Solar veteran Roger Perry discusses the pros and cons of One Tank Vs Two for Solar Back-up
All solar water heaters in Maryland, D.C. and the mid-atlantic provide a family of four with around 75% of their annual hot water load. Most customers use their existing electric or gas sources for the remaining 25% backup (usually needed dead winter). When installing a solar system one question that will come up is “Should I use my existing tank and have it fed by the solar system?” or “Should I remove my existing tank and use the electric back-up that comes in the solar tank?”. A couple of situations make this an easy decision;
- An existing electric water heater with no room for another tank. This is especially satisfying and cost effective if the existing tank is leaking or on it’s last legs. It’s like getting $1500 off the cost of a solar system because that money would have needed to be spent anyway. In this case you would definitely chose a single tank system.
- The other is if you have a gas water heater. While not as cut and dry as the example above, using the electric element would mean using a higher cost fuel for back-up (not so much with propane). Much of this extra cost would be mitigated because the single tank back-up would not run as much because it would be affected by solar input without running a faucet. You would need to run an electric circuit (30 amp, double pole breaker). This may be difficult or very easy depending on the breaker box location and available space in it. Most jurisdictions will also require a master electrician and a permit for this to be done. In this case, I think, most people would shy away from a single tank system unless there was just no room for another tank.
Let’s look at the pros and cons of each system;
SINGLE TANK PROS
- Smaller footprint
- Less heat loss
- Electric element can sense the solar output and not come on from stand-by losses
- Can go “all solar” just by turning off the element (essentially flipping a switch).
SINGLE TANK CONS
- Less back-up in cloudy weather (can be compensated with a larger solar tank which will have a larger back-up capacity).
- Less solar storage when the element is on (can be compensated for with a larger solar tank which will have more solar storage).
TWO TANK PROS
- Usually greater back-up capacity
TWO TANK CONS
- Greater heat loss
- Larger footprint
The secondary backup tank can’t sense the primary solar tank temperature unless a faucet is turned on, sending the water through the two-tank system. This causes the second tank to turn on from stand-by losses when the primary solar tank is already plenty hot.
Going all solar requires operating valves as well as turning off back-up.
Personally I’m a fan of single tank systems. For the most part their two main drawbacks can be compensated for by installing a larger tank. An upgrade from a 80 to a 120 gallon solar tank is only a few hundred dollars. For a 50% increase in solar storage it is a small price to pay.
WASHINGTON, DC: Skyline Innovations, a third party solar developer, engaged Solar Energy Services, Inc. to design and install a solar water heating system on an apartment building on MacArthur Blvd. in downtown Washington, DC.
The solar thermal system will include 20 thermal panels on the south facing roof of the building, as well as a 1,000 gallon solar storage tank. The system will act as a pre-heat to the building’s existing gas water heater, reducing their utility costs by around 30% annually.
FREDERICK, MD: Solar Energy Services, Inc., (SES) a leading solar energy products and services provider, announced today that it will begin work this week on a large solar water heating system for the Frederick County Adult Detention Center in Frederick, Maryland.
The renewable energy system, equivalent to approximately 130kW of power, will consist of 57 Apricus (AP-30C) evacuated tube solar thermal collectors, collecting thermal energy to deliver to the building’s water heating system. With each collector holding 30 tubes, the completed system will generate more than 2,500 gallons of hot water per day for the facility, using a total of more than 1,700 solar tubes.
SES Vice President and founder Roger Perry noted that prisons make excellent applications for solar water heating. “The occupancy is constant and all the hot water needs for laundry, bathing, cooking and cleaning are substantial. Aside from the environmental benefits, this system will pay for itself in a short period of time.”
The solar project is funded in part by ARRA funds, but also from the sale of Solar Renewable Energy Credits (SRECs). In 2011, Governor O’Malley signed a bill into law to include solar water heating in the state’s solar goals, thus allowing solar water heating systems to benefit from the sale of SRECs.
About Solar Water Heating
A very mature solar technology, solar water heating is 3 to 4 times as efficient as solar electric (photovoltaic) technology and therefore can be very cost effective where there is a regular, daily requirement for hot water. Residential, multifamily, prisons, hotels, dormitories, military barracks, industrial processing, health clubs, car washes and restaurants are all very good candidates for solar water heating systems. The solar systems are designed to provide preheating for all domestic hot water, allowing the traditional heating source to provide any supplemental thermal energy as required.
About Solar Energy Services, Inc. and Solar Water Heating:
With more than 30 years of experience, Solar Energy Services (solarsaves.net) is a leading solar firm in the mid-Atlantic, with a unique expertise on commercial scale solar water heating. Based in Millersville MD, SES provides design, installation and service for commercial, institutional and residential applications.
SES gives the skinny on going sunny
- 1. Cut your Energy Losses
In most homes, heating and cooling accounts for the most energy usage. Regardless of where your energy is coming from; gas, coal, solar, electric, wind, etc. a homeowner’s first consideration is to reduce the loss of incoming energy:
• Replace old windows and doors with Energy Star products. This can reduce energy consumption by 7 – 15%.
• Seal up any air leaks throughout the house, attic and basement.
• Insulate! This blocks air loss in the winter and preserves cool air in the summer.
- Consider those Big Appliances
Refrigerator: Keep the condenser coils clean. Keep refrigerator away from oven/washer/dryer and other heat producing appliances. Place with consideration to air circulation.
Stove: Remember that gas is generally a more cost-effective choice than electric.
Attic Fan: An excellent way of pushing hot air outside in the day, and drawing cool air at night.
- Need a new roof?
If you think your roof may need repairing or replacing within the next 5 or so years –it may be worth replacing before the solar panels are installed. If you’re on the fence about replacing your roof prematurely, remember that installers such as SES do provide a Remove and Reinstall service where, for a reasonable fee, the panels will be safely removed then re-installed after re-roofing.
- Small Bite or Full Monty?
Just about every solar energy company sells and installs Solar Electric (Photovoltaic) systems. However, solar water heaters are an entirely different type of solar panel and not every solar company installs them. Thus, not every solar company is likely to tout the cost-effectiveness of this mature technology. Solar water heaters require only a fraction of the roof space (and often a third of the cost) that a solar PV system requires. For a family of four, currently using electric to heat their home’s water – solar water heating may provide the biggest bang for your solar buck, providing around 75% of a home’s annual hot water. However, a family of two heating their water with gas may consider investing in a solar electric (PV) system sized for their usage. Insofar as solar electric (PV), many homeowners cover 60 – 100% of their electrical needs from solar. Some choose to offset as little as 25% and opt to add panels as their budget allows.
- READ your Energy Bill
For electricity, your energy bill should tell you how many kilowatt hours you use per year. This is an important number as you generally do not want to install a system that will exceed your annual consumption. Experienced installers can help you assess this, but a good rule of thumb is to divide that number by 1200kwH and that will tell you the approximate max sized PV system you should consider. That will be represented in kW – probably something like 8 to 10 kW if you are an average consumer. If you heat your water with electric, then solar water heating should absolutely be considered first.
- Best way to pay for your solar system
The beauty of an increased popularity in solar is that there are a number of ways a homeowner can finance their project. Without question, whether immediately or over time, Solar Power is far cheaper than your Utility bill.
Payment plans range from No-Money-Down leasing options to initial investments ranging from $2000 – $50,000 depending on your energy usage and type of solar system. Thanks to current financial incentives, many Marylanders receive over 50% of their upfront investment back the first year. Some of our customers have transferred funds from low yield CDs and even borrowed from 401ks in order to fund their higher-return solar investment. Other homeowners have no interest in ROI’s and fund-juggling and simply want a lowered electric bill/carbon footprint. Thankfully there is a wide variety of financing options available.
- Know YOUR solar energy tax credits, grants and incentives
Any solar salesperson worth his/her salt will visit your home with full knowledge of the available financial incentives for your state and county. For example, an Anne Arundel County resident has the good fortune of FOUR different financial incentives (for both PV AND solar water heating) that combine to offer a huge discount on their system. Acclimating yourself to current incentives for your county will help the sales process be much more informative for you. Every solar homeowner is eligible for a 30% Federal Tax Credit. Then SRECs (solar renewable energy credits), state grants, county tax credits differ across the region.
- Solar Panel Placement
Whether solar water heating or solar electric (PV), a south facing shade-free roof provides optimum conditions for solar panel placement. However, any shade-free roof – including East and West orientations provide excellent rooftops for solar panels. The number of panels installed depends upon system size, roof space and budget. Homeowners with a good amount of spare land may also consider ground-mounted systems, some of which offer solar tracking options where panels are mounted to motorized pole that literally follow the sun, improving solar efficiency by 40 – 45%.
- How many solar panels on the roof?
Insofar as solar water heating, a shade-free area of 64 square feet is typical to house two 4′ x 8′ solar thermal panels (sized to provide a family of four with around 75% of their annual hot water load). Most solar electric (PV) panels measure 3′ 6″ x 5′ 6″. So, a roof that is 30′ wide by 14′ from gutter to ridge will fit two rows of 9 panels. An experienced solar designer will get precise roof measurements and ensure the panels are placed in the most space-efficient and visually appealing design.
- Choosing a solar energy installer
Of course, the author of this blog would like to gleefully exclaim, “Choose Solar Energy Services!”. However, most educated consumers know that the best way of finding the best fit for an installer comes from shopping around for the popular 3 proposals/estimates. There are a lot of solar installers our there in today’s market. Some considerations:
Time in the Business: This matters. Obviously the more systems a licensed installer has installed – the more experience they’ve gained – and the more they’ve refined their installation technique. Just as important, however, is the question of whether the installer will be around in 5, 10 or 15 yrs when perhaps the incentives for solar have declined. An older company is likely to have deeper roots in the industry regardless of current solar trends and incentives. You want your installer to be around for the life of your system, 25 – 35 yrs plus. This narrows the field considerably.
Service Department: Solar Water Heaters require a 3 – 5 yr simple service visit. Does the installer provide this service?
All Options on the Table: A company who offers both leasing AND upfront purchase will likely lay ALL your options out on the table. This also goes for installers who offer both solar water heating AND solar electric.
There should not be a charge associated with a site evaluation of your home for solar energy. This is a necessary part of the sales process and should take place before the cost estimate/proposal is presented.
Happy Solar Shopping!
“If my collector is at 136 degrees, my TST (bottom of tank temperature) is at 161 degrees and my S3 (top of the tank temperature) is at 154 degrees – why is my circulator pump still running? Won’t this cool the bottom of the tank?”
SES says: The pump runs intermittently for a minute periodically when the collectors reach 240 degrees. This keeps the collectors from overheating. Your maximum tank temperature is set to 160. If the bottom sensor, the TST reading, exceeds 160 degrees, the controller will run the pump briefly in the evening to bring the tank temperature back down to 160.
It has been our experience that setting the max temp higher than 160 leads to overheating problems. Yes, you are losing a little heat from the tank when the cooling feature comes on, but at this time of year it is excess heat. You are producing much more hot water than you are using at this time. This is the summer solstice; the collector and tank temperatures will moderate in a few months. Some customers add an extra loop to their solar tank and use that excess heat to heat a swimming pool or hot tub. Most just use control features to manage the excess heat.
Don’t worry about the power consumption. The Grundfos Alpha pump only uses about 5 Watts whether heating or cooling the tank.
WASHINGTON, DC: Earlier this week, Solar Energy Services, Inc. completed the installation of three separate solar water heating systems on the campus of American University…
The Mary Graydon Center, which houses a dining hall as well as various administrative offices, was outfitted with a rooftop solar thermal collection system which included 16, 30-tube solar collectors. These collectors are closed-loop, plumbed to 7, 120-gallon pressurized tanks for a total storage capacity of 8,406 gallons.
Anderson Hall, the largest of AU’s dormitories housing over 770 students, was outfitted with 81, 30-tube solar collectors closed-loop plumbed to a unpressurized 5,000 gallon storage tank.
Letts Hall, housing dormitories and a fitness center, was outfitted with 55, 30-tube solar collectors closed-loop plumbed to 1, 3,111 gallon storage tank.
All three solar water heating systems will serve as a pre-heat to the buildings existing conventional water heating systems.
Click HERE for post-installation pics
WASHINGTON, DC: Solar Energy Services, Inc. completed installation of a fully automatic solar water heating system at Park Tower, an apartment building located in the historic Adams Morgan neighborhood.
The building is home to 125 apartment units throughout its five floors. SES was contracted by Skyline Innovations, a third party solar developer, to install and commission the solar thermal system. It consists of 48 solar thermal panels and three 1000 gallon thermal storage tanks. The system is slated to offset a huge portion of the building’s conventional water heating system.
The building houses 175 units on its 9 floors, and contracted with Skyline Innovations, a third party solar developer, to offset its large heating load with solar. The building will be outfitted with 44 solar thermal collectors and a 3,111 gallon thermal storage tank. The system promises to offset a huge portion of the building’s conventional water heating system.
WASHINGTON, DC: Solar Energy Services, Inc. of Millersville, MD has been contracted by Skyline Innovations, Inc., a Washington, DC third-party solar developer, to install two solar water heating systems at the George Washington University campus in downtown DC.
The systems include a ballasted 30-panel evacuated tube system on the flat rooftop of one dormitory and a similar 60-panel system on the flat rooftop of another dormitory. The 30-panel system design will utilize an existing 2,500 gallon storage tank in the penthouse for solar storage, while the 60-panel system design utilizes an existing 2,500 gallon tank in the basement mechanical room.
Click HERE for post-installation pics