3 ms·

The issue of consider the grid as a kind of battery is that IF you are paid for the energy you inject you are paid FAR LESS than the energy you grab with a so b

by kkfx 4y ago

The issue of consider the grid as a kind of battery is that IF you are paid for the energy you inject you are paid FAR LESS than the energy you grab with a so big delta that's far less than the "efficiency loss" of a battery... When I've made my actual p.v. (here, France, we are allowed to build p.v. systems as generic citizens because before connect any system you need a certification from a third party body) I choose 5kWp because I thought it's enough. Now I understand that to really maximize my self-consumption I need MUCH more peak power because I need to been able to run on p.v. anything at once as much as possible because sunny hours are not that long. It's the same for the actual heating (water-water heat pump) I have a small reservoir because the system is designed to run when I need heat. It should instead be designed to run full power but really MUCH in few hours per day etc. Now, I'm a sysadmin not a p.v. technician not working for anyone in the industry so I find curios that I personally realize that and no one who damn work for perhaps a decades in the industry do not realize the same... About resistive heating: yes it's far from being interesting but it is for a thing: it's extremely cheap and run in any external temp condition. air-water heat pumps do not, water-water (geo or from hot water reservoirs) heat pumps are still dependent on the "external side" temp. A small batch of resistence run by relais piloted via a cheap GPIO board in sequence following the maximum p.v. output possible it's a cheap way to maximize self-consumption. A heat pump can't vary much the compressor absorption witch means that if you need a big one to heat quickly a large mass of water you also need to power it. If you have few smaller you might fire up depending on the available power but it's hyper-costly... IMO having a big heat-pump for when the Sun shine well, a small one for when you can't run the big and you are on-grid/battery and resistive for the rest is the cheapest solution to use at best any kWh you can produce, no proof for that, just an idea, but so far that's the result of my limited experience...

mindslight 4y ago
> big delta that's far less than the "efficiency loss" of a battery I agree with you, I'm just trying to explain why I think there hasn't been much emphasis on optimizing usage with regards to solar. For the most part people do not want to be their own electric company. They want to offset their bill and feel good about creating some solar production. Those that do want to be their own electric company are called "off grid", and end up going down a rabbit hole of custom engineering time that doesn't translate to the larger consumer market. It's closer to farming and that type of ingenuity rather than standard suburban living. For resistive heating, you should also be able to continuously vary the power using a triac dimmer setup, although your solar inverter may be incompatible with this, or you may at least have to massively oversize it. But heat pumps that use variable frequency drives do exist. They're commonly called "inverters", at least in US marketing, and should allow you to vary the power the heat pump consumes. Maximizing self-consumption isn't as important as maximizing the efficiency of that consumption. If a heat pump has a COP of 3, you're better off with a single 1kW heat pump than a resistive array that can sink 1, 2, or 3kW. Add in some storage batteries that can handle the cycling of the heat pump and you can dither its power consumption in time rather than worrying about instantaneous usage. You said above that you've got a wood stove for backup. That's the way I'm leaning for now because heating with solar, heat pump, and battery storage in my climate seems impractical. If you're already doing water for heat storage, I'd recommend looking into setting up the wood stove so that it can heat the storage water, such that a single burn could perhaps give you enough boost for a few days.
- kkfx 4y ago
  > Those that do want to be their own electric company are called "off grid" That's also my point, perhaps not clear in my poor English and quick writing: I do not want to be totally off-grid simply because it's crazy in costs terms for a marginal outcome BUT I want to be "off-grid capable for a potentially long time" witch is again the better "cost optimization" IMO, I mean the sole reason to have a lithium storage is protect themselves from blackouts. Even with skyrocketed energy prices batteries still not pay back at all. So the cheapest individual options are: - just grid-connected p.v., you can lower the bill around 50% and the whole setup pay back at actual grid rate in a not so big number of years 5-10 maximum from a country to another. There is no protection against blackouts [1] - AC-coupled or hybrid inverters with a battery, smaller enough to nearly pay back mixing the blackout backups protection + the little maximization of self-consumption during the day and the little authorized discharge (10-15% DOD) per day Now just an year ago for most people in the western world protection against blackouts was simply too costly and essentially not needed. Blackouts war VERY rare and VERY short if any in an whole year, in few years. Nowadays for various reasons they start to be, at least they loom as an issue how seems getting bigger and bigger. Now running on a backup generator never pay back and have MANY issues, while a not so big battery, recharged by a small generator in few hours (when noise is not an issue etc) offer an expensive anti-blackout protection that probably do not pay back entirely but at least a bit and as for the resistive heating I call it "the best compromise" we can get now. Yes, I got an wood stove (two actually, one potentially hydro even if I never made the plumbing and not even knowing what I really need to add precisely) and I have woods, and a bit of bush on my own, but that's meant for pleasure (seeing the flames sometimes in the evening) and real damn emergency usage. On a regular basis it's not much comfortable to use them, I do not have even enough wood for an entire whole winter... Something I can buy that can work automatically most of the time, enough to pay back a bit is far more welcomed... My reasoning is that I already have p.v. and a small storage (8kWh) as a backup protection for freezers/fridges/VMC/computer/... It's expensive but lower my bill and it already protect me well, even if that happen only three times for few hours and a bit more for just few/less then a minute. It might help to lower the opex of a future EV since I WFH and so I tend to be at home during most days of the week the best I can do to maximize the ROI is using as much energy as I can, of course for something useful, not just to waist it... For instance for AcS I find better when I can (most of the year) heat it with it's built-in resistence instead of the heat-pump because it make the equipment last far longer and I can't use anyway the producible energy. If I decide in the end to expand the hot water storage also for heating well... Calculation are a bit complex and unfortunately that seems not a popular choice so even technicians I can find do not help much... Surely I'll integrate the wood stove, of course, it should be relatively easy and cheap and potentially really useful, but for the rest I do not know... I found very few "big enough" air-water heat-pumps not so expensive, but can't really know how well they can run in winter despite they formal claims. [1] very few inverters/microinverters declare to been able to produce AC from p.v. without the grid or a battery BUT they can't sustain essentially any peak load, witch means you need special equipment that mount/lower their power consumption slowly and can survive a sudden energy drop if just a cloud pass by.

by kkfx 4y ago

mindslight 4y ago

> big delta that's far less than the "efficiency loss" of a battery I agree with you, I'm just trying to explain why I think there hasn't been much emphasis on optimizing usage with regards to solar. For the most part people do not want to be their own electric company. They want to offset their bill and feel good about creating some solar production. Those that do want to be their own electric company are called "off grid", and end up going down a rabbit hole of custom engineering time that doesn't translate to the larger consumer market. It's closer to farming and that type of ingenuity rather than standard suburban living. For resistive heating, you should also be able to continuously vary the power using a triac dimmer setup, although your solar inverter may be incompatible with this, or you may at least have to massively oversize it. But heat pumps that use variable frequency drives do exist. They're commonly called "inverters", at least in US marketing, and should allow you to vary the power the heat pump consumes. Maximizing self-consumption isn't as important as maximizing the efficiency of that consumption. If a heat pump has a COP of 3, you're better off with a single 1kW heat pump than a resistive array that can sink 1, 2, or 3kW. Add in some storage batteries that can handle the cycling of the heat pump and you can dither its power consumption in time rather than worrying about instantaneous usage. You said above that you've got a wood stove for backup. That's the way I'm leaning for now because heating with solar, heat pump, and battery storage in my climate seems impractical. If you're already doing water for heat storage, I'd recommend looking into setting up the wood stove so that it can heat the storage water, such that a single burn could perhaps give you enough boost for a few days.

kkfx 4y ago
> Those that do want to be their own electric company are called "off grid" That's also my point, perhaps not clear in my poor English and quick writing: I do not want to be totally off-grid simply because it's crazy in costs terms for a marginal outcome BUT I want to be "off-grid capable for a potentially long time" witch is again the better "cost optimization" IMO, I mean the sole reason to have a lithium storage is protect themselves from blackouts. Even with skyrocketed energy prices batteries still not pay back at all. So the cheapest individual options are: - just grid-connected p.v., you can lower the bill around 50% and the whole setup pay back at actual grid rate in a not so big number of years 5-10 maximum from a country to another. There is no protection against blackouts [1] - AC-coupled or hybrid inverters with a battery, smaller enough to nearly pay back mixing the blackout backups protection + the little maximization of self-consumption during the day and the little authorized discharge (10-15% DOD) per day Now just an year ago for most people in the western world protection against blackouts was simply too costly and essentially not needed. Blackouts war VERY rare and VERY short if any in an whole year, in few years. Nowadays for various reasons they start to be, at least they loom as an issue how seems getting bigger and bigger. Now running on a backup generator never pay back and have MANY issues, while a not so big battery, recharged by a small generator in few hours (when noise is not an issue etc) offer an expensive anti-blackout protection that probably do not pay back entirely but at least a bit and as for the resistive heating I call it "the best compromise" we can get now. Yes, I got an wood stove (two actually, one potentially hydro even if I never made the plumbing and not even knowing what I really need to add precisely) and I have woods, and a bit of bush on my own, but that's meant for pleasure (seeing the flames sometimes in the evening) and real damn emergency usage. On a regular basis it's not much comfortable to use them, I do not have even enough wood for an entire whole winter... Something I can buy that can work automatically most of the time, enough to pay back a bit is far more welcomed... My reasoning is that I already have p.v. and a small storage (8kWh) as a backup protection for freezers/fridges/VMC/computer/... It's expensive but lower my bill and it already protect me well, even if that happen only three times for few hours and a bit more for just few/less then a minute. It might help to lower the opex of a future EV since I WFH and so I tend to be at home during most days of the week the best I can do to maximize the ROI is using as much energy as I can, of course for something useful, not just to waist it... For instance for AcS I find better when I can (most of the year) heat it with it's built-in resistence instead of the heat-pump because it make the equipment last far longer and I can't use anyway the producible energy. If I decide in the end to expand the hot water storage also for heating well... Calculation are a bit complex and unfortunately that seems not a popular choice so even technicians I can find do not help much... Surely I'll integrate the wood stove, of course, it should be relatively easy and cheap and potentially really useful, but for the rest I do not know... I found very few "big enough" air-water heat-pumps not so expensive, but can't really know how well they can run in winter despite they formal claims. [1] very few inverters/microinverters declare to been able to produce AC from p.v. without the grid or a battery BUT they can't sustain essentially any peak load, witch means you need special equipment that mount/lower their power consumption slowly and can survive a sudden energy drop if just a cloud pass by.