Wednesday, November 29, 2006

A Letter to my Great Great Great Great Grandchildren

Dear great, great, great, great grandchild;

You probably think of my generation as an industrious group. We work hard to maintain a lifestyle that includes big automobiles and mini-mansions. We travel thousands of miles by air or land each year for recreation, and many of us have boats and RV’s. Some of us have personal spas and swimming pools. We’ve consumed most of the world’s supply of oil, coal, and other natural resources, and we’ve destroyed mountains, prairies, rivers, streams, and nearly caused a meltdown of the planet in order to maintain our lifestyle.

My dear grandchildren, some of us try to conserve and protect natural resources, and a few of us are pioneers of what we call alternative energy. Unfortunately, we get very little support. I know it must sound crazy to you, but the biggest subsidies go to oil and coal companies, the worst polluters. It makes no sense until you consider campaign contributions. But I digress.

Please don’t judge us too harshly. Those who profit from oil and coal want us to believe that alternatives offer too little benefit for their high cost. Those of us who work with alternatives know that this is untrue. Many of us are saving money, and reducing our negative impact on the planet at the same time. And we’re doing this now, with technology that must seem crude to you.

The fact that you’re reading this means that the planet has survived peak oil and peak coal. Perhaps some good has come from our selfishness. Because you don’t burn fossil fuels, global warming is less of a problem. Wars are less of an issue now because the little remaining fossil fuels are not worth fighting for.

Of all of our mistakes, I’m sorry for what we’ve done to the mountains most of all. While you’ve done a lot to renew the planet, you’ll never see those mountains in their original splendor.

Your great great great great grandfather, John

Monday, November 20, 2006

PV System Upgraded

My PV system was very useful during the most recent grid power failure, but at the same time I wished that it could have done more. As a result of that experience I decided that the next upgrade would be a better inverter. My present inverter, a 600-Watt modified sinewave type, does a great job running lights, fans, and charging the cell-phone batteries, but has its limitations. Here is a list:

It is not powerful enough to operate my microwave oven and other large appliances.

It doesn’t provide enough starting current to run a small refrigerator.

It causes buzzing in the sound when I run a radio on it.

It causes streaks in the picture of a TV powered with it.

A timer motor runs fast, making it useless as a timer.

I’m afraid to connect expensive devices to it, fearing that it may damage them.

To overcome these limitations, I’ve just ordered an Exeltech 1100-Watt sine wave inverter. I chose the Exeltech because it seems to be more rugged and dependable than others I’ve considered. And, because it’s made in the USA, I suspect that it will be quicker and easier to get it repaired if I do experience a problem. With the Exeltech, I’ll be able to run almost any appliance I can think of.

In choosing an inverter I first had to assess my needs, and then find one that meets those needs while staying within my budget. In the event of an extended grid power outage a typical load on the system will be:

Three compact fluorescent lights 45-Watts
Small chest freezer 90-Watts (When the compressor runs)
Small refrigerator 115-Watts (When the compressor runs)
One fan (medium setting) 30-Watts
A radio 5-Watts
Total 285-Watts

I’ll also be able to use other appliances, such as a microwave oven or a vacuum cleaner, at the same time. Since the microwave is rated at 750-Watts, the total power supplied by the inverter will be 750 plus 285, or 1035-Watts. The Exeltech inverter can handle up to 2200-watts for a few seconds, so a high motor starting current surge from the freezer or refrigerator should not present a problem.

With the exception of a few high-power devices, I’ll be able to run multiple appliances at the same time. For example; if I want to use the microwave, I’ll have to avoid using a vacuum cleaner. Of course I’d have preferred a bigger inverter, but when considering the cost, I decided to put up with a little inconvenience.

Daily needs can be calculated by multiplying Watts times Hours. My short-term goal is a system capable of supplying 1450 Watt-hours. My fully-charged battery bank can provide that amount of power for a day, but my solar panel array is not big enough to keep the batteries charged in the event of a power outage lasting more than a day. I plan to add solar panels next year to overcome that limitation. Eventually, I’ll add even more panels so that my system can be used for heating or cooling.


Monday, November 13, 2006

What is Peukert's Law and Why Should I Care?

A solar photovoltaic, wind, or hydroelectric system consists of just a few different components. With only a basic understanding of electronics, it is easy to grasp every operational aspect of a complete system. Batteries, however, are the only system components that require an in-depth study. In September of 2006 I posted an entry on this blog titled “Understanding Batteries Used in PV Systems”. While that paper can be considered an introduction to batteries, this one might be considered Part 2 of batteries. In this paper I’ll continue where Part 1 left off, and in the process make you a battery expert.

In part 1 I stated that “The discharge rate affects battery efficiency. As the rate of discharge increases, battery efficiency decreases.” Peukert, a researcher, noticed this phenomenon, and applied a mathematical formula to it. Since I never was good at math, I’ll avoid explaining Peukert’s observations in mathematical terms. I’ll show you how to use this phenomenon to your advantage as you design your solar PV system.

Peukert observed that as the discharge rate of a battery is increased, less power is available from the battery. A lightly loaded battery bank doesn’t actually supply more power that that which is pumped into it, which would be a violation of the laws of physics, it simply operates at a higher efficiency.

Manufacturers assign their batteries an Amp-hour rating based on a specific rate of discharge. For example, the 105-Ah rating for a typical marine deep-cycle battery is based on a 20 Amperes per hour (20-Ah) discharge rate. This means that the battery will produce 20-Amperes per hour for a little over five hours. Twenty amperes times five hours equals 100, nearly the same as the Ah rating. From this information it seems logical that if the discharge rate were lowered to only two amperes per hour, then the battery would last ten times as long, or fifty hours. However, when we apply Peukerts equations to this battery, we conclude that the battery will actually last seventy hours. The extra power is due to the higher efficiency obtained because of the lighter load. The chart below illustrates battery capacity when different loads are applied:

Battery Capacity = 105-Ah
Battery Amp/Hour Rating = 20

Discharge Rate (Ah) - Battery Lasts (Hrs.) - Amp-hours Available
1 - 172 - 172
2 - 70 - 140
20 - 5 - 70
100 - 0.43 - 43

(Sorry, Due to the way blogger formats data, I'm having a little trouble lining up data in this chart).

This chart shows that a lightly-loaded battery exceeds the advertised capacity of the battery, while a heavily-loaded battery does not meet the advertised capacity.

You may be wondering why, if the rated capacity of a battery is 105-Ah at 20-Amperes, does the battery only provide 70-Amp-hours at the 20-Ampere discharge rate. More than anything else, this is an advertising gimmick. While you could in theory continue to draw power from the battery until it was completely dead, doing so would damage the battery.

It is important to note that in typical applications, battery loads are not constant. Lights that are used at night, for example, may not be used during the day. A ten-ampere load for 1 hour is the same as a twenty-ampere load for thirty minutes, if followed by a thirty minute no-load period. In both cases, the drain on the battery is about the same.

Now that you understand the effects of light and heavy battery loads, let’s consider how you can use that information to your advantage.

A 10-amp load on a single 100-Ah battery is a significant load. However, a 10-amp load on a battery bank consisting of ten 100-Ah batteries connected in parallel is a light load. In the case of ten batteries connected in parallel, the load current is equally divided between each battery, or one amp per battery. The size of the load hasn’t changed, but the load on each battery is ten times lighter than it was for a single battery.

Keeping in mind that we shouldn’t completely drain the battery, a single battery under a ten-ampere load can be expected to last 8.12 hours. From this, one might expect a bank of ten batteries to last ten times as long, or 81.2 hours. Actually, according to Peukert’s Law, the ten-battery bank should last 162 hours. This is important to keep in mind as you design your solar photovoltaic system. By increasing the battery bank size by a factor of ten, the energy available increases by twenty times. By over-sizing the battery bank, the efficiency of the system has been greatly increased.

This example is hypothetical, and depending upon your battery type and actual load, your results may not be this good. Still, as long as the efficinecy increase is great enough to offset the cost of the extra batteries, you benefit.

The design of a solar photovoltaic system begins with an assessment of the expected system load. Perhaps you’re designing a system for a cottage that is only used on weekends. The load may be high when the cottage is occupied, but little if any power is used the other five days of the week. A good design for this scenario would be to skimp on solar panels, and to over-size the battery bank. Even though your solar panel(s) may be unable to keep up with the weekend load, the over-sized battery bank should have enough stored power to meet your weekend needs. And while you’re using more power than you generate during the weekends, recharging occurs during the other five days of the week when the load is light. As a bonus, you’ll achieve greater battery efficiency with the over-sized battery bank. The fewer-panels/more-batteries design is cost-effective too, since solar panels are much more expensive than batteries.

An emergency power system is another scenario where fewer panels and more batteries might be a good option. If a typical power failure lasts for twelve hours or less, then you only need to provide emergency power for twelve hours. If you experience less than one power outage a week, it doesn’t matter that it takes a week to fully recharge your battery bank. In this scenario, you would simply add up the power requirements of all of the devices you want to use and purchase a battery bank capable of meeting those requirements. If you’re only using the system during a power outage, then even a one-panel system will charge the batteries eventually. You just need to be careful not to chronically undercharge the battery bank, as that could shorten its life.

After you’ve determined the storage capacity needed, the next step is to decide which brand and type of batteries you want to use. High performance batteries tend to suffer less from the negative effects of partial charging and discharging cycles, and can better handle other forms of abuse. In other words, they’ll last longer. But high performance batteries also have a high price tag. If your budget won’t allow you to get the best available batteries, consider deep-cycle marine batteries instead. However, make sure you’re not buying starting batteries. Starting batteries, like those in your car, were designed to provide a high current for a short period of time. Deep-cycle batteries are designed to provide a modest amount of current over a long period of time, which is just what you need for a solar photovoltaic system.

Solar PV technology is a viable substitute for utility-supplied power, but needs to be properly implemented for optimum results. If you overestimate the capabilities of your battery bank, you’re likely to be disappointed. On the other hand, you can use the information provided here to your advantage, ending up with a system that far exceeds your expectations. Your battery bank can provide more power than it’s rated at, and operate within a range that is conducive to long life. Modern charge controllers include features that help to prolong the life of your batteries as well, and it would be a good idea to investigate those features before making any battery decisions.

Once you’ve calculated the expected load, you can use the spreadsheet calculator that you’ll find here (, to determine the optimum size for your battery bank. You’ll see the often-dramatic effects of over- or under-sizing your battery bank for a given load. In addition to the useful calculator spreadsheet, this site provides in-depth Peukert’s Law information.

The Sandia National Laboratories web site has in-depth battery information that you might find useful.

Solar John

Monday, November 06, 2006

Oil Company Finds a Way to Meter the Sun!

It’s hard to imagine a better application of solar photovoltaic technology than to bring electricity to remote areas of developing countries. In an effort to do just that in rural South Africa, Shell International Renewables Limited has partnered with South Africa’s national electricity supplier to develop a “plug and play” system. The system was designed so that individual components cannot be used with any other device, and a prepaid token or magnetic card is required. The user pays an installation charge and monthly fee. Purchasing the equipment is not an option. This sounds like a bad deal to me, but then that is about what I’d expect from an oil company.

On the other hand, organizations like the Solar Electric Light Fund (SELF) also bring photovoltaic systems to rural users in developing countries. SELF is supported through donations, but also make it possible for users to purchase equipment via a time-payment plan. Additionally, SELF trains locals to be dealers, installers, and troubleshooters. The SELF plan sounds like a much better deal than what Shell is offering. Read about them here:

Read about the Shell plan here:

Solar John

Wednesday, November 01, 2006

Renewables, No War Required

In a conversation with Rush Limbaugh today, President Bush stated a few reasons for continuing the war in Iraq. He fears that if extremists take control in that part of the world, the price of oil could skyrocket or that oil shipments might be disrupted. His words convey a lack of faith in our ability to implement renewable energy solutions. In reality, everything we currently do with oil can be done in another way, and often in a better way. The technology is already in place, and it will only improve with time. While there are multiple reasons for being at war, we can and should eliminate this one. If I could say just four words to President Bush, I’d paraphrase one of the mantra’s of the wind-power community; “Renewables, No War Required”.

Politics and the Myth of Clean Coal

One of the reasons renewable energy solutions are so important is that they replace energy sources that are harmful to people and the environment. Coal, for example, is particularly harmful.

The burning of coal for the production of electricity is the largest source of carbon dioxide emissions in the United States, contributing in a major way to global warming. But the problems with coal are not limited to the effects of burning it. Mountaintop Removal Mining is destroying mountains in Appalachia at an alarming rate, and is harmful to the residents of the area in many ways. Unfortunately, practitioners of mountaintop removal mining, such as Don Blankenship, CEO of Massey Energy Co., seem to care little about the mountains of Appalachia or the people who live there.

Coal is big-business in this country, and with that comes political pressure that too often results in actions that are in the interest of the coal industry rather than the interest of people and the environment. Blankenship has been known to contribute millions of dollars to political campaigns, including a massive campaign to unseat a Supreme Court judge. As Beth White, a coordinator with West Virginia Consumers for Justice, put it; “It proves that West Virginia Supreme Court seats (are) for sale.”

At the federal level, the three billion dollar Clean Coal Technology Program is a huge waste of taxpayer dollars. Toxic elements are removed from the coal, but they are not eliminated, they just end up somewhere other than the smokestack. Clean Coal Technology does not address the toxic slurry lagoons that result from the washing of coal. These are often placed in locations where they present a danger to those downstream, and they sometimes contaminate drinking water. One such impoundment failed in 1972, sweeping 125 people to their death and left 4000 others homeless.

The Clean Coal Technology Program is part of the Bush Administration’s Advanced Energy Initiative. It’s the bad part. The money spent on the Clean Coal Technology Program could be better used to fund solar, wind, and other renewable energy projects. As a result, the world would move closer to eliminating the need to produce electricity from coal, and the environment would be better off. Our air would be cleaner, and streams would be free of pollutants. There is no dirtier fuel than coal, and it needs to be phased out as soon as possible. Trying to clean it is the wrong approach.

Sadly, instead of being a good steward of the land, President Bush has placed lobbyists and lawyers from the very industries that they are supposed to regulate into important environmental positions. It is unlikely that any meaningful progress will occur until these positions are filled with people who care more about people and the environment, than they do about big corporate profits.

For more information, visit the websites listed below:

I’ve sent a copy of this paper to my representatives. I hope you will do the same.

Solar John