Building my first Grid-Tie PV system (w/out batteries)



  • BB.BB. Super Moderators, Administrators Posts: 32,008 admin
    Re: Building my first Grid-Tie PV system (w/out batteries)

    By the way, there are Heat Pump based water heaters now too... They have a COP of around 2.0 or possibly a bit more if the area (garage, basement, etc.) is >~55F. 2x as efficient as a pure resistive electric water heater.

    You can read about how they work here.

    Otherwise, insulation, more insulation, double pane windows, possibly a heat recovery ventilator system, etc...

    Measuring your major electrical loads and deciding on what to do can really save you some money.

    Also, many people these days have a few computers/servers in their home running 24x7... It is pretty amazing but these "smaller" loads running 24 hours per day can be real costly in terms of power use... First running the device itself, and second, running the AC to remove the heat from the home.

    A kill-a-watt meter is handy for plug-in devices. A T.E.D. Whole house meter (or equivalent) can also be pretty handy to keep track of the larger loads.


    By the way, here is a thread that has a whole bunch of different information about solar and conservation related stuff/projects/etc. Aimed at newbies--but also has lots of other handy information for others too...
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • icarusicarus Solar Expert Posts: 5,433 ✭✭✭✭
    Re: Building my first Grid-Tie PV system (w/out batteries)

    I both disagree and agree with 'Coot on the economy (first cost) of gas water heat.

    First, demand water heaters can be sized, or multiplied either in parallel or series to produce nearly unlimited hot water at nearly unlimited volumes, assuming a gas and water supply.

    A tank type gas water heater is cheaper up from (first cost) than a demand unit, but depending on usage is likely to be cheaper in total cost per gallon of hot water. They are ideally suited for solar preheat such that if the solar tank is heated to say only 100f the demand only has to heat the final 20% with no standby loss. Using a tank type to augment a preheat forces the tank to try to heat the entire volume. Even the best tanks that have sealed combustion systems have more standby loses through the flue vent than a sealed demand heater does.

    Standby loses that are captured in a heated envelope reduces the heating load on a building, but it also adds to the A/C load.

    As for the OP question about his heat pump. Look at the Seer number and see if it is cost effective to replace it with a different unit. If he has large A/C loads adding ground source or hot water recovery might be the best alternative. If his A/C load is small, he could consider a mini split system, or a number of them. Just like any central heat, if you are heating/cooling space (and volume) you are probably over heating/cooling areas in order to get the temperature correct in the critical areas, as most central heat doesn't zone very well.

    Just thoughts,

  • Peter_VPeter_V Solar Expert Posts: 226 ✭✭✭
    Re: Building my first Grid-Tie PV system (w/out batteries)
    jfavalora wrote: »
    ...and how does a solar hot water heater work. I bath at night... Does it use batteries or am I missing something there? I was considering a nat gas water heater or something similar.

    Solar hot water uses thermal collectors and heats the water either directly in the panels, or more usually indirectly using some kind of transfer fluid and heat exchangers.

    Typically a solar hot water system will have a larger tank, say 80 gallons instead of 40-50 gallons, and the water is heated to a higher temperature, perhaps 165 degrees instead of 130 degrees.
    To avoid scalding yourself with the hot water, the output of the water tank has a mixing valve that mixes the hot water with cold water (if needed) to reduce the temp to about 120 degrees.
    Effectively your 80 gallon tank can provide 100+ gallons of hot water.

    The higher temps means that it will stay hot longer so you can even take a shower in the morning with hot water.

    Even if the area you live in can only heat water 9 months out of the year, that still cuts your water heating bill by 75%
  • BB.BB. Super Moderators, Administrators Posts: 32,008 admin
    Re: Building my first Grid-Tie PV system (w/out batteries)

    One of the other posters here, Solar Guppy, has had good experiences over the years with == Although, he does recommend the heat pump type water heaters these days.

    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
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