September-October 2005

Solar Heat, PV, and Grid-Connected Micro-CHP Plant

Newly arriving 2.5-kW Ecopower, and 4-kW to 15-kW Powerhouse, delivering on- or off-grid CHP

The Year of the Cogen Appliance? Well, maybe not, but it's interesting that three similarly conceived products for combined heating and power (CHP) are being introduced to the US at once, all of them aiming at slices of a potential market for home- and small-business energy.

One—the 5.7 kW Aisin 60 from Japan—is being fine-tuned by ECO Technology Solutions LLC, of Leesburg, VA, for domestic use (see profile Distributed Energy May/June 2005).

Now come two more options—similarly small in size but mighty in potential usability—from PowerPlus Technologies GmbH of Gera, Germany. The first measures just 54 inches long by 30 inches deep and 43 inches high, or about the same total volume as a clothes washer. Fueled by either natural gas or propane, the "ecopower" unit (note the lowercase e) can be variably controlled with a patented, automated modulator which allows precise load-following from 2 kW to 4.7 kW. It's designed for grid connection, so it could easily serve as a peak-shaver for many commercial applications. By capturing the engine's exhaust to make hot water (running through two independently regulated circuits), its rated fuel efficiency tops an unheard of 92%.

Single- and multi-family homes, schools, daycare centers, hotels, motels, agricultural processing stations, car washes, and health clubs are among the applications envisioned. All can rely on standard grid power as their primary electricity source; then, whenever they fire up the fuel for some hot water, the ecopower system would deliver plenty, while also outputting a couple of thousand watts of electricity an hour. The resulting power could either go into immediate use or be sold back to the grid (in states allowing net metering) or, if appropriate (and with some additional hardware), into battery storage.

Also arriving in the US from PowerPlus is the ecopower's slightly larger grid-independent version. It's designed primarily for commercial applications needing stand-alone standby power—e.g., telecom sites, remote facilities, and agricultural stations. Measuring 40 inches by 80 inches by 90 inches, and packed in a steel cabinet for outdoors, the Powerhouse generates 4.2 kW; a second engine can readily be added, doubling this to 8.4 kW. With this second engine, the system can also support a bundled 2.5-ton air conditioning system.

Successful Debut on the Continent
Ecopower units have been marketed in Europe (for which they were expressly designed) going on five years now, notes Mike Cocking, sales and marketing manager for Marathon Engine Systems of East Troy, WI. Over that time they've become something of a "hot item." As of last year, no fewer than 700 units had been sold cumulatively, and current sales are going at a clip of 50 to 80 ecopower units a month.

Cocking knows the ecopower sales numbers first-hand because Marathon makes the specially designed, extraordinarily durable single-cylinder engine that goes into it. The quiet, low-maintenance Marathon 5K is thus exported to PowerPlus for packaging with Europeanized electronics and cabinetry, then retailed. Marathon claims the engine has a 40,000-hour life—effectively, that's ten years of operation, assuming 4,000 normal-duty cycle hours out of the 8,760 hours in a year. "We've had engines going that long" without breakdown or overhaul, he says, "and some, even longer."

Marathon obtained the patent and manufacturing rights from the Gas Research Institute, which spent more than $75 million in development costs, designing the engine for continuous-operation heat pumps running on natural gas or propane.

Its touted maintenance interval is 4,000 hours (i.e., only once a year) and consists of an oil change, spark plug, air filter, ignition cable, and emission adjustment costing "a total of about 150 bucks," says Cocking. After 10 years of service the engine can be replaced with a new one by contacting Marathon's dealership network (www.marathonengine.com).

Design-wise—and perhaps surprisingly—the Euro-styled cogen model was built by PowerPlus GmbH essentially as "a glorified water-heater," i.e., not for electricity primarily. This is just the reverse of priorities here. Cocking explains that in Europe, building codes now mandate frequent boiler replacement; PowerPlus thus saw this as an opportunity to provide homeowners much greater value when they upgrade, by offering a heater that would give power as a sort of "bonus feature." Europeans enjoy a stable grid and don't routinely need backup power, but Euro laws and policies strongly encourage cogeneration. Europe has "true net metering," Cocking notes, meaning that an in-home DG resource may sell electricity back to the grid for the same rate as the purchase cost. Hence, whenever the "glorified water-heater" from ecopower switches on, the owner's electric meter might spin in reverse, and the savings can mount up to lots of euros. One owner in Remsheid, Germany, who favors lots of hot water, reportedly spends nothing for electricity, but gets a check from her local utility for the equivalent of $130 or so every month—all thanks to Germany's liberal net-metering. Euro governments also typically offer molto bello rebates to underwrite upfront cost-efficiency upgrades. All things considered, then, payback on an ecopower will arrive in just three or four years, after which the customer actually owns a little onsite generating asset.

Ecopower and Powerhouse for the US
Conditions certainly differ, though. For one thing, net metering typically pays back rather "grudgingly," according to Cocking. Even so, he anticipates strong market appeal for both the ecopower and Powerhouse. Marathon Engine is now importing and adapting them for domestic sale, and several pilot applications are underway. Full commercial availability is also phasing in.

Critical to winning customers here will be (naturally) the payback prospect. An ecopower retails for $12,500 and, although it's very easy to install, the associated costs for that and for grid connection will likely add another $2,000. Lifetime maintenance can be budgeted in current dollars at $1,500. Total outlay, about $16,000.

Over a 10-year life, then, an owner needs to make back about $150 every month, on average, on utility billings (i.e., on 360 hours of operation). That's $0.42 needed per hour. Because output wattage can be modulated, and other variables come into play, it's hard to pinpoint the precise cost-per-kilowatt, but, assuming 2.5-kW output, the per-kilowatt cost would come to $0.16.

Although that's rather high for many residential customers, the value proposition begins to look much better when compared with peak energy rates and commercial rates in many areas.

The preceding doesn't factor in fuel cost because it is assumed this would be roughly equivalent in any case—being needed for domestic heating and hot water. In fact, as Cocking points out, the ecopower's very high fuel-efficiency actually improves upon that of most in-service boilers, thus bringing the net cost of the CHP benefit down to a range, he says, "somewhere between twelve and fifteen cents per kilowatt for this unit."

As for the off-grid Powerhouse device, this can also be used for cogen. However, it includes a built-in battery pack and inverter, making it better suited for "true remote" applications, Cocking notes. Marathon Engine Systems designed this dual-fuelable generator with cell towers in mind, as well as other remote or unattended and automated operations needing the higher power range. As of early 2005, Marathon had made and sold 26 of these for service in the UK. A US adaptation is currently under development, as is (further down the road)—an off-grid, independent version of the ecopower.

Combined-Energy-Resource Possibilities
Enhancing the value and versatility even more will be a Powerhouse fitted with solar PV collectors or wind turbines. For remote applications, this will effectively achieve the best of both worlds—namely, highly desirable renewable energy paired with highly reliable backup from a fueled source. Better still, both will share one battery, rectifier, inverter, and remote control setup for added economizing. Solar PV energy would then be the primary supply, but then, on overcast days or when the batteries are low, the ecopower generator would come on. (For more on this tandem arrangement, see case study later in this article.)

At the Powerhouse cabinet's current size, attached rooftop PV could yield about .4 kW; more panels could easily be added as needed.

Also for the US versions of these products, Marathon plans to integrate an appropriate cooling system, especially to please customers in the sunbelt—who, Cocking notes, will discover that the ecopower's heat output is already perfectly suited for year-round heating of swimming pools and hot tubs, and powering of the pumps "for a rather low cost."

Still another adaptation and value can be realized by chaining multiple units in series at one site. There's a build-in synergy to be gained by sharing common controls and hookups. One application now being piloted in a cold-weather environment is using two ecopower systems for zoned heating in one large home. Cocking explains, "One [ecopower system] will be in control of the other."

For that matter, the advent of scalable CHP on a micro level presents unusual opportunities for dedicating individualized power units within multi-family housing, to service rural cabins and lodges, or for remote industrial parks needing autonomously controlled heat and power.

Configuration and packaging of ecopower units could also be customized for the local region and conditions. For example, a new housing subdivision constructed in the sunny Southwest could easily do away with grid power altogether by using a combination of rooftop solar PV (as is now being envisioned, for example, in California's "Million Solar Roofs" legislative initiative announced in early 2005) and basement or backyard ecopower generators.

In any case, with or without a grid interconnection, the ecopower comes with built-in controls for integrating with other energy resources in combination, including the grid as the master, and the onsite in-home system as slave. The latter " sees the grid," says Cocking, "and marries up to it, running in synch."

Case Study in Rural Wisconsin: Rustic, Single-Family, Multi-Energized Micro-CHP
In 2003, engineer John Coffin was planning his new home to be built in the scenic countryside surrounding Madison, WI. Long fascinated with do-it-yourself power and cogeneration, he wanted a home that could be self-sustaining, he says, "largely if not entirely off the grid," with solar or wind energy.

Besides which, as he later discovered, a utility line extension would cost him $10,000.

Alternatively, by investing in solar panels, he would earn a state tax credit worth $8,500 (qualifying for it by promising to yield 3,200-kWh annual output). The sum total of avoided costs gave Coffin, as he recalls, ample reason to "go for it."

Sited on a hillside, the spacious home included, Coffin says, "lots of windows" for enjoying the area's panoramic natural views, but which multiply the challenge and cost of staying warm during the cold, dark days of December.

Load-wise, Coffin purchased low-energy lamps and applied good insulation, but he still runs all the usual household appliances, and even installed a wattage-intensive electric oven in a dual-fuel (gas top) range.

To power it all, he devised a system combining solar PV, solar hot water, and one of the first US applications of an ecopower unit, configured for about 2 kW. From this mix-and-match system—which has now completed its first autumn, winter, and spring of operation—he's getting the benefit of clean, renewable energy, yet without sacrificing the flexibility and security afforded by propane-fueled cogeneration. Coffin describes the assorted energy-production components and their integration, as follows:

Solar PV
Coffin purchased 16 Kyocera solar PV panels for a 14-foot by 16-foot ground-mounted array. Keeping them pointed at the sun's arc improves the output by at least 15%, so he also added two motorized axis trackers. Each panel produces on the order of 130 W or better (sunlight conditions permitting), making the measured total yield somewhere between 2.3 kW and 2.5 kW. This goes into sixteen L16 storage batteries, which yield a total of roughly 700 amp hrs of capacity at 48 V.

It's approaching self-sufficiency. "However," Coffin admits, "I did cheat a bit." He opted to lay down a 10-gauged copper wire as a drop line running 1,600 feet to his old home, which happens to sit on the adjacent lot (and is occupied by accommodating new neighbors). This line provides him plus-or-minus 400 W at 110 V, with a 4% voltage drop. It's not really critical or absolutely needed, he points out. However, it does serve as a nice battery extender, i.e., making them last longer because of reduced cycling, and also providing some emergency power backup, if ever needed.

After a year on the job, the solar energy system with battery storage, "really works quite well," he says, and it hasn't required much support.

Solar Hot Water Collection
To gather free heat from the sun as well, Coffin installed seven 4-foot by 8-foot solar heat collectors on a south-facing roof. During summertime these help warm the domestic hot water. Later in the season he redirects the water flow down into the home's well-insulated foundation via radiant floor tubing he installed 1 to 3 feet under the floor insulation. This warms much of the rock-fill below, making for a kind of heat storage bunker. "There's a good month-or-so-worth of heat stored in the rock under the basement," he says, providing a kind of "blanket" effect and zero heat-loss as the weather begins to cool. The warm rock under the house also minimizes humidity and dampness.

As the weather gets cooler in early October, the solar-heated water is directed into the normal 2-inch-deep radiant-floor heating system for maximum solar heating output

Switch On the Ecopower
Starting in late October, Wisconsin's climate turns "really bleak," Coffin says. For 8 or 10 weeks the sun pretty much goes away. What to do?

Coffin went shopping for a generator that would work long hours, be water cooled, and that promised good heat recovery. He looked hard but found, he says, "not a lot on the market." At a power show in Milwaukee he discovered the ecopower, and thought the size, features, price, and engineering all fit the bill nicely. "I didn't need a huge amount of output," he explains. The ecopower was also designed to be remotely controlled, which meant that his solar PV could share the same inverter, "so it was a pretty good fit." Coffin talked to Cocking and volunteered as a beta test site.

Installation in a corner of his basement was largely done by Coffin himself, and coupling the ecopower is designed to be easily handled by any licensed electrician. In Coffin's case there was already a grid-connected solar system, so a DC-output ecopower unit was all that was needed as a supplement. Marathon delivered a modified version called a "Powerblast rack unit," which comes without the weather-proof outdoor cabinet.

Almost immediately after installing it, Coffin recalls, "During the cold-weather season when the heat was really needed, I just switched it on and left it on," optimizing it to put out all the heat it could. With its extremely efficient water-cooled muffler and engine, the vast majority of heat was being recovered and turned into hot water. "In terms of systems efficiency, it is spectacular," he says admiringly. "It's real near 10%," he determined by noting its very tepid vented exhaust.

Captured heat goes into the same loop as the solar system pipe described earlier—making for a timely substitution during those gray days. Water temperature in the exhaust-heated loop comes out at anywhere between 85°F and 120°F, depending on pump volume (or speed) settings. This preheats the domestic hot water. Well-insulated storage tanks ensure that all the outflow is preserved.

Next, Coffin says, a regular hot water heater raises the temp to 105°F as the "final finisher" (if needed), the majority of the work having been done by the generator and/or solar heat system.

Warm water surplus beyond this domestic need also goes into the radiant floor and heats the house from the basement up. Rising heat, Coffin says, "does a pretty good job of keeping the house warm." Supplementing this on the upper floors are wood stoves and a furnace. If the sun should happen to peek out occasionally, "it still throws some extra heat into the system too," he says.

Coffin sums up the tiny generator's role: "It's really a good match for solar, because when the sun goes away I need heat, and when the sun goes away I also need power."

Unaided solar PV suffices for just over half the year. Late autumn—being dark and unproductive of much solar amperage—is also a heavy load period. During the ecopower's five-month maiden run from late 2004 into early 2005, it logged about 2,000 hours. At 2 kW per hour, he notes, "that's a lot of electricity," equal to all the solar he generated for the year.

Because he needs all of the little generator's cogen heat—but not necessarily all of its power—there were even times, says Coffin, when he ran electric heaters as a "luxury," or kept more house lights on, or used a separate electric heat pump as a fresh-air ventilator—all "just to keep the thing busy," so that he wouldn't risk overcharging the batteries.

Juggling Act
As previously noted, the solar PV input and ecopower share a common inverter, which manages and balances the generation. The DC ecopower output charges the 48-V battery bank, and then is inverted into grid-synchronous, single-phase AC. In fully automatic operation, the inverters can start and stop the generator as needed and integrate the three resources—solar PV, the "cheat" line to the grid, and ecopower generator—thanks to the latest-generation electronic features (from either Trace or Outback equipment). Both brands offer programmable controllers and the capability, says Coffin, of "keeping the bottles in the air."

Menu-driven control systems handle specific rated grid inter-tie inputs for the power structure, and do just about everything else that is needed. "Basically," says Coffin, "without the inverter being a pretty doggone versatile box, it wouldn't work worth a darn." For example, the inverter box can pare down the generator's output to what is required for battery storage; whatever can't be stored must be expended—or is exported to the next-door neighbor.

Power Export
This, too, is controllable. Coffin reports that for much of the winter the ecopower was indeed sending a few watts to the old property next door (via the above-described cheat line). A meter kept track. At other times—i.e., on warm, non-sunny days when the ecopower wasn't running because its heat wasn't needed—the cheat line occasionally imported power. Net outflow and inflow balanced to roughly equal (plus-or-minus 350 W or so, both ways) over the first year. Hence, the cheat-line power wasn't and isn't truly needed, he explains, "but it does stabilize the system on a day-by-day basis" and will continue because it will help the batteries live longer. Import-export levels can also be fine-tuned with the inverter electronics.

Permitting
As far as the utility company is concerned, the ecopower "doesn't exist," says Coffin, in a sense because, from a grid interconnection standpoint, the solar PV inverter "is the generator." "The Marathon unit is kind of invisible to them because it merely keeps the batteries more fully charged than the solar panels alone, and it causes me to have more surplus power to export." Thus, no additional permitting was needed. For grid safety, there's a solar disconnect at the adjacent property (i.e., at the end of the cheat line) "and the utility can come and turn me off whenever they want," he says.

Fueling
Becoming more popular than heating oil thereabouts, propane, he says, is "a nice, clean fuel" which he stores in a 500-gallon tank provided by a local co-op. In year one of his ecopower deployment, Coffin expended 800 gallons at $1.10 per gallon—essentially the same as he used for fueling a conventional furnace before.

An ecopower can run on either propane or natural gas (not always locally available in the boonies); and PowerPlus GmbH reports they're working on a new version that can run on digester methane.

Lastly, as a basis for comparison with Coffin's somewhat exceptional application, Cocking notes that the heat generated from one ecopower can heat his 2,700-square-foot home in southern Wisconsin. When the cold weather arrives this year, Cocking will rely on an ecopower to yield roughly the same heat his furnace did. "I'm taking the number of therms that I used last year and comparing it to the number of therms that this unit could manufacture," he says, "so I can heat my house."

In summing-up, Cocking underscores what this "glorified water heater" represents. "It's truly a home appliance. It is compact, streamlined, neat, and it looks good. It's designed to fit in a utility room, basement, or garage, depending on the homeowner's preferred application. When properly installed, it is as quiet as a refrigerator, and runs at the same decibel level… It has very user-friendly controls and a computer interface," he says, noting that it can be remotely monitored. In fact even a utility substation can communicate with it via a phone link, as part of its built-in capability.

"And oh, by the way," he adds. "You get electricity as a side benefit."