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electric boilers?

mattyc
mattyc Member Posts: 33
Does anyone have any experience or feedback on installing all electric boilers? I have a customer who is insistent on installing solar panels on the house and then running an electric boiler for heat/hot water with a high efficiency gas boiler backup. In New york where I am, electric boilers are extremely rare to find. At this point, I would need to make sure that the customer gets the solar panels installed FIRST, since that would be a completely different company doing that part.
After looking at some manuals of some brands, it would seam that I would need one 85k btu unit or two smaller units to heat this house (that wouldn't even be able to heat an indirect storage tank) which looks like I need about 150 Amps! I am not an electrician but I would imagine that would need its own brand new electric panel. It seems like it would use a ton of electricity and who knows if the solar panels would even produce that much?
If anyone has an experience in this area please let me know.
For myself, I recommended just doing the high efficiency gas boiler with indirect and call it a day. I recommended if he really wanted solar, to get a solar water heater. Its not so much that I fear the unknown, but I cannot stand behind installing a system that may not meet the customers expectations, and there are too many unknown variables for myself.
Thanks!
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Comments

  • WMno57
    WMno57 Member Posts: 311
    Sell them a Heat Pump Water Heater for domestic hot water, and a high eff gas boiler(just for backup of course, Ha Ha). What kind of AC do they currently have? How old is it. You may also be able to sell them a Heat Pump, which may handle the heating load in the shoulder seasons.
    Solar panels make DC, which is inverted to AC to power the house and sell back to the grid. The limiting factor here may be the inverter.
    Don't feel bad about running up the bill. In the coming years you will need the money to pay the taxes and kickbacks these green dreamers will vote for. Partner up with a local sparky, so he can get in on the party too. Probably will also need about 5 grand of electrical work just for the fast charger for the Tesla.
  • GGross
    GGross Member Posts: 188
    First things first, what is the actual load of the house? You mentioned looking at brand manuals to come up with 85k BTU. How did an install manual tell you the required load for this specific house? A manual J needs to be done on the house to determine the load

    If this is new construction I highly advise using emitters that will allow for lower water temps, maybe you can use an air to water heat pump instead.

    If you are absolutely stuck with an electric boiler you should now have the load so you can size the boiler, once you have sized the boiler you should be able to provide that information to whoever is handling the solar panels. You are correct that it will be a lot of power needed, but there are people who do know whether a panel array is available for your application to produce what you need.

    Once you have talked to the solar panel providers you should know what to expect from the panels, the homeowner can decide whether they want to proceed. Consider a separate water heater as an option

    I have sold quite a few Electric boilers, I have had great success with Electro industries, the only parts I ever had to change were due to a pretty bad power surge, Argo is another good brand pretty sure they are owned by ECR international (Utica Boilers) any Utica rep has access to this line and Viessmann would be my preferred but they were just released so I haven't had a chance to try. If you have a Viessmann rep nearby (on the east coast you definitely do) you could have one shipped to you, they are in stock up to about 49,000 BTU. Electro industries would be my go to for larger electric boilers.


    https://electromn.com/
    https://argocontrols.com/products/boilers-electric
    Viessmann electric options don't seem to appear on the US website yet
    mattyc
  • Jamie Hall
    Jamie Hall Member Posts: 19,150
    Your surmise on electric power is exactly right, and @WMno57 's comment is helpfl -- but only slightly.

    Physics is a ****. It takes a good deal of power to heat a structure; it takes roughly two to three times the power to do it with electric resistance heating, such as an electric boiler, as it does with a heat pump -- and there is simply nothing that hopes and dreams can do about that.

    Either way, you face a limitation on using solar power for the purpose: the incoming power from the sun is around 1 kilowatt (3400 BTUh) per square meter. That, however, is total incoming, and is measured in the plane perpendicular to the direction to the sun. Solar photovoltaics are improving in efficiency, but about the best you can get (and they are very expensive) at this time is 20%, so you are looking at no more than 200 watts per square meter -- if the panels are sun trackers (again, very expensive) and the sun is shining. Now. Unfortunately, the sun does not always shine, at least in most of the country, and there is that little problem of night time. If you do not have a way to store the power, you are still dependent on the grid; either with adequate storage or with the grid you can only figure, on the east coast, on having 3 hours of usable power out of 24 -- so if you are contemplating on using your PV for heat, and cutting ties -- figuratively or literally -- to the grid -- you need 8 times the panel area.

    To put it another way, your net PV output usable for heating is around 8 BTUh per square foot of panel. This is not an encouraging figure, either for resistance boilers or heat pumps -- and is, bluntly, hideously expensive to achieve.

    (Another point, @WMno57 mentions that you need an inverter to go from panel to 120/240 volt AC for you appliances, grid connected or not. Sine wave inverters in the power class we are talking here do exist -- but again, like the panels themselves and the batteries, the price for them is eye-watering, to say the least)

    (It is worth noting, however, that if you use solar for direct passive space heating -- entirely possible in a well designed house at minimal additional expense, you have ample power available -- why more people don't think of passive solar houses is completely beyond me).

    Assuming that you do want to go with electric heat, your figures are also more or less correct. Obviously the first thing is -- as always -- to determine the actual heating load. Good old Manual J, or the equivalent. An 85,000 BTUh boiler will draw, as you note, around 150 amps at 240 volts single phase. It is unlikely, to say the least, that a residence is wired for that, as that load is in addition to the normal residence load. You will need at least a 300 amp, and I would recommend a 400 amp, service entrance and drop; the power company serving your area may -- or may not -- be able to provide that. Heat pumps for heating are available, but you need to be very cautious if they are the principal source, that they will work without engaging resistance backup at your design temperature. A heat pump would probably want around 75 to 80 amps; there is a possibility that if the service entrance and drop is 200 amp that there may be enough power available for that. I would further caution with heat pumps, however, that all presently available heat pumps, whether air to air or air to water, have relatively low temperature output. If you are looking at an air to water heat pump to power an existing system, you need to make sure you have enough emitter to provide the needed heat at the low temperatures from the heat pump.

    Heat pump water heaters are rather nice, but if they are limited to heat pump mode (most of them have a resistance backup mode) they are painfully slow in recovery. Even in heat pump mode, they draw more power than most normal solar arrays can provide, however.

    Please note that I am not saying you couldn't go to solar PV powered electric heat for a residence. If you have the necessary land area for the solar array, you can. A very rough back of the envelope guess for such an installation would be around 500 grand to a million.
    Br. Jamie, osb
    Building superintendent/caretaker, 7200 sq. ft. historic house museum with dependencies in New England
  • Hot_water_fan
    Hot_water_fan Member Posts: 621
    @mattnyc I'd suggest an air-to-water heat pump. Uses 1/3 the electricity as an electric boiler. Or replace the AC with a heat pump as the least expensive option.
  • Jamie Hall
    Jamie Hall Member Posts: 19,150

    @mattnyc I'd suggest an air-to-water heat pump. Uses 1/3 the electricity as an electric boiler. Or replace the AC with a heat pump as the least expensive option.

    And kindly refer to my comments above as to power requirements and solar feasibility.
    Br. Jamie, osb
    Building superintendent/caretaker, 7200 sq. ft. historic house museum with dependencies in New England
  • Hot_water_fan
    Hot_water_fan Member Posts: 621
    Hot_water_fan said:
    @mattnyc I'd suggest an air-to-water heat pump. Uses 1/3 the electricity as an electric boiler. Or replace the AC with a heat pump as the least expensive option.

    And kindly refer to my comments above as to power requirements and solar feasibility.


    Definitely - the heat loss is needed before anything, 85kbtu might be right or might be 2x too big. Mine uses a max of 17 amps. Not a big deal! With a gas backup boiler, amps shouldn't be a problem at all, since you won't need resistance heat.

    On the solar side, don't 99% of solar customers remain grid connected? Seems unnecessary to stress about batteries. Or just buy solar from a large scale farm, which is what I do, saving 5% in the process.
  • Jamie Hall
    Jamie Hall Member Posts: 19,150
    Yes -- almost all solar customers remain grid connected. If you are purchasing from a large scale farm, is that power direct to your drop, or is it onto the grid, along the grid, and then dropped? Makes a big difference...

    In my humble opinion, residential grid connected solar power with no storage is a bit of a scam, since if the sun goes down you are still totally dependent on the grid's generators... but that's just me.
    Br. Jamie, osb
    Building superintendent/caretaker, 7200 sq. ft. historic house museum with dependencies in New England
  • Hot_water_fan
    Hot_water_fan Member Posts: 621
    In my humble opinion, residential grid connected solar power with no storage is a bit of a scam, since if the sun goes down you are still totally dependent on the grid's generators... but that's just me.


    Similar to passive solar! In any case >80% of 2021 installed solar is NOT residential.
  • hot_rod
    hot_rod Member Posts: 16,557
    First question I would have is what is the budget, and expectations. Not every RE buyer bases the decision on economics :)

    Plenty of solar simulation programs to show power and financial info. I use the SMA app for projections.
    Bob "hot rod" Rohr
    trainer for Caleffi NA
    Living the hydronic dream
  • Solid_Fuel_Man
    Solid_Fuel_Man Member Posts: 2,500
    The 80% number of solar not being residential is due to the incentives for large scale solar farms. Many of them here in Maine. And they are driving our cost of electricity up! When the sun goes down, or it's cloudy, that NG turbine generator has to spool up and down pretty quickly.... I digress

    85K btu/hr is a very large number. How did you come up with that number? 

    If I had access to cheap electricity, I'd be a heat pump guy.... air to water heating a slab or generously sized panel rads. Keep all the refrigerant outside. I don't want r410 in my lungs. 
    Serving Northern Maine HVAC & Controls. I burn wood, it smells good!
  • Hot_water_fan
    Hot_water_fan Member Posts: 621
    edited August 2
    The 80% number of solar not being residential is due to the incentives for large scale solar farms


    Precisely - economies of scale make utility scale solar extremely cheap - they're actually subsidized less than residential systems. They're being installed in huge numbers in Texas because the power is so cheap. Anyway, heat loss then exploring air-to-water seems like some good next steps.
    Solid_Fuel_Man
  • JakeCK
    JakeCK Member Posts: 812
    edited August 2
    First, how is grid connected solar w/o storage a scam? So far this year I have had to pay nothing for electric and actually have a 100$ credit. I've been keeping my house cold this summer too. I mean like frosty has been playing poker with penguins here. It's nice after working outside in the blazing sun at 90f to walk in to a cold house and not worry about paying a 200$ electric bill. Yes my panels will go down with the grid, but I can count the number of power outages over the past 12 years here on one hand.

    Second, it would be more cost effective to rebuild the house to be a passive house instead of trying to have enough panels to heat a house in the dead of winter. And the coldest times of the winter are generally the middle of the night too when the sun ain't shining. That said when I started to run my own numbers I found that it is possible to offset a large percentage of your energy usage over the course of a year with solar and still stay with in reason with expenses.
    Solid_Fuel_Man
  • Jamie Hall
    Jamie Hall Member Posts: 19,150
    edited August 2

    In my humble opinion, residential grid connected solar power with no storage is a bit of a scam, since if the sun goes down you are still totally dependent on the grid's generators... but that's just me.


    Similar to passive solar! In any case >80% of 2021 installed solar is NOT residential.
    The passive solar houses which I have been involved with maintain their comfort levels very nicely for between three to five days without solar input. The storage required is inherent in the design and construction. They require no -- zip, zero, nada -- backup heat.

    Mind you, I havea good deal of enthusiasm for solar power -- PV or passive for structures. I'd just like to see it promoted honestly and correctly, and evaluated shorn of artificial subsidies, never mind hype. It, like all other power sources, has benefits -- and shortcomings, all of which need to be taken into account and balanced against alternatives.
    Br. Jamie, osb
    Building superintendent/caretaker, 7200 sq. ft. historic house museum with dependencies in New England
    Hot_water_fanSolid_Fuel_Man
  • Zman
    Zman Member Posts: 7,356
    I would start by showing them how much power a rooftop solar system would produce. NREL does a nice job with this. https://pvwatts.nrel.gov/pvwatts.php

    I would then add up their heating bills for a typical year and convert them to Kwh so you can show them the delta between what they need and what they can generate with solar. You can also use the annual usage data to backcheck your heat loss calc by using heating degree days.

    "If you can't explain it simply, you don't understand it well enough"
    Albert Einstein
    Hot_water_fanGGrossSolid_Fuel_Man
  • fentonc
    fentonc Member Posts: 109
    @mattyc - where are you in NY? As others have pointed out, understanding the actual heat loss (rather than just the current boiler) is important, as hydronic systems are very frequently over designed. Also, it would seem that there is no point in using an indirect tank for DHW if you're using an electric boiler - just use a standalone electric water heater with identical efficiency (or hybrid water heater, if energy efficiency is their goal). In ConEd territory where I am, natural gas is actually fairly expensive - my last bill had a marginal cost of $2.50/therm vs $0.225/kwh for electricity. At 80% efficiency (so non-condensing), that's about $0.106/kwh-equivalent, so only half the price of electricity. A heat pump with an average COP above 2 would be cheaper to operate than my boiler.

    One of the units from https://arcticheatpumps.com can work with a storage tank w/ integrated backup electric boiler and indirect coil for DHW, which is pretty spiffy.
  • mattyc
    mattyc Member Posts: 33
    Thanks for the comments. @hot_rod I don't think budget is a concern for this job. I believe this is an engineer who wants something "exotic" to show off. Customer now wants a system that will run the electric boilers while the solar panels are actually working and then a high efficiency boiler to pick up the slack only when the solar panels aren't producing lol. To my knowledge such a control doesn't exist....or maybe it does ?....Except for a physical switch that you could flip on/off manually for the rest of your life. I suggested for a air/water heat pump and replace all the element in the house with a low temp element or just do a high efficiency gas boiler and if he really wants, a solar water heater with dual coil for boiler backup. It would be nice to run a solar storage tank for space heating as well..hmmmm
  • Jamie Hall
    Jamie Hall Member Posts: 19,150
    The easiest way to run that switchover is going to be a relay and a contactor. You connect the relay coil directly to the output of the solar panels -- probably 12 volt or 24 volt, maybe 48 -- BEFORE the inverter. Wire the normally OPEN contact to control the high power contactor for the electric boiler. Now when the sun is shining on his solar panels, the relay will pull in and open the circuit to the contactor coil, which will open and shut off the boiler.

    Do NOT, whatever else you do, warrantee this job, either verbally or in writing. It's going to be very expensive to run, and will be disappointing, and your client will come after you for not making miracles happen.
    Br. Jamie, osb
    Building superintendent/caretaker, 7200 sq. ft. historic house museum with dependencies in New England
  • GGross
    GGross Member Posts: 188
    @mattyc
    If you think he may just want something exotic maybe he would go with a solar thermal setup? It won't produce electricity, but Viessmann has controls to allow the system to utilize that solar heat and changeover to gas, or use gas as a supplement so he won't sacrifice comfort and can show off some nice panels. This way he would not need to purchase 2 separate fuel boilers. He could add some PV if there is room left on the roof for a little electricity as well
  • Hot_water_fan
    Hot_water_fan Member Posts: 621
    I suggested for a air/water heat pump and replace all the element in the house with a low temp element or just do a high efficiency gas boiler and if he really wants, a solar water heater with dual coil for boiler backup. It would be nice to run a solar storage tank for space heating as well..hmmmm

    There might not be a need to replace emitters to run lower temperatures. Find out the heat loss, see what water temp satisfies that heat loss, and if it’s close, just use the gas boiler for the coldest hours. An air-to-water heat pump can do a lot more than an electric boiler so hopefully the customer picks that option. 

    Solar thermal is rather rare and people often find it cheaper and more effective to just use solar PV instead, especially if they’re already planning on installing some PV. Extremely cheap to add a few more panels. 
    lkstdl
  • hot_rod
    hot_rod Member Posts: 16,557
    mattyc said:

    Thanks for the comments. @hot_rod I don't think budget is a concern for this job. I believe this is an engineer who wants something "exotic" to show off. Customer now wants a system that will run the electric boilers while the solar panels are actually working and then a high efficiency boiler to pick up the slack only when the solar panels aren't producing lol. To my knowledge such a control doesn't exist....or maybe it does ?....Except for a physical switch that you could flip on/off manually for the rest of your life. I suggested for a air/water heat pump and replace all the element in the house with a low temp element or just do a high efficiency gas boiler and if he really wants, a solar water heater with dual coil for boiler backup. It would be nice to run a solar storage tank for space heating as well..hmmmm

    I would push for the A2WHP option also, if efficiency is part of their desire. I believe the SpackPak Soltice control has the ability to make decisions between two different heat sources.

    I recall an electric boiler control up in the Montreal area that made the switch from electric to oil based on real time electric rates, Henry would know if he is watching.

    I would think a switching control could be built from off the shelf controls. Maybe an induction relay that drop offs the solar when current drops below a level. It would need and anti short cycling circuit so on a partly cloudy day you would prevent banging back and forth every few minutes.

    The HP option brings a cooling component option, that an electric boiler would not. Seeing as your best solar harvest will be the long sunny summer days.

    Turns out cooling bills are going way up in some hot sunny southern areas. An article I read about folks moving to Florida to get away from the cold northern climate areas and budget straining high heating bills are finding cooling cost exceed the cold weather heating costs. Since AC is primarily electrically powered, switching energy sources is not much of an option.

    Back to the drawing board on NG powered AC :)

    Solar DHW makes some sense, but ST for heat contribution is a long shot. SW states can maybe see 20- 30% ST heat contribution with an excess of 300 days a year of solar. Still an $$ proposition requiring large storage vessels.
    Bob "hot rod" Rohr
    trainer for Caleffi NA
    Living the hydronic dream
  • WMno57
    WMno57 Member Posts: 311
    edited August 3

    connect the relay coil directly to the output of the solar panels -- probably 12 volt or 24 volt, maybe 48 -- BEFORE the inverter.

    The voltage produced by an individual panel will vary with shading, temperature, and other variables. An array of panels designed for an off grid system with batteries will at some point (after multiple inverters and other gizmos) output DC power at sufficient voltage to charge the batteries. This has to be a little higher than the battery voltage. Try this on a non-hybrid 12v ICE car with a digital VOM. Engine off, 12.6 volts. Engine running, 14.4 volts.
    The array @JakeCK has on his roof is not an off grid system. No batteries. It is designed to eventually make AC power. The intermediate DC voltages of individual panels, and the cumulative DC voltage of the entire array do NOT need to be multiples of 12v DC. DO NOT PROBE THE OUTPUT OF THIS TYPE OF ARRAY. The DC output of the entire array may be higher than you want to shake hands with.
    Sad story of what can happen when a 600 volt VOM meets 4000 volts.

    A little more about how panels are connected together to form an array. The article states "Traditionally, solar panels produce voltages around 30 V. This is too low to be effectively converted into AC to feed to the power grid. To address this, panels are strung together in series to increase the voltage to something more appropriate for the inverter being used, typically about 600 V."
    https://en.wikipedia.org/wiki/Power_optimizer
    In the 1950s cars changed from 6 volt batteries to 12 volt batteries. In the 1990s the car industry contemplated changing from 12 volts to 36 volts. The charging voltage for a 36 volt battery pack is around 42 volts which is still relatively safe. The charging voltage required for a 48 volt battery pack is higher than "the 50-volt limit used as a guideline for electric shock hazard".
    https://en.wikipedia.org/wiki/42-volt_electrical_system
  • Jamie Hall
    Jamie Hall Member Posts: 19,150
    Thank you for all that, @WMno57 . Nice, if not exactly comforting, to know.

    Not surprisingly, I am well aware of the changes in battery charging voltages for cars -- and, I might add, airplanes and farm machinery, having been working on such critters since sometime in the late 1940s.

    I am quite aware that the voltage output of a solar photovoltaic array will vary with the light intensity falling on it. Many years ago this phenomenon was used to some advantage in "light meters" for applications such as photography (I still have a Weston Master IV meter somewhere). What I was not aware of -- and am quite frankly horrified by -- is that "panels are strung together in series to increase the voltage to something more appropriate for the inverter being used, typically about 600 V". In my humble opinion, this may be satisfactory for commercial scale applications. For residential applications, again in my humble opinion, this is insane. I cannot think of a valid engineering excuse to not provide voltage stabilization -- perhaps with series to parallel automatic switching as required -- other than sheer laziness. Much as I dislike code regulations on occasion, I hope that the National Electrical Code will be revised to eliminate this hazard before there are fatalities.
    Br. Jamie, osb
    Building superintendent/caretaker, 7200 sq. ft. historic house museum with dependencies in New England
  • yesimon
    yesimon Member Posts: 34
    edited August 3
    "panels are strung together in series to increase the voltage to something more appropriate for the inverter being used, typically about 600 V"


    Most of the US rooftop solar market is now using microinverters for each panel so the only voltage in wiring would be the standard 240V AC. Lots of reasons for this despite slightly higher prices: reliability, modularity, lifespan, shading performance, ease-of installation etc. Tesla solar is the major player still doing string inverter but are considered pretty cheap and low-quality overall.

    Back to the original posting, it seems like the homeowner may be uneducated about how much solar kWh will be realistically produced compared to annual electric consumption. Many solar salesmen claim that their system will wipe out your electricity bills. Achieving net zero in the northeast for a SFH usually requires upfront planning or envelope upgrades even with >3 COP heat pumps and favorable net metering laws. With a 1 COP electric boiler it's almost guaranteed that the electric bills will keep racking up.
    JakeCK
  • SlamDunk
    SlamDunk Member Posts: 1,334
    Here is a piece on a battery that could power a house and recharge via solar and last for 30 years. Designed to take many off the grid. It is frustrating to read.

    https://www.npr.org/2022/08/03/1114964240/new-battery-technology-china-vanadium
    PC7060
  • Hot_water_fan
    Hot_water_fan Member Posts: 621
    Achieving net zero in the northeast for a SFH usually requires upfront planning or envelope upgrades even with >3 COP heat pumps and favorable net metering laws. With a 1 COP electric boiler it's almost guaranteed that the electric bills will keep racking up.


    Agreed. Does it matter? If someone knows upfront that their array will save 80% of kwh for a total savings of say 10% per year, seems like a win.
  • JakeCK
    JakeCK Member Posts: 812
    edited August 4
    Yes, my system uses Enphase IQ7+ micro inverters. I have 4 logical arrays, 2 on each 120v AC leg. The only DC current is the short distance from the leads on the panel to the micro that is mounted directly under the panel. I have a total of 42 panels and 42 micro inverters. If grid power is disconnected either by a loss of grid power or from the disconnect/breakers the micros shut down in seconds. This is a required safety function per IEEE 1547. In other words if I shut off the main breaker in the house all of the wires between the micros, combiner box, and the panel should be de-energized and safe to work on. The only voltage would be the DC between the panel and micro, and since it is 1:1 you only have to worry about the voltage that a single panel can generate in full sun. In my case I have 340watt panels, they are rated for 34V and10A. That said 10 amps is still plenty enough to stop your heart if it hits you right.

    There are pros and cons between string inverters vs micro. With micros if one panel is shaded or damaged the rest of the your system continues to function normally. Same if a micro goes down, much greater resiliency over all. It is also safer since the power directly from the panel is contained to a much shorter distance and is at a lower voltage. However the costs are much greater, those microinverters are not cheap and with so much more hardware you will suffer a failure eventually. And since most of the hardware is all mounted together it can potentially be much harder to access and effect repairs. Such as when the system is mounted on a 10/12 roof 30+ feet off the ground.

    Edit: I misspoke, Since my system utilizes a supply side tap and a fused disconnect, the wires between the tap and the disconnect will still be energized even if my main breaker is off! This is actually one of my complaints with how my system was designed. Had I been more familiar with how the installers designed it before hand I would have forced them to do things a little different. Instead of supply side tap -> fused disconnect -> production grade meter -> combiner box -> microinverters -> panels I would have had them install a combo meter box and upgraded the service to 400 amp instead of 200 amps. This would have allowed it to remain under the 120% rule, eliminated the fused disconnect and two holes going through the house, and made it safer to work on it.
  • JakeCK
    JakeCK Member Posts: 812
    yesimon said:
     Achieving net zero in the northeast for a SFH usually requires upfront planning or envelope upgrades even with >3 COP heat pumps and favorable net metering laws.

    And achieving net zero doesn't require the net metering laws be all that favorable as long as they at least allow you to put your excess into the grid. Even if you don't earn any $$$ back for that excess you'll still be net zero if the kwh you produce is >= to what you consume. It does absolutely suck for your ROI tho, and that is when big batteries make financial sense.
  • Jamie Hall
    Jamie Hall Member Posts: 19,150
    Totally agree with @JakeCK here. But I'm a bit of a purist: If your objective is bet zero, or -- perhaps more realistically for most of the built infrastructure, net zero for non space conditioning loads -- then that should be an ethical decision. If it happens that the laws or some subsidies make it cheaper, so much the better But for me at least the initial motivation should be the ethics, then the practicality (which I agree may be influenced by the law or regulations -- as Jake notes, if you can't feed back into the grid, then you're going to need some pretty impressive batteries, for instance) -- then finally the economics. But that's me, and your mileage may differ!
    Br. Jamie, osb
    Building superintendent/caretaker, 7200 sq. ft. historic house museum with dependencies in New England
  • JakeCK
    JakeCK Member Posts: 812
    So I just ran through all of the numbers, again, using my house and solar as an example just so the OP can see what exactly were talking about when we say it is basically not possible to run a boiler off solar panels.

    Over the past 12mos I used 1064CCF of natural gas, this works out to ~31,800kWh. This is to heat a 1476sq ft colonial built in 1928 with an 80% boiler connected to a converted gravity CI system. Only a few rooms have any insulation in the walls, there is only ~6" of blown fiberglass in the attic, and no insulation on the foundation. Wood single pane windows with failing aluminum storms.
    So far this year my 12kW solar system has generated 9592kWh, with projections saying I'll generate about 14600kWh by the end of December.

    Now supposedly my boiler is firing at 80%, but I question that considering the condensation issues I've been having in the flue. But with that number in mind we can immediately reduce that 1064CCF number by %20 and bring it down to 851CCF, or ~25400kWh. This is also how much energy it would take to heat the house as is with an electric boiler, assuming the 80% was correct. As you can see the amount of energy the solar panels generated over the course of an entire year isn't even close to what is required to heat this modest house with an electric boiler. Add in the 10400kWh used for the AC, HPWH, and everything else electric over the past year and we're short by more than half. And remember that electric boiler is going to be doing most of it's work exactly when the panels are producing ZERO energy. One will be paying for every one of those kWh's.

    Now not all is lost, at least when it comes to getting close to net zero. But its going to take more work, a lot more work.

    Lets suppose I replaced the NG boiler with an A2W heat pump and electric boiler backup with a seasonal COP of 2(Trying to be conservative here). We can cut that 25400kWh in half to 12700kWh. MUCH MUCH closer, but still no cookie. But remember this house is pretty drafty, and has a lot of room for improvement. Lets add in new storm windows with low e coating(getting installed 8/26), insulate foundation with 2" r12 polyiso(working on it, about 30% done), blow in an additional 12" of cellulose in the attic bringing it to r48 or so. And dense pack the exterior walls with r13 cellulose. Cellulose is also pretty good at stopping air flow in walls too. And finally and most importantly detailed air sealing, paying close attention in the basement and attic. 2 part spray foam around the rim joist and canned spray foam everywhere else there is a wire or pipe penetrating. Also pay attention to outlets, switches, and around the electrical boxes for light fixtures.

    Now lets take a guess at total heating and cooling reductions. Maybe 15% reduction? That might get us down to around 10,800kWh for heating, and at best shave off a couple hundred kWh for cooling.

    Total? 21,000kWh for an entire year. subtract the 14600kWh solar production and we're still left with a deficit of 6600kWh. Not too bad. Keep in mind there WILL be an electric bill. This is taking advantage of net metering with no batteries. Batteries would help reducing the electric costs, a lot in fact, but they are still very expensive and won't get one any closer to net zero. ROI is still negative I believe. At this point one is only left with 2 options. More solar($$$$$), close to 50% more, or lots more insulation($$$$). Insulation is the most cost effective route but you must be careful and consider moisture movement with in the structure.

    This is just one example. Hopefully it will help you see what is and isn't possible?



    mattycyesimonCanucker
  • Hot_water_fan
    Hot_water_fan Member Posts: 621
    edited August 4
    @JakeCK maybe the OP wasn’t being so literal. It’s not a binary, someone can be 80% solar powered! Doesn’t make you a bad person or make the economics worse for the 80%. I disagree that insulation is more cost effective. Often it is not - diminishing returns are a bummer. Solar is often the opposite. 
  • Jamie Hall
    Jamie Hall Member Posts: 19,150
    See the thread I just posted called Watts Up! The thing about solar is that if you aren't storing it, it's gone. Insulation is always there when you need. Soaking up 12 KW of electricity from a solar array on this lovely July day as I type isn't going to help me or anybody else at oh dark hundred in January at 10 below with a 30 knot wind. If you aren't storing your alternative "energy" (it's really power, not energy), you may feel wonderful -- but you are kidding yourself and everyone else. Your society may burn less coal right now -- but they will have to burn coal sometime (if you speak German, that is...!)
    Br. Jamie, osb
    Building superintendent/caretaker, 7200 sq. ft. historic house museum with dependencies in New England
  • Hot_water_fan
    Hot_water_fan Member Posts: 621
    edited August 4
    @Jamie Hall Whether you like it or not (I don't - I'd rather have utility scale solar), net metering is here, so no, the power isn't gone. If they change that, that'll motivate some to use batteries or push more to just buying it direct from the utility. That doesn't change the fact that $/kwh for solar (either from the roof or from the utility) can often be cheaper than $/kwh saved of insulation (which is often a good idea to a point). It also doesn't change that those kwh are displacing other sources. The perfect needn't be the enemy of the good.
  • Jamie Hall
    Jamie Hall Member Posts: 19,150
    The only real problem I have with net metering (besides the fickleness of the authorities who determine the rates) is that it tends to obscure the need for reliable power generation from sources which can come on immediately when needed, regardless of the whimsies of the sun (it does set, even in the western US), the wind (tends to be absent on hot days) or water (looked at Lake Mead lately?). This distorts the debate and the politics. This tends to result in well-meaning but counter-productive results (the best current examples are in Europe, with Germany as the poster child).

    The minor detail that it tends to favour those who are wealthy enough to install it, to be paid for in electric rates by the poor, who can't, is a minor problem... perhaps...
    Br. Jamie, osb
    Building superintendent/caretaker, 7200 sq. ft. historic house museum with dependencies in New England
  • FStephenMasek
    FStephenMasek Member Posts: 26
    My consulting company inspected a huge thermal solar electric plant in the California desert (curved mirrors). The dirty little no-so secret, each section of it had a large natural-gas-fired boiler. Now, they are demolishing the whole thing and replacing it with photovotaics and giant batteries.
    Author of Illustrated Practical Asbestos: For Consultants, Contractors, Property Managers & Regulators
    mattyc
  • Jamie Hall
    Jamie Hall Member Posts: 19,150
    Bingo! And at least you are in the California desert, and your giant batteries only have to store enough power for say 14 hours of use. Unlike, say, not so sunny New England -- where 3 to 4 days of storage would not be out of line.
    Br. Jamie, osb
    Building superintendent/caretaker, 7200 sq. ft. historic house museum with dependencies in New England
  • Hot_water_fan
    Hot_water_fan Member Posts: 621
    edited August 4
    This is still black and white thinking - reductions of any kind are good! There is no silver bullet energy source, otherwise we'd have 100% market share for one. All energy sources are intermittent and unreliable, it's a gradient. In ERCOT, the energy prices compensate generations based on their availability and solar/wind are still grabbing market share.
    Canucker
  • JakeCK
    JakeCK Member Posts: 812
    edited August 4
    @JakeCK maybe the OP wasn’t being so literal. It’s not a binary, someone can be 80% solar powered! Doesn’t make you a bad person or make the economics worse for the 80%. I disagree that insulation is more cost effective. Often it is not - diminishing returns are a bummer. Solar is often the opposite. 
    Actually the economics of getting to 80% is better then 100% with quicker payback. Since even with favorable net metering it isn't a dollar for dollar payback for power returned to the grid, the more you use immediately the better your returns.
    I accepted the lower ROI by getting to over 100% offset with the expectation I would be converting over most, if not all of my house to electric and getting EV's in the not to distant future.

    And I never said they are bad if only at 80%? I'm just pointing out going to electric boilers with the expectation that one can run them off of solar... Well it just won't work. Period. The coldest hours are almost always in the middle of the night, when there is no sun. Could grid solar storage make up for it? Sure, but try to find a home battery that can power those boilers. You'll probably spend more then what was spent on the house it's self. The best that can be done with current tech is offset a large percentage of that electric usage over the course of an entire year. But you will always still have a bill to pay, and possibly a larger one than NG if using an electric resistance boiler. 

    Look I am an advocate for alternative energy, but you can't be a fanboi. Like wise you can't be an old grumpy fuddyduddy stuck in his/her ways. You have to be open minded to new ideas, objective, and run the numbers. 

    I also want to add that I'm maxed out on viable roof space for PV. Unless I want to throw money away on a 10/12 pitched roof that faces northwest. It'd work ok from 1-4pm lol
    Hot_water_fan
  • Hot_water_fan
    Hot_water_fan Member Posts: 621
    And I never said they are bad if only at 80%?
    I was referring to Jamie's comment, not yours.

    I agree with you! It's possible to offset a lot of electricity usage. If it's 150% or 100% or 50%, it's all good if electric bill + solar cost < status quo, if you're looking at economics alone. If you're evaluating other things, same applies.
  • Jamie Hall
    Jamie Hall Member Posts: 19,150
    Perhaps the differences which we are seeing here -- and everyone has valid points -- are much more related to what I was driving at elsewhere: power vs. energy. In the case of general electric power -- the kind which Joe Sixpack expects when he turns on a light -- you can, indeed, save a good deal of energy with distributed solar -- rooftops and the like. Every watt you get from that is a watt you don't have to get from a coal (in Europe) or gas (in the US) fired power plant. But... when Joe turns on the light, he's not interested in energy. He's interested in power, now. Unless truly excess solar (or wind) energy is stored in some form, it is simply not available to be converted into power when and as needed, and thus does exactly nothing with regard to the need for adequate power generation. Now what this actually means on the grid scale (or an off grid residential application) is that the alternative power generation capacity -- solar panels, wind, whatever -- has to be some multiple -- typically between 3 and 8 -- of the short term peak power demand if it is to be the only source, and that extra power has to be stored as energy to be converted back on demand.

    All too often one sees the claim that such and such a solar array or farm, or such and such a wind turbine farm can power some wonderful number of residences. Quite true. No argument. What doesn't get stated is that they can only do it when their power source -- the sun or the wind -- is available. Without true grid scale storage, such claims are not much sort of a scam.

    The economics and politics of residential or even small commercial solar, or of wind turbines -- or even "grid scale" projects are a completely different question.
    Br. Jamie, osb
    Building superintendent/caretaker, 7200 sq. ft. historic house museum with dependencies in New England
    Hot_water_fanGGrossmattycSolid_Fuel_Man
  • Nimrod66
    Nimrod66 Member Posts: 16
    These responses get pretty technical. The bottom line to me is that 85,000 Btu/hr. is about 25 kW. Most large residential photovoltaic (PV) arrays are 10 maybe 15 kW, maximum output. Those would actually be huge arrays that most roof tops don't have enough space for. Assuming it is even possible to get 10-15 kW on a roof, the array won't be making 10-15 kW 24 hours/day, especially in winter, at night, when it is coldest. Actual output for the PV array might be at maximum output for a couple hours/day in winter. It is therefore completely misguided to think a rooftop PV system can heat a home demanding 85,000 Btu/hr. in New York. If this customer of yours wants low carbon heating, I suggest looking at automatic pellet boilers, which make all the necessary heat on demand at any time of day.