How much pv do i need?

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System
System Posts: 2,511 admin
in Solar Beginners Corner #1
I wanted to cut my meter off and insert a PV array with breaker, battery panel and inverter. But I don't know the amount of power my parts need. I'd like to supply my 100 amp breaker panel with all it needs.

I know I use 31 kwh per day on average.
I know I need PV panels, but I don't know what wattage in sum.
I know I need a battery, probably a 48 volt or more.
I know I need an inverter, maybe 3000 watts???

Can someone help?
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  • BB.
    BB. Super Moderators, Administrators Posts: 33,447 admin
    #2
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    Re: How much pv do i need?

    Short answer... Don't do anything yet.

    Slightly longer answer--Your grid power probably costs around $0.10 to $0.20 per kWHr. And Off-Grid power (solar+battery+inverters) costs closer to $1.00 to $2.00+ per hour.

    The steps we recommend:
    1. Conservation (insulation, replacing power hungry appliances with newer more efficient and smaller, turn off unused equipment)
    2. Measure/understand your loads.
    3. Define what you need for power (kWHrs per day, by season, emergency backup power, grid power+solar to reduce costs, etc.)
    4. Grid tied solar is the most cost effective power at this time. Can be in the range of $0.15 to $0.35 per kWH (depending on lots of variables).
    5. Review your utility's GT Solar policies... Some are very reasonable (by state law), others will charge a bunch of fees, and others yet will 100% say no.
    6. Off grid solar is usually down around choice #50 for most people with utility power.
    7. Wind power is usually down around choice #100
    You can look at your utility bill:
    • under 100 kWHrs per month--Off grid solar might be OK--not too expensive
    • under 300 kWHrs per month--you are doing good for average N. American.
    • 600-1,000 kWHrs per month--typical home in mild weather conditions
    • 1,000-3,000 kWHrs per month--Hot/humid climates, possibly needing better insulation and new high efficiency A/C system
    31kWH per day * 30 days per month = 930 kWHrs per month...

    Look at conservation first. For many people that have never worked on conservation around their home, they can save upwards of 1/2 of their electricity by spending much less money than off-grid solar or even GT solar would cost.

    Energy usage is a personal life-style choice--We attempt to educate people about their options--but, in the end, it is a personal choice.

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
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  • Cariboocoot
    Cariboocoot Banned Posts: 17,615 ✭✭✭
    #3
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    Re: How much pv do i need?
    poorgirl wrote: »
    I wanted to cut my meter off and insert a PV array with breaker, battery panel and inverter. But I don't know the amount of power my parts need. I'd like to supply my 100 amp breaker panel with all it needs.

    I know I use 31 kwh per day on average.
    I know I need PV panels, but I don't know what wattage in sum.
    I know I need a battery, probably a 48 volt or more.
    I know I need an inverter, maybe 3000 watts???

    Can someone help?

    Welcome to the forum.

    I've got to ask the crucial question: why do you want to do this?
    If it's to save money, it won't; off-grid power is far more expensive than grid power.
    31 kW hours per day is huge by off-grid standards. So in any case you'll want to get that number down. You can start by purchasing a Kill-A-Watt meter for about $30 and start measuring all your loads. Inevitably you will find some that are using more than is necessary. You should think about getting rid of anything that heats with electric and replacing it with natural gas or propane.

    Another thing you might consider is a grid-tie PV system, if that's feasible in your location. In any case you still need to get a firm handle on your loads first.
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  • waynefromnscanada
    waynefromnscanada Solar Expert Posts: 3,009 ✭✭✭✭
    #4
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    Re: How much pv do i need?

    31 kwh per day on solar? It can be done, but you had better be a millionaire and be prepared to give up that title. Unfortunately, most of us North Americans have been brought up to be grossly wasteful of electricity, indeed grossly wasteful of all energy sources. The sad part is that our energy suppliers have been behind the encouragement of such wasteful practices for their own personal profit, and that encouragement ranges from lying to their customers, convincing them it's cheaper to leave lights on 24/7, than to turn them off when not in use, to never turning the thermostat down at night because it supposedly takes far more energy to bring the temperature back up in the morning. We have to step back, take a serious look at how much energy we are consuming, where and why we are consuming that energy, and what we are getting for that use. I regularly visit homes where computers, some of them sucking back almost 200 watts, are being left on 24/7. That adds up to almost 5 kwh of wasted electricity right there! And those satellite TV receivers and set top boxes can suck up another 18 kwh per month, not to mention leaving the big screen TV running, just in case someone might see something they may want to watch. And don't even mention those hot water tank draining 40 minute showers twice a day. There are just so many places and areas in the average home where with a bit of thought and planning, HUGE energy savings can be realized. The question is, are we willing to make those changes.
    Many people think all they need do is stick a $200.00 solar panel on the roof and their energy problems are over. Well, not quite. :p
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  • ggunn
    ggunn Solar Expert Posts: 1,973 ✭✭✭
    #5
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    Re: How much pv do i need?

    I used to man a booth at trade shows, and when a tire kicker would come up to me and start asking about solar, the first thing I would ask them is what they want to accomplish with a PV system. Far too many times their immediate answer would be "I want to cut my ties to the grid!"

    Um, no you don't, not usually. The grid where you are would have to be either hideously expensive, or grossly undependable, or both, for it to be a sound economic decision to go off grid where the grid is available. The survivalist mentality aside (you guys have your own reasons for wanting to get off the grid, most of which are apart from economic ones), off grid living is not for most folks who have a choice.

    It is incumbent upon us who are involved in this industry to educate our potential customers, not just to sell them stuff.
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  • solar_dave
    solar_dave Solar Expert Posts: 2,397 ✭✭✭✭
    #6
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    Re: How much pv do i need?

    Head over to the grid-tie section of this forum. Grid tie is the most cost effective way to use solar. You in effect use the Grid as your battery, without the cost and maintenance headaches of having a battery bank.

    31Kwh is not unheard of, My system produces about 70-75 kWh a day here in Arizona but then I need that much to cool over 31,000 cubic feet of house and such when the temps climb to 115F like they will today, along with running a pool pump , deep freeze, charge a Chevy Volt ...
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