Guidance for Grid-tie

I have started researching solar panels for the house pending the CAP/TRADE legislation which looks like our dweebs in DC will pass. I for one don't like the idea of paying the govt $2,000/yr for no reason and I definitely don't like the idea of "sharing the wealth" to 3rd World countries, especially when my retirement was earned from the military.

Many websites require sq footage of your home, refer you to a "sun hour" map, and some ask for 6 month or 12 month electric usage.
I don't see how home size can be relevant, except for mounting panels. As for the map, I have a solar sensor. Averaging w/m2 produces varying results and they don't compare to the 4.5 kw hrs on the map. As for current (no pun intended) electric usage, it would seem more wise to use 12mnth, realizing summer months producing more electricity w/ solar panels, but using more of it.

There are many forum members with electrical/power plant/engineering backgrounds in this area. I look forward to your insights on what I can do to figure a "no-bs" idea of the kw system I really need. I would ideally like a 100% free from the grid system, but realistically envision a close to 100% grid-tie system.

Our avg 12mnth meter usage for 2008 was 1400. For 2009, I'm estimating 1600.

Comments

  • BB.BB. Super Moderators, Administrators Posts: 28,599 admin
    Re: Guidance for Grid-tie

    Just for clarification, your usage is an Average of 1,400-1,600 kWhrs per month (vs 1,400-1,600kWhrs per year).

    Well, our standard answer is Conservation first. It is almost always cheaper to conserve a kWhr than it is to generate a kWhr.

    Just to give you a very rough idea of the cost of various forms of power (averaged over 20 years):

    $0.10-$0.30 per kWhr utility power
    $0.15-$0.40 per kWhr Grid Tied solar (no battery bank)
    $0.45-$0.75 per kWhr Hybrid Solar Inverter (both GT and Off Grid power)
    $1.00-$2.00+ per kWhr True Off-Grid Power

    Conservation ideas can vary widely depending on location...

    For example, if you are in Florida, you might run your A/C system most of the year (both for cooling and dehumidification). Making sure you have a high SEER heat pump system can save you lots of electricity (if you have an older system) plus you can use a desuperheater to make almost free hot water.

    But, for me, we don't have A/C, expensive electricity, and pretty reasonable (for now) priced natural gas--so a normal tanked natural gas hot water heater is still hard to beat cost wise.

    Zoning your home, such as installing a mini-split A/C / Heat pump to heat/cool a portion of the home can help reduce costs.

    Most climates can use a check on the amount of insulation. Adding tons of attic insulation helps both in hot and cold climates. I really like to retrofit single pane widows with double pane vinyl windows and low-E gas (not sure argon fill will last for years). Etc.

    If you want to play with your own numbers for making solar power... There is a pretty simple program to to try: PV Watts website.

    Just select the city with similar weather patterns closest to your home, put in 1 kW (minimum program accepts) for 1,000 watts of solar panels and use derating=0.77 for Grid Tied, or 0.52 for Off-Grid system efficiency (assuming AC power and flooded cell batteries).

    For example, a 10kW Off-Grid system in Tampa Fl (0.52 derating):
    "Station Identification"
    "City:","Tampa"
    "State:","Florida"
    "Lat (deg N):", 27.97
    "Long (deg W):", 82.53
    "Elev (m): ", 3
    "PV System Specifications"
    "DC Rating:"," 10.0 kW"
    "DC to AC Derate Factor:"," 0.520"
    "AC Rating:"," 5.2 kW"
    "Array Type: Fixed Tilt"
    "Array Tilt:"," 28.0"
    "Array Azimuth:","180.0"

    "Energy Specifications"
    "Cost of Electricity:"," 9.0 cents/kWh"

    "Results"
    "Month", "Solar Radiation (kWh/m^2/day)", "AC Energy (kWh)", "Energy Value ($)"
    1, 4.56, 677, 60.93
    2, 5.21, 695, 62.55
    3, 5.72, 832, 74.88
    4, 6.52, 898, 80.82
    5, 5.92, 830, 74.70
    6, 5.56, 740, 66.60
    7, 5.46, 744, 66.96
    8, 5.70, 788, 70.92
    9, 5.32, 713, 64.17
    10, 5.41, 766, 68.94
    11, 4.83, 678, 61.02
    12, 4.24, 624, 56.16
    "Year", 5.37, 8986, 808.74
    You can see a 10,000 watt solar panel Off-Grid system will only meet about 1/2 of your estimated monthly needs (around 700-800 kWhrs per month).

    The same system 10kW and 0.77 for Grid Tied system will generate:
    "Station Identification"
    "City:","Tampa"
    "State:","Florida"
    "Lat (deg N):", 27.97
    "Long (deg W):", 82.53
    "Elev (m): ", 3
    "PV System Specifications"
    "DC Rating:"," 10.0 kW"
    "DC to AC Derate Factor:"," 0.770"
    "AC Rating:"," 7.7 kW"
    "Array Type: Fixed Tilt"
    "Array Tilt:"," 28.0"
    "Array Azimuth:","180.0"

    "Energy Specifications"
    "Cost of Electricity:"," 9.0 cents/kWh"

    "Results"
    "Month", "Solar Radiation (kWh/m^2/day)", "AC Energy (kWh)", "Energy Value ($)"
    1, 4.56, 1027, 92.43
    2, 5.21, 1050, 94.50
    3, 5.72, 1257, 113.13
    4, 6.52, 1356, 122.04
    5, 5.92, 1260, 113.40
    6, 5.56, 1128, 101.52
    7, 5.46, 1137, 102.33
    8, 5.70, 1203, 108.27
    9, 5.32, 1086, 97.74
    10, 5.41, 1160, 104.40
    11, 4.83, 1027, 92.43
    12, 4.24, 948, 85.32
    "Year", 5.37, 13638, 1227.42
    This exact same number of solar panels with a Grid Tied System will generate much closer to what you current usage is.
    "Station Identification"
    "City:","Tampa"
    "State:","Florida"
    "Lat (deg N):", 27.97
    "Long (deg W):", 82.53
    "Elev (m): ", 3
    "PV System Specifications"
    "DC Rating:"," 10.0 kW"
    "DC to AC Derate Factor:"," 0.770"
    "AC Rating:"," 7.7 kW"
    "Array Type: Fixed Tilt"
    "Array Tilt:"," 28.0"
    "Array Azimuth:","180.0"

    "Energy Specifications"
    "Cost of Electricity:"," 9.0 cents/kWh"

    "Results"
    "Month", "Solar Radiation (kWh/m^2/day)", "AC Energy (kWh)", "Energy Value ($)"
    1, 4.56, 1027, 92.43
    2, 5.21, 1050, 94.50
    3, 5.72, 1257, 113.13
    4, 6.52, 1356, 122.04
    5, 5.92, 1260, 113.40
    6, 5.56, 1128, 101.52
    7, 5.46, 1137, 102.33
    8, 5.70, 1203, 108.27
    9, 5.32, 1086, 97.74
    10, 5.41, 1160, 104.40
    11, 4.83, 1027, 92.43
    12, 4.24, 948, 85.32
    "Year", 5.37, 13638, 1227.42
    Given that an Off Grid system with the same number of solar panels probably costs almost 2x the amount of a GT system and generates less electricity--Off Grid is usually only useful for people that use relatively little electricity and/or are far away from a utility feed.

    There is the option of Hybrid Inverter / Solar... Basically it has an inverter that can "do grid tie", plus there are backup batteries to run the inverter like a UPS for your home when the power is out... Might be very nice if you live in an area with hurricanes, ice storms, etc. where power can be out for weeks at a time. You will have less power (batteries are less efficient)--but you should have enough to run the minimum amount to keep comfortable in an emergency. You may not have as many batteries as a true off grid solution would have--but enough to use the solar + backup genset (for bad weather) to get you through.

    Here is a simple diagram of how the various options look in drawing form.

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • System2System2 Posts: 6,290 admin
    Re: Guidance for Grid-tie

    Thank you very much for going in-depth; very useful.

    Yes, I avg 1600 kwhrs/mnth.

    I will try various combos w/ the calculator.
  • icarusicarus Solar Expert Posts: 5,108 ✭✭✭✭
    Re: Guidance for Grid-tie

    Your 1600 kwh/month is ~ 53 per day, a fairly large chunk for PV. As Bill rightly suggests, conservation first, followed by some more conservation, and finally little more conservation.

    The general rule of thumb is for every dollar spent on conservation will save ~$10 in PV costs. There are many obvious things, such as extra insulation, insulated glass. High efficiency appliances/furnaces/heat pumps etc. Hvac that captures waste heat for hot water, allow your ac to work more efficiently, with the added bonus of giving you some hot water. Solar water heat comes at a much cheaper cost than does Pv solar.

    After you look at the obvious stuff, look at all the little things, like wall wart power supplies, the phantom loads from electronics etc.

    Consider changing any heat generating appliances (furnace/water heater etc0 to gas or propane. Resistance electric heat is hugely inefficient even if it comes from PV. (You are way more efficient to capture the heat directly!) Gas demand water heat depending on your water usage.

    I would guess with some tweeking you should be able to drop your electrical use by 10% without trying real hard. 20-40% is surely a do-able goal.

    Good luck,

    Tony
  • System2System2 Posts: 6,290 admin
    Re: Guidance for Grid-tie

    I guess we all have to start somewhere. Thank you for the crunch awareness factor to make PV work.

    I have looked into TED5000 to see where it goes and what loads are doing. The house is new/energy Star apps, high insulation, gas heat, electric everything else.

    Also looking into PowerSave to help w/ initial loads for heat/ac/dryer/etc.

    Being in AL, with dew pts in the 60s/70s in the summer eats 2200kwhrs/mnth, whereas winter is only 1000kwhrs/mnth.


    Any further insights are much appreciated. I'm putting together a pg to help others sort through all this. May I barrow recomendations posted in this thread?
    http://www.knology.net/~blackjack52/wxsolar.php
  • BB.BB. Super Moderators, Administrators Posts: 28,599 admin
    Re: Guidance for Grid-tie

    On the TED, looks like a nice product and can really help you see where your power is going.

    One warning--the standard TED will not work properly with Grid Tie Solar PV / Net Metered homes. It cannot measure the direction the power flows (with GT, power may flow out or into a home).

    You have to get the version that supports Net Metering (I think they have it now).

    Regarding the POWER-SAVE. Are you talking about a Power-Save 1200 or equivalent?

    If you are, save your money. The Power-Save 1200 (and the larger versions) are just a motor run capacitor designed to "fix" power factor from larger motors. Depending on your particular inductive loads, many of the newer ones are already Power Factor Corrected. And, in any case, the normal home metering does not charge for poor power factor--you are charged for the real power you use.

    PowerSaver 1200 is pretty much a scam (over priced at the very lest). There are a few threads here that discuss the details of PoweSaver and power factor issues too.

    Lastly, if you want to go off grid--then look at piping the natural gas or propane to the drier, stove, and hot water heater (Hot water and lots of air conditioning can perhaps make a desuperheater worthwhile for you--use the hot side of the AC to heat your hot water).

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • Solar GuppySolar Guppy Solar Expert Posts: 1,959 ✭✭✭
    Re: Guidance for Grid-tie

    AL has some of the lowest electric rate in the country ... I doubt you will find a case that solar can save you money in your location ... what was your last bill in kWh charges? ... I'd guess 8.5 cents?
  • System2System2 Posts: 6,290 admin
    Re: Guidance for Grid-tie
    BB. wrote: »
    On the TED, looks like a nice product and can really help you see where your power is going.

    One warning--the standard TED will not work properly with Grid Tie Solar PV / Net Metered homes. It cannot measure the direction the power flows (with GT, power may flow out or into a home).

    You have to get the version that supports Net Metering (I think they have it now).

    Regarding the POWER-SAVE. Are you talking about a Power-Save 1200 or equivalent?

    If you are, save your money. The Power-Save 1200 (and the larger versions) are just a motor run capacitor designed to "fix" power factor from larger motors. Depending on your particular inductive loads, many of the newer ones are already Power Factor Corrected. And, in any case, the normal home metering does not charge for poor power factor--you are charged for the real power you use.

    PowerSaver 1200 is pretty much a scam (over priced at the very lest). There are a few threads here that discuss the details of PoweSaver and power factor issues too.

    Lastly, if you want to go off grid--then look at piping the natural gas or propane to the drier, stove, and hot water heater (Hot water and lots of air conditioning can perhaps make a desuperheater worthwhile for you--use the hot side of the AC to heat your hot water).

    -Bill

    Copy on the PowerSave. Thanks. New home/new appliances. Definitely looking into using a/c to heat water.
  • System2System2 Posts: 6,290 admin
    Re: Guidance for Grid-tie
    AL has some of the lowest electric rate in the country ... I doubt you will find a case that solar can save you money in your location ... what was your last bill in kWh charges? ... I'd guess 8.5 cents?

    7.9 cents last mnth. But envision that going way up if the EPA/Cap& Trade goes through. I also envision the cost going even further in 2011. By that time, solar business will be in full swing, thus cost for solar systems will increase.
  • Solar GuppySolar Guppy Solar Expert Posts: 1,959 ✭✭✭
    Re: Guidance for Grid-tie

    Your rates are slow low as Hydro is your primary power source, that's not changing for AL , probably ever

    Your best payback will be things like Geo-Thermal for your AC and Heat needs, more insulation, Geothermal Hotwater or one of the new Heat Pump hotwater tanks.

    These will have probably 20X faster return and with the talk of a cash for clunkers for home energy improvements of 50%, it beats solar by a mile in your case.

    If you want to have solar for reasons other than economics that's fine, but at least do an honest assessment at your rates because your looking at 100+ year payback for a system that will need parts every 5-10 years best case ( electronics ).
  • System2System2 Posts: 6,290 admin
    Re: Guidance for Grid-tie

    That makes sense-Hydro. Looking at NG tankless water htr now to replace electric; probable 1/6-1/8 of the electric bill. See what can be done, like everyone has suggested, on making what we already have, more efficient.
    Thanks everyone.
  • Solar GuppySolar Guppy Solar Expert Posts: 1,959 ✭✭✭
    Re: Guidance for Grid-tie

    Look at the new energy star heat pump hot water tanks ... better than NG, less than half the electric of a regular HW tank and you get a 30% tax credit today for putting one in ... Gas makes little sense if your worried about fuel price or tax increases

    http://www.geappliances.com/heat-pump-hot-water-heater/

    http://www.ruud.com/products/tank_water_heaters/hpwh/
  • BB.BB. Super Moderators, Administrators Posts: 28,599 admin
    Re: Guidance for Grid-tie

    Regarding a tankless water heater... If you use a fair amount of hot water, the tankless will not save that much energy.

    And if you have modern balancing valves (tub/shower) and single handle faucets--You will probably find tankless heaters are a pain in the behind to get stable hot water unless you choose the type where you can set the hot water temperature for your need (lower for washing hands/shower, higher for washing clothes/automatic dish washer).

    Check the energy star tags for each appliance and compare their prices to that of what you pay. The national averages sometimes have virtually no relationship with your local utility charges.

    Here is a nice PDF report from 2002 (earlier systems) out of Connecticut about heat pump water heaters.

    From the report, they do report that, on average, there appears to be pretty nice energy savings (maybe 200kWhr or a bit less per month for a family of 4-5?). Works out to (very roughly) a 50% savings in electricity usage?

    However, some limitations to watch for. If your room is in the 54-45F range, the units may use their electric defrost heaters. Below 45F, will use the electric resistance heater. On the other hand, if you need dehumidifying--a nice advantage to get water at the same time.

    If the heater is used in an unheated space, it appears it approaches COP of 1 near 32F. The COP>2 for temperatures above 70F.

    In a heated space, the Heat Pump is a local Air Conditioner -- So, if you are heating your home in Winter--The home's heater (gas, heat pump, oil, etc.) will be supplying the heat to heat the hot water--so, in theory, the utility bill for your home heating will go up by the amount the heat pump based heater reduces your hot water charges.

    The GE unit appears to have a 10 year warranty--but only 1 year on parts. There where substantial repairs/failures in the 2002 study.

    The RHEEM heat pump water heater unit looks to be around $1,500 each.

    If you are in a warm climate with high electricity rates--looks very interesting. If you are in a cold climate (below 50F? in winter)--perhaps not so good.

    My 2 cents worth.

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • Solar GuppySolar Guppy Solar Expert Posts: 1,959 ✭✭✭
    Re: Guidance for Grid-tie

    BB, I think you off your you heat pump knowledge?

    Heat pumps can extract heat below 32F, the issue becomes frost on the coils and what all modern units I have used or read about is just run in reverse for a few minutes every hour to defrost, even with the defrost cycle included, they have a COP of more than 1.

    From memory, most heat pumps have a COP of 3 at 32F and above 40F 4+, I have never see, or read about a Heat pump that has resistive heating in the outside unit to defrost maybe your confusing this with AUX heating elements in the Air Handler that kick in when the thermostat notices a large temperature differential.

    The HW tanks do extract enegry from there surrounding, so a garage based HW unit is best ... will cool your Garage in the 8+ hot months most southern states have FOR FREE. In the North, stick the HW tank in the basement, where the ground keeps things temperate year round

    I personally think they are the cats meow, you 24/7 performance for costs about 1/3rd of solar hot water, nothing can match the cost performance of these units.

    Clothes dryers are next for this technology ...
  • icarusicarus Solar Expert Posts: 5,108 ✭✭✭✭
    Re: Guidance for Grid-tie

    A little difference of opinion on tankless. Clearly, if you use ac for much of the year then heat pump hot water is as SG suggests, the "cat's Meow"

    On the other hand, if you don't have to use ac, then the equation begins to fall to solar with demand back up. I don't fully agree with Bill regarding tank vs tankless, as I think it is very subject to household use patterns. If you have large uses 365 then perhaps the balance comes in to tanked. On the other hand if your usage changes on a daily/weekly monthly basis then the advantage comes to tankless. For example, if you are gone 2 days per month, or you shower at the gym 3 days a week or what ever then your usage pattern might warrant the tankless.

    As a supplement for solar pre-heat the modern tankless are hard to beat. Additionally, the modern, modulated tankless units, with remotes if you desire are very easy to use, and are easily tailored to what ever use you require.

    As for the suggestion that you need hotter water for dishwashing, I have to say that I think that is a non issue. For example, the Takagi in our rental is set at ~114f if memory serves. If you are doing dishes by hand, it is hotter than you can put your hands into. (Contrary to popular perception, there is little hygienic benefit of hotter water until you get to VERY hot water ~160f. At that temp, you can't hand wash dishes anyway!) Most dishwashers have a hot water heater cycle in them anyway to boost the water temp to "sanitize" the hot water. I have never done the calc to see which is more efficient, but there is a fairly small amount of water in a dishwasher.

    As for hotter water for laundry. I don't believe that hotter than ~110 has any added benefit than cooler water. (I confess I am not a laundry expert, but I do all mine (when I do it) in warm water).

    In any case with a remote, you can dial in any temp you desire. The one rub against tankless that I will admit, it the lag time between water flowing through the heater and the time it takes to fire,, usually a few seconds, this can cause an interruption of hot water for a few seconds if you turn it off and then back on.

    Finally, the equations get confused depending on how any waste heat is either used (like in a living space) or wasted (like in unheated garage) and if you then have to pay to get rid of this unneeded heat using ac. A tank losing heat to the house is a benefit during heating season, a liability during cooling season. Not a big deal, but one to consider non the less

    Tony
  • BB.BB. Super Moderators, Administrators Posts: 28,599 admin
    Re: Guidance for Grid-tie

    Solar Guppy,

    I was looking for actual usage reports with detailed test reports... The one I found was in that PDF link from 2002. Which shows COP values and the amount of energy used by the defroster.

    Are the new ones better, probably. But, if you follow the numbers from the your GE link:
    *Based on DOE test procedure and comparison of a 50-gallon standard electric tank water heater using 4881 kWh per year vs. the GE Hybrid water heater using 1856 kWh per year

    From the report, they showed just under 200 kWhrs a month energy savings in Conneticuit. Taking the above numbers:

    (4881-1856 kWrhs per year) / 12 months per year = 252 kWhrs per month

    Somewhere, I read the testing was done at 70F (I think--can't find it at the moment). Assuming Connecticut is on the cold side of 70F--That is not far off from the pdf report's value.

    The GE Water heater does have a Hybrid Mode:
    Hybrid mode – Use less energy while still experiencing fast recovery times. While the unit uses the heat pump as its primary means to heat the water, the standard electric elements may activate if a faster water temperature recovery time is needed. When the system determines that demand has been met, it will automatically revert back to using the heat pump only. This is the default mode the electric water heater is shipped in.

    So, if you are in a cold region and have high water demand, is is possible for COP to fall because it does use backup electric heat.

    Going through the GE FAQ:
    What is the ambient temperature requirement to operate in eHeat™ mode? In order to protect the eHeat™ system and for highest efficiency the Hybrid heat pump electric water heater will operate between 45°F - 120°F. Anything below or above this temperature range will cause the water heater to automatically operate in standard electric mode to continue to provide hot water.

    The GE Water Heater is around $1,700 according to GE and their Energy Factor (COP?) is 2.35

    If you read the PDF Report (again from 2002), the units they tested (different brand) all had resistance defrost heaters and some started at 54F and all where cycling at 45F and below.

    Given that the GE unit will not use the heat pump below 45F--They may have been able to skip the defrost heater at the expense of adding a backup/supplementary standard resistance water heating element.

    I have not read through the Ruud version of the specifications yet... But pretty much everything reported in the 2002 report is very similar to the limitations and ratings of the 2009 GE version.

    I am not sure where I have gone wrong? At least for the GE, I don't see a COP>3 or the ability to operate under 45F.

    And, don't get me wrong--I agree that using this type of system in warm areas is probably a good idea. But if the home has Natural Gas and cooler weather/winters and the water heater is installed in conditioned space--They need to look a the details or they will not get the savings they planned on.

    Obviously nothing is "free" and running, essentially, an A/C system in a home that requires heating in winter/cold weather is just transferring the "true costs" of the heat from the water heater to the home heating system.

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • sub3marathonmansub3marathonman Solar Expert Posts: 300 ✭✭✭
    Re: Guidance for Grid-tie

    I think it is possible that the "heat pump hot water" that icarus is talking about is a "hot water recovery unit" that works with your A/C. That system, at least in Florida, really is fantastic. Where we used to live, I would turn the breaker off and it would provide all the hot water from May through the end of October. However, with the new house and an 18 SEER A/C they said that it really wouldn't be any benefit (I still wonder though). The really great part is that it also boosts the efficiency of the A/C unit too by about 0.5 SEER, and it only added about $500 if I remember to the cost of the system when our old house was being built.

    Solar Guppy mentioned a couple of heat pump water heaters. While B.B. was looking into the G.E. unit, I was looking into the Rheem unit. It stated "The most energy efficient setting is Energy Saver mode, it works by extracting warmth from the surrounding air, concentrating the heat, and delivering it to the water. This mode provides an industry leading 2.0 energy factor (EF) and a first hour delivery comparable to a standard 50 gallon electric model." It had another Normal mode which also suplemented the heat pump with electric element heat if needed, and was rated at 1.5 EF, and Electric Only which would then operate as just a regular electric water heater using elements.

    Then I had to look up the Energy Factor (EF) and try to correlate it with the Coefficient of Performance (COP) that Solar Guppy mentioned, which is apparently just for the heat pump portion of the water heater. You could have a great COP but still get a poor EF if the tank wasn't well insulated, for example.

    But even saving half the energy of an electric water heater, at 1/3 the price of solar water heating, it seems that the solar water heating will still surpass it at some further future point as opposed to comparing it to a regular electric water heater. Of course, that is if you can have the solar water heating to supply all the water heating needed. I don't know what percentage that people who have it are able to achieve.
  • BB.BB. Super Moderators, Administrators Posts: 28,599 admin
    Re: Guidance for Grid-tie

    Regarding Sanitary needs for Hot Water... I agree that for hand washing and showers, very hot water is a waste of energy and a scalding hazard. I can't use 160F water to hand wash.

    And, the newer clothes washers do have on-board electric heaters to bring hot water temperate way above that available from the faucet... Claim it makes for great whites with less harmful detergents (there is supposed to be a profile where the water starts cool/warm where enzymes in the "soap" are active and the rising profile eventually breaks down the enzymes and improves the detergent action. Just from what I have read on other laundry forums (yes, there are laundry forums just like there are solar forums :roll: ),

    However, there is a definite reason that hot water needs to be over 122F at the faucet (which means 140+F in the tank). Need the sterilization effect to keep Legionnaire's bacterial colonies found in water lines and "cool" hot water tanks in check.

    In one report I read, electric hot water heaters in hospitals tended to show legionnaire contamination vs gas fired. It appears that this is because the colonies grow in the "cool" sediment at the bottom of an electric water heater. A gas water heater heats through the bottom/center of the tank--so these tend to be the hottest areas which kills of Legionnaire. So, the OSHA recommendations:
    • Scale and sediment supply the environment needed for growth of Legionnaires' disease bacteria (LDB) and other microorganisms.
    • Dead legs and non-recirculated plumbing lines that allow hot water to stagnate also provide areas for growth of the organism.
    • Temperatures maintained below 60°C (140°F) encourage growth of LDB and other microorganisms.
    I agree that a tank-less heater can be a real savings when not a lot of hot water is used... However, if natural gas in a home--the savings in hot water heating costs is probably less than the costs to install/maintain a tank-less heater. Plus, there are real issues with many of the "modern" balancing valves in trying to manage temperature from a simple tankless-system.

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • icarusicarus Solar Expert Posts: 5,108 ✭✭✭✭
    Re: Guidance for Grid-tie

    Bill,

    The reality is there are very few "simple" tankless models out there. A couple of Bosch units are the only ones that I know of that are still in production. I know that Paloma has stopped production of the PH-6/PH-12 series and I suspect the PH-24 will soon stop. (Mores the pity if you ask me!)

    That said, the difference between the older generation heaters and the new generation is day and night, and any modern tempering/balancing valve should have no trouble handling a tankless input.

    Tony
  • System2System2 Posts: 6,290 admin
    Re: Guidance for Grid-tie

    Wow, this is harder than buying the dang house.

    I have alot of research.

    They really have you either way. What will electric rates do, what will NG do, etc. Save here, waste there.

    We have a Roman tub that gets used 4x/wk and shower everyday.

    I think it was mentioned that heat pumps are more beneficial in my setup; garage installed hot water for benefitting in Apr-Oct heat.

    However, the tankless NG seems more on-demand and the Rheem has the remote feature.

    Hands-in-the-air.

    Maybe I should just wait to see what those politicians will do to us.
  • RandomJoeRandomJoe Solar Expert Posts: 472 ✭✭✭
    Re: Guidance for Grid-tie

    I had to chuckle when I read an article in the local paper at work today, made me think of this thread. Seems the local electric company (Oklahoma Gas & Electric, OG&E for short) is fighting the EPA at the moment. Right now our power is primarily from coal-fired plants. The EPA has mandated they install some scrubbers - get this, not to reduce any particular emission, but to "improve the views" (they are apparently a bit hazy thanks to the plants) at some nearby wildlife areas!

    The catch is, OG&E already has plans to switch from coal to natural gas fired production, just not in the same timeline the EPA wants. Rather than grant them the few more years to switch out the EPA still wants the scrubbers. Which OG&E estimates will result in a 1/3 increase in utility rates - the largest ever increase. Supposedly, the state legislature can affect the EPA's decision but is so far reluctant to do so.

    Funny side-note, OG&E is actually supported in opposition to the scrubbers by some environmental groups! And some people question the EPA's ruling anyway - how do you objectively quantify "improved views"?

    Yeah, I'll probably get it either way - electricity rises by 1/3 to install scrubbers, keeping the gas appliances makes sense. They switch to gas, my gas rates will probably rise... (Should still be cheaper than gas-derived electric, I suppose...!) Ah, well. Guess I'll just sit back and enjoy the ride! :p
  • Solar GuppySolar Guppy Solar Expert Posts: 1,959 ✭✭✭
    Re: Guidance for Grid-tie

    Personally, I would use the Heat-Pump HW tank, you can always find ways to make electric ( solar for example ) if things get out of hand, but you can't just make your own NG well. Just because NG is cheap now, it was 3X the price just 18 months ago so its worth remembering its very volatile priced compared to regulated electric
  • icarusicarus Solar Expert Posts: 5,108 ✭✭✭✭
    Re: Guidance for Grid-tie

    SG,

    While that is true in the abstract, it is just fundamentally much more efficient to "make heat" from other sources other than electric, no the least of which is direct gain solar. Solar heat collectors run at +30% efficiency (if memory serves) vs ~15% for Pv. All else being equal it is cheaper to build a system (especially diy) to capture 100,000 BTUs using direct gain, than to generate Pv, then convert that power to heat.

    In a practical, real world situation, few people have (or are likely to have in the short term) enough PV to justify resistance electric hot water. I also think that if energy conservation (for whatever a number of reasons) is important for all of us, then using all the energy we produce efficiently is critical. If one has excess production from PV, it seems more efficient to send your excess to the grid, and use solar or gas as a secondary to solar. (if you are not using Heat pump, which as you have pointed out is the best of all worlds, assuming you have a need for ac.

    Tony
  • System2System2 Posts: 6,290 admin
    Re: Guidance for Grid-tie

    Hydro...now it's clear why AL offers incentives for wood burning. NOT.
    And we have the highest per capita of PHDs.

    Stuff like OG&e and AL incentives, and I'm sure quite alot of others, really makes you wonder how much of that green stuff the legislature is smoking.


    Thanks for the contribution.
    TED - IN
    Solar - OUT (for now until we see how far we have to bend over)
    Heat pump - IN
    Powersaver - OUT
    SMARTER - DEFINITELY
  • Solar GuppySolar Guppy Solar Expert Posts: 1,959 ✭✭✭
    Re: Guidance for Grid-tie

    To be clear, why I posted heat pump hot water ( and I provided the links :roll: ) I was referring to the new energy star heat pumps ... these are brand new and commercially made by big name like Rudd and GE, these are not the same built in the garage type units that I suspect the 2002 doc would have BB posted.

    DeSuper Heater is the term for heating a hot water tank that has a heat exchanger in it. This is actually VERY old technology and works great by using the excess heat from a AC condenser unit. With the new heat pumps ( SEER 15+ ) you would need to be in a place like AZ to see a benefit

    And best of all worlds in ground based Geo Thermal ... using the closed slink loops in trenches. These have the DeSuper Heaters built in and due to the near constant ground temperature exceed 25 SEER ... I believe they can efficiently heat, even with the high efficiency as the unit can selectively choose the ground loop or the heat exchanger where DeSuper heaters are a add on an not integral to AC Condensers
  • a0128958a0128958 Solar Expert Posts: 316 ✭✭✭
    Re: Guidance for Grid-tie
    ... And best of all worlds in ground based Geo Thermal ... using the closed slink loops in trenches. These have the DeSuper Heaters built in and due to the near constant ground temperature exceed 25 SEER ... I believe they can efficiently heat, even with the high efficiency as the unit can selectively choose the ground loop or the heat exchanger where DeSuper heaters are a add on an not integral to AC Condensers

    My closed loop water-to-air geothermal heat pump system that's currently in heat mode for heating my residence, at the moment is operating at 4.2+ COP. Geothermal based heat pump systems are the 'real deal,' if designed and installed properly.

    Best regards,

    Bill
  • russruss Solar Expert Posts: 593 ✭✭
    Re: Guidance for Grid-tie

    The GSHP is what İ wanted for our new home but the cost differential for the system was too great. We would have had to use wells (3) of about 135 meter depth each.

    The additional savings as compared to an air source heat pump would have never paid back the difference.

    COP straight electric = 1 say 100 Dollars per month

    COP for ASHP = 3.5 say 28 dollars per month

    COP for GSHP = 4.5 say 22 dollars per month

    İ ended up with an ASHP hydronic system (air to water)
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