Want to go green and off grid? Fed up with hearing about it at technical conferences? In the first of an occasional series, U.S. environmental writer Melissa Weilt talks to Sandia Laboratories researcher Tom Hund, who has put into practice what his paymasters preach.
The current U.S. trends towards alternative and renewable energy have roots in three decades of research supported by industry and the Department of Energy. Back in the 1970s, when the oil embargo shocked the world into the realisation that we could no longer sustain our rate of oil consumption, research was begun to develop solar energy into a viable option for heating and electrical power. The practical use of solar energy is the result of far-sighted visionaries in the field, and the progress has been slow but steady. The true believers in solar energy have carried the torch through many long years, and now that the effects of global warming are upon us and the environment is in the balance, solar energy’s time has come.
Tom Hund of Sandia National Labs was pioneering solar energy his way by building his solar-powered house. Nestled in the bucolic mountains just outside Albuquerque, New Mexico, is the off-grid solar home Tom designed and built slowly, as an on-going project, over the past 30 years. Anyone who knows Tom well will testify that one of the things that really animates him is his solar-powered home. Like many in the battery industry, Tom Hund has a unique perspective on power and has made it his life’s mission to harness as much as he can for his home.
It was his interest in alternative energy and concern for the environment that laid the foundation for his determination to build a home that would not only utilise solar power but run completely independent of the utility grid. Since the early days of his career in solar energy at Sandia National Laboratories, solar system and PV panel costs have dramatically dropped from over $10 per watt in the early 1980s to less than $4 per watt at present. Now the technology is so widely available that countries such as Japan and Germany have encouraged businesses and new housing communities to install solar panels on roofs to reduce the need for electricity from large utility power plants.
Tom found his piece of the New Mexico wilderness – 20 acres of rolling hills and imposing pines in the mountains – in 1977. He started with a primitive off-grid PV and wind system when he discovered the cost of bringing in utility power was about the same as putting in an off-grid system. At the time (1979) the utility company wanted about $6,000.
With no experience in carpentry, Tom set out to build a highly engineered solar home – from the rock box and foundation to the roof slope and placement of solar grids – himself, as a labour of love and an exercise in do-it-yourself innovation. (In the end he built it all, except for a new addition off the kitchen.) But though he’d researched every detail thoroughly, the analytical thinker nonetheless found he was forced to learn as he built, all the while soaking up advice from his colleagues at Sandia and books on solar energy.
A high performance solar home—especially one that does not have the back-up security of the utility grid—relies on a systems-engineered design. Thus Tom’s first consideration was the fundamental design of the home. He chose to build at an altitude of 7,200ft at a location that would provide optimal prime solar exposure. The house is south-facing to maximise the solar energy resource.
The first wave of solar homes was built in New Mexico in the 1970s, when Tom was in his twenties. “I was profoundly affected by those solar energy pioneers,” Tom smiles. “I saw how practical it was, and decided back then that I wanted a completely solar home of my own. Certainly my experience at Sandia Labs helped make that a reality. If I hadn’t worked in the solar and battery industry, I wouldn’t have known about the appropriate lead-acid battery designs for solar applications. The battery—more than any other single component —affects the performance, reliability and cost of an off-grid solar home.”
“It is often a matter of simple problem-solving when it comes to batteries in an off-grid home,” Tom continues. “You have to become a battery expert if you’re going to minimise problems in the system.”
The most costly and potentially problematic components of the system are the batteries, not the PV or power electronics. To date, in 27 years, Tom has used four sets of batteries. They have been the most expensive and labour-intensive part of his home power system. The latest set of batteries has been running reliably for about four years and should continue for about ten more.
The solar roof panels provide 2,400W of power at peak sunlight. Because Tom’s home is so efficient, his energy usage is only about 150 kWh per month, whereas the typical house may suck 400-1,200 kWh/month from the utility grid at about US$7-12 cents per kWh. Tom of course credits his frugal energy use to the design of his home. An efficient solar home requires appropriate management of the solar resource so that there is not too much, nor too little, heat and electricity. It’s always a question balance and compromise. The combination of excellent insulation, thermal mass ‘rock box and basement’, and a natural convective air flow design regulates the house temperature to within comfortable limits.
Tom is paying slightly over 30 cents per kWh (based on a 20-year amortisation) whereas the average U.S. homeowner pays between 7 and 12 cents per kWh. But because of Tom’s efficient house design, his energy consumption is just a fraction of that of a typical home, so his energy costs are comparable to a ‘typical’ grid-connected home. The important thing to understand is that in high solar resource areas it is possible to be ‘off grid’ for about the same cost as a typical ‘on-grid’ home because of the energy efficiency improvements. “Besides,” Tom says, “it’s not always about cost, it’s about principle.”
His centrally located garden sunroom provides 30-50% of the home’s winter heat though passive solar energy. Optimally designed to face south, it provides a perfect respite from the chills of winter. “If I am starting to get a cold, I get a cup of hot tea and sit in the sunroom,” says Tom’s wife. “The warmth and humidity in the air clears my system, and certainly brings a sense of peace.”
Tom’s two boys and wife Marianne appreciate living in a 100% solar home. “It is cool to live in our house,” says six-year-old Owen. “Everyone always wants to know what it is like.” Marianne says that their house is often a favourite topic of conversation with visitors; people are fascinated that they aren’t on the electric grid. “I’ve never lived in a house that is perfectly cool in the summer and perfectly warm in the winter,” she says. She also points out something else she’s learned: that the biggest power drain is the laundry room.
From a distance, the house doesn’t look much different from any other house nestled in the mountain pines; but on closer inspection, the solar panels on the roof are a dead giveaway that this isn’t your ordinary frame house.
From an engineering and safety perspective, Tom says that grounding is the single most important issue for solar homes. “When you have multiple energy sources, grounding is critical,” says Tom. “In the photovoltaic system grounding is important because the electronics used in the inverter are very sensitive. Most ground rods in the Southwest have a ground resistance of at least 300 ohms… yet they should be in the 5 ohm range. Thus, any lightning strike can result in very high voltage spikes. Ground loops will also cause your inverter to malfunction, which can be dangerous and cause fires.”
One of the primary reasons that the home is so efficient is the rock box that was built at the centre of the home. Surrounded by walls and a working fireplace, the rock box is a room 8ft x 8ft x 16ft filled with large stones. These stones hold heat in the winter and radiate cool in the summer – a very primitive concept, but hugely effective. The home stays relatively cool (in the 70s) in the heat of the summer when afternoon temperatures can approach the high 90s. In the winter the main floor easily maintains its warmth. The key to making this temperature control system work is the cool night-time summer temperatures at an elevation of 7,200ft and the bright winter days in which the sun heats the greenhouse and active hot-air solar collectors.
Visiting during one of the hottest days of the summer, I found the interior incredibly cool and comfortable. I asked whether the house needed much air conditioning to maintain such a pleasant temperature and Tom explained that he uses an evaporative ‘swamp’ cooler to keep the house cool. In the summer the cooler removes the late afternoon heat from the house, bringing it to a comfortable level. The cool night-time temperatures at 7,200ft lower the temperature of the entire house, including the thermal mass of the basement and rockbox. The well-insulated walls keep the house cool until late afternoon in summer.
In winter the active hot-air solar collectors and greenhouse heat the house. including the basement and rock-box. At night this thermal mass radiates heat to keep the house comfortable until morning. If the sun doesn’t shine then propane gas heats the house and runs a generator to charge the batteries and power the house. Typically this generator will run only about four times in a normal year.
Tom Hund is a senior engineer and works in the Power Sources Component Development Dept. at Sandia National Laboratories. He is presently working for the Department of Energy’s Energy Storage Program testing batteries and supercapacitors for utility applications, and he builds and tests li-ion battery packs for defence programmes.
Fact: Worldwide photovoltaic installations increased by 1,460MW in 2005, up from 1,086MW installed during the previous year. In 1985 annual installation demand was only 21MW.