Solar System Questions

WindmillHillWindmillHill Registered Users Posts: 2
Hi everyone, I'm new to this forum so Greetings from me to you!

I would like a solar system to power a 700 watt oil filled radiator for a maximum of 7 hours every night.

I understand that I will need solar panels, batteries, a charge controller, inverter, and cabling. But I need to work out -

1) How many solar panels I need and the correct wattage.
2) How many batteries I need at the correct ampHour rating.
3) The correct inverter.

But I am very new to all this and I don't know where to start. As I say all I need the system to run is a 700 watt oil filled radiator for maximum 7 hours every night.

As I live beside the sea I think it might be beneficial to add a wind turbine to the system at a later date.

If anyone could help me figure out what requirements my system will need that would be great !! Thanks a lot.


  • gww1gww1 Solar Expert Posts: 963 ✭✭
    Re: Solar System Questions

    My guess at it would be a 2500 watt solar aray and a min of 400 amp hour battery at 48 volts. If you went 24 volts you would need an 800 amp hour of battery. I believe this is close to the bottom and more pv would be better. I am sure bill will come along and put this in a better perspective. I posted cause I wanted to say that the turbine even in a good area is not cost compeditive with solar all though a good area helps. It is the inferstructure of turbines that make them more expensive then just the price of a turbine. Bigger is probly more cost smart then small but still questionable. Also I you try making (and maby buying) one, you have special problims due to location. Being by the sea probly helps your wind speed but brings along with it very humid and corrosive air. If the turbine had magnets like mine (neo) They have been known to not last even five years due to the type of air you live in. There are other options but then things get heavier as they are not as efficiant. This is just my opinion from reading and the few little things that I play with that are listed in my profile.
    Good luck
  • WindmillHillWindmillHill Registered Users Posts: 2
    Re: Solar System Questions

    Thanks for your detailed response. Sounds expensive!
  • BB.BB. Super Moderators, Administrators Posts: 32,007 admin
    Re: Solar System Questions

    If your choice is Electricity or nothing (if you have natural gas or possibly oil, perhaps not so much savings--Local costs vary greatly)--And you are in a relatively moderate climate, look at an air sourced Mini-Split Heat Pump system (basically an air conditioning system running in "reverse").

    They can be upwards of 2x as efficient as pure resistance heaters. Some of them will even work fairly well (efficiently) with snow on the ground.

    However, not everyone has had good results... Possibly because of problems with the installer, and if the home does not have good insulation/weather proofing. Installing central heat+hot water vs just a smaller mini-split for a couple rooms can help keep installation and heating costs lower too:

    Make sure you understand all of the costs... Don't just use government incentives for "green" energy--They may not reduce overall costs, or can leave you with a white elephant (many companies/products disappear as soon as the government credits go away).

    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • icarusicarus Solar Expert Posts: 5,433 ✭✭✭✭
    Re: Solar System Questions

    700 wats for 7 hours is 4.9 kwh! Using my simple off grid formula you will need about 2200 watts of solar and associated battery bank for such a load. Might cost upwards of $8-12,000. Very expensive indeed.

    The basic rule of thumb is, (all calcs determine the battery size,bthe battery size determines the PV size and other component sizes) take the name plat rating of thepv, divide in 1/2 to account for all cumulative system loses, incuding PV efficincy, controll loses, chargin loses, inverter loses etc) then take that number and multiply that number by 4 to account for the averqge hours of "good sun" one can reasonably expect, per day, averaged over the course of the year. So 2200*.5=1100*4=4.4 kwh. You can adjust the numbers to your liking, but be advised the 4 hour number is pretty constant, if you fudge it up too much you will run the risk of not having enough capacity, on average over time.

    At 24volts, you would need a battery bank in the 800ah range (24 vdc) or 1600 for 12, 400 for 48. A very expensive battery! Just for comparison, a 12 volt battery bank made up of common golf cart batteries would be about 24 6 volt batteries, at say [email protected] or about $3800 in batteries that have a limited life span.

    Tht 1600 ah battery bank (12 vdc) will deliver a total of ~ 19kwh before being completly discharged. To keep the discharge rate below 25%, it would deliver 4.8 kwh. If you wanted to discharge to 50% routinely, you could halve the size of the battery bank, but you would reduce the life span by more than half IMHO.

    As you can see this gets difficult and expensive.

    Good luck and keep in touch,


    Sorry for the duplication of effort, others are too fast.


    PPS. That 900 watts is around 3000 BTUs/hour. Getting 3000 BTUs/hour out of a fuel fired heater is a peice of cake. Depending on your situation, a diirect vent propane, or fuel oil heater is likely to be waaaaay cheaper in the net than trying to Solaris an electic of the same size. For example assuming ventilation is available, a simple catalytic heater with disposable bottles would put out 3k BTUs. I wouldnt sleep with one going, but ther are lots of vented heaters, RV furnaces etc that would work with minimal PV input.(some with none!)
  • westbranchwestbranch Solar Expert Posts: 5,183 ✭✭✭✭
    Re: Solar System Questions

    Question: does that heater have to be on at night only, or can you preheat during the day? reason is you can use some of the PV power during the day once your battery is fully recharged, entered the absorb phase, about mid day if you have sufficient PV panels.
    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
  • solarvicsolarvic Solar Expert Posts: 1,060 ✭✭✭✭
    Re: Solar System Questions

    Just wanted to say my oil filled heater uses 1200 watt and is not that big. I have 2 of them for emergency use if my gas well stops in the middle of the night. solarvic
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