This recent project in Madbury, New Hampshire features both a flat plate solar hot water array, and 5kw of solar electric production

The dizzying drop in cost of photovoltaic (PV) panels is great news that’s making headlines, as well as shifting the way architects, green builders, and even solar installers think about venerable solar thermal technology.

With high-efficiency electric heating equipment available, and PV at record-low prices, doesn’t it make more sense to install an electric water heating system and then use PV to generate electricity to offset that electric load? Isn’t that “Solar hot water?”

Well… not so fast. While electric water heating backed up by PV works great for certain cases, the full story is a bit more nuanced. For homes occupied year-round with moderate (60GPD+) hot water consumption, solar thermal remains a clear winner for domestic hot water loads (the game is changing in solar space heating, but we’ll address that another time).

Solar Thermal: A Use it or Lose It Solution

For solar thermal to make sense you should occupy your home during the summertime, so as to take advantage of free hot water during peak production months. Unlike photovoltaic systems, which are able to bank excess summertime production for the winter by selling power to the grid, solar hot water systems are not good at providing storage for more than a few days at a time.

When properly sized, a solar hot water system will provide around 76% of year-round hot water consumption: 100% of the hot water a household consumes from May to September (and not too much excess), and ~50% of hot water use in the off-season.

Clearly, a home needs to be occupied in the summertime for solar thermal to make sense:

A Tale of Two Houses

For an active family, solar thermal is the least expensive way to meet year-round domestic hot water loads.

Solar thermal technology is much more efficient at converting sunshine to heat than photovoltaic panels are at converting sunshine to electricity (~60% vs. ~19%, respectively). This means that more hot water is available, at a lower cost, than a comparable electric-powered system. The differences are minor for a house with small hot water loads (<30gal/day) but as a household's hot water needs increase, solar thermal outpaces an all-electric system pretty quickly.

Let's compare the options for two houses. The former is a single person moving into a high-efficiency home. She uses a meager 20gal/day of hot water. Another is a family of 4 in a conventional home, which uses around 60gal/day.

Using a new, efficient electric tank, the single person will use around 1,600 kWh of electricity each year to heat water. To offset that with PV, she will need around a 1.3kw system. We will assume she has already maxed out state rebates on a previous PV system for "plug loads" (i.e. all of their other power needs) but still qualifies for the 30% federal tax credit. At a rate of $4.5/installed watt, the 1.3kw system + nice electric heater will come out to around $5,095. That's indeed less expensive than a solar thermal system, which will cost about $6,700 after state and federal rebates, and still require a bit (~$200) of electricity each year for water heating.

Things change quickly with a family that uses 3 times that amount of hot water (common, even conservative in many cases). In the 4 person household, we'll say the home uses 4,700 kWh/year for water heating. A 3.7kw PV is needed to offset the larger load. Again, assuming a federal credit but no state rebate, the PV system + nice water heater comes out to around $11,500. Now the solar hot water system, at $6,700 net, is the obvious choice (even if this home has not used up state PV rebates). Even adding a bit of PV to cover backup water heating (1kw will cover that $200/year nicely), the whole system comes out to around $9,200 total.

In short, the choice between one option or another depends a great deal on the behavior of a home's occupants and the size of a home. Seasoned solar designers will look at the overall picture of a home rather than assuming that "one size fits all."

Solar Hot Water Versus Heat Pump Water Heaters

Schematic of a Stiebel Eltron heat pump water heater

The introduction of heat pump water heaters makes the the solar hot water vs. electric water heating debate more complicated. For a cost of around $3,000 installed, these high-efficiency electric water heaters offer 2.5x more heating per kWh than conventional water heaters.

We recently calculated a demand of around 1289kWh/yr to run one of these units for a new construction project, or about the same annual production as installing 1kw of PV panels.

Based on an installed price of $4.5/watt for PV, this hypothetical hot water system results in an installed cost of around $7,500 prior to incentives, which are worth $1,950 (note that most PV systems are a minimum of 1.88kw so more likely the PV system would be sized a bit larger and meet some part of other household loads as well).

While the heat pump and PV solution hold a slight cost premium (around $1,150 less) than solar hot water in this case, it's not quite a clear case against solar hot water:

• If you are already investing in a PV project, adding solar thermal opens up additional state rebate money you would not other tap into. At $1,000 or $1,500 (ME and NH, respectively), the state rebates for solar hot water are more generous than for heat pump water heaters.
• Heat pumps are noisier typically than a solar hot water tank. This matters most in new, efficient buildings where mechanical rooms may be close to living quarters.
• Heat pumps achieve their higher efficiency by using ambient air temperature to heat water - in the wintertime this means using heated interior space for water heating, which adds to the overall heating load of the building, thus more energy is consumed to keep the building at a comfortable temperature.
• Warranties on heat pumps and solar hot water equipment are similar (10 years), though we feel that the long-term maintenance costs of solar hot water will be less than service costs of heat pump systems.
• Solar hot water collectors will take up less space to produce a household's hot water than a comparable PV array offsetting an electric device. This is important for households that want to make the deepest cut into their electric bill as possible and have limited south-facing roofspace.

Solar Thermal Stays Strong

The dramatically shifting landscape of solar electricity makes for exciting times. It's never been better to invest in a photovoltaic system, particularly while both Maine and New Hampshire have generous state rebates.

That being said, solar hot water systems still make great financial sense in many cases. Here's the takeaway:

Good Candidates for Solar Thermal Water Heating:

• Will replace an inefficient, high-mass boiler or older propane/electric tank for water heating
• Occupy the home year-round
• Use a fair amount of hot water
• Have adequate space to install a 80-100 gallon storage tank

Good Candidates for Solar Water Heating with Electric + PV:

• Vacation or seasonal homes
• Already have an efficient water heating system (on demand or efficient electric tank)
• Meager hot water needs
• Not a lot of space available for mechanical systems

When Bill Babb and his wife Barbara retired from their jobs as school teachers, controlling monthly costs was an important way to maintain the good life. Investing in financial markets looked shaky, and they wanted to see something positive result from their efforts. After seeing a presentation by a former student, Hans Albee, they started looking seriously at a solar energy investment – and they liked what they saw.

“For years, the upfront cost was an issue with solar,” Bill says, “But when we looked at it recently we were pleasantly surprised – the cost of solar panels had dropped considerably, and with state and federal incentives, we found we could purchase a system that would be a better investment for us than the stock market. Barbara and I both agreed that the cost of energy will only rise, and rise faster than it has in the past.”

As a pragmatic environmentalist (and climate change skeptic), Bill was attracted to solar’s minimal impact on the natural landscape. He likes that his clean power doesn’t add turbines to untouched landscape, block up or contaminate waterways, or contribute to air pollution. He also likes the impact solar has had on his monthly bill.

“We were expecting the system to produce around $50 a month of power, but so far it’s produced closer to $60-70,” Bill says. “We’re happy to be banking some power for the winter months, and seeing our electric bill dramatically reduced. The system has done everything I wanted it to do from day one.”

Solar Hot Takes it Farther

Bill and Barbara’s positive experience with solar electricity lead them to adding a solar hot water system, which further reduces their home’s fossil fuel needs by allowing their boiler to go dormant for 5-6 months of the year. We caught up with Bill just a few weeks after the system was installed, and he reports that so far, it had stayed well above the 110 degree mark that would trigger his boiler to turn on.

“The furnace has been turned off for weeks and we have had plenty of hot water, even without changing our lifestyle” Bill says, “On days that are a cloudy mix with little direct sun, we’re surprised at how much heat the system produces. We like it!”

Forrest Lowe’s combination domestic hot water and pool heating system uses 6 flat plate collectors to deliver ample heat to his pool in the summertime (Photo courtesy Forrest Lowe)

When Forrest Lowe and his wife were seeking their perfect retirement home, they knew they wanted a quiet spot by the water. Longtime Brunswick residents, they fell in love with a house on Coffin Ice Pond, which years ago supplied ice for the town. What Forrest didn’t expect, however, was to also fall in love with the pool that came with the house.

“At first I was lukewarm about the pool,” Forrest says, “But ultimately it grew on me, though we knew we had to find another way to heat it because the propane heater that came with it was smelly, and extremely expensive to operate.”

A Better Way to Heat a Pool

While most pools are heated by propane, a small but growing cadre of pool owners are harvesting Maine’s abundant solar energy to open their pools earlier and keep them open longer into fall. The same solar thermal technology that heats domestic hot water can help heat a pool, as Forrest learned from his friend Rick Williams, who recently had ReVision Energy install a solar hot water system on his home in Yarmouth.

“Rick introduced me to [ReVision Principal and Engineer] Fortunat, who was great through the whole process. He helped me come up with a 5 flat plate solar hot water collector system, which I ended up expanding to 6. I wanted an overkill system because I wanted our pool to heat up quickly and stay hot longer.”

Hot Water, By Design

Part of the challenge of keeping Forrest’s pool warm is that he is reluctant to use a pool cover, which he finds cumbersome for one person to deploy. As such, the pool loses heat overnight, a reality that’s compensated by the outstanding performance of his solar water heating system. Whenever the sun is shining, Forrest’s flat plate collectors heat up his home’s 105 gallon solar storage tank before dumping excess heat into his pool.

“I am amazed at how effective this system is at heating the pool,” he says. “It only takes a little while to get the domestic hot water up to temperature and then starts dumping into the pool. On a nice sunny day you can feel the warm water pouring out the jets!”

A Great Solar Season

Forrest is thrilled at how the solar hot water combo system allows him to extend the season of his pool as well as enjoy it more during the season (there have been a number of days when the pool approached 90 degrees… balmy!). On a good sunny day he’ll see more than a 4 degree rise in the pool – no small feat considering the pool’s 25,000 gallon capacity. He loves the free fuel from the sun and the satisfaction that comes from clean solar energy. On the domestic hot water side, he notes that his boiler rarely fires in the summer, and estimates saving at least one oil delivery per season.

“To me this is not just about saving money,” Forrest says, “It’s about avoiding pollution and getting independent of fossil fuels.”

And, of course, enjoying his pool. Enjoy the sun, Forrest!

A recently installed solar hot water system in Gorham, New Hampshire

Now’s the time to get in your reservation if you want to benefit from New Hampshire’s generous residential solar hot water rebate (averaging $2,600 for most homes).

We’ve received word that the reservation window has been reduced from 12 months to 3 months (that is, the window you have between submitting a pre-approval and having your installation completed), per request from the DOE.

The state is encouraging homeowners to complete all of their solar hot water installations by this October. Due to the popularity of the program we encourage you to contact us today if you want to get a system installed this season. The commercial rebate program still looks good.

The good news is that financially the program still has plenty of funds, though we are told most of the DOE money (which funds the $2,000 portion of the rebate) has already been committed. In general, the solar rebates made possible by ARRA funds are running out, so rebates may likely never be as good as they are today. With oil prices high, and set to go higher, the time is really right for solar!

Click here to see the whole update from New Hampshire PUC.

What About RGGI?

In February/March of this year New Hampshire shocked much of the Northeast by presenting a bill that would pull the Granite State out of RGGI, the Regional Greenhouse Gas Initiative. We called upon lawmakers to think about the long-term implications of such a move and stand up to support RGGI.

This past week, the NH Senate voted to revise rather than repeal RGGI. Businessweek reports:

The Senate voted 16-8 Wednesday to approve an amendment proposed by Senate Republican Leader Jeb Bradley to a House bill. The amendment retains the state’s participation in the program but limits how the money is spent by dedicating it to well-established energy efficiency programs run by the utility companies.

The amendment replaces a bill passed by the House in March that would end the state’s participation in RGGI, but the Senate lacks the votes to override a gubernatorial veto of that legislation. Bradley’s proposal is meant as a compromise.

Gov. John Lynch has not said he would veto the House bill, but he opposes efforts to end New Hampshire’s participation in the greenhouse gas initiative.

“You can’t always get what you want,” Bradley said, “but what we need today is good government. … We have got to fund programs that work.”

Bradley estimates New Hampshire’s program costs the average ratepayer 35 cents per month. His proposal would drop the monthly cost to 17 cents.

Full story here: http://buswk.co/iNiwPp

The Latest from Maine

Legislation that will continue Maine’s solar rebates for the foreseeable future is expected to pass, however the program still has not been given an alternative funding mechanism yet. While the tract looks promising, we still urge you to contact your state legislators if you have not already and ask them to support solar rebates. For those who have advocated on behalf of solar rebates so far… thank you!

We understand around $500,000 remains in the program, which should sustain the ME state solar rebates for at least the next 6 months. We’re hoping to see an effective funding alternative make it into place for a more sustainable continuation of the program before the current funds are exhausted.

The solar hot water system on University of New England’s Campus Center will save roughly 3,960 therms of natural gas annually, a savings of roughly $5,500

The University of New England is the latest college campus to show leadership in sustainability with the installation of 21 flat plate solar hot water collectors on their Campus Center.

Made possible by a $50,000 American Recovery and Reinvestment Act (ARRA) Grant, the system will heat water to between 80-140 degrees before it is fed into an existing gas boiler.

The total annual energy output of the system is estimated at 237,615,000 BTUs per year, which at a typical boiler efficiency of 60% will save roughly 3,960 therms of natural gas annually.

Below is a schematic of the system, consisting of the panels and multiple pre-heated solar storage tanks:

The Portland Press Herald reported this on the project:

The project, administered by Efficiency Maine, is expected to provide up to 50 percent of the Campus Center’s hot water energy supply. The real-time digital monitor also being installed will enable the university to determine cost and energy savings.

“Everyone is excited about it, ” said Alethea Cariddi, the university’s sustainability coordinator, adding that the project is part of a “multi-pronged strategy the university is taking to achieve our climate neutral goal.”

Full article: http://www.pressherald.com/news/maine-UNE-biddeford-Solar-university-campus.html

UNE’s Sustainability Coordinator, Alethea Cariddi, leads the university’s efforts to pursue climate neutrality through behavioral change and energy efficiencies. She says, “The solar hot water project on our Biddeford Campus Center is UNE’s first experience with renewable energy sources … Reducing our energy demand, increasing our efficiency of energy use and utilizing renewable energy sources is the multi-pronged strategy the university will be taking to achieve our climate neutral goal.”

In November 2008, UNE President Danielle Ripich signed the American College & University Presidents’ Climate Commitment, pledging along with other higher education leaders across America to reduce greenhouse gas emissions on campus and raise awareness of the issue of climate change.

From our Schools and Nonprofits Solar Photo Gallery:

See more installations in our Solar Projects Map

Sun shines down on a set of solar thermal collectors installed on the refurbished Mill at Saco Falls.

Earlier this month music and celebration marked the opening of an old mill building in Biddeford that has been converted into housing units.

The 66 apartments Mill at Saco Falls showcase the greenest type of green building – taking an existing structure and repurposing it, preserving the building material as well as the cultural heritage of the historic structure.

Listen to the MPBN report:

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The Portland Press Herald also reported:

[Nathan Szanton of Maine Workforce Housing LLC] said the project entailed maintaining the mill’s historic character while incorporating significant green features. For example, solar panels on the roof that heat water required strategic placing to keep them out of sight, because the modern look of the panels would detract from the historic appearance of the building

The solar thermal panels on the Mill at Saco Falls are arranged so that the street-view of the historic building is not affected – only the consumption of fossil fuels!

The solar array consist of 25 American-made flat plate solar hot panels that will produce more than 1,000,000 Btu’s of energy on a bright sunny summer day.

The solar heated water is pumped into a massive 1,350 gallon storage tank, which is plumbed into the main domestic water feed.

In the summertime, the sun alone will be enough to heat the tank for showers, dishwashing, etc. In the colder months it will serve as a pre-heat for an existing gas boiler.

The high-volume solar thermal system will provide more than half of the building’s hot water needs – saving over 3476 Therms of natural gas annually!

Standing atop the river that made Saco and Biddeford boom towns in prior centuries, the new project is a strong statement to the marriage of tradition and our renewable energy future.

Randy Lane, proud owner of a ReVision Energy solar hot water system, is going to be opening up his home at 8 Abby Lane in Richmond, Maine on Thursday April 16th from 6-7:30pm.

This will be ReVision Energy’s first ‘sponsored’ Solar House Party event and we hope you consider joining in the fun!

Randy, a 30 year veteran of the building trades, designed and built his home with both active and passive solar applications in mind. The passive solar system is a solarium / greenhouse designed by Lane to provide supplemental space heating.

The active solar hot water application was designed and installed by ReVision Energy. There are 90 evacuated tubes installed on the south facing roof, mounted on a stainless steel racking system at 45 degrees to optimize year round performance. These collectors heat a 160 gallon, super-insulated dual coil storage tank. Hot water from the storage tank supplies both domestic use and supplemental space heating. The system is backed by a high efficiency propane boiler. Lane has been monitoring the energy his systems produce and reports that his savings are quite impressive.

Randy has taken the information he has learned from his own experience and applied it to his building practices. Randy is the founder of New Earth Solutions, Inc., a green general contracting company whose goal is to bring energy efficient solutions to new construction or remodeling clients at an affordable price.

The open house is a chance for those interested or curious about passive or active solar design to come and see it for themselves. There will be a representative from ReVision Energy present to describe how the solar hot water system works. There will be a tour of the systems and plenty of time for questions and answers. The event is free and all are welcome. Please plan to meet at 8 Abby Lane in Richmond by 6pm. If you have questions please contact Jen at (207) 221-6342.