posted on June 23, 2013 |
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In Haiti, electricity is both costly and unreliable. In the town of Mirebalais, about 60 km from Port-au-Prince, residents pay $0.35 per kWh and the grid goes down for an average of three hours per day. For the town’s newly built hospital, Hôpital Universitaire de Mirebalais, both the cost and the intermittency are unacceptable.
Partners in Health (PIH) is a Boston-based non-profit organization whose mission is to bring modern medical science to those most in need. In effect, PIH spreads a little proverbial sunshine to the underprivileged. In this case they’re collecting sunshine and turning it into cheap, reliable electricity. PIH coordinated an effort to design and install a grid-tied solar power system that exceeds all of the hospital’s daytime energy needs. Surplus energy is sold back to the grid during the day. At night the hospital runs on grid power, with diesel-powered generators available in case of a nighttime power failure.
The hospital’s roof sports more than 1800 photovoltaic (PV) panels, each capable of generating up to 280 watts. (I’ll save you a trip to the calculator - that’s 500 kW of peak DC power.) The panels feed five 95 kW grid-tied inverters, which provide over 400 kW AC. You can see its live production here. Hôpital Universitaire de Mirebalais is now the largest hospital in the world that uses solar power to generate more than 100% of its electrical needs during peak sunlight hours.
If you’re wondering about the concrete blocks on the roof, project engineer Ann Polaneczky explains, “We have a membrane roof that can’t have perforations, so our racks sit on the roof unbolted and are held down by these CMU [concrete masonry unit] blocks. The racking & block quantities were structurally designed for 120 mph [193 km/hr] winds so that the panels are safe up there even in a hurricane.” Wow!
Since PV panels are less efficient at higher temperatures, the roof was painted white to minimize heat absorption. The white surrounding also reflects more light onto the PV panels, providing two benefits for the price of one. The panels sit about a foot above the roof to maximize air flow. As far as panel maintenance is concerned, they’re simply rinsed with plain water four times a year. Two local electricians, trained by engineers who designed and installed the equipment, will continue working at the hospital to maintain its electrical system.
In addition to its solar panels, the building was designed to maximize energy efficiency. Passive ventilation techniques help to naturally cool the building and reduce the need for air conditioning. The white roof also contributes to that effort. (Did I say the white roof provided two benefits for the price of one? Make that three.) Motion-sensor lights cut 60% off the energy needed for lighting. Overall, the building’s design and the PV panels should save the hospital about $379,000 every year. With a $2.2 million initial investment, the system will pay for itself in just under six years.
If you’re planning a photovoltaic system, whether it’s for a large-scale operation like a hospital or just a small residential set-up, you can take a number of lessons from this project. First and foremost is to reduce the amount of energy you use. A kilowatt saved is equivalent to a kilowatt generated, and it’s usually less expensive. Passive heating and cooling are free sources of energy, so use them. Second, if the grid is available, connect to it; the grid is the cheapest form of “virtual storage” there is. Third, whether on-grid or off-grid, a gas-powered generator, used sparingly, is probably a better back-up power solution than extra batteries. I know it burns fossil fuels, but it’s much less expensive and with an ample fuel supply it can provide power through long periods of overcast skies and grid outages. For a small home, a battery bank large enough to provide two days of autonomy can set you back more than $12,000 and the batteries need to be replaced every ten years or so - more often if you deep-discharge them frequently. If you're off-grid, maybe you can live with one day's worth of battery storage and a backup generator. Finally, for municipal or business projects, the payback period for many sustainable energy systems is short compared to the expected life of the building. (That's true for long-term homeowners as well.) At the college where I teach, we convinced the administration to put a geothermal heating/cooling system into a new building. Seeing the $1M price tag, they were reluctant at first. When the architects calculated a six year payback period, they jumped on it!
Hôpital Universitaire de Mirebalais, a state-of-the-art medical facility, was funded by several non-profit organizations, including the Red Cross, the GE Foundation, and Artists for Haiti, an organization founded by actor Ben Stiller and art gallery owner David Zwirner.