Shower Thought: Solar power is almost free when sunny, very expensive at night.

softdownsoftdown Solar Expert Posts: 2,171 ✭✭✭✭
Many figures have been bandied about that compare the costs of solar to grid power. The general consensus, that I have seen, is that typical off grid power may costs 3-5 times more than typical grid power. Makes sense when considering equipment, wear and tear, batteries, and maintenance.

Then it dawned on me. It isn't that simple, solar power is close to free when the sun is shining and the batteries are charged. The costs when cutting into the reserve power of the batteries though? Thinking ~ten times the costs of grid power. Maybe more. These numbers are rather extreme simplifications of course.
First Bank:16 180 watt Grape Solar with  FM80 controller and 3648 Inverter....Fullriver 8D AGM solar batteries. Second Bank/MacGyver Special: 10 165(?) watt BP Solar with Renogy MPPT 40A controller/ and Xantrex C-35 PWM controller/ and Morningstar PWM controller...Cotek 24V PSW inverter....forklift and diesel locomotive batteries


  • petertearaipetertearai Solar Expert Posts: 390 ✭✭✭✭
    you can do the maths many different ways . suppose you are on grid . and have s holiday home used 4 days a month ... then with say... line charges $2 per day . then grid power per KW looks expensive.
    2225 wattts pv . Outback 2kw  fxr pure sine inverter . fm80 charge controller . victron battery monitor . 24 volts 450 ah surette batterys . off grid  holiday home 
  • MrM1MrM1 Registered Users Posts: 404 ✭✭✭
    There are several ways to "slice" the grid-tied vs off grid Value
    REC TwinPeak 2 285W 3S-3P 2.6kW-STC / 1.9kW-NMOT Array / MN Solar Classic 150 / 2017 Conext SW 4024 Inverter latest firmware / OB PSX-240 Autotransfomer for load balancing / Trojan L16H-AC 435Ah bank 4S connected to Inverter with 7' of 4/0 cable / 24 volt system / Grid-Assist or Backup Solar Generator System Powering 3200Whs Daily / System went Online Oct 2017 / System, Pics and Discussion
  • NANOcontrolNANOcontrol Registered Users Posts: 120 ✭✭
    Most systems are designed with "I Want It Now" mentality and that is quite expensive.  Add to that, they are just a collection of black boxes and not an integrated system.  I run a camp on just a car battery. I have PV hot water, refrigeration, and even a dishwasher with heated dry. I operate major loads when the sun shines. Any extra power goes into heating water and not the poor diversion methods others use. A microprocessor allots power to each load and makes the system efficient.  The general consensus is batteries cost $0.12 a KWH of use so you loose right out of the gate.  An undersized 300-400w of panels on a water heater to supply supplemental heating is about the most efficient use of panels. Nearly 100% of potential power is utilized because the heating element never turns off.
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