Kilowatts Or Amps?

Options
chris77
chris77 Registered Users Posts: 6 ✭
in Solar Beginners Corner #1
Wind & Sun Members,

Whe I see a solar panel advertised as "100 watts", certainly it can power more than a 100 watt lightbulb. What is the units I need to find on a solar panel to determine how much more electricity one solar panel can create than another?


Thanks,


Chris
· Share on Twitter

Comments

  • Cariboocoot
    Cariboocoot Banned Posts: 17,615 ✭✭✭
    #2
    Options
    Re: Kilowatts Or Amps?

    Welcome to the forum, Chris.

    Watts is it: Volts * Amps. It is a relative term that can be used for comparing two solar panels. It is not an absolute term, because on average a "100 Watt" panel will not produce 100 Watts throughout the day even with good sun.

    What your utility sells you is a quantity of electricity: kilowatt hour. That is 1000 Watts for an hour, or any mathematical equivalent thereof.

    In a typical day your solar panels might receive 5 hours of "equivalent good sun" during which they will produce their averaged output, which is usually about 77% of the "nameplate" rating. So a 100 Watt panel would produce an average 77 Watts for 5 hours, or 385 Watt hours (0.385 kW hours).

    So when you compare two panels, a 200 Watt panel will produce more power under the same conditions than a 100 Watt panel.

    Unfortunately that's not all there is to it, because they can have different Voltages too which makes some more usable than others in a given application.

    There are a lot of terms connected with solar. Here's a glossary of some of them: http://forum.solar-electric.com/showthread.php?6136-Glossary
    · Share on Twitter
  • chris77
    chris77 Registered Users Posts: 6 ✭
    #3
    Options
    Re: Kilowatts Or Amps?

    Cariboocoot,
    Is there a preferable voltage if you're using a solar panels to reduce electric billl on a 100 amp service home?

    Thanks
    · Share on Twitter
  • waynefromnscanada
    waynefromnscanada Solar Expert Posts: 3,009 ✭✭✭✭
    #4
    Options
    Re: Kilowatts Or Amps?

    Hi Chris, I also welcome you to the form.
    I see by you're profile that you re interested in lowering your electric bill. Hate to say it, but solar is not the way to do that. But there IS a way, and that way is conservation. In fact, as has often been said on this form, "Conserve, conserve, conserve".
    This is not to say there is not a place for solar, especially if you go grid tie, but you must be prepared to dish out money to get there.
    The unfortunate thing is, there are many scam artists out there telling folks that all they have to do is send money and "the secrets" to lowering their electric bill will be revealed. Unfortunately the only thing revealed, is that the "customer" has been taken by the scam artist.
    All that said, virtually all my daily electrical needs (without waste) are being met by an off grid system. It cost a lot to get going, and if I had known in advance how much it would cost, I would have backed off, but it's also addictive. Haha And in fact, I'm very happy with it, not because it lowers my bill, but because it gives me independence from the grid whenever it goes down.
    It does however require a different mindset than that of the general population which has been brought up to consider the wasting of electrical energy to be quite normal. They don't see their waste, they only see and complain about the high electric bills.
    I'm definitely NOT trying to steer you away from solar, rather if that's the path you decide on, I want it to be with your eyes wide open.
    · Share on Twitter
  • Cariboocoot
    Cariboocoot Banned Posts: 17,615 ✭✭✭
    #5
    Options
    Re: Kilowatts Or Amps?
    chris77 wrote: »
    Cariboocoot,
    Is there a preferable voltage if you're using a solar panels to reduce electric billl on a 100 amp service home?

    Thanks

    This depends on how you do it.

    The most efficient way is to do what is known as a grid-tie install. With that the solar panels feed a grid-tie inverter directly, which then supplies whatever power the panels can produce as AC current to your household. Any 'surplus' production not used by the house is sold back to the grid. It is necessary to do this with the co-operation of the utility and it requires inspection and permits to be safe and legal. There are limits as to how much power you can 'back feed' based on the size of your service and sometimes other local restrictions. GT inverters can use any type of panel so long as the Voltage adds up to enough to power the inverter. Typically they run around 400 Volt arrays, so you would have several panels in series to provide sufficient Voltage (and consequently power). Another option on this line is the micro-inverter, which works on a basis of one panel to one inverter. They are about 200 Watts output each, and are usually put together in an array of panels+inverters to meet the desired power level.

    The other way to do it is to take a portion of the household needs "off grid". This involves batteries, a battery-based inverter, and solar panels + charge controller to replenish the batteries. It is much more expensive that grid-tie or indeed utility power. Think of it as GT solar power costing $0.50 per kW hour and OG solar power about twice that. Makes utility power look pretty cheap, eh?

    If your goal is to reduce your electric bill the first thing you should look in to is conservation. On average, utility power is cheaper than solar power (unless you have a very good buy-back program from your utility). As such, buying a Kill-A-Watt meter and checking the real power consumption of things you plug in is a good first step at this.
    · Share on Twitter
  • chris77
    chris77 Registered Users Posts: 6 ✭
    #6
    Options
    Re: Kilowatts Or Amps?

    A lot of helpful information. I would think with all the electronic wizardry on the market that someone makes a device that would allow my electricity from my solar panel (at the right amperage) into the electric lines in the house first an hold back the grid electricity untill needed. It seems pretty logical. Why isn't is so?
    · Share on Twitter
  • westbranch
    westbranch Solar Expert Posts: 5,183 ✭✭✭✭
    #7
    Options
    Re: Kilowatts Or Amps?

    that what 'Coot has described ... a Grid Tie system...
     
    KID #51B  4s 140W to 24V 900Ah C&D AGM
    CL#29032 FW 2126/ 2073/ 2133 175A E-Panel WBjr, 3 x 4s 140W to 24V 900Ah C&D AGM 
    Cotek ST1500W 24V Inverter,OmniCharge 3024,
    2 x Cisco WRT54GL i/c DD-WRT Rtr & Bridge,
    Eu3/2/1000i Gens, 1680W & E-Panel/WBjr to come, CL #647 asleep
    West Chilcotin, BC, Canada
    · Share on Twitter
  • Cariboocoot
    Cariboocoot Banned Posts: 17,615 ✭✭✭
    #8
    Options
    Re: Kilowatts Or Amps?
    chris77 wrote: »
    A lot of helpful information. I would think with all the electronic wizardry on the market that someone makes a device that would allow my electricity from my solar panel (at the right amperage) into the electric lines in the house first an hold back the grid electricity untill needed. It seems pretty logical. Why isn't is so?

    It can be done with enough GT capacity, but panels only make power while the sun shines. If you want to offset utility use 24 hours a day you need to store power in batteries, and 'harvest' all of it when the sun shines. This is even more expensive.
    · Share on Twitter
  • chris77
    chris77 Registered Users Posts: 6 ✭
    #9
    Options
    Re: Kilowatts Or Amps?

    I don't mind saving money only when the sun shines. What is GT capacity? What is the name of the device that will allow my electricity over the grid's. Will a solar panel supply enough amps?
    · Share on Twitter
  • waynefromnscanada
    waynefromnscanada Solar Expert Posts: 3,009 ✭✭✭✭
    #10
    Options
    Re: Kilowatts Or Amps?
    chris77 wrote: »
    I don't mind saving money only when the sun shines. What is GT capacity? What is the name of the device that will allow my electricity over the grid's. Will a solar panel supply enough amps?

    Name of the device is exactly as Coot has described and others have repeated: Grid Tie Inverter. And the capacity is how many panels you have on your roof. The TG inverter must of course be sized to match.
    Note: Many people mistakenly have the idea that all they have to do is stick a $200 solar panel on their roof and all their electricity woes will be over. Well that could be true if all they have and use is a couple of LED lights that are only on during daylight hours. Beyond that, to install "a" solar panel and expect it to lower your bill would be like spitting into a river and expecting the water to rise. Useful solar gets VERY expensive and complicated for the average homeowner, which is what we've been trying to get across. Solar CAN work, but it's generally way more expensive than grid power, and huge investments must be made up front. There is no free and easy ride when it comes to energy cost reduction, other than "conserve, conserve, conserve", and no matter how often, or in how many different ways the question is asked - - the true answer remains the same!
    · Share on Twitter
  • Cariboocoot
    Cariboocoot Banned Posts: 17,615 ✭✭✭
    #11
    Options
    Re: Kilowatts Or Amps?

    Here's a link to some example system quotes to give you an idea of what you'd need and what it would cost: http://www.solar-electric.com/grtiesyexqu.html

    Note that the sizing is based on the nameplate Watt rating of the array, not the daily kW hour production capacity. This is because that will vary depending on where it is located.

    To get an idea what kind of production you could get where you are and what the cost benefit of it would be you can run a few simulations with PV Watts: http://www.nrel.gov/rredc/pvwatts/grid.html

    It is always best to do this before you start spending money. ;)
    · Share on Twitter
  • chris77
    chris77 Registered Users Posts: 6 ✭
    #12
    Options
    Re: Kilowatts Or Amps?

    How about this approach. I heard that in Israel by law water heaters can only be run on solar or other alternative energy. What are your thought on that. It sounds like it would be a lot of start up costs for just a water heater; once started you may as well do the whole house. It seems they know something if all they are doing is heating water for a water heater. Maybe they're not even using solar panels but black painted water pipes. What do you think?
    · Share on Twitter
  • Cariboocoot
    Cariboocoot Banned Posts: 17,615 ✭✭✭
    #13
    Options
    Re: Kilowatts Or Amps?

    That would be direct solar-thermal system, and it is much more efficient and cost-effective than PV in most places.

    If you want a good look at some projects of that nature you can't do better than Build It Solar: http://www.builditsolar.com/
    · Share on Twitter
  • BB.
    BB. Super Moderators, Administrators Posts: 33,443 admin
    #14
    Options
    Re: Kilowatts Or Amps?

    Yes, you can even make your own solar thermal collector (copper tubing, metal plate, inside an insulated box with glass cover sheet). Then you have a pump that, when the sun is shining takes "cold" water from your water heater storage tank, pumps it through your solar collector, then puts hot water back into the tank.

    There are a few details for safety, control, protect against freezing (if an issue), and scalding (you don't want boiling water coming out of your tap).

    Here are some places to read:
    Solar Thermal can be a nice source for space heating and hot water... And usually is "cheaper" per kWhr/BTU vs Solar PV Electric. Also, Solar Thermal lends itself very well to do it yourself projects. Note, these are plumbing projects and have their own issues (leaks, pump failures, installation issues trapping air, anti-freeze, storage, heat exchangers, etc.):

    Solar Shed and other Solar Thermal Links

    A good place to start reading is Home Power Magazine... They have a free past issue online--and have a lot of articles you can read for free. I don't always agree with them and their reviews--but they are a fun and enlightening read:

    Home Power Mag

    Note, these days, there are now water heaters that use a Heat Pump to warm the water.... Basically, think of the reverse of your home refrigerator. With a heat pump water heater, the water gets hot and the air outside (home, garage, etc.) gets cold. And they are, typically, at least 2x as efficient vs pure resistive heating. Here is one US Brand:

    GeoSpring Hybrid-Electric Heat-Pump Hot Water Heater

    If you have air conditioning, you can also install a heat exchanger to produce domestic hot water from your A/C system too.

    In the US, these heat pump water heaters (they do have backup electrical resistance heaters for very cold weather/if you need a lot of hot water) are becoming more popular than solar thermal systems. Cheaper to install and to maintain vs solar thermal systems (a bit of a plumbing nightmare at times).

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
    · Share on Twitter
  • ggunn
    ggunn Solar Expert Posts: 1,973 ✭✭✭
    #15
    Options
    Re: Kilowatts Or Amps?
    chris77 wrote: »
    A lot of helpful information. I would think with all the electronic wizardry on the market that someone makes a device that would allow my electricity from my solar panel (at the right amperage) into the electric lines in the house first an hold back the grid electricity untill needed. It seems pretty logical. Why isn't is so?

    Here are some basics:

    A solar module (panel) produces electrical energy from sunlight. This is DC (direct current), which is different from the electricity you buy from the utility, which is AC (alternating current). To convert the electricity from solar modules from DC to AC you need a device called an inverter. The simplest and least expensive solar electrical system is a grid tied system (the "GT" someone mentioned earlier) which feeds electricity from your inverter into the grid. It reduces the amount of electricity you buy from the utility by offsetting the usage charges on your electric bill. The way and the amount that your bill is offset depends on the deal that you get from your utility company, and it's different from company to company, location to location.

    It's not as simple as putting a solar panel on your roof and hooking it to your electrical system, and to produce enough electricity to significantly offset your bill takes a bunch of them plus an inverter.
    · Share on Twitter
  • chris77
    chris77 Registered Users Posts: 6 ✭
    #16
    Options
    Re: Kilowatts Or Amps?

    I wish it was that easy. The inverter solves the DC problem. Stopping the flow of electricity into your house and alowing electricity from your soalr panel doesn't sound like rocket science, sounds like a gate used in computer processors. Why would anyone want to make a deal with the grid - the goal is to avoid the grid.
    · Share on Twitter
  • waynefromnscanada
    waynefromnscanada Solar Expert Posts: 3,009 ✭✭✭✭
    #17
    Options
    Re: Kilowatts Or Amps?

    Some people ask questions, they get good honest answers from people who know what they're talking about, but won't listen, because it isn't what they want to hear.
    So they have to learn the hard way .
    · Share on Twitter
  • Cariboocoot
    Cariboocoot Banned Posts: 17,615 ✭✭✭
    #18
    Options
    Re: Kilowatts Or Amps?
    chris77 wrote: »
    I wish it was that easy. The inverter solves the DC problem. Stopping the flow of electricity into your house and alowing electricity from your soalr panel doesn't sound like rocket science, sounds like a gate used in computer processors. Why would anyone want to make a deal with the grid - the goal is to avoid the grid.

    You can avoid the grid if you want to. You'll just pay a lot more for electricity than you do now.

    I have a house in town with utility power: $0.10 per kW hour.
    I have a cabin in the woods with solar power: $4.63 per kW hour (so far). It would be half that if it were year-round: $2.32 per kW hour.

    The grid can be the best friend you've got: a great big 'battery' with endless capacity that is someone else's problem to maintain.
    · Share on Twitter
  • Photowhit
    Photowhit Solar Expert Posts: 6,003 ✭✭✭✭✭
    #19
    Options
    Re: Kilowatts Or Amps?

    I do think grid tied may be cost effective in some areas if you consider all costs and tax credits, particularly if you can are allowed to do most of the installing.

    But NOTHING beats not needing the energy.

    How much electric do you use? Try to see if you can use 1/2 that much, makes you think...

    Big users of electric are things that heat and cool;
    So water heater, can you install a switch and only heat water for an hour or less a day? Look into Grey boxes
    Refridgerators are big users, have you considered a new energy star fridge? or better how about doing a freezer conversion, it could save 3/4 or more of your refridgeration costs particularly if you are using a freezer as well. This works on using more insulation and not allowing for the cold air to 'drop out' of the fridge when you open the door.
    Air Conditioning, you can save simply from turning up the thermostat, ceiling fans or fans in general help you feel cooler in a warm enviroment. are you cooling the whole house but only need to cool a small area! might look into Mini split A/C units. You can even turn off your central air and just A/C a sleeping room on timer. A well insulated house will take much less to heat and cool.
    If you Heat with electric, have you considered a wood stove? it uses a carbon nuetral fuel and will warm you twice (old joke, but heck I'm old...)

    Can you tell me right now what is drawing electrical current in your home? Most people who live off grid can! Fridge on Thermostat, one 13watt compact florescent, my laptop, 2 small drain wall warts charging my cell, Mp3 player, and my TV (42 watts), and media player 5 watts, I think my 'T' amp is also on, it's on the same power strip but draws tiny amount of power 2-3 watts. I can tell you I have enough hot water for tonights shower and I'll need to turn it on for an hour around noon, so I can wash and get ready for pool league...
    Home system 4000 watt (Evergreen) array standing, with 2 Midnite Classic Lites,  Midnite E-panel, Magnum MS4024, Prosine 1800(now backup) and Exeltech 1100(former backup...lol), 660 ah 24v Forklift battery(now 10 years old). Off grid for 20 years (if I include 8 months on a bicycle).
    - Assorted other systems, pieces and to many panels in the closet to not do more projects.
    · Share on Twitter
  • stephendv
    stephendv Solar Expert Posts: 1,571 ✭✭
    #20
    Options
    Re: Kilowatts Or Amps?
    chris77 wrote: »
    Why would anyone want to make a deal with the grid - the goal is to avoid the grid.

    To get around this problem, it helps to not use the word "grid". Think of it as a company leasing you an AC enormous battery at very cheap price. ;)
    · Share on Twitter
  • ggunn
    ggunn Solar Expert Posts: 1,973 ✭✭✭
    #21
    Options
    Re: Kilowatts Or Amps?
    chris77 wrote: »
    I wish it was that easy. The inverter solves the DC problem. Stopping the flow of electricity into your house and alowing electricity from your soalr panel doesn't sound like rocket science, sounds like a gate used in computer processors. Why would anyone want to make a deal with the grid - the goal is to avoid the grid.
    For a grid tied system it's not rocket science at all, in fact it takes care of itself. The PV feed into the grid and your loads drawing from the grid are separate systems. Your PV system feeds its entire production into the grid and you draw out of the grid what you need for your loads, and you pay for the difference. The loads do not know or care whether the electrons they use came originally from your PV system or the power plant down the road. Don't avoid the grid; use it to your advantage.
    · Share on Twitter

Categories