Solar Power

SunPower announced this week that it was chosen by the U.S.

Continued here: 
SunPower Develops Projects for U.S. Government

For decades, designers of solar power systems have faced a knotty set of interlocking challenges. Solar panels produce DC at relatively low voltages, but inverters require a relatively high input voltage to be able to convert the power to AC and send it to the grid

Read the rest here: 
Solar Array Design: Parallel Wiring Opens New Doors

Solar hot water is not a new concept. The sun has been heating water for all the eons that water has existed on the Earth. If you notice, in weather reports near coastal cities the water temperature of the ocean is report. As the summer approaches and the sun’s rays are strongest, that water temperature goes up. That’s solar water heating in its simplest form.

To heat water for the home, the concept is almost as simple. By concentrating the sun’s ray by using a solar collector and passing water through the system into a storage tank, the water is heated only by the sun.

The most common type of solar collector is the flat plate collector. A thin, rectangular box placed on the roof at an angle that will collect the sun’s rays, usually pointed toward the south. The box’s flat, transparent cover concentrates the sun’s heat. Inside the thin box are small tubes which carry the liquid to be heated. The tubes are attached to an absorption plate which is painted black to absorb as much of the sun’s heat as possible. As heat build up inside this rectangular box, the liquid is heated and then moved into a storage tank. Another flow of cool water is then allowed to enter the solar heater and the cycle is repeated.

The storage tank for this type of solar water heating system can be a simple hot water heater that has been modified. The heating coils are no longer required and the insulation for the tank has been upgraded. Keeping the hot water hot once it is in the storage tank until it is used by the household is accomplished by making the storage tank extremely well insulated. Otherwise, the heat gathered by the sun would be lost over time.

There are basically two types of solar water heating systems to choose from: active and passive. By far, the active hot water system is more common and most effective. The active system uses a small pump to actively pumps most the water into the solar collector and into the hot water storage tank. Passive hot water solar systems rely on the force of gravity and water’s natural tendency to flow to move the water. The active system is by far the most efficient system.

The initial investment in a solar hot water system is easily offset by the savings in electricity or natural gas over only a few years. In fact, if you choose to build the components of a solar hot water heating system yourself, you can recoup the costs in an even shorter period. The process for building an active solar water heating system is not very difficult and anyone with basic tools and equipment and a good knowledge of how to read design plans, correctly measure materials, and effectively and safely use tools can build a basic system for their home hot water heating system or for a heating system to maintain their swimming pool at comfortable temperatures long before the sun has heated the pool to comfortable temperatures.

Plans for basic hot water heating systems can be obtained from the U.S. Government or over the Internet. Most libraries also have books on solar hot water heating systems that include basic plans.

In some parts of the country, solar hot water is used to supplement and reduce the cost of water heating. In warm climates, the solar hot water can provide all the hot water a normal family requires. The exact specifications you select for your solar water heating system will depend in large part on whether you want to generate all your household’s hot water or simply supplement and save heating costs for your family’s needs. Many households that use a solar hot water system keep a small, traditional hot water heater so that hot water can be ensured during extremely cold periods or during periods that clouds cause the sun’s rays to be less effective in heating water.

In order to design an effective hot water heating system for your solar water heating system, you will need to determine the size and equipment and predict the energy consumption needs. Software programs can be obtained to calculate peak loads and heating efficiency. Software costs money and many people want to know how to perform this analysis without software tools.

Several factors will impact performance. The amount of sun available is one factor; the outdoor temperature is another major factor. Here is a simple method of calculations your needs.

The first step is to estimate daily hot water needs in gallons (Gallons) and a nominal tank size (Tank Size). For two people, the average needs are 40 to 50 gallons per day. Add 15 to 20 gallons for each additional person or additional bedroom in the home to allow for family expansion. Tank size should be large enough to hold slightly more than the needs for one day. If you determine that 70 gallons per day should provide for your need, select a 75 gallon tank.

GALLONS _________________

TANK SIZE ________________

Next, determine the temperature of the cold water that will supply your solar water heating collector panel (ColdTemp). To do this, collect water and use a thermometer to find the temperature on several different occasions. Average the figures to create ColdTemp data.

ColdTemp _______________

Determine the energy needed (BTUNeed) to raise the water from ColdTemp to desired temperature. 122 degrees F is average for desired hot water temperature. If you need higher or desire lower temperature, determine the temperature by using a thermometer to check the temperature of hot water that you want.

To calculate BTUNeed, use the following formula:

BTUNeed = 8.34 X Gallons X (122 – Coldtemp) X Standby loss factor

If you do not use 122 for your desired water temperature, change the 122 in the formula above to your own desired hot water temperature.

To add the standby loss factor, determine the insulation on the storage tank you will use. If you have 1 inch foam or 2.5 inch fiberglass insulation, use 1.20 for the standby loss factor. If you have 2 inch foam insulation, use a factor of 1.12.

Next, you will need to determine the size of solar collector panel you wish to build or purchase. First, determine the penalty factors that will impact sizing. From the chart below, list your system factor.

System Factor Chart

Direct system with no heat exchanger 1.20

Indirect system with heat exchanger 1.30 between collector and storage tank

Systems with SRCC system certification 1.00 and Q NET ratings

To determine tilt factor, you’ll need to determine the pitch of your roof. Most common are 20 to 30 degree pitch which has a tilt factor or 1.0. A flat roof carries a tilt factor of 1.25, a 3 to 7 degree pitch carries a factor of 1.15 while 7 to 12 degrees of pitch carries a factor of 1.09, 12 to 16 degrees carries a factor of 1.5. A roof pitch of 30 to 37 degrees carries a factor of 1.01, 37 to 43 degrees has a factor of 1.04. A 43 to 50 degree roof pitch carries a factor of 1.12.

If you wish to determine an extremely exact tilt factor, you’ll want a site analysis performed by a solar energy professional. These numbers are meant to give you an accurate estimate for do-it-yourself calculations.

Tilt Factor ________________

Orientation factor is determined by which way your solar collector will face. A south or almost directly south facing collector carries a factor of 1.0. Southeast or southwest orientation has a factor of 1.15, east or west facing collectors have an orientation factor of 1.4.

Calculate your penalty factory using this data and the formula:

Penalty = System factor X Tilt Factor X Orientation Factor

Next think about how much of your hot water needs you wish to have met by your solar hot water system. This will be the RateRequired. The national average is 70%, but you can use a higher or lower number if you choose.

RateRequired = BTUNeed X .70 (or percent your determine) X Penalty

The RateRequired figure will equal the BTU/day you will need.

Next you need to determine what the efficiently of the solar collector you wish to use will provide. This is very easy for a purchased solar collector because there will be an FSEC label stating the BTU Rating which is the BTU per day the collector is capable of delivering. If you plan to build your own collector, locate similar collectors and use the ratings from that panel.

BTURating _______________ is BTU per day from label or similar collector label

Gross Area = ___________________ feet squared.

To determine how many solar collectors with the specifications you entered above, calculate;

Number = RateRequired/BTURating rounded to the nearest whole number.

To learn the total area of your collectors:

TotalArea = Number of Collectors X Gross Area

TotalArea = ___________ feet squared

Now, calculate the solar fraction:

SolarFraction = % of need met which is average of .70 X Number of collectors/number

SolarFraction = _______________

If the solar fraction is less than .65, your system is probably undersized and you should consider adding another collector or using more efficient collectors.

This information will help you ensure that solar water heating system you are considering will meet most of your needs. If you plan to have backup hot water heating capability, 70% will represent a huge savings. Only in the most temperate climates could a 100% capability be expected during the coldest part of winter.

Solar water heating systems have become more popular in recent years because of the rising cost of traditional energy sources and concern for the environment. Yet, solar water heating is nothing new. In ancient times, water was placed in urns or bowls in the sun to provide warm water for bathing. During the frontier days of America, water was placed in the sunshine in buckets to heat. Bath tubs in the frontier were often wooden troughs allowed to fill with rain water and heated by the sun during summer months. As early as the late 1800′s, commercial solar water heating systems have been available.

Today, solar water heating systems are mounted on a home’s roof and are quite non-obtrusive. A thin roof plate or several plates to collect the sun’s rays are seen on many homes, both new and old. The owners of these homes enjoy reduced energy bills every single month. They also know that they are using green energy and reducing their impact on the earth’s fragile environment by contributing much less to greenhouse effect and global warming trends.

For many families, solar water heating systems can provide all the hot water required. Location, design, how the solar collectors are positioned and the number and size of the collector boxes will affect the amount of hot water produced. Most families choose to retain traditional water heating capability to provide hot water in periods where the weather results in less hot water production from the solar water heating system.

What makes up a solar water heating system? Most solar water heating systems consist of a hot water storage tank, a solar collector box or boxes which absorb the sun’s rays and energy, and for active water heating systems a pump and controls are required.

Passive Solar Water Heating Systems

A passive water heating system powered by the sun is the simplest solar water heating system available. The water tank is often inside the solar collector box and is stored inside that tank. The water in the storage tank integrated into the solar collector heats and when hot water is turned on, water comes out of the storage tank and into the home. More cold water comes into the tank to fill the tank to capacity. This type of system is best used in mild climates. These systems are also used frequently for heating swimming pools which are only used during the summer in colder climates.

Active Solar Water Heating Systems

An active solar water heating system is the most common type used in the United States. It includes a pump which moves water from the cold water supply into the solar collector which is often made with small copper tubing, and when heated the pump moves the hot water into an indoor, well insulated storage tank for use on demand.

Solar Collector Types

The most common solar collector design used for hot water systems consists of a copper plate, painted black that has water tubes attached to it or placed just above it. As the sun’s rays fall on the plate, they are absorbed creating heat. The heat from the sun warms the water in the tubes that are above or connected to the copper plate. Once the water is heated in an active system, it is moved into the storage tank for use when needed.

Integral solar collectors combine the water heating function into the solar collector panel. This is the method used in most passive solar water heating systems. Some active water heating systems use this design as well, but this is not the most common collector type for home solar water heating systems. These are often used for swimming pool heating rather than for the entire water heating needs of the household.

An evacuated or vacuum tube solar collection system use a group of tubes filled with a liquid, often diluted antifreeze. Because the liquid medium is maintained in a vacuum, little of the absorbed solar heat is lost. The heated liquid is then used to heat water which passes through pipes heated by the evacuated liquid medium. These collectors are almost always roof-mounted and can be used for swimming pool heating, household water needs and even for home heating.