David Butcher's 4 Phases of Solar Electricity

After years of experience with photovoltaic energy, including teaching workshops on assembling your own solar panels from individual cells, I have come to the conclusion that there are four reasonable targets for individuals to consider when choosing a solar electric system. One of the difficult decisions to make when choosing a solar electric system is to choose a size that makes sense for your location, budget, and personal goals.

I have developed a simple solar power calculator to help with selecting the size of a photovoltaic array. It is not as accurate as the calculations you would receive from a certified solar installer, but it is good enough to give you a rough idea of the size array you would need to generate a certain amount of power, and the equivalent petroleum fueled generator.

It really helps to plan a system, and the corresponding investment, if there is something measurable to design for - financial incentives, power generation capabilities, or potential positive (and negative) environmental impact. I believe there is not a single size system that is "perfect" for any situation, only system that reflect choices and circumstances at the moment the system was designed and placed into service. For that reason, I consider any system to simply represent a "phase" of adopting solar electricity, and I will refer to the systems by the phase they represent from now on.

In the next section I have identified four clear, understandable phases of adoption of solar electricity. These phases cover all systems, big and small. Selecting a particular phase for your first solar electric project will enable you to make the decisions you need to successfully reach the goal of placing the system into service, and attaining the associated benefits. Sit back, relax, and enjoy the four phases, one of which I hope is right for you.

Four Phases of Solar Electricity

Phase 1 - Stop the Meter

Design Goals Design Details Benefits
Almost anyone can install a Phase 1 photovoltaic system! The goal of this system is to be able to generate exactly as much energy as your house uses, when everything is "off." It sounds easy, but it is not. The average house uses between 50-100 watts of power even when everything is off!!! How can that be? The answer is that many appliances and systems use power even when they are off. Here are some examples:
  • Anything with a clock or time display
  • The thermostat for your heater
  • Your doorbell
  • Burglar alarms
  • Outdoor watering and lighting systems
  • GFI Outlets (Ground Fault Interrupter)
  • Anything that responds to a remote control
  • Laptops that are "off" but plugged in (will be charging)
  • Every rechargeable item with a little "black box" that is plugged in to charge it
  • Automatic garage door openers
And of course, there may be more. Fountains, air purifiers, hot water circulating pumps, constantly running furnace fans, aquarium pumps, etc. all use electricity continuously. You get the idea. There may be dozens of electrical items running while you think everything in your house is "off." The goal of Phase 1 is to balance out the energy used by these items, during the sunny hours of the day, when the grid needs the most help it can get. Essentially, if you can stop your meter during there periods, your house load will "disappear" from the grid.
To achieve Phase 1, you must begin by determining how much energy your house uses, when you believe everything is turned off. Here is a technique for making that measurement:
  • Make sure everything in your house is "off." That means no TV sets, radios, lights, and the refrigerator (and any other major appliances) as well.
  • Find a clock or watch with a "seconds" display, and take it to your electric meter.
  • Time how long it takes for the disk in the meter to revolve one time. Watch for a black mark on the edge of the disk. If the disk is spinning rapidly, you should suspect that something is running in the house. Go back inside and verify that everything is off. If the meter is still spinning rapidly (under ten seconds for a revolution, for example) time how long it takes for ten revolutions.
  • Look on the face of the meter - there will be a "factor" number, which you will need for the next step. On my meter, it is Kh 7.2, and it is on the lower right part of the meter face.
  • Plug your measurements into this formula:
    watts = (Kh factor x number of disk rotations x 3600) / number of seconds
    For example: , with a Kh factor of 7.2, and 60 seconds per revolution, your house is using (7.2 x 1 x 3600) / 60 = 432 watts.
  • Congratulations! That number is your target capacity number for your Phase 1 system.
Armed with you target capacity number, you are ready to design your system. Here is what I recommend:
  • Use a "grid tied" system. Do not use any batteries. This will be cheaper, simpler, and the system will have low "embodied energy" - that means it will not take a lot of energy to build the system itself.
  • Choose parts that can be used on a larger system in the future. Remember, this is just a phase ;-) You may wish to expand to a Phase 2 system later, and your Phase 1 system could be part of that plan!
  • Plan on designing and installing the system yourself. Phase 1 systems are typically too small to be profitable for solar energy businesses to install. It's up to you!
  • The minimum system will be a single solar panel and a "grid tie" inverter. See the equipment sources list below to locate the parts you need.

Equipment sources for Phase 1 systems:

Information Links:

Expect to pay approximately $6/watt for a Phase 1 system if you install it yourself. I am not affiliated with any of these sites.

The grid needs you! There is no electricity shortage in California, or anywhere else in the US. There definitely is a problem with handling peak loads. The peak loads occur in California during the summer, in mid-afternoon. Here is a great place to see how we are doing: California Power Grid System Conditions. As you can see, here in California we only experience problems with capacity when the sun shines. If you can remove your house load during that period, you will be reducing energy use at the most critical time. When electricity supplies are short, there is nothing more important than reducing peak loads. If you commit to Phase 1, and succeed, you will indeed be making a difference.

Phase 2 - Earn the Discount, or Stop the Surcharge

Design Goals Design Details Benefits
Phase 2 systems are designed with a simple goal. Many electric companies have adopted a tiered rate structure, or a rate structure which compares current and historic use. The bottom line is that the electric companies are adopting a "punish consumption, reward conservation" approach. Bravo! New electric generation plants are SO expensive, and SO difficult to build in the current regulatory environment, that the electric companies have determined that simply building new power plants to meet increasing demand is the not the answer. The answer is lowering (or stabilizing!) demand, and they are developing incentives for users who play along. That is the basis for the Phase 2 system.

The goal of a Phase 2 system is to offset (generate the equivalent of) enough electricity use to avoid surcharges, or qualify for conservation incentives. Of course, doing both would be even better! How do you decide how large a system to build? All you need to answer this question is your most recent electric bill.

The goal of a Phase 2 system is to generate enough electricity to "stabilize" your usage at a level BELOW any surcharges (if there are tiered rate schedules) or to reduce your use sufficiently to receive a "conservation discount" on your bill.

For example, in California, both programs can be simultaneously active. There is ALWAYS a tiered rate structure evaluated against a "baseline" usage. When you exceed that level, you start paying more for the extra electricity. The maximum is 130% of the normal rate. It would be nice to avoid that. At time of heavy use, California has also offered a 20% discount on your bill if you use 20% LESS electricity than you did during the same period a year ago. That would be excellent! As you can see, Californians could possible qualify for both benefits by doing one thing - lowering their electricity use. The Phase 2 system is designed to do exactly that. Analyze your bill - look for opportunities for lower rates or discounts based on use. Calculate how many kilowatt hours you would need to reduce your consumption by to qualify (it should be relatively simple to do, but call your power company if you can't figure out what the number should be!). That number is the target for the monthly capacity of your Phase 2 system.
Note: Take seasonal changes in your bill into account! You may wish to average a year's worth of bills to find a number that works year-round.

Phase 2 systems should be grid tied. While it is possible to design a Phase 2 system with battery backup, Phase 2 systems are typically too small to "carry" a full house load for more than a few tens of minutes. To keep the complexity and cost of the system down, a grid tied system is the best choice. Grid tied system are maintenance free, compact, safe, and popular.

After you have determined how many kilowatt hours (KWH) you need to generate each month, the next challenge is to determine what equipment will be required. Here is a rough formula to help:

First, determine how many KWH you need to produce each day:
KWH/Day = Your Required Monthly KWH Reduction / 30
As a rule of thumb, a Photovoltaic system generates about 4 times its nameplate capacity in watts each day. It varies considerably by the season, but that is a good enough rule of thumb to calculate approximate system sizes. Divide your total daily energy needed by 4 to see peak Photovoltaic output requirements.
Photovoltaic System Peak Watts = ((Your Required WH/Day ) / 4)

Examples:

  • To reduce your use by 10 KWH/Month: ((10,000 / 30) / 4 ) = 83.3 watts peak output
  • To reduce your use by 30 KWH/Month: ((30,000 / 30) / 4 ) = 250 watts peak output
  • To reduce your use by 100 KWH/Month: ((100,000 / 30) / 4 ) = 833 watts peak output
Ok - ready to shop? There are two choices:
  • Design and build a "big little" system - a large Phase 1 system
  • Design and build a "little big" system - a small Phase 3 system (but grid-tied)
Make your decision based on the amount of power you need to generate. My advice is to use an expanded Phase 1 system to generate anything up to 800 watts or so, and a scaled-down Phase 3 to generate anything more than that.

If you choose scale up your Phase 1 system, simply duplicate it as many times as needed to generate the power you need. Most Phase 1 systems can be be duplicated as completely independent sets of equipment. The panels in each set do not even have to be physically near each other! This can be convenient for oddly shaped roofs.

If you decide to use a scaled down Phase 3 system, the best thing to do is read on - and see what a Phase 3 system requires in the next section.

Money in your pocket, less dependence on centrally generated electricity, a smaller "footprint" on the grid, less pollution (of course!) and insurance against future rate surcharges.

One nice benefit to this scale system is that you are not 100% invested in a large system. You can still grow the system and continue to shave off costs from your electric bill if you choose, or adjust the size if your energy use grows.

The final benefit is not so obvious. The cost of photovoltaic panels and much of the related equipment is dropping, and the technology is improving. If you postpone your transition to the next level, you may well enjoy a smaller cost and better equipment when you do eventually decide to proceed.

Phase 2 systems are cool! Pay the minimum you can for electricity, generate a surplus when the grid needs it, and wait for prices to come down on the ultimate systems - Phases 3 and 4. You can't loose!

Phase 3 - Break Even - Generate What You Use

Design Goals Design Details Benefits
Brave choice! Generating substantial amounts of electricity using photovoltaic panels is not the complex engineering challenge it used to be, but it is still not as simple as it could be. There are three key considerations to think through before beginning this project:
  1. Do you have enough space for the panels?
  2. Will you be grid-tied, independent, or a hybrid of both?
  3. What will the system cost, and how can it be financed?
Item #1 can be calculated through analysis of your electric usage, and some rough calculation based on key factors, such as system efficiency, system solar exposure, and local weather. Here is an example calculation:
Variables:
Average monthly electricity use: 500KWH/month.
Efficiency of overall solar system: 75%
Efficiency of individual panels: 12%
Percent of sunny days/year: 50%
Percent of unobstructed solar exposure: 70%
Panel prices: $4/watt
Inverter prices: $1/watt
Installation: 20% of system cost (Optimistic!)

Generation Calculations:
Daily energy use:
  500 / 30 = 16.6 KWH
Daily generation requirements at 75% efficiency:
  16.6 / .75 = 22.1 KWH
Daily generation requirements with 50% sunny days:
  22.1 * 2 = 44.2 KWH
Daily generation requirements with 70% solar exposure:
  44.2 / .7 = 63.1 KHW

System sizing calculations:
Hourly generation requirement (8 hours/day):
  63.1 / 8 = 7.9 KWH
Watts per square foot of panel:
  .12 * 100 = 12 watts
Panel space required (square feet):
  7900 / 12 = 658 sqft. (15 ft X 45 ft, for example)

System cost calculations:
Estimated panel price:
  7900 watts * $4/watt = $31,600
Estimated inverter price:
  7900 watts * $1/watt = $7,900
Installation at 20% of hardware cost:
  .2 * $39,500 = $7,900
Total: $47,400

(Note: California incentives at $4/Watt could reduce the price considerably!)

As you can see, the system required to generate all the power you use can become quite large. The calculations above are very rough, but they are close enough to give you an idea of what will be required to construct your system. Note that this example is calculated very conservatively. In areas with more sunshine, the required panel size will shrink considerably, or the amount of power this size system will generate will go up. You may copy these formulas in to a spreadsheet - Excel, for example - and you would be able to change the variables to match your particular system plans and environmental characteristics. Any competent solar systems vendor should be able to work through these calculations with you as well.

Don't worry too much about the accuracy of the calculations with respect to breaking even. If you select a system that is too small, you will occasionally generate less than you use, and if you go too big, you will occasionally generate more. There is no magic in generating EXACTLY as much energy as you use, and many of the variables in the calculations really are highly variable - for example the number of sunny days in a year.

If the calculation result in an impractically large or expensive system, consider these approaches to reduce the required size:

  1. Conserve energy to reduce system costs. If you reduce your energy use by 25%, the system cost will go down by the same amount. For this system, that would be over $10,000, which is sufficient cost savings to fund the replacement of every electric light, appliance and gadget in the average home with a more efficient version. Conservation or increased efficiency of the use of the power will reduce the cost of the system.
  2. Increase the system efficiency to reduce system size. Consider more efficient inverters, more efficient panels, and try to improve the exposure of the system to the sun (tree trimming, location, etc.) More efficient panels and inverters will add cost to the system.

Here is a rule of thumb that has escaped the grasp of almost everyone in the energy industry, and our government leaders as well: If you increase the efficiency of power generation, end user energy costs go up. If you increase the efficiency of power utilization, those costs go down.

This paradox occurs because spending a dollar on conservation results in more energy saved than spending the same dollar on generation would generate. This is especially true when generation costs are high, as in a solar system.

Phase 3 systems are beyond the capabilities of the average homeowner to install, in most cases. These are serious power plants, capable of generating enough power to be quite dangerous. There are many variations of design to choose from, including our old favorite, the grid tied system, standalone systems with immense battery backups, and even "hybrids" that feature both connections to the grid AND sufficient battery power to "ride through" blackouts.

Equipment sources for Phase 3 systems:

Information Links:

Generating as much electricity as you use is awesome! It is also extremely rare. The systems required to generate what an "average" household or business uses are simply too large and expensive. That is gradually changing, as the cost of the generating systems comes down. As electricity costs continue to climb, and prices for solar generation system gradually come down, it will make increasing economic and environmental sense to generate at least a portion of the electricity a structure requires on site.

Phase 4 - Become a Power Generator

Design Goals Design Details Benefits
Coming Soon Coming Soon Coming Soon

I hope you enjoyed reading about my four phases of solar electricity. I would love to hear your comments and suggestions. Please use the form below to send them along! And please, if this page made you feel motivated, or excited about getting started with solar electricity, do something! Choose a phase, make your plans, and DO IT!

David "Photons, not Neutrons" Butcher


Disclaimer

This information is provided in good faith but no warranty can be made for its accuracy. Follow these suggestions at your own risk! If you notice something incorrect or have any comments, or information to add to these pages, feel free to mail me.
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David Butcher
davidbu"at"www.los-gatos.ca.us
Tel (408) 978-5495
Los Gatos, California 95030

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