Major System Components Based on an evaluation of anticipated domestic hot water demand, the proposed closed loop antifreeze solar hot water system consists of:
- (2) Wagner EURO C20 AR flat plate solar thermal collectors with Sunarc solar glass.
- (1) Caleffi 119G solar storage tank with electric element backup
- (1) Flowstar solar pump station by Stiebel Eltron; includes temp. gauge, flow meter, and PRV
- (1) Stiebel Eltron SOM 6 plus Delta T controller with variable speed pump control
The system is designed for primary solar domestic water heating with seamless automatic backup from the electric element in the tank.
System Operation Whenever the rooftop collectors are warmer than the water in the bottom of the storage tank, a differential temperature sensor automatically activates a solar circulating pump. Sun-heated antifreeze pumps up to the collectors, then down through a heat exchange coil located in the bottom of the storage tank. In the spring, summer and fall, the system will provide a significant fraction of the household’s domestic hot water for showering, laundering, dishwashing, etc.
This is a closed-loop system, meaning that the non-toxic propylene glycol antifreeze never comes in contact with the domestic water supply. In case of unusually high hot water demand, or an extended period of cloudy weather when there isn’t enough sun to heat the top of the tank to its set point, the back up electric element will take over. The integration of the solar hot water system and the backup element will ensure that you always have an ample supply of hot water.
System Overheat Protection Under certain conditions solar hot water collectors can reach temperatures of 350 degrees F or more. Glass, copper and aluminum live comfortably at these high temps, but the propylene glycol heat transfer fluid in the system needs to be kept below 250 degrees to prevent acidification.
ReVision Energy incorporates ‘steamback overheat protection’ into every solar hot water system to protect the heat transfer fluid from a ‘stagnation event’ which can occur during power outages or during long stretches when hot water is not being used (i.e. you are away on vacation) and the solar circulating pump shuts down to prevent overheating the storage tank. Steamback is a robust, well-proven strategy developed in western Europe and widely accepted as the best industry standard (rather than building a separate heat dump zone).
Steamback is simple and elegant: when the solar pump has stopped and the collectors reach approximately 250 degrees F, a small amount of the water in the water/glycol mix begins to boil. As the water boils and turns to steam it expands to several thousand times its liquid volume, thereby forcing all of the propylene glycol out of the collector and into a specially sized expansion tank where the fluid stays cool and happy until the collectors fall back below the boiling point. At this point the water condenses, contracts and the system will self-recover as soon as the solar pump starts running again.
You can learn more about this important system design feature at http://www.renewableenergyworld.com/rea/news/article/2011/08/steamback-shows-promise-for-solar-water-overheating
System Performance This solar hot water system is expected to:
- Produce roughly 11,592,000 Btu’s of clean, renewable heat energy annually
- Offset roughly 4,906 lbs of C02 emissions from fossil-based energy sources
Incentives This system qualifies for the following state and federal rebates:
- The solar system is eligible for a 30% federal tax credit. This credit (not deduction) is subtracted directly from an existing tax liability. Please consult with your accountant or tax professional to ensure that you will be eligible for the tax credit.
- This system is eligible for an Efficiency Maine Solar Thermal Rebate. Incentives are based on projected annual energy production and must be cost effective to be eligible.
our solar contractor is Revision Energy. here’s a detailed description (excerpted from Revision’s system design/proposal) of the PV (photovoltaic) system.
Economic & Environmental Return on Investment – This solar energy system uses a clean, renewable ‘fuel’ called sunshine. Because it displaces finite, polluting and increasingly expensive fossil fuel, the solar energy system is guaranteed to pay for itself through avoided costs. After you get all of your initial solar investment back, the system will continue to deliver a valuable household revenue stream for years to come. Every time energy costs go up, your financial return on investment improves proportionally. Plus, the system will be eliminating thousands of pounds of CO2 emissions each year, delivering a powerful environmental benefit for you, your community and future generations.
PV (photovoltaic) Major System Components Based on an evaluation of available roofspace, site configuration, and energy demand, ReVision Energy proposes a roof-mounted photovoltaic array of 7.20 kilowatts (nominal).
The system features these major components: (30) 240 watt Monosilicon Canadian Solar photovoltaic panels; CS6P-240M or equivalent (www.canadian-solar.com) and (1) SMA Sunny Boy 7000 US grid-tied solar electric inverter (www.sma-america.com).
Whenever sun shines on the solar electric panels, they will generate direct current (DC) electricity. That DC electricity is transmitted to an inverter, which then converts it into AC electricity which can be used in your home. Any electric loads (TV, dryer, electronics, etc.) operating while the sun is shining will use available solar electricity. Any excess will flow out to the grid and you will receive a credit for the production.
Whenever the sun is not out, you will continue to purchase grid electricity as you do now. The local utility company will install record electricity you feed into the grid. If at the end of the month your generation is greater than your consumption, you will earn a credit on your next bill. You can bank your surplus from month to month for up to a year.
System Performance The proposed 7.20 kilowatt system is expected to generate roughly 8,830 kilowatt hours of clean electricity annually and offset roughly 11,479 lbs. of CO2 emissions annually
These predictions are based on weather data specific to location and adjusted based on conditions at the site. Snow accumulation and shading of the array will effect system production. Production will vary from year to year. Data estimates based on that of NREL PVWatts: http://rredc.nrel.gov/solar/calculators/PVWATTS/version1/.
Incentives This system qualifies for the following state and federal rebates:
- The solar system is eligible for a 30% federal tax credit. This credit (not deduction) is subtracted directly from an existing tax liability.
- This system is eligible for a Solar Electric Program rebate from Efficiency Maine. This rebate offers an incentive of $500 per 1,000 kWh of annual projected production up to a maximum of $2,000 for residential installations.
a post describing the solar thermal (hot water) system will follow in a few days.
once again, i find myself in the position of using most, if not all, of my 30+ years of architecture knowledge, talent, and experience to help my daughter and her family. it’s a uniquely rewarding opportunity. often times i have wondered if the primary purpose of my becoming an architect those many years ago was to help jessica overcome the abundant physical and built environment challenges she faces on a daily basis. i know, a bit strong on the fatalism, but….
now, there’s this little guy. his presence has expanded my thinking. he’s the next generation – the continuum. now, when i think of the future and what it might hold for our world, our society, our community, our environment, i find myself thinking a lot about his world. the world that louie will know long after my time has come and gone.
these days my wonderment includes “what have i done to help that world be better than the world i’ve known?” i may never know the answer. but, i’m hoping that my work on this project will provide a safe, comfortable and nurturing environment to support louie’s upbringing and development. maybe the energy savings designed into this house will help louie’s world be a little better? maybe the durability and energy-efficiencies of this house will save his parent’s money that can further louie’s education? maybe growing up in a house built in an established, sustainable neighborhood will provide louie with an improved world view as an adult?
who knows, maybe someday louie will thank his nonno for deciding to become an architect a long, long time ago?
in advance of today’s “storm of the century”, yesterday was a beautiful, sunny day! would have been a great day to be making some of that FREE electricity, but our roofer struck again. so, PV installation completion delayed yet another week. guess i was a bit premature in heralding our clearance of subcontractor hell, huh? but, hey, it’s not all bad. sheetrock is steaming right along. ALL sheetrock has been hung and most has received first coat of finish. so, with that abundant sunshine making deep interior penetration yesterday, the living space was lit up (and warmed-up!). jessica, todd and louie made a quick tour – they LOVE it! all-in-all, a pretty good day.
as predicted in the last post, the fun has officially started! one of my favorite phases of construction is sheetrock. for the first time, the spaces really start to take shape. suddenly, the rooms seem larger. and, the house brightens as daylight bounces around the interior. most of the second floor was sheetrocked in three days. this week we expect to get the most of the first floor hung. so, we could be painting (primer) in a few weeks.
looking ahead a bit, IF all goes well, we could be making electricity by the end of the week!!!!