Building new home

Hello Folks

My wife and I are going to be building a home in the Florida Keys. I wanted to solicit input from the group on some things I know everyone has strong opinions on.

Panels, PV Panels or metal roof integrated. ( make it part of the roof ). Since I am going to be putting the roof on the building I may be able to put the panels on the roof and have to worry about damage. Folks always point to wind as the major source of damage, but they forget salt.

Grid Tie Inverters , SMA, Schneider, Outback Power ?

I have many other questions but I wanted to at least start asking and doing research. I think my largest challenge will be finding a reliable contractor.

Regards and thank you for taking the time to read this.
-j

Comments

  • BB.BB. Super Moderators, Administrators Posts: 32,921 admin
    Re: Building new home

    First steps--Consideration. If this is new/major construction, anything you can do to reduce power usage will be a big help. Obviously, based on your local needs (i.e., is this an "open" construction because of moderate temperatures, or will this be a "sealed" type (double pane windows, insulation, weather stripping, etc.)?

    If you are already living in the area--Getting a Kill-a-Watt type meter, whole home power monitor, etc. so you can monitor your existing power needs will be a big help in planning your conservation needs.

    Next, appliances/equipment selection. It is almost always better to spend your money on conservation than to generate power (Energy Start rated appliances, high SEER/etc. rated A/C-Heat Pump systems, if you don't have natural gas/propane then solar hot water or even heat pump based water heater can save lots of money on energy).

    After you have done all of the above, measure your power usage (daily kWH used, peak power needed, etc.).

    Now you know your power needs (and have reduced those needs by a much as practical), you need to ask what kind of solar power are you looking for.

    Do you want Grid Tied Solar? Cheapest/least maintenance needed to make solar power. Your utility needs to support GT solar and net metering. Does not supply power if you grid is down.

    There is hybrid solar power--Basically can operate by feeding power back to the grid, or off grid (with batteries, solar panels, backup genset), etc... Still more costly than GT solar, plus battery maintenance. But generally still less $$$/kWH than pure off grid solar.

    And there is off grid solar (no grid). solar+batteries+inverter+charge controller+backup genset. Your power may cost you on the order of $1 to $2+ per kWH--Hence why we always start with conservation.

    And there is GT Solar + Backup genset... Many times the most cost effective choice if your power is down for hours/days... If you have weeks/months of power outages, perhaps Hybrid solar is a better choice.

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • inetdoginetdog Solar Expert Posts: 3,123 ✭✭✭✭
    Re: Building new home
    BB. wrote: »

    ... if you don't have natural gas/propane then solar hot water or even heat pump based water heater can save lots of money on energy.

    I have seen claims that propane is actually more expensive than electrically driven heat pump. I guess that really depends on the local costs of propane and of electric power. How close is it really for "typical" electric rate of around $.15 / KwH?
    SMA SB 3000, old BP panels.
  • BB.BB. Super Moderators, Administrators Posts: 32,921 admin
    Re: Building new home

    Here is an energy comparison calculator.

    If you use $0.15 per kWH, "break even point" for propane is roughly $2.70 per gallon (assuming electricity is 100% efficient and LP is 78%).

    Using a heat pump based stand alone water here that is 2-3x efficient will cut the break even point to 1/2 or 1/3 of $2.70 per gallon of propane.

    Very possible that heat pump based water heater on Solar PV or off grid solar PV is a better deal than propane.

    Solar Guppy has said (as I recall) that he believed that a heat pump water heater was better (more cost effective, less maintenance) than solar thermal hot water for his home in Florida.

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • inetdoginetdog Solar Expert Posts: 3,123 ✭✭✭✭
    Re: Building new home
    BB. wrote: »
    Here is an energy comparison calculator.

    If you use $0.15 per kWH, "break even point" for propane is roughly $2.70 per gallon (assuming electricity is 100% efficient and LP is 78%).

    Using a heat pump based stand alone water here that is 2-3x efficient will cut the break even point to 1/2 or 1/3 of $2.70 per gallon of propane.

    Very possible that heat pump based water heater on Solar PV or off grid solar PV is a better deal than propane.

    Solar Guppy has said (as I recall) that he believed that a heat pump water heater was better (more cost effective, less maintenance) than solar thermal hot water for his home in Florida.

    -Bill

    Thanks Bill,

    Now all I have to do is find the appropriate comparison factor for an on-demand water heater compared to a conventional tank type electric or propane and therefore indirectly to heat pump.
    It looks like solar preheat for an on-demand propane heater just does not work out well given the relationship between flow rate and output temperature at minimum burner setting of the on-demand heater.
    SMA SB 3000, old BP panels.
  • BB.BB. Super Moderators, Administrators Posts: 32,921 admin
    Re: Building new home

    From what I have seen, the typical natural gas/propane tankless heater is 80% efficiency (in some cases, you may hit 90-95% for a condensing water heater). An electric water heater (resistance) is 98%. Overall, those numbers are close enough to give you an idea (I used 78% for propane and 100% for electricity when I played with the numbers above).

    Regarding preheat--From what I remember, you have to find a water heater designed to work with a solar preheater. Bosch had several models (years ago, when I last looked) that had various options--and working with a preheater was one of the options.

    With solar hot water, you should always have a tempering valve to prevent scalding anyway. If there was an issue with a tankless water heater not turning the flame low enough--I wonder if you can set a tempering valve to a lower temperature (say 90F vs 120F) so the tankless heater would work OK and not overheat the water.

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • icarusicarus Solar Expert Posts: 5,436 ✭✭✭✭
    Re: Building new home

    Most "modern" gas tankless water heater will work fine with preheated solar water. What I call " modern" is versions with electronic control boards, and adjustable output temps. The older style simply called for heat regardless of the input temp. The newer ones will only heat to the set temp. When the set temp is lower than the input temp, the heter doesn't have to fire at all. There can be issues with low flow firing, when the Pre heat temp is just about the same as the dialed in output temp.

    Tempering valves are a must in an installation where temps are likely to get above ~120 (unless you are the only user, and you are aware and willing to take the scalding risk!).

    As others have said, if you live in an area that needs extensive A/C nearly year round, hot water heat recovery is more efficient than direct solar. I would think that A/C is a near must in the Keys!

    Tony
  • inetdoginetdog Solar Expert Posts: 3,123 ✭✭✭✭
    Re: Building new home
    BB. wrote: »
    From what I have seen, the typical natural gas/propane tankless heater is 80% efficiency (in some cases, you may hit 90-95% for a condensing water heater). An electric water heater (resistance) is 98%. Overall, those numbers are close enough to give you an idea (I used 78% for propane and 100% for electricity when I played with the numbers above).

    Regarding preheat--From what I remember, you have to find a water heater designed to work with a solar preheater. Bosch had several models (years ago, when I last looked) that had various options--and working with a preheater was one of the options.

    With solar hot water, you should always have a tempering valve to prevent scalding anyway. If there was an issue with a tankless water heater not turning the flame low enough--I wonder if you can set a tempering valve to a lower temperature (say 90F vs 120F) so the tankless heater would work OK and not overheat the water.

    -Bill

    As I understand the problem, based on the installation and user manuals of the tankless we have, the flame can be throttled down as low as 1/10 of max output, but no lower and cycling on and off to maintain temp is not an option because of the low heat capacity of the exchanger.
    So if at the flow rate used (say .5 GPM) the lowest flame will raise the temp of the water from, for example, 100 degree preheat to 140 degrees, and the setpoint is 120 degrees, then the on-demand heater will try to microcycle or else just shut down.

    So it may be necessary to set a higher output temperature and use a mixing valve to allow the tankless to work at low flow rates. Then the problem becomes that with mixing and a low-flow shower head the flow rate of hot water through the heater may drop below the lower limit for the tankless (typically .5 GPM) and it will shut off automatically. The latter problem seems to be a common one on tankless heater forums and user reviews. The simple solution of replacing the low flow shower head defeats the energy savings which started the whole thing!

    There is no doubt that solar preheating can increase the maximum flow rate of the tankless at full output and can also decrease the energy usage for a given hot water demand. There are just these interesting edge cases!
    SMA SB 3000, old BP panels.
  • BB.BB. Super Moderators, Administrators Posts: 32,921 admin
    Re: Building new home

    Yep Inetdog--That was what I always saw as an issue with tankless and preheating. That and needing a large gas line/exhaust stack because of the high firing rate of the tankless burner.

    I wonder if the heat pump based water heater will bypass much of the tankless market.

    Also looked at a high efficiency tanked heater--That really looks like it would work nicely for me. But not cheap. And at this time, none are even listed at the Energy Star site.

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • inetdoginetdog Solar Expert Posts: 3,123 ✭✭✭✭
    Re: Building new home
    BB. wrote: »

    I wonder if the heat pump based water heater will bypass much of the tankless market.

    -Bill

    It would certainly take away the biggest efficiency argument for tankless. There is still the high capacity argument for those who like to take 20 minute showers or have large families.
    For really cold areas, the use of outside air for the heat pump source is not practical, but the use of indoor heated air adds another factor to the energy calculation which is easy to overlook. Summertime is a simple story.
    SMA SB 3000, old BP panels.
  • rollandelliottrollandelliott Solar Expert Posts: 834 ✭✭
    Re: Building new home

    Panels, PV Panels or metal roof integrated. ( make it part of the roof ).

    There are zero metal roof integrated systems that I know of. There is a thread about solar panels as roofing systems I started a couple of years ago, that might interest you. The two solutions I found were in Europe.

    http://www.s-5.com/solar/index.cfm

    is probably the most well know way to attach panels to a metal roof.

    There is a company called Unirac that made solar laminates that glued onto the roof and they went out of business. Their panels are being clearanced all over the internet for around 50 cents a watt, but thin film solar does not have a reputation of lasting long, take your chances.

    Lastly, Many florida utility companies offer $2/watt rebates. The rebate money is generally gone within an hour of being available. But My sister applied and was accepted by Progress energy.

    As far as inverters go. I wouldn't worry about what brand to use, they are similar in my brief two year experience with them. SMA, power one and fronius all seem to be good so far for me.

    I guess cooling the building is going to be the biggest expense so I would simply use tons of insulation and even consider a berm house that has earth around the sides.

    Good luck.
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