Clean Power solar exposure world map

Published on December 13th, 2011 | by Guest Contributor


How Much Do I Need? An Answer to the Most Common Question in Solar Power

December 13th, 2011 by  

We have the pleasure of working with hundreds of people every day that want to reduce their energy bills, go green and jump on the solar power bandwagon. And the question we see over and over again is: Just how much do I need and what will it cost? We’ll tackle that question here and show you how we calculate system size and cost. We have simple solar calculators that can do this on our website but so many people have asked how this is actually calculated that we thought we’d give a quick solar design lesson.

Start With the Consumption

We spoke to someone just yesterday who wanted solar panels on a 8’x22’ trailer. We asked him what his usage was, and his answer floored us. He was using 7000 kilowatt-hours per month, about 6 times the average household consumption. As it turns out, the trailer was an enormous ice maker. This illustrates that homes and buildings of all sizes vary widely in their energy consumption. A 1200-square-foot house in Florida might use 3 or 4 times what a similar house in Missouri uses because of air conditioning and different types of HVAC units.

So, when planning a solar system, you have to know what you use. The easiest way to do this is to simply look at your power bill. You’ll want to look at the “kw-hrs” number, which is short for kilowatt hours. A kilowatt hour is 1000 watts running for 1 hour. This number will determine just how many watts are required to almost completely eliminate your power bill.

Factor in Your Location

We also have to account for where you live. We deal with many customers who live in extremely sunny locations like the Southeast and the Caribbean. But we also get calls from the Northern Territories in Canada, where sun exposure is far less. A 10,000-watt system in Atlanta will generate much more power in a year than a 10,000-watt system in Alaska. The same is sometimes true of locations that are geographically much closer to each other. For instance Spokane, Washington has almost twice the sun exposure of Seattle, Washington.

To account for sun exposure, weather patterns, and latitude, we use a number called ‘full sun hours’. This doesn’t mean the hours that the sun is in the sky, but is a weighted number that helps us determine how a solar panel system will typically perform in a given area. Most of the US has a number between 3 and 5. Some areas close to the equator have a number closer to 7. A solar exposure map with more detail is below:

solar exposure world map

Now Calculate Wattage Produced

So, now we have the basic information that can help us get a rough idea of what a system will look like. Here’s a simple formula that will get you close to your number:

Monthly Consumption (kw-hrs) = Rough solar kilowatts

(30 x Sun-hours for your area x .80 to account for efficiencies)

Now, an installer will tell you that does not account for things like shading, the angle of solar panels, etc., and they would be right. But, for rough calculation, this will suffice.

Now Calculate a Rough Installed Cost

We have determined a general system size, so let’s crunch some numbers to see what this will cost. Installed solar costs vary widely across the country, but a good rule of thumb these days is equipment and installation for a standard grid tie, roof-mount system will cost between $4 and $5 per watt. So, if we take the average of that number and the result of the previous calculation:

Rough solar kilowatts x 1000 x $4.50/watt = Rough solar cost estimate.

Now, the installed cost per watt can vary for any number of reasons:

  • Difficult installation
  • Higher labor rates
  • Inadequate roof space
  • Remote location
  • Travel time for installers
  • Special equipment requirements
  • Special building code requirements

But, for most people, this will give them a good idea of what solar power will cost for grid tied systems. And, of course, this does not account for incentives at the local, state and federal level. In many areas where installation is more expensive (such as both the East and the West coast) incentives are also higher.

Now you can take on the next important question: Where am I going to put all these solar panels?

Kriss Bergethon is a solar expert and writer from Colorado, visit his solar panels site for more information.

Electric meter via shutterstock

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  • aden

    please help me it is for my studies. my question is how do the long hours of sunshine help us?

    • Bob_Wallace

      If I understand your question correctly you can get very accurate data by using the irradiance calculator on the Solar Electricity Handbook web site.

      Put in the information for your country and nearest city and you’ll get monthly averages.

  • ML Hayes

    If your wealth were denominated by the amount of energy you could generate in excess of what you consume, that fact would change a lot of th eeconomic dynamics of the planet. Many of the technologies that are currently being employed to convert naturally occuring phenomena such as sunlight, wind, tidal energy, geothermal and biologically based renewable fuels would take on a different dynamic perspective.

    A uniform currency based on energy production could gradually be globally employed to address production issues for many forms of public and private ventures. We have in our capacity, the ability to calculate such ramifications as the removal of speculative factors from energy production. Variations in distributive capacities would continue untile a global smartgrid were deployed, but otherwise, the base unit for purchase would be a fraction of a watt.

    Other factors such as the capacity to store the surplus energy until it was needed would need to be considered in the light of population densities and potential colonization of parts of the planet that are currently underpopulated as a result of energy and fresh water scarcity.

    I don’t think anyone has mentioned that fresh cleah water would be one of the byproducts of using conversion energy to produce hydrogen and using hydrogen as a fuel to produce electricity. Globally accepted of currency based on the triple benefits of clean power, clean water and cleaner air as quantified by infrastructure dedicated tothe production of these qualities would be good as gold. In addition, if the power so produced were mandated in its use, then clean up of legacy pollution and contamination could a be used to give premium value to various regional ventures. Additionally, the collaboration of governments to initiate innovations in restoration of biological ecologies that contribute to biodiversity of the planet would assure that humanity could cohabitate in substainable manner with the fixed limits of the planets resources.

    Currently, we humans overpopulate about 2/5ths of the inhabitable surface. Wider distribution of humans would present a number is issues unless we learn to supply adequate power to all residents of the planet. Making energy production from convertable sources and the storage ot that energy safer to transport or distribute would drive personal production of energy much as personal production of food sources drove industrialization in the early mechnization periods of the 17th, 18th , and 19th Centuries.

    Food production will not go away but greater energy efficientcy would link the nutrition industry to the consumer in / energy producer new ways. We all realize htat we cannot continue to expand the consumerism methodology of global economics indefinitely. The alternative to constant exploration is inteligent expansion of the conversion technologies to optimize the consumption to creation ratio for every human being on the planet.

    It is impractical to consider that the governments will be able to incintivize every individual without trying energy production to the individuals most basic instincts. Primitives peoples that currently are subjeted to de-politicalization when such decision are considered or made, would in effect gain significant advantages given most such peoples cannot currently be taxed to support this kind of proposition.

    A currency based on a community’s ability to collaborate is subject to political pressures that may evolve from non-energy related issues. For this reason, the individualized effort must be designed to synchronize with distribution underwritten by the governments which, in turn are coordinated within a grid that allows power to flow freely across borders for commercial and residential purposes.

    Altenative production such as goods for merchantile, construction, and public use would be taxed based on their pollution and contamination abatement requirements. This strategy would allow factors of geography and ecological sentivity to be accounted for in a weight manner where the extraction of natural resources for production of consumables could be measured based onthe depreciable value of sum total of components issues.

    What this would mean to investors is a clearer idea of the weighted value of one location of extraction over another in terms of restoration costs, depletion expenses and marketing expenses where distance to markets and market size are virtually global considerations.

    What this would mean to ordinary people is that relocation to remote or foreign communities would be less risky and more profitable based on forwarded considerations for future retirement or occupational conversion from production service to some form of contributory services such as agribusiness or custom product manufacture.

    These aspirations could be conducted by parties that utilized thier skills to create autonomous operations that did not contribute pollution or contamination to their local environments and produced sufficient energy to be self-sustaining. As a global community such operations would allow merchantile activities to to exist with minimal government regulation to assure safety and quality.

    There may be a lot of details not mentioned here, but the main facts need to be addressed as can we use energy a a means to drive a global economy?

  • Worried for the country

    Does this site censor comments it doesn’t agree with? Embarrassing if it does especially after is asks:”Speak your mind”

    • Actually, we just changed over a bunch of stuff in our backend and it knocked our commenting system, Disqus, out. Result is that all comments are currently being held for moderation. (But about to approve them… if they aren’t spam.)

  • Worried for the country

    Hey, I’m all for solar but it doesn’t lower costs. The industry predicts the cost of new solar in 2014 will be about $.28/kwh. That is double what I pay to my utility today and I’m in a high cost area.

    Research should continue and I am hopeful that someday it will be competitive with natural gas or nuclear.

  • Ralph Perez

    Factoring in the charging of an electric car battery might also be good. Especially if the car has a quick change type battery.
    Our local utility companies, banks, tax assessors and building departments are forcing up the cost of installing solar. Each of these entities need to look at what is happening across the US to lower each of these costs locally.

  • ML Hayes

    Why push solar energy? Well the Sun has been around for a long time and the solar energy it produces will likely continue to reach this planet far into the future. More importantly, solar resources are the most common to the most people on the planet.

    There is another reason that is only starting to play its hand in human destiny. If humans were (or going to be) able to reduce their collective energy objectives to a common denominator, we should (could or would) see that energy is the one component to our universal satisfaction; and that everyone must acquire some degree of energy to obtain any level of satisfaction. Energy has many states from the readily convertible to the not so easy to employ for a satisfying purpose. This covers the spectrum of human energy consumption from pedestrian strolling to petroleum and it includes all the alternatives in-between.

    If you consider intellect as another form of energy as you would solar and wind, it is easier to understand the links between what we are doing and what we must do in the future. That is the near future. Unlike mechanical, chemical or nuclear conversion methods, intellectual energy can only be employed in turning ideas into realities. That means communication is the act necessary to generate satisfactory results. Endpoint results are manifested by the employment of other forms of energy to produce a process, product or service that is valuable enough to warrant mercantile or commercial exchanges.

    I do not believe there is an alternative to this strategy that allows us to co-exist in a harmonious non-violent manner.

    In the not to distant future, each human being will be required to contribute to the community pool of energy stored around the planet. Energy stored from conversions of renewable sources will meliorate demand spikes in distant locations through wave propagation techniques that allow distribution to be sync’d with productive capacities.

    In such scenarios, the ability of individuals to create more energy that they personally consume will determine wealth of those individuals. Socially, geographic autonomy will be dictated by the ability of a region to export its excess energy and therein the political identity of a group or metropolitan area will spring from their collaborative ability to optimize energy production with consumption objectives.

    The facts are things are already working like this except for the part about individuals producing the ‘excess’ energy and that being the same as money in the bank.

    Our alternatives to this concept are bleak because historically they are based on energy in the form of destructive force. You cannot compete with me if I destroy you or your capacity to produce. The immediacy of starvation, water deprivation and accompanying diseases from either or both make these alternative potent considerations.

    I guess you can call this negative energy, but it gets its persuasion in the same manner as the positive kind through the ability to produce commercially viable products and services. Only those in the market for arms and armies to use them want the production. There really isn’t any rational need for it. Well, perhaps there would not be if energy production were the endpoint as opposed to energy control.

    • Anonymous

      I can tell you quite simply why we should push solar.

      Cheap electricity.

      Solar has now reached grid parity in sunny parts of the US. That means that panels installed today and financed over the next 20 years will produce power at the price of power today.

      Next year the price of fuel-produced electricity will almost certainly be higher. The price of the solar-produced electricity will not rise.

      Two, five, ten, fifteen and twenty years from now the price of fuel-produced electricity will almost certain continue to rise, becoming more and more expensive over time. The price of the solar-produced electricity will not rise.

      Thirty, forty, one hundred years from now (if we still use any fuel for electricity) the price of fuel-produced electricity will continue to increase and increase and increase. The solar panels, at the end of the first twenty years, will be paid off. The price of the solar-produced electricity will be about zero cents per kWh.

      Current high quality solar panels are degrading between 0.1% and 0.2% per year. Assuming a 0.2% drop in output per year a solar array installed
      today should be producing about 82% of their original electricity per year.
      And producing it for about zero cents per kWh.

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