Introduction - what have I gotten myself into?

Discussion in 'General Discussions' started by Noobie, Dec 14, 2018.

  1. Noobie

    Noobie New Member

    I recently purchased a house near Boston. We are doing quite a few upgrades/renovations to the house.

    Next spring, if everything goes according to schedule, we will be installed 3 WaterFurnace Series 7 units (3ton, 4ton and 5 ton) with vertical wells. It's a large house, and not that well insulated, although every repair we make (mostly water leaks) we bump up the R value when we open the house's roof (slate, rubber, metal).

    In addition to the geo, we will install an electric boiler to run the baseboards and radiant bathroom heat. Right now, that hot water is supplied by the Viessmann oil boiler which we will be removing. We are planning to install a heat pump in the utility room for domestic hot water.

    We have a large existing solar farm, and are adding 32kw of Sonnen battery capacity. I am hoping, in the event of a grid outage, to be able to heat/cool and run other household electrical devices overnight. It would not be a problem to turn off the electric boiler in the event of an outage, as the baseboards and radiant heat are not critical.

    As my username suggests, I am a complete newbie at this. Any words of wisdom are appreciated.
     
  2. ChrisJ

    ChrisJ Active Member Forum Leader

    Welcome to the forum,

    WaterFurnace makes high temp water to water heat pumps that could be used to do baseboards and domestic hot water.

    Money spent on air sealing and insulation can reduce the amount of upfront costs by having smaller or less equipment.
     
  3. Cadman

    Cadman New Member

    Is your existing solar farm grid tied? Is the planned battery capacity just for backup in case of power outage? I ask because battery storage is usually a 'last resort' move, or for smaller off-grid applications.
     
  4. Noobie

    Noobie New Member

    Yes, it's grid tied. The battery capacity is both for grid outage backup and also for providing power during the time when the sun isn't shining. I've only been in this house for less than a year, but we seem to get frequent, albeit short, power outages here.

    I'm not sure what you mean by "last resort" move. Can you explain that, please?

    I'd like to be mostly off grid, but there are considerable incentives to remaining on the grid, both financial and otherwise.
     
  5. nc73

    nc73 Member Forum Leader

    Being off grid can get expensive, battery replacement etc. staying on the grid is the best balance.
     
  6. Noobie

    Noobie New Member

    Yes, that’s what I decided.

    I’m not sure whether or not I will take the approx $2000/year for 10 years “adder” incentive that makes me do weekly “exercise” cycles to supply the grid during peak times. If it were truly once a week, I might, but apparently (I’m not a lawyer) the wording on MA SMART program is open to interpretation, and in times of stress, they could commandeer more power from me. Still get 30% tax credit.
     
  7. Cadman

    Cadman New Member

    As nc73 pointed out, anytime batteries are involved, you'll have ongoing maintenance and replacement cost, then there's charge balancing to consider since they're usually wired in series to increase voltage. I'm also curious how the batteries are integrated? Usually PV is designed for grid tie, or battery, but not both.

    With my 10kw arrangement, I use the grid as my "battery". Feed into it during the day when usage is low, and draw off it at night when the sun goes down. But, our electrical service is also dead reliable. If you plan to use the same AC loads during outages that you'd use normally, you might be better served with a generator.
     
  8. Noobie

    Noobie New Member

    We are currently using the grid as our battery, but it really sucks to see massive energy production from our solar panels while we stumble along on our 8kw propane generator. It’s enough to run essentials, but that’s with an oil furnace (we intend to get rid of).

    Battery was a non-starter with Tesla due to constraints. The new Somnen battery apparently will work as backup when grid is down and time shifting when grid is up.

    Installing a larger generator isn’t an attractive option. When we have extended power outages (eg, last winter) it usually means fallen trees make deliveries impossible in our rural setting with one access road.

    32kw battery is the largest Sonnen available for residential use. fwiw, the propane 8kw generator will help charge the battery should it run low, but i think it would take a very prolonged grid outage coupled with crummy weather for the duration to make it necessary.
     
  9. Noobie

    Noobie New Member

    I forgot to reply to the first part of your post. They’re made for consumers, mounted indoors, and they are guaranteed to maintain a fair amount of capacity for many years (at least 10,000 cycles). Honestly, I’ll probably be dead before they need replacing, and whoever buys my house can worry about it.

    I couldn’t find a US link, and apparently a link requires mod approval. Google sonnen battery for a description.
     
  10. nc73

    nc73 Member Forum Leader

    If you could downsize to the minimum and maybe run DC instead of AC, it could work.
     
  11. Noobie

    Noobie New Member

    I forgot to reply to the first part of your post. They’re made for consumers, mounted indoors, and they are guaranteed to maintain a fair amount of capacity for many years (at least 10,000 cycles). Honestly, I’ll probably be dead before they need replacing, and whoever buys my house can worry about it.

    I couldn’t find a US link, and apparently a link requires mod approval. Google sonnen battery for a description.
     
  12. Noobie

    Noobie New Member

    I have to admit my ignorance here. I honestly don’t know what you’re referring to about DC vs AC.

    ETA: I know what the terms mean, but that’s it.
     
  13. Cadman

    Cadman New Member

    In a usual grid-tie PV system, you have the DC side which is what the PV panels produce, and the AC side which is the output of your inverter. You design for the highest DC voltage your inverter and cabling can handle (400-500-600 volts), and let the inverter take care of producing a steady 240 volt AC on the output. To maximize the DC voltage, panels are wired in series-string.

    If you're designing for an 'off grid' solution, you'll have a charge converter/controller matched to your battery bank. Input is usually much lower voltage than for a grid-tie arrangement and so your panel wiring scheme will be different as well. Battery capacity will be in amp-hours, but you'll want to limit discharge to something like 50%, so only half that advertised capacity is available. If you intend to run AC equipment (120VAC) off this kind of arrangement, then you'll have an inverter also. But because there are losses in the DC to AC conversion, those with this type of setup tend to use a lot of 12VDC appliances (including additional wiring in the house to support it), 12V LEDs for lighting, and definitely avoid any sort of electric heating (air or water). You can see concessions tend to be made.

    So when Tesla or Sonnen offer battery pack solutions like this, it tends to be less about optimization, and more a re-package of existing tech. The limitations, however, still exist.
     
    Noobie likes this.
  14. ChrisJ

    ChrisJ Active Member Forum Leader

    Is that a heat pump water heater(tank) or another geo water to water heat pump?
     
  15. nc73

    nc73 Member Forum Leader

    Yes what Cadman said :)
     
  16. Noobie

    Noobie New Member

    ChrisJ, it’s just a plain old air sourced hot water heat pump, maybe 80 gallon tank

    Cadman, thanks for a clear explanation.
     

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