Power Systems

Renewable Energy System Basics

We receive more emails about renewable energy system basics than we can possibly answer, so this page is our attempt to answer the most common questions that we get. We do offer paid consulting services, focused mostly on designing off-grid power systems and small wind energy. Contact us if you are interested.

Quick Links to this page

• What do the terms 'on-grid,' 'off-grid,' and 'grid-tied' mean?
  
• I will be building a new home, and want to make sure it's as energy efficient as possible. I am considering including a renewable energy system.
  
• Seven Steps to a Sustainable Building--what you should look at FIRST before investing in solar or wind power.
  
• My electricity bills have gone sky-high for my existing home. How many solar panels or wind turbines do I need to power my 4,000 square foot house?
  
• I did my homework, and I think my home is a good candidate for a renewable energy system, how do I do the math to find out for sure?
  
• I need a small, simple remote power system for my RV. I hate running a noisy, smelly gasoline-powered generator at campsites. People throw rocks and rotten tomatoes at my RV when I run the generator at night.
  
• Example system diagram
  
  
  
  

  What do the terms 'on-grid,' 'off-grid,' and 'grid-tied' mean?

  All RE systems have three elements in common:
  • Power Sources: Devices that generate electricity, such as wind turbines, photovoltaic panels, micro-hydro plants and fossil fuel generators.
  • Power Storage: A way to store energy for use when there is no power coming in.
  • Loads: All the lights, appliances, and gadgets that you run in your house.
  RE systems can be classified into three types:
  • On-grid: Powered exclusively by purchasing electricity services from your local electric utility, from the local power lines.
  • Off-grid: The system is not connected to the power grid (power lines from the utility company). Power is stored in a bank of batteries that run the loads. Extra power is used for air or water heating.
  • Grid-tied: The system is directly connected to the power grid. Power is not really stored, instead the grid is used as a “battery.” If the grid experiences a blackout, there is no power for loads--the house is blacked out too. Extra power is sold back to the utility.
  • Grid-tied plus battery backup: The system is connected to the power grid. Power is stored in a battery bank, so if the grid experiences a blackout the house still has power to run loads. Extra power is sold back to the utility.

  I will be building a new home, and want to make sure it's as energy efficient as possible. I am considering including a renewable energy system.

  Congratulations, you are in the ideal situation for renewable energy! You can design your home from the ground up to be energy-efficient, and invest a potion of your capital into directly incorporating solar, wind and hydro power to power your new home. Visit the US Department of Energy's Energy Efficiency and Renewable Energy website for more ideas about what 'green' features you can incorporate into your home's design.
• You don't need to be extremely wealthy or be building a custom home to be energy-efficient and make your own power! This article discusses new, efficient modular homes that come equipped with solar panels and more.
• Then (after you've done your homework on Department of Energy website), contact a local architect or contractor that's experienced with energy-efficient homes and renewable energy and ask for a feasibility evaluation at your site. Some of the features you may be able to include in your new home would be:
  • High insulation R-values for the home, including the windows.
  • Passive solar space heating, including thermal mass for heat storage.
  • Radiant floor heating via solar thermal.
  • Solar hot water heating, which can also be combined with radiant floor heating.
  • Proper shading and swamp cooler options in hot climates.
  • Efficient appliances, like fridges, dishwashers, clothes washers, etc.
  • Efficient lighting.
  • Skylights and light tubes to reduce winter lighting loads.
  All of the above options can greatly reduce the size of the renewable energy system you'd need to install to make your home completely or partially self-sufficient.
  
  
  
  
  Our friend and neighbor Andrew Michler is a green building consultant, his business is Baosol Sustainable Building Consulting. His guidelines in this short brochure are right on the money--if you are building a home from scratch, start at the bottom step and work your way up. If you are retrofitting, you'll come in somewhere farther up. The lower down the stairs you can start, the more efficient your home will be. There are more pages that explain each step in detail -- click the image above or GO HERE to dowload the whole PDF. Note that for larger buildings used for commercial purposes, you can consult with an ultrasonic flowmeter supplier in order to make sure you're as energy-efficient as possible.

  My electricity bills have gone sky-high for my existing home. How many solar panels or wind turbines do I need to power my 4,000 square foot house?

  First, you need to understand that houses don't use electricity, people do! Your power usage depends on the lights and appliances that you've installed in your house, and how often you run them. Here's an example of the step-by-step process you should complete to determine if a renewable energy system can help you with your power bills.
  • First, you need to find out how much electricity you use. Your power bill will have this figure, and you need to find both the monthly and yearly figures. These will be given in kilowatt-hours (kwh) on your bill. The average US home uses about 750 kwh per month.
  • Now, despite how high your electricity bill seems to you, keep in mind that grid power is CHEAP and heavily subsidized compared to renewable energy! In a location with good average wind speeds, the average US home would need a 24 foot diameter wind turbine flown on a 100 foot+ tower to break even with the utility bills--at an installed cost of at least $50,000. Or, a large solar array at a similar cost. Depending on your location, one or the other might work better, or a combination of both solar and wind. In sunny Phoenix Arizona, you'll need fewer solar panels than in foggy Seattle Washington.
  • The next logical step would be to calculate how much energy you could expect from a wind turbine or solar panels at your location, right? Nope. First, you need to try and conserve energy. It's always cheaper to replace older, inefficient lights and appliances with new, highly efficient models than it is to power the old ones with renewable energy.
    • Replace every light bulb in your house with a fluorescent (FL) or compact fluorescent (CF)--that's a no-brainer.
    • Replacing your old fridge with a newer model will cost you some money--but much less than the solar or wind capacity you'd need to run it.
    • Installing double-pane windows (in cold climates) or shading systems and swamp coolers (instead of air conditioning) in hot climates could save you many hours of run time on your heating and cooling systems--which are often the biggest single electrical load you use in your home.
    • Electric ranges and clothes dryers are right out, get gas-powered versions.
    • Replace your electric water heater with a gas on-demand version.
    • Change your habits. Don't leave your big-screen TV on all the time just for the noise--play the radio instead. Turn lights off when you leave the room. Install a 'smart' controller for your heating and cooling systems. Put on a sweater if the house gets a bit chilly. You'd be amazed at what a difference such small lifestyle changes can make in your power bill!
    • Visit the US Department of Energy's Energy Efficiency and Renewable Energy website and get free information about energy conservation strategies for your home.
  • NOW watch your power bills for another couple months. The kilowatt-hours per month figure you get after making all the conservation efforts you can is the one you should use for your calculations.
  • Next, do your homework. You'll be investing a lot of money in renewable energy if you go through with it, and it would be silly to not understand what's going on. Once again, the US Department of Energy's Energy Efficiency and Renewable Energy website is where you want to start--it's free, and it's your tax dollars at work. Thoroughly explore all the links and free downloadable Consumer's Guides under 'Making your own clean electricity.' Make sure you thoroughly understand what equipment you'll have to purchase, and that you'll need approval and permits from both your local building inspector and your local electric utility to install any sort of renewable energy system.
  • Now, you can get down to business! First research any available Federal, State or local tax credits or subsidies that are available to you. Such policies can make the difference between a renewable energy system that pays for itself within 5 years, or one that takes decades to pay back.
  • Find out if your state has laws about 'net metering' by the electric utilities. You can look up your state laws on this US Department of Energy web page. In some states, only certain utility districts allow new metering. Net metering simply means that your electric meter can run backwards from power that you produce on site to offset the amount of power you used each month. Without net metering, a renewable energy system will never pay you back, or may not even be allowed.
  
  
  
  
  

  I did my homework, and I think my home is a good candidate for a renewable energy system, how do I do the math to find out for sure?

  So, you have net metering laws in your area, and maybe government tax credits or subsidies. You are conserving energy, and using as little electricity as possible. You understand all the information about grid-tied systems in those US Government 'Consumers Guides.' Here's how you start to do the math. Actually, those guides you just read will also explain where to start, but we repeat it here, below.
  • You'll need to have your new (post-conservation) kilowatt-hours per month information for your home available.
  • If you're serious, contact a local renewable energy contractor and ask about what real-world figures are available for the RE systems they have installed in your area.
  • Calculate your potential power input.
    • For solar, first find out if any local laws or covenants restrict what you can install, whether its for solar thermal or solar electric. If there is a problem, it's possible that those restrictions could be illegal -- many states and local governments have 'solar access' laws that ensure the availabilty of both sunlight and the right to install a renewable energy system.
    • Make sure you have a suitable site. In the Northern hemisphere, your solar panels must face south, and in the Southern hemisphere they must face north. The farther you are from the equator, the more tilt toawrd the horizon the solar panels will need, and the more possibility for obstruction by trees, buildings, etc. Right at the equator, solar panels would be mounted flat, facing straight up. Any obstructions may mean a huge decrease in the amount of solar energy available to you, whether for heating or electricity.
    • The average amount of solar energy available each day for your location (called 'insolation') has most likely been measured very accurately, right on the ground near where you are. Go to this very handy world insolation chart and find out how many average 'full sun hours' you have available.
    • Now you are armed with the information you need to predict power input. Those 'full sun hours' are already averaged to take into account the average weather patterns for clouds, rain and snow, and compensate for the suns angle in morning and evening. Multiply full sun hours by how big a solar array you are considering. For example, if you have 6 full sun hours available and buy 1000 watts of solar panels--that's an average of 6 kwh per day. It could be more in summer and less in winter (depending on your latitude) but you now have a good average prediction to work from, and compare to your average power usage in kwh.
    • For wind power, first keep in mind that wind turbines need to fly on tall towers, at least 30 feet above any obstruction within 300 feet. Flying a wind turbine near the ground is like mounting a solar panel in the shade! And, keep in mind that wind turbines need to be quite large to make any dent on your utility bill--the average US home in a good wind location would need a 23 foot diameter, 10kW turbine on a tall tower to break even on utility bills. For these reasons, wind turbines are most suitable only for rural and semi-rural areas on large pieces of property.
    • Don't let anyone tell you that a small, rooftop wind turbine will help your utility bills--they are trying to scam you. There's a finite amount of power available in moving air, and at slow wind speeds the only way to get any usable power is with a large turbine. High winds are very, very rare, so it makes no sense to install a turbine that only gives you usable power in high winds. Rooftops are also a terrible location, with lots of obstructions and turbulence.
    • Check into any local covenants and regulations about wind turbines and towers. The more rural your location, the less likely there will be restrictions. Some restrictions you may run into include tower height, and possibly laws that the 'fall zone' of your tower must lie entirely on your property.
    • Make sure you are in a location with reasonable wind speeds. First go to the NREL Wind Atlas and see which wind zone you are in. Then, see if there are any local wind power systems in your area, and talk to the owners and/or installers to see how much potential there is.
    • If all this has not scared you off of wind power yet and you are still considering a subtantial investment in a wind turbine and tower, consider purchasing or renting a logging anemometer and tower to take actual wind measurements at your location for a year. Estimates 'off the top of your head' will be wildly inaccurate--the figure of 'average wind speed' that you need to make any predictions of power output also includes all the hours that the wind is not blowing at all. Some local governments and universities have subsidized programs for property owners to rent logging anemometers at low cost.
    • Once you are armed with a reasonable estimate of your site's average wind speed, you can start to do the math. Go to a reputable wind turbine manufacturer's website, such as Bergey or Southwest Wind Power and compare the estimated annual power output figures (in kwh) of their different sized wind turbines at your site's average wind speed. See how those numbers compare to how many kwh you use each month.
    • Keep in mind that the cost of the wind turbine is only part of the whole deal--a tall tower will cost you at least as much as the turbine that flies on it. And, you have the other system costs to consider too--which you already researched at the US Deprtment of Energy website, right?
    • Also keep in mind that wind turbines have moving parts, and need regular matintenence. Solar panels are a mostly 'install and forget' way to generate power, but wind turbines are not. Factor in the cost of having a qualified wind power technician service your machine every year or two if you are not willing or able to do it yourself.
    • We highly recommend that you read this article, The Bottom Line About Wind Turbines. It's highly informative, and will also help you avoid the numerous small wind turbine scams out there.

    I need a small, simple remote power system for my RV. I hate running a noisy, smelly gasoline-powered generator at campsites. People throw rocks and rotten tomatoes at my RV when I run the generator at night.

    • First, conserve as much power as you can. Replace all your lights with compact fluorescents or LEDs. If you have a TV in that mobile palace, replace it with a flat-screen LCD model. Reduce your power usage as much as you can. Such components as propane heater fans and water pressure pumps are generally very easy to run off of a small solar power system.
    • For the basics on doing the math to calculate how much power you use versus how much you can generate with a solar panel, refer to this article about how to design a solar power system for a pop-up camper.
    • This article gives a good overview and good links about the basics of RV renewable energy systems.
    • Wind power and RVs are not generally compatible. Since wind turbines need to be flown high above any nearby obstructions to be effective, a tall tower is needed. That's not an easy thing to carry on your RV--and a tower that's actually mounted on your RV is a recipe for disaster! Plus the fact that you usually park your RV in the shade, under some trees, right?
    
    
    

    Example System Diagram

    Here's a basic rundown on how a remote power system functions, and a diagram of a typical system. Click on any highlighted keyword to jump to a page about that subject.

        First, your electricity is produced by solar panels, wind generators, hydro generators, and/or a gasoline generator.  This electricity is usually in the form of 12 volt direct current (12 VDC).  Some gasoline generators produce 120 volt alternating current (120 VAC), and require a battery charger to convert this to 12 VDC.
        Your electricity then flows to your batteries through a charge controller, with a meter in the line to tell you what's happening with the system.  The charge controller shuts off the charging current when your batteries are full.
        When you run 12 VDC lights or appliances, the current flows from your batteries, through a meter and fuse box to your appliance.  Devices that run off of 120 VAC take their power from an inverter, which converts the 12 VDC to 120 VAC.  Inverters are availble that can power your whole house through regular AC wall outlets, or in small versions that can run only one device at time.
     

    Below is a diagram of  a sample power system:

     

    This page is still in progress...we have LOTS of information to add!