The Energy Corner

I have started bimonthly column dedicated to saving energy. It will cover any ways I can think of that people can save energy. I will also do my best to answer questions about energy production and usage.

I have been in the solar business for over 25 years. I have a good knowledge of the science of energy and what can be done to save energy. I will spend time describing how different types of solar energy production work. As well as energy usage in homes and vehicles.

The basics of energy:

“Energy can neither be created nor destroyed” This is the first law of thermodynamics. What this means is that the amount of energy you can get out of something cannot be more than is put in. Work is defined as the amount of energy that it takes to raise an object to a certain height or temperature i.e. potential energy. The amount of work you get out of a system cannot be more than you put in.

Heat can be changed into motion and motion can be changed into heat. You can also exchange weight for distance, mechanical advantage. If you have a 2 pound weight at one end of a lever on the ground and a one pound weight at the other end of the lever in the air you will lift the 2 pound weight if the length of the lever is more than twice as long on the one pound side. The two pound weight now has more potential energy than it did before. And the one pound weight has less. The potential of the whole system has not changed. In reality friction in the bearing and air have removed a very small amount of that potential from the system.

Motion can be changed into heat, a simple example of this is rubbing your hands together. You can change heat into motion by putting water on the stove to boil. The cover on the pot will jump around as the steam escapes.

There are many other form of potential energy we use every day. Electrical charge is one of them. Heat potential is another. A spinning wheel another. If one object is warmer than another i.e. a piece of steel in the sun is warmer than the surrounding air than work can be done with that difference. Another is chemical energy or burning. The potential energy of the gas being used by a stove is greater than the by-products of the combustion. A gas under pressure in a spray can is another example of potential energy. And if you were to heat that can the potential would go up until the can ruptured. What a mess.

All substances can be looked at in terms of their potential energy. And every one of them has potential in many of the ways described above. A piece of wood has chemical potential in that it can be burned and may have potential in the it can fall lifting something else. It is perhaps warmer than the surrounding area having heat potential.

We as human animals take the energy of our food and convert it into work.

So in order for us to get work done we use something at a higher potential to raise the potential of something else.

Bill Sibner

Prime Solar Co.

646 8383

Ways to use the energy of the sun. heating.

Obviously the simplest way to use the heat of the sun is to heat something. Some of the things that are commonly heated are; water for domestic use, water for pools and homes.

Solar panels are used to heat water. They are very different from PV panels. Water or some other heat exchange fluid is circulated through the panels. The panels are often insulated and have a sheet of glass over them. The heat is then collected in some type of container. This can be a large water tank, perhaps 120 gallons, a pool or a spa. The water can be circulated with a pump, an active system, or if the tank is above the panels the warmer water will rise into the tank, this is called a thermosiphon system.

In this part of the country there is very little active solar heating of homes. This is because most of the time we want heat the sun is not shining. The cost to store large amounts of water or otherwise store heat is prohibitive. On the other hand passive heating can be very effective. Roof overhangs that allow sun into a series of south facing windows can warm a home. If the sun falls on a concrete slab and warms it, the home may stay comfortable all night. Using curtains or other window coverings at night can help keep the warmth in. There are many variations of this idea that can be designed into new construction or remodels that will help homes stay comfortable.

Well insulated homes consume less energy and are more comfortable. Vented attics help keep a home cooler in the summer. A little known fact is that setting the heating thermostat 5 degrees lower can save as much as 50% on heating bills. Radiant heating is a great idea for new construction. In a home with a slab floor the heat radiating off of the slab warms your body even when the air is a little bit cool. This means that you can set the thermostat lower saving energy. These systems are also silent and are better for people with allergies as dust and pollens are not blown around like with a forced air heater. They can be used in conjunction with solar water panels.

Solar for heating water can be very cost effective. In homes using electricity or propane to heat the water the payback can be under four years. As the price of natural gas goes up the payback is approaching that. A good solar water heater will last 20 years with minimal maintenance. The new rebates will include one for solar water heating that offsets the electric usage of an electric water heater. The details are being worked in the pilot program in San Diego and the rebate should be available by the end of the year. There is also a 30% capped at $2000, federal tax credit.

Typically a large storage tank, 80 to 120 gallons, is used to store hot water. When a faucet is opened pressurized cold water from your water utility company forces the warm water from the solar tank into the standard water heater and then out your faucet. Many systems have bypass valves that allow you to take the standard water heater out of circuit during warmer months so that you can use the solar water directly.

The solar water can be very hot. A valve should be installed with any solar water heater for domestic use that automatically mixes cold water with the hot if it is too hot.

The water in the storage tank is heated by solar panels. There is a pump with a control on all active systems. When the water in the panels is a preset temperature above the water at the bottom of the tank the pump comes on. It stays on until the temperature of the panels drops to where it will no longer effectively heat the tank. On a good sunny day the pump will run all day. On a marginal day it will cycle on and off. The pump is small enough that it is not a large electricity drain.

Freezing panels is also a consideration in this area. The two most common forms of freeze protection are freeze recirculation and freeze dribble. With a recirculation system the pump comes on and circulates water from the tank up to the panels. In this area the heat loss is not too great. The other is a freeze dribble, a valve on the panels opens up allowing a small amount of water to escape, this water is replaced by warmer water in the tank keeping the panels from freezing. The two methods are sometimes used on conjunction so that in a power outage on a cold night the panels will not freeze. The freeze dribble valve is completely mechanical.

Spas can be heated with either glazed or unglazed panels as their desired temperature is not nearly as hot as domestic hot water. Pools are almost never heated with glazed panels.

Often the desired temperature of the pool is lower than the daytime air temperature. This means that even if the solar panels were not in the sun they would still heat the pool. Insulating the panels would decrease their efficiency and the glass does reflect some heat. The speed at which the water is circulated through the pool panels is fast enough that the panels are only a few degrees over the temperature of the pool.

A pool contains a large volume of water, in the thousands of gallons. The typical collection area of pool panels is usually about 75% of the surface area of the pool. For instance with a 20 by 40 foot pool you have 800 square foot. This would require 600 square feet of solar absorber. To do this with glazed panels would be prohibitively expensive in most applications. Pool panels are a great way to heat a pool and will usually add three month or more to the unheated swimming season.

]]> http://www.prime-solar.com/2008/03/17/heating-with-solar/feed/ http://www.prime-solar.com/2008/03/17/alice-in-rebate-land/ http://www.prime-solar.com/2008/03/17/alice-in-rebate-land/#comments Mon, 17 Mar 2008 22:48:04 +0000 solarbill http://69.89.31.99/~primesol/?p=25

There are a number of incentives for new solar installations. I will go over the residential ones here. Please bear with me as the rules are rather complicated.

There is a 30% federal tax CREDIT. It is limited to $2000 at the moment. There is talk in congress of changing that. Proof of installation of an approved system should be included with the tax return for this credit. This is fairly straightforward.

For existing homes in our area SCE is handling the rebate. A net metering agreement is required with SCE.

There is a rebate mandated by the California Public Utilities Commission. At the moment it is $2.50 per watt($3.25 for non-profits). This watt is calculated by using the California Energy Commission rating for the panel combined with various other figures. It is too complicated to go into here.

It is required that you take the SCE energy survey. You can find this on line at:

https://websafe.kemainc.com/scescg/gatewaysce.asp

It will give you an idea of where your electricity is going. It will also give your solar contractor helpful info on sizing your system.

Other requirements include:

Reservation request application

Signed installation contract

System description worksheet

Printout of Expected Performance Based Buydown tool calculations

Copy of electric bill

A building permit

Cost breakdown worksheet

All of which your contractor can help with.

You may also be required to prove that you paid for the system.

SCE Rebate Program

If you feel as I do that this is altogether too much paperwork you might call or write your local representatives and the Governator.

For new home the California Energy Commission is handling the rebate. The rules are similar to above with a few exceptions. Obviously an energy survey would be meaningless on a new home so that is not required. It is required that you prove that the new home is 15% above the title 24 energy calculations for the home. This requires bringing in someone qualified to make this determination. We can help you find someone to do this. You can get more info at :

Consumer Energy Center

The typical pool system uses an unglazed collector. The area of the collector is usually about 80% of the surface area of the pool. It will add about 3 months to the unheated swimming season. When the sun is out water from the pool is circulated through the collectors heating it. In many cases the pool has an attached spa. Valves can be turned so that the solar heats the spa.

A grid tie system is the most common form of Photovoltaic(PV) system for a household. These are systems that use an inverter to match the voltage and frequency of the electricity coming from the utility. The power from the utility is often referred to as grid power or just the grid. The inverter pushes the electricity being produced by the solar panels into the house wiring system. If the system is producing more electricity than the house is using the difference is sent back into the grid to be used elsewhere. This return of electricity turns the meter backwards. When the solar is producing less electricity than the house is using the grid makes up the difference. If the grid goes down the system shuts off. This protects linesmen from being shocked by the power from the solar when they think they have shut the power off. This is the least expensive solar solution as it does not need batteries or dedicated circuits.

• Off-Grid

An off grid system is a stand alone system. Such a system would be seen where connecting to the grid is not practical. These systems use the panels to charge batteries. Some loads such as pumps can be run directly off of the batteries. Other loads that require 120v or 240v are supplied through an inverter. These inverters usually have the ability to start a generator in the event that there is not enough power stored in the batteries.

• Battery Backup Systems

Are a hybrid of the above two systems. When the grid is up the system functions much as the grid tie does. It also keeps batteries charged. When the grid goes down certain circuits are kept powered these are referred to as the critical circuits. These may include lighting, refrigeration, heater fans and computers. These systems are used by households and businesses that are concerned that an interruption of power would be too inconvenient or damaging.

Passive systems work in a similar fashion to _________.  The difference is that there is no pump.  The tank is located above the panels and the hot water rises into the tank.

Off grid systems use the solar panels to charge batteries. The power is then taken from the batteries. Some appliances can use the DC power from the batteries directly. Other appliances use power that is converted by the inverter to AC. These systems are sized so that they can do 100% of the usage. They can also be tied to a generator so that in the event there is not enough electricity from the sun the generator will kick in.

A battery back up system is a combination of the two. It is a system with batteries that is also tied to the grid. It has the advantage of supplying power to a few circuits when the utility power goes out.

The disadvantages to a battery back up system are that it costs more and needs more maintenance. It is also less efficient compared to a grid tie system, it takes more panels to produce same amount of useable power.

SDHW systems use sunlight to heat water.

• Active
• Passive

The most common way to use solar to produce electricity for a home or business is a grid tie system. These systems have the advantage of being relatively simple. There are no batteries and they take very little maintenance.

The solar panels are wired into an inverter. The inverter changes the Direct Current of the solar panels into Alternating Current. The inverter matches the phase and voltage to that of the power coming from the utility. This allows the power to be fed back to the utility. Any power that is being produced and not used is fed back to the utility turning the meter backwards. At times when there is no solar output or not enough to cover all the electricity that is being used, the difference is made up by the utility. This arrangement is called “net metering” The biggest downside is that if the electricity goes out the solar shuts off as well.

Active systems have solar panels on a roof or a ground rack. They are plumbed to a tank usually in the garage. A small pump circulates water from the tank through the panels thereby heating the water. The pump comes on when the water in the panels is hotter than that in the tank. When water hot water is drawn in at a faucet the incoming water forces the water from the solar tank into the standard tank and then out of the faucet. If the solar water is not enough, the standard tank will come on and heat it.