting point of 90 degrees Fahrenheit). Then at night, as the salt freezes at temperatures below 90, the air around the tubes is heated in similar fashion as a radiator. The warm air is then free to rise into rooms above it or it can be channeled into other rooms through ductwork, just as cold air then returns to the chamber to be re-warmed.

Passive Solar Cooling

Finally, in many parts of the United States and elsewhere, as much (and usually more) energy is expended on cooling of homes in the summer as is spent on heating in winter. In Arizona, for example, air conditioning is very nearly a necessity of life. Thus when the Arizona Solar Center produces an article on passive solar cooling strategies stating that “passive cooling techniques can be used to reduce, and in some cases eliminate, mechanical air conditioning requirements in areas where cooling is a dominant problem,” they are either onto something or have been driven insane from the heat. The truth is that passive solar cooling systems and strategies are surprisingly innovative and imaginative.

Many of the principles of passive solar heating are also applicable to passive solar cooling, especially insulation and weather-stripping. Movable insulation shutters for winter nighttime containment of heat gain can also retard heat gain during summer. Thermal masses inside the house can act as thermal “sponges,” absorbing heat and slowing internal temperature rise on hot days, and can be cooled down by nighttime ventilating and/or by use of mechnical cooling during nighttime off peak hours. If the mass is located near a skylight, window or vent, the thermal mass can be exposed to nighttime air to release the heat absorbed by the mass earlier in the day.

The simplest passive solar cooling technique is to paint your chimney black, especially if the chimney is at the highest point in the house and if hot air throughout the highest points of the house are not blocked. Though that seems counterintuitive, it creates an airflow that sucks hot air out through the chimney. Even better is a design for a solar cooling tower.

A less counter-intuitive and surprising effective passive solar cooling strategy involves the use of reflective or white roofs. On September 7, 2008 at the California Climate Research Conference, the Lawrence Livermore Berkeley National Laboratory released a study which estimated that if all urban roofs in the temperate and tropical climatic zones of the world were painted white, global warming would be slowed by 11 years. The report went on to state that if every rooftop in 100 major cities was painted white it would offset an entire year of the earth’s CO2 emissions, the equivalent of 44 metric gigatons of CO2. The study was based on an estimate of an average sized roof of 1000 square feet. Just one such roof painted white offsets 10 tons of C02, the average annual emission from two mid-sized automobiles. Cooling energy use savings would be an estimated 20%, saving annual energy costs $1 billion in the United States alone.

Beginning in 2005 California mandated that all new commercial flat roofs must be painted white and that all sloped roofs be painted “cool” colors. Georgia and Florida are also providing incentives to property owners who paint their roofs white.

Other passive solar cooling strategies and systems include hydronic cooling, circulating water instead of forced air, rock bed heat exchangers, undergrade air chambers, indirect gain mass walls (used to increase ventilation rates in adjoining spaces), maximum utilization of cool air inlet vents and ducts, ceiling vaults and thermal chimneys (to promote rapid air change), roof top sprinklers, open ponds with water walls, shading, earth tubes, wind turbines and reflectors.

Active solar cooling systems may also employ fans and evaporative coolers, as an aid to, or in conjunction with passive systems.

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