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Sun Volt

Sun Volt Solar

earth, the final frontier

Clean Energy, Clean Environment

We are at a cross roads in human history, we can choose to continue on as we have been, or we can make a change to improve our future and quite possibly the future for several generations to come. We are here to promote energy independence, a better environment, a secure future and a higher return on investment for your hard earned dollar. It is what I believe in, it is why I am in the solar business.

What happens to a solar system when it snows?

01 Mar 10 | Solar Electric, Solar Hot Water, solar thermal

I have good customers, they ask good questions.  One such question asked of me lately has been “what happens to my solar system when it snows?”  Since I have both a solar thermal system and a photovoltaic system on my house, I can tell them.  Enough sunlight gets through the snow that the panels begin to heat up.  This, in turn, causes the snow to slide off.  Here is a picture of a ground mounted system after receiving over two feet of snow:

Ground mounted PV array after blizzard

Ground mounted PV array after blizzard

It helps that the panels are tilted to 40 degrees, roof mounted systems likely will not shed snow like this.  Still, on a roof mounted system, the snow will melt off, it might take a little longer.  The only system I would be careful of in this climate would be an evacuated tube collector.  Because the tubes have a vacuum, no heat is transfered to the glass envelope, which is really good for collecting heat, but not so good for melting accumulated snow off the collector.

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01 Mar 10 | Solar Electric, Solar Hot Water, solar thermal | Comments (0)

Solar Power: Save money, increase the value of your home

20 Dec 09 | Sales, Solar Electric, Solar Hot Water, solar thermal

I have been going over some of the bills from the last few years. My utility company, Central Hudson Gas and Electric has been increasing the cost of electricity by 9% annually.

central hudson electric rates

Nine percent per year seems like quite a bit, especially since inflation has been running around two to three percent. The increases of fuel costs and energy products in general has far outpaced inflation. Projected out 25 years, the cost per kWh is $1.53! I don’t expect it to get that bad, but one never knows.

Here are some solar facts:

Based on conditions here in NY state:

  • The average home owner chooses to install a 4 KW DC photovoltaic system. This generates 4500 to 5000 KWh per year.
  • With rebates and incentives, the final system cost is about $10-11K.
  • Over the course of the system life (25 years), the electricity generated will cost $0.09 per KWh. Currently, NY electricity averages $0.158 KWh (increasing at 9% per year).
  • Without inflation, that equals a savings of $29,000.00.

Also, based on conditions in NY state:

  • the average home owner chooses to install an 80 SF/80 Gallon solar hot water system. This will supply a family of four with 80% of their hot water annually.
  • With rebates and incentives, that system cost is around $3,800.
  • Over the course of the system life (25 years), the energy converted by this system will cost $0.03 per KWh. Currently, NY electricity averages $0.158 KWh (increases 9% per year)
  • Without inflation, that equals a savings of $16,500.00.

Of course, these are long term investments. In order to realize this type of savings, a homeowner will have to stay put for 25 years. That is a rarity these days.

Solar systems retain almost all of their pre-incentive/rebate value when added to a structure as a capital improvement. Here is a list of residential home improvements and the values added to a typical house:

  1. Two story addition: 94%
  2. Bathroom remodel: 93%
  3. Major Kitchen Remodel: 91%
  4. Solar System: 90%
  5. Basement finish/remodel: 89%
  6. Siding: 88%
  7. Roof Replacement: 85%
  8. Deck: 84%
  9. Hot tub: 84%
  10. Family room addition: 82%
  11. Sun room: 75%
  12. Garage addition: 70%
  13. Backup power generator: 58%

Of course, if the rebates and incentives are considered, then the installation of a solar system is cash positive from day one. What this means is the homeowner pays $11-12K but gets $32,000 of additional home value. I can’t think of a better deal than that.

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20 Dec 09 | Sales, Solar Electric, Solar Hot Water, solar thermal | Comments (0)

Solar Site Assessment Tool

07 Dec 09 | Solar Electric, Solar Hot Water, solar thermal

File under: Yeah, there’s an app for that.

Sun Tracker mashup

Sun Tracker mashup

I received an e-mail from Andrew about a Solar Site Assessment app for 3G iPhones.  I’ll let him tell the story:

I live in Vancouver, BC, when evaluating my own home for a solar installation I discovered a gap in the solar tools market. I have a lot of trees in my backyard and was interested in doing my own shade analysis assessment. So, I looked around and found expensive tools and manual sun plots, and nothing in between. At the same time my son happened to get an iPhone. I was intrigued with the built in compass and inclinometer capabilities, and putting two and two together I come up with an iPhone based solar assessment tool.

You can check out more at their website:

www.imeasuresystems.com/

I know in New York State, NYSERDA requires a site assessment be submitted for each application.  In order for a site to qualify for the NYSERDA rebates, it has to be 80% unshaded or more.  The rebates themselves are performance based, e.g. the better the site, the more the rebate.  This app has the ability to print out a site assessment, which is key.

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07 Dec 09 | Solar Electric, Solar Hot Water, solar thermal | Comments (0)

Variable Speed pumps

10 Oct 09 | Solar Hot Water, solar thermal
TACO 00 VT solar circulator pump

TACO (Thermal Appliance COmpany) is one of my perennial favorites.  I have used their circulator pumps for all of my solar hot water installations.  I like them because they are efficient units, well made, rugged, easy to service and are manufactured in Rhode Island, which, last time I checked, was a part of the United States.

What has me intrigued today is their 00-VT variable speed control product line for solar hot water applications.  They appear to have integrated a Differential Temperature Controller (DTC) into a variable speed motor drive and attached it to a circulator pump.

From the TACO website:

The (00VT) circulator continually adjusts its speed, maximizing the output of the collector, increasing the usable higher temperature water throughout the day, eliminating short cycling and increasing system performance by 20%.

Features:

  • All-in-One Pump and Variable Speed Solar Control
  • Available in Several Sizes, 006, 008, 009 and 0011
  • User Definable Line Voltage Output,
  • Supports Drain Back Applications
  • Freeze Protection for Open Systems
  • Holiday Function, Minimizes Collector Stagnation
  • Adjustable Storage Tank Maximum Setting

Makes a lot of sense to reduce the pump speed based on the Δt of the heat exchanger. This reduces electrical use of the circulator pump, increases the heat transfer efficiency of the heat exchanger and eliminates short cycling.  From the literature, I cannot tell if the pump has an full featured differential temperature controller which would eliminate the need to install a separate one.

I called the factory to ask that question, but did not receive a good reply, so the question remain unanswered.  I believe next spring I will purchase one of these units to experiment with.

The variable speed motor controller is one of two designs, either a variable frequency drive (VFD) which will work on some permanent split capacitor motors such as the 00 circulator pumps use, or a TRIAC device.  One issue with variable speed motor drives is they can often cause RFI (radio frequency interference) if they are not properly shielded and grounded.  It would be interesting to learn which type controller this pump uses and whether or not it produces RF noise.

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10 Oct 09 | Solar Hot Water, solar thermal | Comments (0)

Hot Water tank stratification

03 Jun 09 | Solar Hot Water

There are many considerations to ensure that a solar domestic hot water system will perform at it’s optimum. The collectors should be facing south, tilted to latitude, unshaded,  etc.  One consideration that is usually not thought about or understood is the storage tank.  Like any energy storage system, there are some physics that accompany a hot water storage tank.

Stratification simply means to divide into layers.  Heated water rises because it is less dense than cold water.  The warmest water will be found in the layer right at the top of the tank, hence, most tanks have their hot water outlet at the very top of the tank.

When pumping water out of a solar storage tank, through a heat exchanger and back again, it is very important not to completely mix the water in the tank.  In most SDHW systems, the temperature sensor for the storage tank is at the very bottom of the unit.  If the tanks gets mixed, chances are the collector temperature and the tank temperature will reach equilibrium and the system will shut off.

If the solar storage tank water is pumped slowly, so that the tank stays stratified, the system will net much more heat.  This works especially well in a two tank system where tank number one is the solar tank which pre-heats the water going into tank number two, which is the back up heating system.  If done correctly, both tanks will  have a thermocline about 1/3 up from the bottom of the tank.

There are two good ways to accomplish water side heat exchanger pumping without breaking the solar tank stratification.

  1. Use a small ac pump, such as a TACO 003B and throttle the output side of the pump with a ball valve.  This pump uses very little electricity (rated for 42 watts, 115 VAC) and therefore is pretty efficient.  Restricting the flow slightly with a ball valve will not hurt it.  The water going into the heat exchanger from the solar tank should be about 5 – 10 degrees (Δt = 5-10° F) cooler than the water coming out.
  2. Use a PV powered DC pump.  There are two DC pumps that run directly from a 12 volt PV panel, the Liang D5 series and El Sid.  These can also be throttled on the output side for temperature rise of 10 degrees from input to output.    The advantage of this system is that the pump speed will adjust to the available sunlight (thus available heat) making the system more efficient.  The disadvantage is it is more expensive.

Experience shows that a good rule of thumb is 0.0125 gallons per minute per gallon of storage.  Therefore, for an 80 gallon storage tank, optimum flow rate on the storage tank side of the heat exchanger would be 80 gallons x 0.0125 = 1 GPM.  For a 120 gallon tank, 1.5 GPM and for a 240 gallon tank, 3 GPM.  This will generally give a 10 degree temperature difference between the top and bottom of a vertical tank.

Tank stratification is an important design factor that is often not thought of when a dual pumped internal or external heat exchanger system is installed.

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03 Jun 09 | Solar Hot Water | Comments (0)

Can plastic piping be used in a solar hot water system?

12 May 09 | Solar Hot Water, Training, solar thermal

Short answer: Don’t do it.

Plastic piping such as PEX, PEX AL PEX, PVC, ABS, etc. can be safely used with hot water systems, radiant floor heating and so forth.  It is much cheaper and usually easier to work with than copper or stainless steel.  That being said, it is not appropriate for use in any solar thermal application.

Solar thermal systems have much less control over high temperatures than conventional fossil fuel based systems.  Summer time collector stagnation temperatures can easily reach 300° F.  At these temperatures any plastic piping will melt.  This will cause the Heat Transfer Fluid (HTF) to leak creating a big mess and likely an insurance claim.  The only type if piping that should be used in a collector loop is copper or stainless steel.

Even copper fittings with rubber gaskets (AKA Pro-Press or Viega fittings) are only rated for 250° F.  They should not be used in a solar loop either.

It is worth the extra time, effort and expense to solder copper piping and or purchase stainless steel tubing for use in the solar loop.  This will ensure that the system works well for years to come with no leaks and no call backs.

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12 May 09 | Solar Hot Water, Training, solar thermal | Comments (0)

Calculating energy needed to heat water

05 May 09 | Solar Hot Water, solar thermal

In order to properly size a Solar Domestic Hot Water (SDHW) system, a few pieces of information are needed:

  1. Current and future occupants of the house or average hot water use.
  2. Water supply temperature
  3. Desired hot water temperature
  4. Stand by loss of heating unit

We know that in this area (Mid Hudson Valley) ground water temperature averages 53 degrees.  I know this because I have personally measured the well water temperature at all of our SDHW installations.  This is a good starting point.

Most people desire their hot water temperature to be between 110 to 120 degrees.  There are some applications where hotter water (laundry, dish washers, etc) is desired.  For general purposes 115 degrees is a good ending point.

We also can base average hot water useage on the number of occupants of any house.  The rule of thumb is 20 gallons per person for the first two people, 15 gallons per person for any additional people.  This means that the average family of four uses 70 gallons of hot water per day (20+20+15+15 = 70).

Standby losses for water heaters generally range from 5-10% for electric and oil fired systems and 40% for natural gas or propane water tanks.

For the purposes of Solar Hot Water, an appropriate unit of energy would be the BTU.  If we were using SI units (metric) it would be the Mega Joule (MJ).  Since most HVAC contractors understand things in terms of BTUs, it is easiest to use this unit.

A BTU is defined as amount of heat required to raise the temperature of one pound of liquid water by one degree Fahrenheit.   That is close enough for our purposes.

Therefore, the formula to calculate energy use is:

BTUneeded= 8.34 x Gallons x (desired°F-supply°F) x Standby

Where:

  • BTUneeded = BTUs needed to heat the water for one day
  • 8.34 = Weight in pounds of one gallon of water
  • Gallons = Gallons of hot water used in one day
  • desired°F= Desired temperature of the hot water
  • supply°F= Cold water supply temperature
  • Standby= Standby loss of the heating appliance

A typical family of four heating their hot water with electric or oil would expect to use:

BTUneeded = 8.34 x 80 x (115°F-53°F) x 1.10 = 45,503 BTU/day

A typical family of four heating their hot water with gas or propane would expect to use

BTUneeded = 8.34 x 80 x (115°F-53°F) x 1.40 = 57,913 BTU/day

To get an idea of cost, BTUs need to be converted to energy units that are used for electricity, oil, and gas.

  • Electricity has 3412 BTU per kWh.  Therefore 45,503 ÷ 3412 = 13.3 kWh.  Going rate per kWh is about $0.16.  13.3 kWh x $0.16 = $2.13 per day or $778.83 per year
  • Heating oil has 138,700 BTU per gallon.  Therefore 45,403 ÷ 138,700 = 0.33 gallons.  Going rate per gallon $2.459.  0.33 gallons  x $2.459 = $0.81 per day or $269.19 per year.
  • Propane has 93,000 BTU per gallon.  Therefore 57,913 ÷ 93,000 = 0.62 gallons.  Going rate per gallon $2.428.  0.62 gallons  x $2.428 = $1.51 per day or $549.46 per year.
  • Natural gas has 102,000 BTU per CCF.  Therefore 57,913 ÷ 102,000 = 0.56 CCF.  Going rate per CCF is $1.633.  0.56 CCF x $1.633 = $0.93 per day or $338.42 per year.

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05 May 09 | Solar Hot Water, solar thermal | Comments (0)

Tools for the solar installer, Thermal and hot water systems

29 Apr 09 | Solar Hot Water

Solar thermal installers deal with a different set of tools than Photovoltaic.  Most solar thermal systems rely on some type of plumbing and pump system to move heat transfer fluid through a set of panels and back to a storage tank.  Solar thermal panels are generally larger and heavier than photovoltaics.  Drainback systems need to have all of the pipe slope back to the drainback reservoir.  All of these considerations require different expertise and working requirements.

Most solar thermal installations are placed on a south facing roof.  Often, a bit of carpentry is required to attach the solar collectors to the roof.  This is a basic list of power and hand tools for solar thermal installations:

  1. Claw hammer
  2. Small pry bar
  3. Hand tools including a full set of standard sockets, wrenches and screwdrivers, needle nose pliers, diagonal cutters, etc.
  4. Medium and large pipe wrenches
  5. Medium and large channel lock pliers
  6. Vice grips
  7. 18 volt cordless drill
  8. Jig saw or reciprocating saw (AKA Sawzall)
  9. Hack saw
  10. Tubing cutter
  11. Right angle drill
  12. Spade type drill bit set
  13. Drill bit set
  14. Digital Volt Ohm Meter (DVOM)
  15. MAPP gas torch, preferably something with a built in igniter
  16. Pipe cleaning supplies, flux, solder, etc
  17. Ridgid propress crimping tool
  18. 24 foot fiber glass extension ladder
  19. Small transfer pump
  20. Extension cords
  21. Work lights
  22. Garden hose, short and long lengths, plus Female/Female end adaptors
  23. Personal safety equipment such as safety climbing harness, safety glasses, heavy work gloves, etc.

In addition to the above tools, having all of the fittings and valves available on the truck saves a lot of time.  I always buy extra fittings because I know that I will eventually use them.  Having a spare pump and controller is also recommended.  These are the only active parts in a solar thermal installation and are thus the most likely to fail out of the box.

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29 Apr 09 | Solar Hot Water | Comments (0)

Solar Hot Water System components

27 Mar 09 | Solar Hot Water, Training

Solar Domestic Hot Water systems are a great way to save money, cut down on the use of fossil fuels and do a big favor for the environment.  We have install many of these systems over the last two years and they work very well, even in the middle of winter.

I decided to install drain back systems because I like their simplicity and their easy maintenance.  The average home owner can very easily keep track of the water in the sight glass and add water if needed.  They perform well and when properly installed are pretty much bullet proof.  I like that.

This is an 80 square foot 80 gallon storage tank system.  Enough to provide 80% annually of the hot water for an average family of four.

AET AE-40 collectors on roof

AET AE-40 collectors on roof

The system components consist of Flat Plate collectors:

AET AE-40 collectors

AET AE-40 collectors

These are Alternative Energy Technology AE-40 collectors.  They are elevated slightly from the roof pitch to facilitate snow removal and better drain back performance.  They are also tilted to the left so that the water drains out of the bottom of the collectors when the pump is off.  This is a very important detail to avoid freeze damage.

pipe to and from the collectors on the roof

pipe to and from the collectors on the roof

The piping is 3/4 L copper tubing insulated with closed cell (AKA Rubatex or Insultube) R-5 foam insulation.  Where ever possible, the insulation is slid over the ends of the pipe instead of cut lengthwise and placed over the pipe.  The ends and any slit pieces are glued together with special glue called R-420.  The exterior runs are covered with PVC jacket to protect the insulation from UV damage and improve the system appearance.

10 gallon drainback tank

10 gallon drainback tank

The drain back tank is mounted on a shelf attached to the basement wall.  This is a 10 gallon stainless steel drain back tank with an internal heat exchanger.  It has a sight glass which is marked with the proper fluid levels for when the system is running and when it is off.

The solar loop pump is a TACO 009BF5.  I use bronze pumps in the solar loop of a drain back system because the water gets sloshed around quite a bit and becomes oxygenated.  A cast iron pump will rust and foul the site glass.  It also keeps the solar loop a “potable water system” and thus avoids and questions about the single wall heat exchanger in the drain back tank.  The pump is mounted below the lowest fluid level in the drain back tank.  At the very bottom of the solar loop is the drain valve.

The storage tank loop is a TACO 006B4.  This is a larger pump that normal because the storage tank is located about 15 feet away in another room.  This configuration is slightly unusual, however, it was the only way to fit the solar system in a crowded basement.

In the storage tank loop there is an air vent at the highest point in the loop to bleed out any air that may become trapped in that loop.  Trapped air can cause pump cavitation and or reduce the flow in the loop storage tank loop.  For maximum efficiency, the loop needs to move about 4-6 gallons per minute from the bottom of the storage tank through the heat exchanger and back to the top of the storage tank.

80 gallon solar storage tank

80 gallon solar storage tank

The storage tank is an 80 gallon off the shelf unit with a 12 year tank warranty.  It has electric back up elements which are not connected because the home owner has an indirect oil fired tank connected to their home heating system.

Eagle 2 differential temperature controller

Eagle 2 differential temperature controller

The system controller is a DTC-2 (AKA Eagle 2) by IMC.  I really like these controllers because they have temperature reading for the storage tank and the collectors.  They also have variable set points for the high limit and temperature on differential.

Watts 1170 tempering valve on output SDHW system

Watts 1170 tempering valve on output SDHW system

Finally, the output to the backup heating tank has a Watts 1170 tempering valve.  This is very important because the solar storage tank temperatures can get very high durring the summer months.  With out a tempering valve scalding water can be sent to the showers and sinks in the house.

Every time I commision one of these systems, I think to myself  “There is less oil.”

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27 Mar 09 | Solar Hot Water, Training | Comments (0)

What ever happened to those solar panels Carter installed on the White House?

27 Jan 09 | Solar Hot Water

The short answer is, Reagan took them off.  After that, we sort of lost track of them.  Now, a couple of Swiss film makers tracked them down and made a movie about it.  It was back in May of 1979 when the first oil shock was still fresh in our memories that President Carter decided that solar power was the way to go.

The most interesting quote is this:

“A generation from now this solar heater can either be a curiosity, a museum piece, an example of a road not taken or it can be just a small part of one of the greatest and most exciting adventures ever undertaken by the American People…”

Of course, we all know that the panels were removed by President Reagan in 1986 because they weren’t necessary… oil is cheap, after all. Shortly after that, the federal tax incentives were canceled and the first US solar industry collapsed.

The documentary is called “A Road Not Taken” and was shown at the Maine International Film Festival in Waterville, last July. For more information, check out roadnottaken.info or moralequivalent.info. Incidentally, the White House solar panels ended up on the roof of a cafeteria at Unity College, in Maine. They, in turn auctioned them off in 2003 as the panels had reached the end of their useful life.

h/t Huffpo

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27 Jan 09 | Solar Hot Water | Comments (0)
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