Understanding Solar Energy

Converting a gas water heater to electric and/or solar is one of the best bang for the buck on decarbonization too. Something that should be done before buying an electric car or swapping out your gas furnace for a heat pump. Though I'm terrible at following my own advice, I still have a gas water heater, just because I needed to replace my car and furnace before I needed to replace my water heater. That said, the sunk cost fallacy applies to carbon emissions just as hard as it does to dollars so I have little excuse for not replacing it except laziness (and space on the breaker panel...)

Is it a fallacy though? It doesn't make sense to buy a new EV if you still have a gas car that's working fine. In the same vein, I wouldn't want to throw out my gas furnace or water heater to replace with electric, creating waste and requiring the manufacturing of a new unit

That only applies if you're only going to get less than 1 year of use out of a heat pump. A heat pump has an "embodied CO2" of 1.7t, which is about the same as the annual CO2 emissions of a gas furnace.

Can you explain how it's not a fallacy? Compare your lifetime emissions of replacing a gas car with an EV now versus at the "end of life" of the gas car. Emissions will always be lower if you replace now rather than later.

Imagine if everybody switched to EVs right now, en masse. Emissions over the next decade, and every subsequent decade, would be massively lower. Waiting for every gas car to reach end of life before switching is always going to be higher emissions, always.

Similarly, the "waste" already happened when the gas heater was manufactured. There's no additional waste when it's decommissioned. It's a sunk cost, there's no getting that back. The only question is if you switch to lower emissions now, or you switch to lower emissions later.

Now, if you bring money into it, sure, there could be a financial motivation to keep emitting higher amounts of emissions. But if you take monetary considerations out of it, it's always better to stop emitting sooner rather than later.

I'd love to have some serious push back against this. The best I've ever got is "that doesn't sound right..." without any engagement with the quantitation or the ideas. Which is exactly what I would expect if it was a fallacy.

You’re incorrect, buying a new EV when you have an ICE car doesn’t actually destroy the ICE vehicle.

There’s a bunch of different possibilities to consider, but if you drive more than the average person buying an EV and selling your ICE is great for the environment. If you rarely drive then keeping an old ICE car out of the hands of a frequent driver has real value etc.

As to the environmental impact vs retrofitting an ICE vehicle into an EV, the grid has gotten a lot cleaner over time so many of the old assumptions around EV’s are outdated. Comparing the emissions from extracting, transporting, refining, and then burning gas vs the same with EV’s built with a cleaner grid and more electrified infrastructure now heavy favors EV’s. And these calculations just keep favoring EV’s more every year.

If you want to DIY a solar PV water heater I made a whole website about it with instructions and a simulator to estimate what your payback period could be.

https://www.pvh2o.com/

Resistance heating is so 20th century. Granted, you likely cannot do a DIY air source heat pump build, but the COP is so high for such systems, that it's probably worth it to just buy it.

My mom had a Heat Pump water heater at her house and I was always having to go and fix it or clean the filter. It would start beeping loudly in the middle of the night when it wanted attention. The hot water was frequently not very hot.

Hopefully the new heat pump water heaters are better. The advantage of resistance heating is simplicity and cost, with no moving parts. Solar panels are so cheap now they make it hard to justify the expense of the heat pump, assuming you have room to mount the panels.

a COP of 4 can certainly justify having to install 3-4x less panels.

it disappoints me (but thrills me) that improvements in PV efficiency and cost have made solar thermal hot water more or less pointless.

I think you’re assuming when you switch to EV the ICE car disappears. But more likely it got traded to someone else who has less money, eventually making it possible for someone to own a car who otherwise wouldn’t have.

So the emissions stayed the same and you added the carbon embedded in the new EV.

What would that person have bought otherwise? Another ICE. If Person A kept the ICR there would be two people driving them instead of one ICE, one EV.

I do really appreciate shifting this from the "the consumer must make the right choice" to "what choices result in overall better outcomes" but we must do the full accounting.

> But if you take monetary considerations out of it, it's always better to stop emitting sooner rather than later.

No, it might or might not, depending on (a) the embodied emissions of creating the new product and (b) how soon it will be replaced by something even more efficient.

It's easiest to understand the importance of point (b) by going to extremes: Suppose that, every week, a new model of EV comes out that uses 99% as much energy as the previous year's model. If some nonzero proportion of electricity is generated from fossil fuels, then ignoring point (b) would imply that the rational thing to do would be to buy the new car each week, regardless of how much CO2 went into building it.

Heat pumps have COP of 4 when reaching temperatures needed for room heating. Hot water is way hotter than that. The more the difference between outside air and heated water, the less the COP becomes. I don't expect COP of 4 at 200 fahrenheit

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.

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...

• https://www.kaufland.de/product/502015379/?search_value=balk...

True, but you never need 200F for DHW. This is even dangerous (scalding) and harmful to the piping. Typical temperatures for heat pump derived DHW are around 120F (45-50C), with some (bi)weekly cycles to avoid legionella build up at 150F(65C). Your statement is generally true, because a heating installation that is optimized for heat pump works at 85-100F, however in practice not many installations in old buildings are like that.

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-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.

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.

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.

If your concern is storage you want as hot as possible, less boiling. Thermostatic mixing valves can bring the temp down to a safe temperature for use.

Losses are higher but you store more energy per L, which is often the limiting factor.

But you only need to store enough for a day or two. So you can alternatively just go bigger

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 )

not necessarily. if he bought your car and traded up from a real clunker with worse fuel efficiency the net result is likely better.

> So the emissions stayed the same and you added the carbon embedded in the new EV.

Well no, there will be a chain of people all upgrading their cars to better ones. The final car will drop off the bottom of the chain, so you trade an EV for what is likely to be the worst performing car environmentally.

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.

Is energy per liter often the limiting factor? Suppose a 70m² apartment with 3-meter ceilings costs US$3000 a month because it's in an expensive city center like San Francisco or Manhattan. That's still only 17¢/liter/year. Expanding your hot water storage space from 45 liters to 200 liters consumes space worth US$27 per year of your rent. Even that cost seems far too low to be a limiting factor, and the vast majority of people live somewhere much cheaper than that.

I think that what actually costs money is not the space but the tank. Higher temperatures mean not only more expensive materials and shorter lifetimes for tanks and piping but also higher conductive losses.

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.

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.

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.

> The final car will drop off the bottom of the chain

Maybe not. The $500 used car lot will take them, and some will get shipped off to third world countries.

And maybe the clunker was junked, orrrrr it was subsequently resold, or put on a ship to the global south and it’s clunkers the whole way down…

Not so great in areas with winter.

You should calculate the battery parts again. I'm currently installing mine in Germany and the cost parity is getting close.

As hot as possible is not the way to go. Heat pump COP will degrade dramatically if you try to boil the water. It is not even possible with the popular refrigerants (R32, R410a and even R143a), because they will exceed their critical temperature. If you cannot afford the space for a bigger DHW tank, then there are two options:

1. Consider PCM heat storage (still relatively new technology, but works well with heat pumps)

2. Maybe the problem shall be solved at the building level, not individual apartments.

Yes, but same logic can be applied to EVs.

Someone that that switches to EV today will pass that EV to a second owner down the line. The sooner the fleet starts switching to electric, the sooner the carbon emissions, primary energy needs, gas usage and particle emissions dive.

But now you're dealing with probabilities, weighed against the certainty of the original EV purchaser emitting less.

Try this: if everyone in the US suddenly purchased EVs, and ditched their ICE cars, flooding the market with old ICE vehicles, would emissions decrease in the world or increase? I think it's pretty clear that the vast majority of the old ICE vehicles would be junked, and there'd be marginally more vehicle-miles-travelled, so the huge wins of everyone using EVs would counteract any increase in vehicle miles from suddenly having cheaper ICE available around the world.

So I would argue that the single person doing that action would have the general same trend as if everyone did it.

Cars don’t last forever, and shipping junk cars from the US to the global south doesn’t make economic sense. Eventually there’s a bottom of the chain.

> But now you're dealing with probabilities, weighed against the certainty of the original EV purchaser emitting less.

Welcome to public policy.

> Try this:

No, I’ll stay in the real world. Your thought experiment isn’t possible, and extrapolating from it isn’t useful.

It does and they do. A used car is cheaper to source than a new one which means it can be sold to more consumers at higher margin.

Every taxi I rode in the Bahamas was a 2nd gen Jeep Grand Cherokee with the CEL on.

The bottom exists, but it’s not here.

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.

if it works in germany, czech republic, poland

which is higher latitude than 99.99999999% of USA or 80% of canada population

then it will work even in USA too.

Again read my first post, it is NOT about reaching 100% offgrid which is expensive, and nonsensical for most people

it is about reaching 100% offgrid for 80 % of time and 10-99% offgrid 20 % of time. Which is so cheap in europe that youre generating totally free energy after 6-7 years PV system paid for itself.

Interesting note: this is about six times cheaper per watt than residential solar systems in the US.

I don’t doubt used cars are shipped out of the US, but I’m pretty confident quite a few cars are junked in the US as well, as any junkyard demonstrates. I’d be pretty surprised to hear that junk cars (a subset of used cars) are shipped and resold.

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.

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.

> Maybe not. The $500 used car lot will take them, and some will get shipped off to third world countries.

If you're saying electric cars are pointless, and we should keep making ICE cars, because for a period of transition from ICE to EV some older ICE cars will go overseas, then I'm not sure there's much else to say. I disagree that that's good logic, I suppose.