4 ms·

Problem being that electric water heating is a lot more expensive in e.g. Germany where gas prices are lower than electricity prices per kWh delivered. (~12 vs.

by fho 2y ago

Problem being that electric water heating is a lot more expensive in e.g. Germany where gas prices are lower than electricity prices per kWh delivered. (~12 vs. 39 eurocent per kWh) So blindly converting a gas water heater to electric will roughly quadruple your water heating cost.

ben_w 2y ago
Only a problem when you're limiting yourself to resistive heating. Heat pumps can heat water, not just air, and are several times more efficient than resistive. I've got a heat pump, and I'm in Germany. Also, if you're in Germany, you can get a balcony PV system from half the supermarkets a few hundred euros, and those are designed to be installed DIY without needing an electrician. Limited power, sure, but way cheaper than €0.39/kWh delivered: • https://www.lidl.de/p/vale-balkonkraftwerk-ecoflow-820-w-800-w-wifi-full-black-solarmodule/p100379477 https://www.lidl.de/p/vale-balkonkraftwerk-ecoflow-820-w-800... • https://www.kaufland.de/product/502015379/?search_value=balkonkraftwerk https://www.kaufland.de/product/502015379/?search_value=balk...
- kragen 2y ago
  Your first link seems to be 349€ for 800Wp including microinverter. German utility-scale PV has a capacity factor averaging about 12% IIRC, but presumably a balcony system will be lower because it isn't optimally angled for the sun, say 8%. Then that's about 64W, which is 560 kWh per year. 349€ over 10 years would be 35€ per year, about 0.06€/kWh. That's still about six times the cost of wholesale low-cost solar panels: https://www.solarserver.de/photovoltaik-preis-pv-modul-preisindex/ https://www.solarserver.de/photovoltaik-preis-pv-modul-preis... 64 watts is about 40–50 liters per day of hot water heated resistively, presumably closer to 150 liters per day with a heat pump. But it seems like the heat pump is only saving you the 700€ for two more such balcony systems, assuming you have the space. Moreover, you don't need a microinverter for a resistive heater.
  - ben_w 2y ago
    Oh indeed, balcony systems are small and limited — the constraints that led to them are: (1) DIY-safe, (2) useful for rented apartments (limited window or balcony fencing space, may not be allowed to fix something to an exterior wall). I'm not sure if you're allowed to just resistively dump an off-grid PV system into a resistive heating system, but I guess if you did, you could indeed save on the cost of the inverter.
    - kragen 2y ago
      I believe that even in Germany you can connect a low-voltage solar panel to a battery or heating element without any licensing approvals beyond CE. Low-voltage wiring poses much less risk of electrical shock and is consequently exempt from most safety regulations.
    - Calwestjobs 2y ago
      efficiency of no MPPT is around 10 percent lower then with MPPT system so no issue. 2000 watt is maybe max what you can have on balcony - physical size, and 2000 watt inverters are like 20 $. well connecting anything to grid is/should issue, offgrid noone cares.
      - kragen 2y ago
        You might be able to hang an additional balcony system out a non-balcony window or something, or just keep it inside the window. Less insolation, but maybe not so much less that it's unprofitable.
  - kragen 2y ago
    Interesting note: this is about six times cheaper per watt than residential solar systems in the US.
- fho 2y ago
  We actually do have a Balkonkraftwerk im Garten :-) Now that the sun is out for longer periods each day we are "wasting" energy to the grid a lot. I don't really see how to capture that energy though. 1. Buying a battery quickly shifts the break even points to decades. Without a battery I estimate 3-4 years. 2. I would love to heat water, but renting a place limits my options a lot. I was looking at electrical boilers to supplement the gas heater. But we are limited on space for small heaters below the sink and big heaters in the main water path. (Also we can't change the plumbing for legal reasons.) 3. The next best thing is some imaginary insulated water heating kettle that I can control to only use exactly the excess energy. No idea if such a thing exists.
  - notTooFarGone 2y ago
    You should calculate the battery parts again. I'm currently installing mine in Germany and the cost parity is getting close.
  - Huppie 2y ago
    You probably thought of this already but we mostly do load shifting. If you have moderate PV output (like with balcony solar) that can probably use up most of your production. Consider running the dishwasher (if you have one) or washing machine / dryer (if you don't dry that in the sun directly) during the day. Granted, we work from home _a lot_ and also have an EV so it's a lot easier to do load shifting for us, but just shifting the dishwasher and washing machine to 'sunlight hours' already made a pretty decent difference.
    - fho 2y ago
      Yeah, we do that. Given that most home appliances use more than 800W (even in Eco modes) we often use more than our production. E.g. our washing machine uses 1000W over a prolonged period of time which would be perfect to run on a sunny day. But it does so by switching the 2000W heating element so it averages to 1000W ... So we repeatedly export 800W (without any form of reimbursement) and import the missing 1200W back. And that is the case for all of our appliances. (I have a sensor to monitor that) Don't know if more modern machines are better in this regard, our machines are about 5 years old now. edit: I don't want to sound bitter about it. The Balkonkraftwerk works perfectly fine to power our base energy load.
Calwestjobs 2y ago
solar pv heating. my PV system is paid after 6 years of use. if i use current prices for energy. last two years market/spot prices were even higher than that. so in reality it was paid even sooner. and pv system does not disappear as soon as it is paid, it continues to work. so i have next 4-10 years remaining of lifetime of a inverter. so for next 4-10 years i am having 100% REALLY REALLY FREE hot water, again for 80% of time... etc vis original comment. when inverter ends its life in next 4-10 years then i will buy new one, without changing panels. so payback time will be even quicker. calculations/models of biggest engineers, experts, etc. do not involve thinking about using pv system after it is paid... ( not insult, just exposing state of things )
- fho 2y ago
  Yes, but ... A PV system is not accessible to many. We have a small 800W system in our garden, but for many the price or just getting permissions from their landlords makes a PV system unfeasible. Also, if you are heating with solar you could heat water directly. But that path is also only available to house owners.
  - Calwestjobs 2y ago
    PV + heatpump maybe. PV + resistive heater yes. solar thermal is not worth price wise. solar thermal can be feasible only for big installations as is in stralsund, leipzig... - megawatts. solar PV is order of magnitude cheaper in small systems (per actual provided output per year, not just rated wattage) AND because hot water energy needs are much higher than for example tv, notebook etc, so after your hot water is heated, you can charge your devices with it, you can not do that with solar thermal. so if people size their systems for winter sunny day, they will have excess in summer so you can use that for other things like bikes, lawnmowers ... of course there is ratio of people living in blocks of flats / townhouses and people living in family houses / rural, so every situation is unique. so townhouses should be connected to central heating network and heating network provider should chase efficiencies of scale, that is better, faster, cheaper for everyone ( europe / germany context ) if urban density does not allow otherwise. similar situation with electric cars, a lot of people is crying that there are not enough chargers for them, those are "city" people, but in reality most people live in rural setting or family houses and in germany every house already has more than enough electrical capacity to charge from outlet, you can charge car from 2.5kW which is same wattage as most electric kettles. yes it charges over night (10 hours) only 100 km but every house can do that already. faster charger can be bought. of course situation in cities is quite different, you can not just put extension cord from window. which is feasible in rural setting / family houses. even in berlin roughly 50 % of people do not live in townhouses / high rises.

by fho 2y ago

ben_w 2y ago

Only a problem when you're limiting yourself to resistive heating. Heat pumps can heat water, not just air, and are several times more efficient than resistive. I've got a heat pump, and I'm in Germany. Also, if you're in Germany, you can get a balcony PV system from half the supermarkets a few hundred euros, and those are designed to be installed DIY without needing an electrician. Limited power, sure, but way cheaper than €0.39/kWh delivered: • https://www.lidl.de/p/vale-balkonkraftwerk-ecoflow-820-w-800-w-wifi-full-black-solarmodule/p100379477 https://www.lidl.de/p/vale-balkonkraftwerk-ecoflow-820-w-800... • https://www.kaufland.de/product/502015379/?search_value=balkonkraftwerk https://www.kaufland.de/product/502015379/?search_value=balk...

kragen 2y ago
Your first link seems to be 349€ for 800Wp including microinverter. German utility-scale PV has a capacity factor averaging about 12% IIRC, but presumably a balcony system will be lower because it isn't optimally angled for the sun, say 8%. Then that's about 64W, which is 560 kWh per year. 349€ over 10 years would be 35€ per year, about 0.06€/kWh. That's still about six times the cost of wholesale low-cost solar panels: https://www.solarserver.de/photovoltaik-preis-pv-modul-preisindex/ https://www.solarserver.de/photovoltaik-preis-pv-modul-preis... 64 watts is about 40–50 liters per day of hot water heated resistively, presumably closer to 150 liters per day with a heat pump. But it seems like the heat pump is only saving you the 700€ for two more such balcony systems, assuming you have the space. Moreover, you don't need a microinverter for a resistive heater.
- ben_w 2y ago
  Oh indeed, balcony systems are small and limited — the constraints that led to them are: (1) DIY-safe, (2) useful for rented apartments (limited window or balcony fencing space, may not be allowed to fix something to an exterior wall). I'm not sure if you're allowed to just resistively dump an off-grid PV system into a resistive heating system, but I guess if you did, you could indeed save on the cost of the inverter.
  - kragen 2y ago
    I believe that even in Germany you can connect a low-voltage solar panel to a battery or heating element without any licensing approvals beyond CE. Low-voltage wiring poses much less risk of electrical shock and is consequently exempt from most safety regulations.
  - Calwestjobs 2y ago
    efficiency of no MPPT is around 10 percent lower then with MPPT system so no issue. 2000 watt is maybe max what you can have on balcony - physical size, and 2000 watt inverters are like 20 $. well connecting anything to grid is/should issue, offgrid noone cares.
    - kragen 2y ago
      You might be able to hang an additional balcony system out a non-balcony window or something, or just keep it inside the window. Less insolation, but maybe not so much less that it's unprofitable.
- kragen 2y ago
  Interesting note: this is about six times cheaper per watt than residential solar systems in the US.
fho 2y ago
We actually do have a Balkonkraftwerk im Garten :-) Now that the sun is out for longer periods each day we are "wasting" energy to the grid a lot. I don't really see how to capture that energy though. 1. Buying a battery quickly shifts the break even points to decades. Without a battery I estimate 3-4 years. 2. I would love to heat water, but renting a place limits my options a lot. I was looking at electrical boilers to supplement the gas heater. But we are limited on space for small heaters below the sink and big heaters in the main water path. (Also we can't change the plumbing for legal reasons.) 3. The next best thing is some imaginary insulated water heating kettle that I can control to only use exactly the excess energy. No idea if such a thing exists.
- notTooFarGone 2y ago
  You should calculate the battery parts again. I'm currently installing mine in Germany and the cost parity is getting close.
- Huppie 2y ago
  You probably thought of this already but we mostly do load shifting. If you have moderate PV output (like with balcony solar) that can probably use up most of your production. Consider running the dishwasher (if you have one) or washing machine / dryer (if you don't dry that in the sun directly) during the day. Granted, we work from home _a lot_ and also have an EV so it's a lot easier to do load shifting for us, but just shifting the dishwasher and washing machine to 'sunlight hours' already made a pretty decent difference.
  - fho 2y ago
    Yeah, we do that. Given that most home appliances use more than 800W (even in Eco modes) we often use more than our production. E.g. our washing machine uses 1000W over a prolonged period of time which would be perfect to run on a sunny day. But it does so by switching the 2000W heating element so it averages to 1000W ... So we repeatedly export 800W (without any form of reimbursement) and import the missing 1200W back. And that is the case for all of our appliances. (I have a sensor to monitor that) Don't know if more modern machines are better in this regard, our machines are about 5 years old now. edit: I don't want to sound bitter about it. The Balkonkraftwerk works perfectly fine to power our base energy load.

Calwestjobs 2y ago

solar pv heating. my PV system is paid after 6 years of use. if i use current prices for energy. last two years market/spot prices were even higher than that. so in reality it was paid even sooner. and pv system does not disappear as soon as it is paid, it continues to work. so i have next 4-10 years remaining of lifetime of a inverter. so for next 4-10 years i am having 100% REALLY REALLY FREE hot water, again for 80% of time... etc vis original comment. when inverter ends its life in next 4-10 years then i will buy new one, without changing panels. so payback time will be even quicker. calculations/models of biggest engineers, experts, etc. do not involve thinking about using pv system after it is paid... ( not insult, just exposing state of things )

fho 2y ago
Yes, but ... A PV system is not accessible to many. We have a small 800W system in our garden, but for many the price or just getting permissions from their landlords makes a PV system unfeasible. Also, if you are heating with solar you could heat water directly. But that path is also only available to house owners.
- Calwestjobs 2y ago
  PV + heatpump maybe. PV + resistive heater yes. solar thermal is not worth price wise. solar thermal can be feasible only for big installations as is in stralsund, leipzig... - megawatts. solar PV is order of magnitude cheaper in small systems (per actual provided output per year, not just rated wattage) AND because hot water energy needs are much higher than for example tv, notebook etc, so after your hot water is heated, you can charge your devices with it, you can not do that with solar thermal. so if people size their systems for winter sunny day, they will have excess in summer so you can use that for other things like bikes, lawnmowers ... of course there is ratio of people living in blocks of flats / townhouses and people living in family houses / rural, so every situation is unique. so townhouses should be connected to central heating network and heating network provider should chase efficiencies of scale, that is better, faster, cheaper for everyone ( europe / germany context ) if urban density does not allow otherwise. similar situation with electric cars, a lot of people is crying that there are not enough chargers for them, those are "city" people, but in reality most people live in rural setting or family houses and in germany every house already has more than enough electrical capacity to charge from outlet, you can charge car from 2.5kW which is same wattage as most electric kettles. yes it charges over night (10 hours) only 100 km but every house can do that already. faster charger can be bought. of course situation in cities is quite different, you can not just put extension cord from window. which is feasible in rural setting / family houses. even in berlin roughly 50 % of people do not live in townhouses / high rises.