I live in Germany, where these plug-in systems (Balkonkraftwerk -- or 'balcony power plant') are cheap and very popular, and where -- at about $0.45 per kWh -- electricity is more expensive than in any market in the USA. Earlier this year we upgraded our 800W system by an additional 4 x 500W panels plus two batteries with a total of 5.76kWh storage, all of which cost €2000 /~$2300 delivered, no tax! On a sunny day, we're already generating 12kWh of solar energy: as of March (when we installed the new system) we've generated over 604 kWh, or about $270 worth of electricity! Since we haven't even hit the summer solstice yet, it's not unreasonable to assume we'll more than double that amount before winter, so the system will ostensibly pay for itself in less than 4 years. Here, most people rent their domiciles (house or apartment); while the law says you have to inform your landlord and register your devices, the landlord cannot deny you permission to install the system.
We now have 6 panels (2x400W, 4x500W) all plugged into the same microinverter. It's only allowed to feed up to 800W into the house (we have it set for less, actually, so the batteries have something to discharge when the sun goes down), which is why the batteries are so important for the peak times. But it's just one system that feeds via a normal electric plug on the balcony into the house... The microinverter/main battery unit also has 2 AC sockets on the back, so we can even plug something power-hungry like a mobile air condititioner directly into it, bypassing the 800W limit. We'll try that when it gets hot. :-) So far, we've managed to keep the loss (feed-in to the city electric) to a minimum, about 2.5kWh/day. But next week we're getting the smart meter installed.
I live in northern California, where peak demand rates are $0.41. Our 10-panel, 2,800w rooftop system installed in 2016 wasn't generating enough power for the heat pump & EV we purchased in 2023. I recently installed a 4-panel, 1,600w +3.8kWh battery BrightSaver system that is now eliminating any peak demand charges as well as most of the new off-peak load. The inverter failed after 1 month, and BrightSaver sent me a replacement.
I wonder how many people are looking to get in on this general idea as a business? My guess is... a LOT. Here in Albuquerque a company called Pii Energy is developing a product which is apparently also a value add to the EcoFlow STREAM Ultra, but for residential.
My latest discovery is the Anker Solix F3000. This is a typical power station (solar charge controllers/battery/inverter all-in-one) and they sell accessories to allow bidirectional current flow and power monitoring to prevent back-feeding to the grid. It does require a little work inside the electrical panel.
I'm up to about 10 kW in DIY solar projects, so I guess I'll need a house. My NE facing apartment isn't going to cut it.
I think the Bi-directional inlet box is meant to be wired directly to a circuit breaker, but this creator put a plug on it and wired a dedicated circuit to plug it in. He links to the "Power Saver Kit", which includes one Bi-directional inlet box, but supports another one, which you can buy separately. I think it's a pretty good video. Comments indicate he may have made a mistake in identifying line 1 and line 2 of split phase inside the panel. I think I'd go with a 20A circuit for something that can provide up to 1800 watts.
These products typically have good UPS functionality, and that might what you're looking for with your fridge. You have to sacrifice some resilience to do arbitrage. But if you can count on some solar, you can keep a fridge running with a pretty modest battery.
David's use of the word "arbitrage" seemed a tiny bit off to me, so I asked my friend ChatG, and their response follows. In summary, IMO "energy arbitrage" more precisely captures "charging when rates are low, and using/exporing when rates are high" than plain "arbitrage". Temporal arbitrage is also good, but as we all know, energy is power over time, so for this application, energy arbitrage is best, becuase energy captures both the temporal notion and obviously we are dealing with energy.
Classical arbitrage means exploiting a price difference with essentially no market risk. You buy and sell the same (or equivalent) asset simultaneously in different markets.
Examples:
* Buy gold in one market for $3,300 and simultaneously sell it in another for $3,305.
* Buy electricity in one wholesale market and simultaneously sell it in another connected market at a higher price.
This is the classic “buy low, sell high” where the profit is effectively locked in.
By contrast, charge when electricity is cheap and use it when expensive is usually called:
* Temporal arbitrage (the most common term in the energy industry)
* Energy arbitrage
* Storage arbitrage
Here you’re buying electricity at one point in time and using (or selling) it at another. There is some risk:
* Future prices may not end up as expected.
* Batteries have round-trip efficiency losses (typically 85–95%).
* Battery degradation has a cost.
For example:
* Charge a battery overnight at $0.08/kWh.
* Discharge during a peak period when electricity costs $0.40/kWh.
Even after accounting for efficiency losses and battery wear, this can produce economic value. In the energy industry, this is widely referred to as energy arbitrage, even though it isn’t “risk-free arbitrage” in the strict financial sense.
Similarly, buy low, sell high is a broader concept:
* If you buy a stock today hoping it rises next month, that’s speculation or investing, not arbitrage, because the future price is uncertain.
* If you simultaneously buy and sell equivalent assets to lock in a guaranteed profit, that’s arbitrage.
So, in short:
* Charge when cheap, use/sell when expensive: commonly called energy (or temporal) arbitrage.
* Buy low, sell high later: usually investing or speculation unless the profit is effectively locked in.
* Buy low and simultaneously sell high in another market: classical arbitrage.
Few resi customers in my region are on rates with demand charges, but TOU rates are growing. Especially for households with on-site EV charging. I’ve been searching for such a solution that can charge during off-peak and discharge during peak rate hours.
Is it fair to say this is a demand-charge arbitrage play aspiring to a decarbonization mission? Do the economics hold once enough storage erodes the spreads the business is built on?
I thought this was a great discussion. My impression is that a lot of people still think about "power generation" as something that must be effected on the Industrial Revolution model: ship in raw materials (natural gas, coal), create a product (electrons), then ship that product out to customers (via transmission and distribution lines). This conversation points out that using the Industrial Revolution production model for electrons is nuts. I love the work of Lorenzo Kristov and LF Energy, who envision local energy production everywhere. Local production reduces reliance on T&D systems for household consumers, increases regional resiliency, and frees grids from the gridlock they presently experience.
Interesting discussion! Plug-in DERs have potential, but the real revolution hinges on how well we integrate them into existing infrastructure and policy. It's not just about the tech; we need a cultural shift in how we think about energy consumption and grid resilience.
Is it permissible to do this in a sub metered “commercial” system? We are in a small cohousing community and have been told by the utility that we can’t have solar on buildings not on the parcel where the main service is. (In Mass.)
I live in Germany, where these plug-in systems (Balkonkraftwerk -- or 'balcony power plant') are cheap and very popular, and where -- at about $0.45 per kWh -- electricity is more expensive than in any market in the USA. Earlier this year we upgraded our 800W system by an additional 4 x 500W panels plus two batteries with a total of 5.76kWh storage, all of which cost €2000 /~$2300 delivered, no tax! On a sunny day, we're already generating 12kWh of solar energy: as of March (when we installed the new system) we've generated over 604 kWh, or about $270 worth of electricity! Since we haven't even hit the summer solstice yet, it's not unreasonable to assume we'll more than double that amount before winter, so the system will ostensibly pay for itself in less than 4 years. Here, most people rent their domiciles (house or apartment); while the law says you have to inform your landlord and register your devices, the landlord cannot deny you permission to install the system.
How did you get to install way more than the 800W system? Does it work like 5 different 800W systems?
We now have 6 panels (2x400W, 4x500W) all plugged into the same microinverter. It's only allowed to feed up to 800W into the house (we have it set for less, actually, so the batteries have something to discharge when the sun goes down), which is why the batteries are so important for the peak times. But it's just one system that feeds via a normal electric plug on the balcony into the house... The microinverter/main battery unit also has 2 AC sockets on the back, so we can even plug something power-hungry like a mobile air condititioner directly into it, bypassing the 800W limit. We'll try that when it gets hot. :-) So far, we've managed to keep the loss (feed-in to the city electric) to a minimum, about 2.5kWh/day. But next week we're getting the smart meter installed.
Understood — thank you for the detailed explanation!
I live in northern California, where peak demand rates are $0.41. Our 10-panel, 2,800w rooftop system installed in 2016 wasn't generating enough power for the heat pump & EV we purchased in 2023. I recently installed a 4-panel, 1,600w +3.8kWh battery BrightSaver system that is now eliminating any peak demand charges as well as most of the new off-peak load. The inverter failed after 1 month, and BrightSaver sent me a replacement.
I wonder how many people are looking to get in on this general idea as a business? My guess is... a LOT. Here in Albuquerque a company called Pii Energy is developing a product which is apparently also a value add to the EcoFlow STREAM Ultra, but for residential.
My latest discovery is the Anker Solix F3000. This is a typical power station (solar charge controllers/battery/inverter all-in-one) and they sell accessories to allow bidirectional current flow and power monitoring to prevent back-feeding to the grid. It does require a little work inside the electrical panel.
I'm up to about 10 kW in DIY solar projects, so I guess I'll need a house. My NE facing apartment isn't going to cut it.
I'll need to look into those as well.
What's the accessory called?
My dream setup would be a battery that takes solar that I plug a refrigerator into that I can also plug into a wall outlet.
Then I get some resilience if power goes out and the ability to arbitrage electricity for TOU rates.
Take a look at this video: https://youtu.be/lTHb5wWA44M?si=fbI_TvEVx3JTaXlG
I think the Bi-directional inlet box is meant to be wired directly to a circuit breaker, but this creator put a plug on it and wired a dedicated circuit to plug it in. He links to the "Power Saver Kit", which includes one Bi-directional inlet box, but supports another one, which you can buy separately. I think it's a pretty good video. Comments indicate he may have made a mistake in identifying line 1 and line 2 of split phase inside the panel. I think I'd go with a 20A circuit for something that can provide up to 1800 watts.
These products typically have good UPS functionality, and that might what you're looking for with your fridge. You have to sacrifice some resilience to do arbitrage. But if you can count on some solar, you can keep a fridge running with a pretty modest battery.
David's use of the word "arbitrage" seemed a tiny bit off to me, so I asked my friend ChatG, and their response follows. In summary, IMO "energy arbitrage" more precisely captures "charging when rates are low, and using/exporing when rates are high" than plain "arbitrage". Temporal arbitrage is also good, but as we all know, energy is power over time, so for this application, energy arbitrage is best, becuase energy captures both the temporal notion and obviously we are dealing with energy.
Classical arbitrage means exploiting a price difference with essentially no market risk. You buy and sell the same (or equivalent) asset simultaneously in different markets.
Examples:
* Buy gold in one market for $3,300 and simultaneously sell it in another for $3,305.
* Buy electricity in one wholesale market and simultaneously sell it in another connected market at a higher price.
This is the classic “buy low, sell high” where the profit is effectively locked in.
By contrast, charge when electricity is cheap and use it when expensive is usually called:
* Temporal arbitrage (the most common term in the energy industry)
* Energy arbitrage
* Storage arbitrage
Here you’re buying electricity at one point in time and using (or selling) it at another. There is some risk:
* Future prices may not end up as expected.
* Batteries have round-trip efficiency losses (typically 85–95%).
* Battery degradation has a cost.
For example:
* Charge a battery overnight at $0.08/kWh.
* Discharge during a peak period when electricity costs $0.40/kWh.
Even after accounting for efficiency losses and battery wear, this can produce economic value. In the energy industry, this is widely referred to as energy arbitrage, even though it isn’t “risk-free arbitrage” in the strict financial sense.
Similarly, buy low, sell high is a broader concept:
* If you buy a stock today hoping it rises next month, that’s speculation or investing, not arbitrage, because the future price is uncertain.
* If you simultaneously buy and sell equivalent assets to lock in a guaranteed profit, that’s arbitrage.
So, in short:
* Charge when cheap, use/sell when expensive: commonly called energy (or temporal) arbitrage.
* Buy low, sell high later: usually investing or speculation unless the profit is effectively locked in.
* Buy low and simultaneously sell high in another market: classical arbitrage.
Few resi customers in my region are on rates with demand charges, but TOU rates are growing. Especially for households with on-site EV charging. I’ve been searching for such a solution that can charge during off-peak and discharge during peak rate hours.
Is it fair to say this is a demand-charge arbitrage play aspiring to a decarbonization mission? Do the economics hold once enough storage erodes the spreads the business is built on?
I thought this was a great discussion. My impression is that a lot of people still think about "power generation" as something that must be effected on the Industrial Revolution model: ship in raw materials (natural gas, coal), create a product (electrons), then ship that product out to customers (via transmission and distribution lines). This conversation points out that using the Industrial Revolution production model for electrons is nuts. I love the work of Lorenzo Kristov and LF Energy, who envision local energy production everywhere. Local production reduces reliance on T&D systems for household consumers, increases regional resiliency, and frees grids from the gridlock they presently experience.
Interesting discussion! Plug-in DERs have potential, but the real revolution hinges on how well we integrate them into existing infrastructure and policy. It's not just about the tech; we need a cultural shift in how we think about energy consumption and grid resilience.
Revolution at all levels is needed if we will survive.
Is it permissible to do this in a sub metered “commercial” system? We are in a small cohousing community and have been told by the utility that we can’t have solar on buildings not on the parcel where the main service is. (In Mass.)