Hacker News Board Hacker News, browsed like a classic message board
Live data from Hacker News

Think of your home as (small) profitable power plant

bostonglobe.com

Post reply on HN
Print view View original

51–60 of 74 posts

Re: Think of your home as (small) profitable power plant

#51

Post by brk »

I've done these calculations, particularly after putting an 11.6Kw solar array on our last house, which was in St. Petersburg, FL, one of the sunniest places in the US.

We sold the house after having the system for ~6.5 years, but we were tracking for a 9 year ROI. My cost was ~$23K out of pocket at the time, with power bills of $500-$800/mo., depending on time of year. I think our average daily consumption was 69Kwh, and the system produced the majority of that most days.

Assuming an average power bill of $600/mo., $23K would cover roughly 3 years of power bills. However, if the money was invested in a decent-ish portfolio, it would be earning some interest along the way, which could stretch what it covers to 5+ years. Anyway, when I did all the math, the solar panels never really made money, but what they did was smooth out our monthly expenses and gave some hedge against rate increases.

The new house is the same general area, and our use is about the same, but going to wait to see if solar takes a bigger decrease in cost before doing another array. It's mostly maintenance-free, but I did not output decline when the panels got dirty, and one panel died about 1 year after installation (and by then the installer company had gone out of business).

Re: Think of your home as (small) profitable power plant

#52

Post by midasuni »

ComputerGuru wrote: post #28

To me, the obvious reason why solar would be a gamble is that I have no guarantee I’ll be living here in the same home five years - let alone twenty - from now and I can’t take it with me when/if I move.

As a buyer I would value an existing solar/battery system, especially one with actual generation data, thus would pay more

Re: Think of your home as (small) profitable power plant

#53

Post by PaulKeeble »

midasuni wrote: post #43
PaulKeeble wrote: post #18

Solar and batteries pays off pretty quickly and can bring you to a net zero position on electrical needs fairly easily (excess sold in summer, importing in the winter). On an annual basis I now power half of another home in addition to my own. If I take the total expected output over 25 years my electricity cost is 1/4 of what it would be from the grid per KW/h. I went 6 months last year importing almost nothing from…

I’ve been wondering about just battery and inverter and using an agile tariff. How large an inverter did you get and what happens at full load (oven, kettle, electric shower and hairdryer all on at same time) which is presumably combined higher than the inverter?

My inverter is 3.6KW and can put out 4KW to the home. There is a normal limit for 3.6 in the UK for max export unless you do a more complex DNO99 application so that is the typical values. Above that you pull from the grid for the excess. I can run the oven (1.5KW) and kettle (2KW) but not a hair drier in addition. You change your behaviour a little with these solutions, you put the washing and dishwasher on when you have excess power or do them at night when it's cheap,you wait for the kettle to finish before hair drying. But the price isn't really driven by these rare combined events anyway, they don't matter in the grand scheme of things as most of your needs get met by the inverter and batteries.

Re: Think of your home as (small) profitable power plant

#54

Post by 1234letshaveatw »

bluescrn wrote: post #36
M95D wrote: post #5

I wish I had my own roof.

In the same position. There's very few 'green tech' options for apartment dwellers. It all has the prerequisite of owning a large and very expensive home. You need significant space for a solar(+battery) installation. Or for a heat pump. Charging an EV at home requires you to have a garage or driveway, and we all know that public chargers are going to do a massive bait+switch, hiking prices way up once companies runn…

A large and very expensive home or... A cheap and small one works as well.

A garage or driveway or... a dirt 2 track also does the trick.

No need to overstate things.

Re: Think of your home as (small) profitable power plant

#55

Post by ljf »

blagie wrote: post #49
ljf wrote: post #41

Earlier quoted context omitted.

Agree on some points here - in the UK I spend about £300 combined on gas and electricity. But your boiler sounds interesting - if it is 40 years old it will be wildly inefficient compared to boilers from the last few years - on changing our 10yo boiler we saved about £100 a month across the year - But I only expect that boiler to last 10 to 15 years - but that is OK, by then I'm sure I'll be moving to electric heatin…

I'm not quite sure how a boiler can be efficient or inefficient. It seems like for every watt of power going in, I get one watt of heat out. That's basic thermodynamics. If heat doesn't make it into the water, it still ultimately heats my house. Perhaps language issue? My boiler heats the water for my radiators which heat my house. That's not the same as my hot water tank, which heats running hot water. Here, where m…

Modern gas boilers can extract far more heat from burnt gas than older boilers. https://www.britishgas.co.uk/home-services/boilers-and-heati...

Older gas boilers (esp if 40yo) are likely to be less than 60 percent efficient, potentially far less.

Modern ones can be over 90% efficient - this was a big saving for me on my hot water and the gas power central heating radiators. With older boiler you lose a lot through the flue/exhaust, so it never gets to heat your house.

Re: Think of your home as (small) profitable power plant

#56

Post by friend_and_foe »

brk wrote: post #51

I've done these calculations, particularly after putting an 11.6Kw solar array on our last house, which was in St. Petersburg, FL, one of the sunniest places in the US. We sold the house after having the system for ~6.5 years, but we were tracking for a 9 year ROI. My cost was ~$23K out of pocket at the time, with power bills of $500-$800/mo., depending on time of year. I think our average daily consumption was 69Kwh…

I'm curious, it boggles my mind how people get energy bills that high. Do you pay 90¢ a kilowatt hour or something? What are you doing in your house to use that much electricity?

Re: Think of your home as (small) profitable power plant

#57

Post by Cthulhu_ »

PH95VuimJjqBqy wrote: post #39
hattmall wrote: post #16

75,000 in savings over 6 years is $12,500 a year, which means this person's utility bills were over $1000 a month!? I know that my house is wildly inefficient and $300-$400 a month is the worst it gets with extreme weather. Talking with friends and family my bills are higher than normal, most are around $200 and less in the milder months. A quick search shows $469 being average us Utility bills and that includes wate…

> I know that my house is wildly inefficient and $300-$400 a month is the worst it gets with extreme weather. I lived in a house for 4-5 years where it struggled to stay cool in the summer and the bills would get up to $300-$400 a month as well. One year I had an HVAC guy out to clean my unit and I was asking him questions (which I did every year) and this was the first guy to tell me when he generally sees issues li…

I know in my country (NL) modern houses are built to an energy efficiency standard, so that 15 odd year old houses like mine are pretty efficient and well-insulated; how is that in the US?

Over here if you have an older house you can get subsidies or attractive mortgage rates if you spend it on improving your house's energy efficiency, it's worthwhile looking for schemes like that.

Actually I should look into that myself; I don't need to improve insulation, but switching to electric heating and adding solar panels and a heat pump would be interesting, especially given we need air conditioning during the hottest periods nowadays.

Re: Think of your home as (small) profitable power plant

#58

Post by _m_benjamin »

M95D wrote: post #5

I wish I had my own roof.

I own my place but only the floor. I'm in a 2-unit condo, so I don't own the roof per se. That means if the guy upstairs has a toilet overflow, I get the downstream effects (that happened; not fun).

I wish I had a standalone home (floor to roof and all in between) - especially in an area where the retrofits from the article were possible. I've been 11 years in my current place and now I _really_ know what to look for next time.

I suppose it's like anything: once you've spent enough time to see how small cracks will widen; enough time to know what gutter configurations will cause; where the architecture might collect rain and cause flooding; where rodents can find ingress -- once you're pretty battle-worn, a new house shines different.

My wife is looking at places and because I've run maintenance, we look at things quite differently.

Re: Think of your home as (small) profitable power plant

#59

Post by blagie »

ljf wrote: post #55
blagie wrote: post #49

Earlier quoted context omitted.

I'm not quite sure how a boiler can be efficient or inefficient. It seems like for every watt of power going in, I get one watt of heat out. That's basic thermodynamics. If heat doesn't make it into the water, it still ultimately heats my house. Perhaps language issue? My boiler heats the water for my radiators which heat my house. That's not the same as my hot water tank, which heats running hot water. Here, where m…

Modern gas boilers can extract far more heat from burnt gas than older boilers. https://www.britishgas.co.uk/home-services/boilers-and-heati... Older gas boilers (esp if 40yo) are likely to be less than 60 percent efficient, potentially far less. Modern ones can be over 90% efficient - this was a big saving for me on my hot water and the gas power central heating radiators. With older boiler you lose a lot through th…

I see. That makes sense.

That actually seems like a very solvable problem with older boilers by adding something like a heat exchanger on the flue / exhaust. That should be a >90%.

Re: Think of your home as (small) profitable power plant

#60

Post by ljf »

blagie wrote: post #59
ljf wrote: post #55

Earlier quoted context omitted.

Modern gas boilers can extract far more heat from burnt gas than older boilers. https://www.britishgas.co.uk/home-services/boilers-and-heati... Older gas boilers (esp if 40yo) are likely to be less than 60 percent efficient, potentially far less. Modern ones can be over 90% efficient - this was a big saving for me on my hot water and the gas power central heating radiators. With older boiler you lose a lot through th…

I see. That makes sense. That actually seems like a very solvable problem with older boilers by adding something like a heat exchanger on the flue / exhaust. That should be a >90%.

Sounds like a great engineering challenge! I don't know a lot about boilers, but I do know that obstructing the flue in any way risks carbon monoxide poisoning - which may be the reason these things don't (yet?) exist.
Post reply on HN