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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.

Why Tax breaks are needed

29 Apr 08 | Commentary

I have been watching the news about the House and the current bill to extend the tax breaks granted two years ago. It is a bit troubling to think that my business is in the hands of congress, but there it is.

When I read things like this:

Continued congressional delays over extending tax breaks to solar, wind and other renewable-energy companies could threaten the clean-technology industry’s growth and the jobs it creates.

I begin to wonder what is really going on. Are we just kidding ourselves in thinking that somehow we, the ordinary citizen, can affect change in America’s energy policy? A policy that has to date, been dictated by faceless mega corporations who can manage to turn the tables to their benefit regardless of what the majority of American’s want. I am beginning to wonder…

Since I deal almost exclusively in solar thermal, losing the federal tax subside would put a serious damper on my sales effort. In fact, I would say it would put me out of business.

That sucks.

It sucks because I believe in solar energy. Will it solve all of our energy problems? No. Can it make a significant dent (greater than 30-40%) contribution to our energy needs? Yes, with enough support, the combination of solar thermal and photovoltaics can generate a huge quantity of energy for our use.

The problem is we are going up against the powerful elite who run the current energy supply system like their own fiefdom. Guess who is playing the role of surf? Profits are to be guarded at all costs without regard to the future, the environment, or the greater good. They have mega cash and are willing to spend it on any effort that will maintain status quo. What we are trying to do is akin to attacking an aircraft carrier with a sling shot.

It sucks because when I see my own electric bill has been reduced by at least $60 per month by a solar domestic hot water system, I know this stuff works. It is proven technology that has been perfected by state of the art solar selective coatings and insulation.

It sucks because we are only asking for a level playing field. If this is a free market economy, and that is a big if, then let market forces decide what is better. The oil and coal industry receive huge subsides from the federal government, on top of the huge profits from the American people. Wouldn’t it be nice if we (the renewable energy sector) could compete economically with that?

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29 Apr 08 | Commentary | Comments (0)

The other Solar Thermal; Solar Hot Air Collectors

22 Apr 08 | solar thermal

Your Solar Home Solar Sheet 100GWe have written a good deal about solar thermal on this blog. One thing that has not been covered are Solar Thermal air collectors. These units look similar to hot water collectors, only they use air as the Heat Transfer Fluid (HTF).

Solar hot air collectors have several advantages; They are easier to install and many do-it-yourselfers can install one or two hot air panels in a weekend. They can be mounted on south facing walls or roofs. Shading by deciduous trees is not an issue, since summer time heat production, in most cases, is not desired. They do not contain liquid, so freeze protection is not necessary. They also can most often be power by a small PV panel, which means they require no outside energy input.

The main disadvantage is they have no heat storage capacity, nor can their heat output be transported easily to another part of the building. When the sun is shining, you get the full effect of the sun’s energy (about 1 KW per M2), minus the incident angle losses. For the average solar hot air collector in a category C environment, that is about 10-14 KBTU/day per Ft2. They are also slightly less efficient than liquid flat plate collectors because water is a better HTF than air.

There are two companies that make SRCC certified solar air collectors, Your Solar Home and Environmental Solar Systems. They consist of a flat plate collector with solar selective coating in and aluminum frame. Both units have DC powered fans, one comes with a 14 watt PV panel, the other comes with a wall transformer for 120 VAC. They look comparable in size/output and price. One is made in Canada, the other in Massachusetts.

A real DIY person could potentially make their own solar thermal panel if they had the proper motivation.

Update: Stephen let me know that my research was not a through as it should have been:

You missed the solar hot air units from Newfoundland Canada. I am a reseller of the product.They have over 1000 of them out in the real world. They work well in Newfoundland where they only get 1500 hours of sunlight.

Their website:

Cansolair Solar Panels

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22 Apr 08 | solar thermal | Comments (0)

The price of Solar Energy

16 Apr 08 | Sales, Solar Hot Water

The prices of home energy in New York State, week of April 14, 2008:

  • Heating oil: $3.974/gallon
  • Propane: $2.953/gallon
  • Natural Gas: $1.413/Therm
  • Electricity: $0.175/kWh

Source: NYSERDA

The New York State Energy Research and Development Authority (NYSERDA) tracks energy prices with in the state and posts them to the Energy Prices and Supplies page of their website.

This is a great resource for the renewable energy dealer/installer as it allows you to make direct comparisons to the cost of solar energy. The logical way to do this would be to divide the systems projected lifetime production by the net capital cost.

Example:

A solar hot water system is purchased in Ulster County, NY. It consists of flat plate collectors totaling 80 Ft2, a tank and some miscellaneous pumps, piping, valves etc. The expected lifetime of that system is 30 years ±5 years.

A check of the NREL insolation maps indicates that Ulster County receives 4.4 kWh/M2 per day. Convert 80 Ft2 to M2 (80 Ft2 x 0.09290304=7.432243 M2) The above solar array should expect to produce 4.4 kWh/M2 x 7.432 M2 = 32.701 KWh per day, less efficiency and losses, which total around 60%. Therefore, the above solar system should be expected to produce 32.701 kWh x 0.40 = 13.08 kWh per day, without shading.

Yearly that adds up to 13.08 kWh x 365 days = 4774 kWh/year. 4774 kWh x $0.175 = $835.51 per year. Thus, this home owner can expect to save $835.51 per year in electricity costs.

The net system cost is the installed cost minus the tax incentives, or $7,500.00 – ($7,500 x 0.3 (≤$2,000)) – ($7,500 x 0.25 (≤$5,000)) = $7,500 – $2,000 – $1,875 = $3,625.00

If this system were paid for with 60 month loan:

Principal amount: $3,625.00
Payment amount: $71.61
Interest rate: 6.900%
Interest compounding: Monthly
Total payments: $4,296.51
Total interest: $671.51

Total system cost $4,296.51

Simple System payback $4,296.51 ÷ 835.51 = 5.1 years.

Simple system savings, without utility rate increases, 25 years x $835.51 = $20,887.75 (this is likely low by about $5K).

Therefore, the cost of heating your water with solar is the amount of energy saved, multiplied by the life of the system, divided by the cost of the system, or: 4774 kWh x 25 years = 119,350 kWh. $4296.51÷119,350 kWh = $0.036/kWh.

The cost of solar hot water vs electric hot water is

3.6 cents vs 17.5 cents per kWh.

The average rate of CO2 emissions during electricity production is 1.34 pounds/kWh (source, US Department of Energy). Therefore, the above system will save 119,350 kWh x 1.34 = 159,929 pounds of CO2 emissions, or about 80 tons.

To give you an idea of how much that is, it equates to about

  • 130,000 vehicle (average car) miles
  • 101,000 vehicle (large SUV) miles
  • 347,000 train (AMTRAK, light rail or subway) miles
  • 266,000 air miles
  • 61,500 tractor trailer (heavy truck) miles (loaded)
  • burning 7,175 gallons on heating oil
  • burning 40 tons of coal

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16 Apr 08 | Sales, Solar Hot Water | Comments (0)

Congress passes Clean Energy Tax credits

11 Apr 08 | Commentary

Much to the credit of the Senate, who, by a 88-8 vote passed the language of Cantwell-Ensign bill as a part of another, less important thing about housing or something. All I can say is YAAAAHOOO!

This is indeed good news for all of us who have been collectively holding our breath since last December when the first attempts were made to pass an extension on the renewable energy tax credits.

The bill now needs to go to the house, where it may be sliced and diced, but I am optimistic as the house has been friendly in the recent past to the renewable energy tax credits.

What this bill does:

  1. extend the investment tax credit for commercial solar power installations for 8 years
  2. extend the residential solar investment tax credit for one year and remove the current $2000 credit cap
  3. remove the exemption on utilities for claiming these tax credits
  4. allow the tax credit to offset alternative minimum tax
  5. extend incentives for energy efficiency improvements

What this bill does not do:

  1. Penalize the big oil companies for making too much money by removing their subsides
  2. Establish where the money will come from for the 6 billion in subsides noted above

I can live with that and hope that next year, a long range renewable energy bill is passed.

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11 Apr 08 | Commentary | Comments (0)

Formulas for Solar Hot Water Systems

09 Apr 08 | Solar Hot Water

Something that I get asked quite often is “How do you know this will make enough hot water?” That is a very good question and there are several rules of thumb regarding the size of Solar Domestic Hot Water (SDHW) systems. A properly sized SDHW system will provide between 70-80% of the annual hot water. While it would be nice to provide 100 percent, this is not a realistic goal in the Northeast because of the limited daylight hours during December and January.

General rules of thumb are:

  1. Allow 20 gallons per day of use for the first two people
  2. Allow 15 gallons per day of use for each additional person

So the basic house with four people would need 70 gallons of hot water per day. The closest conventional water heater sized to that use is 80 gallons, therefore an 80 gallon SDHW system would be appropriate for that household.

Solar Collector surface area is based on the size of the solar storage tank. Again, these are rules of thumb that have been tried and tested since the 1970’s for SDHW systems:

  • Northern New England: 1Ft2/0.75 gallons
  • Northeast, New England, Mid Atlantic and Northwest: 1ft2/1.0 gallons
  • Midwest and Mountain States: 1Ft2/1.25 to 1.5 gallons
  • Southeast, Sunbelt and Hawaii: 1Ft2/1.5 to 2 gallons
  • Sunbelt desert areas: 1Ft2/1.75 to 2.25 gallons

Calculating Energy to heat water

If you are not interested in rules of thumb, here is how to calculate the actual energy required for any SDHW system. First, use the Hot Water Formulas and Calculations to determine how much hot water will be used. That use needs to be converted to a unit of energy. In the US, we use BTU, while the rest of the world uses Joule as a measurement of energy.

The basic formula is:

Energy (BTU)= Vgal x 8.345 x (Texpected – Tin) x eff

Where:
Vgal is the volume of water in gallons
Texpected is the expected hot water temperature
Tin is the temperature of the cold water supply
Eff is the system losses

The temperature for both the cold water supply and the expected hot water need to be know to calculate (Texpected – Tin). This is called the Δ T (delta T), or change in temperature. For example, the incoming water supply from a well is 45 degrees F. The expected hot water temperature is 125 degrees, this leads to a Δ T of 125 degrees – 45 degrees = 80 degrees.

From the above rules of thumb, or the Hot Water Formulas and Calculations, the example household is using 70 gallons of hot water per day.

A gallon of water weighs 8.345 pounds. It takes 1 BTU to warm 1 pound of water 1 degree Fahrenheit.

Therefore, 70 gallons of water x 8.345 pounds is 584.15 pounds of water. To 584.15 pounds x 80 degrees F = 46,732 BTU, plus efficiency losses and system losses. Efficiency losses in a SDHW system are in the solar collector glazing transmissivity, heat exchangers, pumps, etc. Generally they run around 10 to 15 percent. System losses are stand by tank loss, piping loss, etc. Generally they run about 10 percent.

Therefore, the entire solar collector array will need to collect 125 percent of the required BTUs noted above, or 46,732 BTU x 1.25 = 58,415 BTU per day.

Below are comparisons of how much conventional fuel would be used to heat the water in the example household:

  1. Electricity has 3,413 BTU per kWh. Electric hot water systems are 100 percent efficient, but have standby losses. Therefore (46,732 BTU x 1.10)/3,413 = 15 kWh per day. At $0.175 per kWh utility company rates, that equals $2.625 per day
  2. Propane has 91,600 BTU per gallon. Propane hot water systems are about 65 percent efficient and have stand by losses. Therefore (46,732 BTU x 1.55)/91,600 = 0.80 gallons of propane per day. At $3.05 per gallon, that equals $2.41 per day
  3. Natural gas has 100,000 BTU per Therm (Therm is 1 CCF or 100 cubic feet). Natural gas hot water systems are about 65 percent efficient and have stand by losses. Therefore (46,732 BTU x 1.55)/ 100,000 = 0.73 CCF per day. At 1.60 per Therm, that is $1.15 per day
  4. Heating oil (#2 distillate) has 140,000 BTU per gallon. Oil fired hot water systems are generally 80 to 85 percent efficient and may or may not have standby losses. Therefore (46,732 BTU x 1.2)/ 140,000 = 0.40 gallons per day. At $3.97 per gallon, that is $1.59 per day.

Calculating size of solar array based on energy needed

Here is where things get a bit complex. Every location has a different amount of Insolation which is the amount of solar radiation received on a given surface. The NREL (National Renewable Energy Lab) has a program called PVWATTS which can give very specific data on a month by month basis. This is important for sizing of solar thermal space heating systems. Usually this data is given in units of kWh/Meter2 per day. That is acceptable because that can be converted to BTU/Ft2 per day by multiplying kWh/M2 by 317. Each kWh equals 3,413 BTU, A M2 equals 10.76391 Ft2. Therefore 3,413 BTU/10.76391 = 317.

I like to pick a moderate month, such as April or September, and size the SDHW system to meet 100 percent of the load in that month. I often find that this is the best compromise for the New York region as it will give more hot water than needed during the summer months, and less during the winter.

The example household requires 58,415 BTU per day from the solar system. According to the PVWATTS program, a solar collector tilted at latitude for the month of April will receive 4.63 kWh/M2 per day. Convert to BTU per Ft2, 4.63 kWh/M2 x 317 = 1,579 BTU/Ft2, therefore 58,415 BTU/1,579 BTU/Ft2= 37 Ft2.

That would be a perfect world theoretical solar collector and it is a good median figure. Like many things, there are other considerations:

  1. The efficiency of the collector absorber plate coating
  2. The efficiency of the Heat Transfer Fluid (HTF)
  3. The incident angle of the sun on the surface of the collector in both the horizontal and vertical axis
  4. The ambient temperature of the collector
  5. The internal temperature of the collector and the HTF

At this point, the equation becomes a calculus problem and a somewhat complex one at that. The general idea is to increase size to overcome the collector losses. Field work indicates that in the Northeast, doubling the theoretical size works well. This equates to about a 50% loss over the theoretical model noted above. This is how the above noted rules of thumb on collector size vs. storage tank size are formed.

1. Absorber plate coating also called “Black Chrome.” Solar selective coating has come a long way since the 1970’s. Basically, it is a type of paint that accepts and converts more energy, in the form of visible, infrared and UV light, from the sun and converts it to heat without radiating it back into the atmosphere. These are highly specialized products and are not normally available to the general public.

2. Heat Transfer Fluid or HTF. HTF removes the heat from the absorber plate and transfers it to a heat storage tank. It can be water, antifreeze, oil, etc. Water is the best HTF as far as efficiency is concerned, but can present freezing problems.

3. Sun incident angles on the collector surfaces. A solar collector is at it’s optimum when the sun is 90 degrees from the surface. The further away the sun is from perpendicular, the less dense the energy is that is striking the surface.

4. The solar collectors have operating categories based on the ambient temperature (Ta) that the collector is in vs the water temperature within the collector (Ti). This is known as the Ti-Ta. In the summer time when the Ti-Ta is 36 or less degrees Fahrenheit, the collector is operating as a Category C unit. In the winter time when the Ti-Ta can be 90, 100 degrees or even greater, the collector is operating as a Category D unit.

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09 Apr 08 | Solar Hot Water | Comments (0)

Solar power backup for Critical Household Systems

06 Apr 08 | Solar Electric, wind power

Almost everyone has experienced a black out. Thankfully, they are often for short periods and the line men work hard to get the power back on to everyone as quickly as possible. However, if major damage is inflicted upon the power grid, it can take quite a while to repair. Are you prepared to live without electricity for days, weeks or even months?

Many people have installed gas or diesel generators to power their houses. These units can run reliably for days or even weeks at a time, but they also require refueling. After Hurricanes Ivan in Pensacola and Katrina in New Orleans, it was discovered that motor fuel can often be in short supply after major disasters as the electric transfer pumps required to move the fuel from storage to use are inoperative. It can also be difficult to deliver fuel due to blocked or flooded road ways.

Additionally, generators require maintenance, the engine oil needs to be changed, they need to be  exercised periodically.  Solar panels need almost no maintenance, perhaps in a prolonged dry spell, the dust could be washed off once in a while.  Even that is optional.

As solar powered backup system requires no fuel and if properly sized can run your critical household electric load indefinitely. These systems can be individually sized according to the load calculations. Additionally, they can be configured as a normally solar powered system that is backed up by the electrical grid. If a location has a good wind resource, a small wind turbine and be used to augment the solar system during inclement weather.

Instead of using the PV panels to merely to keep a battery bank charged, the PV panels and battery bank can be the primary source of power. The electrical grid can be used as a standby in case the batteries get too low. A reserve charge can be built in to the battery bank to run the critical loads in absence of both sun and grid power.

This is best of both worlds.

Critical loads

Indentifying critical loads is the first step. At my house we have a well pump to supply water, an oil fired boiler for heat, an electric refrigerator, two sump pumps to keep the basement dry, and two circulator pumps on the solar hot water system. I would also like to power the computer network and one or two outlets for lighting. All of these appliances have name plate information which give the power consumed. If the loads are given in watts, they need to be converted to amps. To do this, use Ohm’s law, which states:

P=I x E

where P is the power in watts, I is the current in Amps and E is the Voltage.

Thus if something if something draws 300 watts, you would divide that by 120 volts and get 2.5 amps.

Load Name
 Manufacture/Model
 Load Current @ 120 VAC (Amps)
 Load Power (Watts or VA)
 Duty Cycle (percent/hr)
 Amp/day (Amps x duty cycle x 24)
Well Pump
 Goulds 10GS10422
 7.9*
 948
 2
 3.8
Boiler, heating
 Dunkirk/Grundfos
 4.3
 516
 10
 10.32
Refrigerator
 Kenmore
 2.1
 252
 10
 5.1
Solar Hot Water Pumps
 Taco 009B and 006B
 1.8
 216
 20
 8.64
Computer Network
 Various
 0.3
 36
 100
 7.2
Water Filters
 Kenmore
 0.3
 36
 100
 7.2
Misc loads, lights, etc
3.0
 360
 40
 28.8

Total power required is 2364 watts, if all loads are one at the same time, which is unlikely. Additionally, the well pump requires a large starting load, something in the range of 5,000 watts. This will have to be figured into the sizing of the inverters.

Total storage is 71.06 Ah per day at 120 VAC. Some of these loads are seasonal, e.g. the boiler will not run in the summer, but the refrigerator will likely run more. Over all, I think this represents a good picture of my critical household loads.

I plan to have a 24 VDC battery bank running two inverters tied together to derive 240 VAC for the well pump. I estimate a 355.3 Ah battery bank will give me 24 hours, but there are other considerations:

I would like to run for several days without recharging because sometimes stormy weather lasts for quite a while. Therefore 355.3 x 3 = 1065 Ah.

A battery bank should never be discharged by more than 40 percent. Doing so leads to shorter battery life and increased operating expense. 1065 Ah x 1.4 = 1493 Ah.

Finally, the inverter has some losses. A good inverter usually operates at about 95 percent efficiency. 1493 Ah x 1.05 = 1567 Ah.

That is a pretty big battery bank

The inverter chosen is a Xantrex SW2524 Plus, which as an internal battery charger and an optional controller for starting a generator. I plan to use the generator starting contact to close a power contactor from our house panel, which will be used to recharge the batteries when they reach 55 percent discharge and grid power is available. If the grid is not available, we have a 15 percent reserve, which means I will load shed until the batteries can be recharged.

Next consideration is the size of the solar array charging this battery bank. The total daily storage from above is 71.06 Ah. All solar panels are sized in Watts, therefore, using Ohm’s law, we have P=71.06Ah x 120 Volts = 8,527.2 watts or 8.5 kW rounded total charging per day.  We have about 5 sun hours per day average, so 8.5 kW / 5 = 1.7 kW of charging power.

I will be using a MMPT charge controller to charge the battery bank, as well as tracking mounts for the panels, both of which will increase the efficiency of the system.

Finally, I will be using a 400 Watt Southwest Windpower wind generator to keep the batteries topped off during story conditions. Without the wind turbine, I would have to double the size of the Battery bank.

Here is a list of parts:

  • Batteries; Surrette 4-KS-21PS 4V 1557 Ah, 6 each
  • Inverters; Xantrex SW 2524 plus, 2 each
  • Inverters, Xantrex SWI stacking kit, connects two inverters to generate electric for 230 VAC loads
  • Inverters, Xantrex GSM generator starting module
  • Charge controller, Blue Sky Energy Solar Boost 3024i MMPT controller
  • Photovoltaic panels, Sharp NE-170U1 170 watt panel, 10 each
  • Tracking Mounts, Zomeworks URTF90, 2 each
  • WInd Turbine, Southwest Windpower Air X 24 VDC
  • Wind Turbine Tower Kit, Southwest Windpower 45 ft

Total cost, retail $26,000.00

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06 Apr 08 | Solar Electric, wind power | Comments (3)