Beckett SolarHot User Manual

CORP ORATI O N

GUIDE TO SELECTING AND INSTALLING A

Solar Hot Water SyStem

By Dan Gretsch, P.E.

Renewable Energy Made Simple.

USA: R.W. Beckett Corporation • ph: (800)645-2876 • fax: (440)327-1064 | Canada: R.W. Beckett Canada Ltd. • ph: (800)665-6972 • fax: (519)763-5656 | www.beckettcorp.com

GUIDE TO SELECTING AND INSTALLING A

Solar Hot Water SyStem

Introduction

There has been a lot of press lately about the growth of renewable energies and the need for energy independence. There have been articles written about Solar Electric (PV), wind, ethanol, biodiesel, and hydroelectric. At heart a pragmatist, I have researched each of these technologies in turn

and been disappointed to nd that for whatever reason these technologies have little to offer me at the

current time. I thought solar electric offered a lot of promise until I researched the cost vs. the savings. It takes 20+ years (with government incentives) to pay back the cost of the investment! While the economics of wind are very attractive, the fact is that I live in a state (North Carolina) where wind is only

viable (according to the government energy ofce) along a tiny sliver of the coast and ridgelines of the

mountains. Unfortunately, I don’t live in the 1% of the state that has adequate wind speed to generate electricity. It was at this point in my investigation that my job took me south.

Brazil is a developing economy. Because of this, their government maintains a very high import tariff on items that are/can be manufactured in the country. They do this to protect the jobs of the workers in the country. The policy has the added effect of increasing the cost for many goods since foreign competition is virtually eliminated as a result of the high tariffs. In 2004, Brazilian per capita

income was one-fth of the United States. Because of lack of development in the nancial markets,

it is uncommon for people in Brazil to take out a mortgage to buy a house. Rather, they build their

home and pay for it out of their earnings (remember they are making one-fth of what we make in the

U.S.). Finally, as I visited various friends and co-workers who were building houses in Brazil, I noticed that they were all installing solar hot water systems in a country where the wage rate is relatively low,

nancing is virtually non-existent, and many goods are priced higher than in the U.S. How can this be

happening? When I asked a friend, he replied, “Because it makes economic sense.” Clearly, I had to get more information.

When I returned home, I researched solar hot water systems and found that he was correct. Where solar electric systems take 20+ years to get a payback, solar thermal systems pay back in 5-7 years. If you consider the added value to the home ($4000 - $5000 according to a recent study by the American Institute of Architects, Washington Post-August 6, 2006) the payback can be instantaneous.

If you roll in the federal (and many state) tax credits available, you end up with an investment that

increases the value of your home dollar for dollar, pays you 30-50% back on your next tax bill, and pays

you back 14% per year. I can think of no other investment that even comes close. So why haven’t people jumped on the bandwagon?

Unfortunately there are many reasons. First, lack of familiarity with the technology. When many people think of solar they are interested in powering their microwave or refrigerator. However, anywhere from 12-30% of a home’s energy bill is used for generating hot water. If you consider hot water plus space heat, that number goes up to as high as 50%. I would attribute the confusion over solar to the amount of press that has gone into covering the solar electric industry.

Second, they think the collectors look ugly on the roof. I have included a number of pictures of installed solar collectors in this book and will let you decide. In a country where we didn’t think it too ugly to run power lines everywhere, didn’t think television antennae, satellite dishes, and roof penetrations

for vent pipes were too ugly, I nd the inconsistency in this argument to be challenging. I will address

one approach to make them more cosmetically appealing in the section “Siting of Collectors.”

Third, people don’t know where to go to get one installed. This is a very real concern. There are two websites: www.ndsolar.com and www.sourceguides.com that will point you in the direction of solar installers in your area. The number of people doing installations is pretty low. The number of people advertising that they do installations is even lower. This shortage of installers drives the cost and aggravation up. Part of the motivation for writing this book is to help eliminate this concern. I am hoping to do that in two ways. For those of you that are interested in installing a system, I am hoping that I will provide the details and encouragement to go out there and do it. There are a few who will have this installed on their own home and feel called to spread the word by getting out there and helping others install systems. I applaud this group and want to be here to support you as you try to change the world.

Finally, there are people who will claim they want to install one, but can’t because of zoning rules. Many states have solar access laws where the ability to install a solar hot water system is written into state law and trumps any local zoning regulations. If your state doesn’t have solar access laws,

I encourage you to contact your state representative to make sure it gets addressed during the next

session.

-Dan Gretsch

Section 1: Selecting a Solar Hot Water System

Chapter 1: What is Solar Thermal?

There are many people who are confused about what solar thermal is. It is exactly what its name

implies, heat from the sun. From our youngest days we learn that the sun makes things hot. Many of us have tried to walk across blacktop with bare feet in the summertime and realize how hot the ground actually is. Some have concentrated the sunlight through a magnifying glass to burn a leaf. These are

experiences that most people can relate to. Solar thermal seeks to take the heat that the sun naturally

provides and tries to channel it in ways that make it useful for our day-to-day energy needs. In this

book, I am not going to give you instructions on how to paint a water tank black and stick it in a box

so you can be amazed at how hot it gets. I will walk you through what you need to know to install a modern, state-of-the-art, solar hot water system. A quality system today will provide 40-80% of your hot water needs for free. Don’t worry; the other 20-60% will be supplied by a backup energy source so you won’t ever have to take a cold shower.

Solar hot water, also called solar thermal or Solar DHW (domestic hot water), is the process where the sun heats water and then you store the heated water in a storage tank. Almost everyone has tried to take a drink from a hose in the yard in the summertime and gotten very hot water coming out of the hose

at rst. That is all solar thermal is, with a little more attention on trying to collect that heat.

Like the magnifying glass for burning the leaf, the solar collectors manufactured today are nely

tuned to capture and store the sun’s energy so you don’t have to think about it. A properly installed

system should be unnoticeable to the hot water users in the house, with a few exceptions. First, we

generally use larger tanks for storage than an average 40-gallon tank for a home. An 80-gallon tank is pretty standard. The larger tank means we have more hot water available before we run out. That’s right, you will have more hot water with a solar hot water system than you will with a conventional hot water heater. Second, the utility bill will be noticeably smaller. Third, you will start to notice how many other people have solar hot water panels on their homes or businesses. There are 1.5 million homes/ businesses in the United States that use solar hot water. Of those, over 94% say that it was a good investment.

There is not a renewable technology available today that provides a better combination of environmental

and nancial benets than investing in a solar hot water system.

News Flash: The federal government provides a 30% tax credit with no limit for solar hot

water systems that are installed on primary residences after January 1, 2009. In addition,

a number of states provide either tax credits or rebates for a solar hot water system. A

standard Beckett SolarHot system will pay for itself in 5 to 7 years, depending on usage.

Chapter 2: Siting the Collectors

Proper placement is all about the sun. The solar electric world has developed many complicated schemes to ensure that the solar collectors are always pointed as directly at the sun as they can be.

They do this because the efciency (the amount of energy striking the surface that turns into usable

energy) of solar electric panels is in the teens. That’s right, their ability to convert sunlight to electricity

is generally around 17% efcient. With a panel that is only 17% efcient you need to make sure it

is maximizing the direct sunlight. However, a solar thermal panel can be as high as 80% efcient at transmitting direct sunlight into usable energy. Because of the much higher efciency, siting is not as

critical, although it is still important.

You want to install your solar panels in a spot that receives direct sunlight from 9 a.m. to 5 p.m. on December 21st. Ideally, you would also like to install your collectors facing directly south and angled to match the latitude of your site. It is at this point that many people get discouraged. Some of the

common problems with nding an ideal location are: wrong tilt, wrong angle, and shading. I will address

each in turn.

Issue #1—Wrong tilt: Many solar collectors installed in the past sought to get the perfect angle for solar collection by using special mounting hardware to incline the collectors at the “perfect” angle. This

is almost entirely unnecessary. While it is true that if you tilt the collectors at exactly the same angle as your site’s latitude you will maximize the solar radiation on the collector, the difference between

perfect and not perfect is virtually immeasurable. Running the numbers in a simulation, I found that for Raleigh, North Carolina (latitude 35.70), if you mount the collectors between 00 and 600 the worst performance is only 9% off of optimal. While the ideal angle for my solar collectors is 35.70, I installed

my solar collectors ush to the 12/12 pitch roof with roughly the same annual performance I would have

achieved had I mounted them at the “ideal” angle.

The general rule states that if your collectors are mounted at an angle less than your latitude you will receive more heat in the summer and less in the winter. If your collectors are mounted at an angle greater than your latitude your winter heat gain will be higher and your summer lower. That is the rule,

but as you can see from the previous example, the actual annual performance difference is small.

Issue #2—Wrong Direction: “My house sits on my lot in such a way that the section of roof I want to install the collectors on points southeast or southwest or due east or due west.” While it is true that due south is the optimal orientation, a solar thermal system is pretty forgiving in this regard as well. Your collectors can be pointed within 450 of south and not see more than a 3.5% reduction in their output. If you get much beyond 450 off of south, I would recommend increasing the area of your collectors before I would recommend angling your collectors perfectly toward the sun. If you don’t have a compass handy, I would suggest downloading a copy of Google EarthTM free from the Internet. With this software you can get a satellite image of your home that includes the compass rose. Using this snapshot, you will

know the exact orientation of your home.

Picture 1: This is a snapshot from Google EarthTM showing a street address and how that building sits relative to South. As you can see from the picture, the street is almost due south from the building so any collectors should be be installed facing

the street.

If you want to know the exact impact of your tilt and direction on the performance of your system you

can go to www.retscreen.net and go through their solar calculator. They have weather data from every weather station in North America, as well as a database of most solar collectors available today. You simply enter the weather station that is most appropriate for your location, indicate the tilt of the collector as well as the orientation (azimuth), and the software will spit out the overall energy produced. You compare that with the perfect orientation and you can see what impact your siting decision has on the overall output of the system. Feel free to play around with this database. It provides a wealth of information.

Don’t be discouraged if you can’t gure out all of the other inputs because they are not pertinent to the

question of what impact your siting has on the performance of your system.

Note: Later in the book we will discuss sizing of the collector area. The rules of thumb that we go over are based on collectors being pointed south and angled to match the latitude of the site. If you need to

use an angle and pitch that signicantly reduces the solar gain of your collectors (as measured by the

Retscreen database), I recommend adding collector area to get back to the same quantity of energy collected.

Issue #3—Shading: If you mount your collectors in a location where they are shaded during a portion of the solar day or are shaded during a portion of the year, you will reduce the output of the system.

There are no exceptions to this rule. While you can increase the number of collectors to increase your

heat gain while the sun is shining, a shaded solar collector won’t collect any heat. Now you are torn. You want to do the right thing for the environment by going with solar energy but it seems like you are moving in the wrong direction if you have to cut down trees to get there. I can help with this a little. The

BP solar website can show you that the environmental benets of installing a system equals the impact of planting 1 acre of trees. So unless you live in the forest, the environmental benet of adding a solar

hot water system is greater than the harm of removing a few trees. We removed 2 trees from our site (1 pine and 1 walnut) and it broke my heart to do it, but I knew pollution-wise we would be better in the

end. An unexpected benet was that by removing those two trees, our yard and smaller trees in it have ourished.

Chapter 3: Sizing a System

In this chapter we will only cover sizing of systems for domestic hot water. While these same principles and systems work well for space heating, the bulk of initial applications lie in the hot water sector.

There are a couple of rules of thumb that are useful for sizing solar hot water systems. Granted, these rules of thumb apply for the average person/families water usage. If you bathe once a month and wash all of your dishes in the creek, they will provide more hot water than you need. If you have teenagers who participate in sports and like to take multiple 30-minute hot showers per day, the sizing will probably provide a smaller fraction of your hot water. Depending on your location, the size of the

system, and your usage patterns, you should expect a solar hot water system to provide between 40-

80% of your hot water needs. This is also a rule of thumb. Personally, we have turned off the back-up elements in our hot water tank so that the sun is providing 100% of our hot water. This may lead to a

few showers that aren’t quite as hot as some would like, but the environmental and nancial benets

are worth it for us.

The Beckett SolarHot Advantage: Our systems are scalable. It is easy to add additional collectors to the system. It’s just as easy to use a larger hot water tank or put two standard tanks together in case you decide that you need additional hot water storage.

Sizing the collector area: The maximum energy you can get out of your system is controlled by a

few things, including the square footage of collectors on your roof (or in your yard). The more square footage of collectors you have, the more potential you have for collecting solar energy. The rule of

thumb says that if you live in the South, you should have 20 sq. ft. of collector area for the rst two people in the household and 8 sq. ft. of collector area for each person after the rst two. The truth is that

the farther north you are, the less sunlight you receive and the colder your groundwater is (therefore requiring more heat to get it to 1200F). If you live farther north than Virginia, you would want to install 20

sq. ft. of collector area for the rst two people and 14 sq. ft. per person for any additional people.

For example, a typical family would need:

Northern climate:

Occupants Ft.² per person Total Ft.²

1 20 ft.² 20 ft.²

2 20 ft.² 40 ft.²

3 14 ft.² 54 ft.²

4 14 ft.² 68 ft.²

5 14 ft.² 82 ft.²

6 14 ft.² 96 ft.²

Southern climate:

Occupants Ft.² per person Total Ft.²

1 20 ft.² 20 ft.²

2 20 ft.² 40 ft.²

3 8 ft.² 48 ft.²

4 8 ft.² 56 ft.²

5 8 ft.² 64 ft.²

6 8 ft.² 72 ft.²

This rule of thumb doesn’t take into consideration the quality of the solar collector that you use. It is possible to have a solar collector that only produces 2/3rd of the potential energy because the absorber is painted black vs. using a selective coating, or because it uses lower quality glass that doesn’t allow as much light to pass through. This rule of thumb is appropriate for high quality solar collectors, such as

the Beckett SolarHot’s Platinum collector series. I am dening a high quality solar collector as having

either black chrome plated absorber or having some form of selective surface. The glazing (glass) on the collector needs to be high-transmission tempered glass. Avoid plastic glazed collectors since the clarity of the plastic will degrade quickly over time and ruin the value of your investment.

The Beckett SolarHot Advantage: Our platinum series collectors use selectively coated all-copper absorbers with high transmission solar glass. Flat-plate collectors

will perform well while laying at on most rooftops and are considered by many to be

far more aesthetically attractive than evacuated tube collectors.

System performance is based on three factors:

• First, the amount of energy absorbed by the collectors, which is controlled by the collector area

as well as their efciency at absorbing the solar energy.

• Second, the size of the storage tank controls how much of the heat that you absorb in from the

collectors that you can keep. If you have a storage tank that is too small for your collector area, you will heat the tank up very quickly and then the system will either need to dump the heat (in a glycol system) or just sit there. If the storage is too small (40 gallons), you will rapidly deplete the heat

you have stored and then switch over to auxiliary heat. Because a solar hot water system is just

that – a system – if you cut corners on a single piece of the system you are impacting the overall performance of the system. An 80-gallon water heater is only $100 more than a 40-gallon water heater so no need to put $3000 into an installation and only get 50% of what you could have gotten had you put in $3100.

• Third, how efciently the heat from the collectors is transmitted to the storage tank.

Sizing the Storage Tank: The size of the storage tank is also dictated by where your geographic location. If you live in the Sunbelt, you should have 2 gallons of storage for every 1 sq. ft. of collector. In northern climates, we have seen systems as low as 1 gallon of storage for every sq. ft. of collector, but you should aim for 1.5 gallons or more of storage for every sq. ft. of collector.

The Beckett SolarHot Advantage: Our system integrates hot water tanks of multiple capacities into the solar system. This creates a scalable, economical solution for your hot water storage needs. These tanks come with built-in electric heating elements

for those days when the system needs auxiliary heat to meet the hot water needs.

We have covered the guidelines for sizing collectors as well as the storage tank. There are a couple of overriding factors to consider when trying to size an installation. It will take the same pumps, controls, piping, pipe insulation, and valves for a small system that it will take for a large system. Be careful of sizing a system for the minimum when you could cover a larger % of the hot water load and allow for future family growth or the sale of the home to a larger family for only a slight increase in incremental cost.

Example: A couple decides they want to do their part and install a solar hot water system. Based

on the calculaons they need 40 sq. . of collector area and a 60-gallon tank. To cover a larger percentage of their hot water load and to take into consideraon future family growth or sale of the home to a larger family, I would recommend installing 64 sq. . of collector and 80 or 119 gallons of storage. The incremental cost would be around $500, but the addional usability of the system would be much greater.

Tanks come readily available in 40, 50, 80, and 119 gallons. They can be combined to make storage

systems of whatever conguration you want, (i.e. two 50s to make 100 gallons of storage). When you

start using components of a non-standard size, the cost (particularly the cost per KW) of your system

rises pretty quickly. I have found on hot water tanks it is signicantly cheaper to use groups of standard

size hot water tanks (40, 50, 60, 80, 119 gallons) rather than use specialty tanks or tanks larger than

119 gallons. So, for a household that requires 64 sq. ft. of collector area, I would use 2-4’x8’ collectors

and either an 119-gallon storage tank or an 80-gallon tank plumbed with a 40-gallon tank.

Total Ft.² Gallons per ft.² Gallons of Storage Rqd.

64 1.5 96 64 2 128

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