Comment on How I Installed DIY Solar Power and Started Running My House on Batteries
captain_aggravated@sh.itjust.works 4 days agoI know more about electronics than finance.
What I would do is take a more holistic approach to your home’s power system, with solar panels as one very useful tool in a well-stocked tool belt, that also includes:
- A time-of-use power plan from your energy company.
- A whole house battery
- A smart or programmable thermostat
- A few outlet timers
- An electric car charger with timer or some similar solution
I am currently on a standard rate power plan, I pay 14 cents a kilowatt-hour no matter the time of day. My power company offers a time-of-use plan that varies between 29 , 11 and 7 cents per kilowatt hour depending on the time of day. The game becomes, buy as little power as possible during the 3 hours it’s 29 cents, and as much as possible during the 5 hours while it’s 7 cents.
This might mean doing laundry and dishes at 1 in the morning, setting a timer to charge your EV at 1 in the morning, setting a thermostat to turn air conditioning off between the hours of 6 and 9, that sort of stuff. A battery system can store energy when it’s cheap for later use when it’s expensive. Solar power is then a further reduction in the amount of power you buy; in my area depending on time of year the solar producing parts of the day are either in mid- or discount-price times, so the bulk of your savings are coming from discounts and time shifting. They’d likely be more valuable during extended power failures than day to day power savings, as you’re unlikely to generate a dollar per day.
partial_accumen@lemmy.world 3 days ago
I know a decent amount about electronics, finance, and home solar.
Regional differences change the “best case” behavior drastically. For example, in my Midwestern state (with a still pitiful solar install base statewide), your list would be nearly the exact wrong ideal behavior. My state is about 10 years behind the leading states as far as solar installs and policy. So think back to California rules 10-15 years ago and that’s a pretty good idea what rules apply in my state which is quite an upside for solar home owners.
This would be a bad thing in my state. This would mean you would get paid the lowest amount of per KWh at the best time of production.
Bad choice financially in my state. We have 1:1 net metering so the grid is the most cost efficient battery. I do have 10KWh of solar battery storage, but I don’t charge/discharge it daily and really have it for backup needs in case of a grid outage. Nothing about buying the battery is a good idea financially though in my state.
Not as useful on a heat pump where you want to generally run the same temp 24/7/365 to give the heat pump the most time to extra energy from the outside air and avoid large temperature swings triggering power hungry electric strip backup heating. A programmable thermostat is still useful for the occasional vacation hold though.
Not needed if not using TOU.
Generally not needed when not using TOU. Additionally, many EVs themselves have the timer built in so no need to have a timer on the EVSE. Full disclosure, I do charge EVs from midnight to 4AM because I have a separate meter from my electric company with a tariff that is “distribution fee”-free for every KWh for EV charging. This stacks with my 1:1 net metering, so I essentially get paid to charge EVs at night.
I have no doubt you’ve chosen a good path for your state and electric company. You’ve put a lot of thought into optimizing it. My post is just highlighting that the rule to optimize against vary widely by region even in the same national borders.
Do you have a non-exporting solar system? If not what price to get per KWh during the various times of the day with your TOU power plan?
captain_aggravated@sh.itjust.works 3 days ago
I don’t currently have a large scale system; I’m currently running my fridge and a few other things off of a portable solar/battery setup, as part of researching a whole home system. I’m on a standard rate plan, I pay 14c/kWh round the clock.
The ToU price and schedule for my region looks like this:
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Peak is ~29c/kWh, Off-Peak is ~11c/kWh, Discount is ~7c/kWh. So I could save money if I just switched to the ToU plan and threw my main breaker 3 hours a day.
My local energy company’s exporting solar program is bad and about to get worse, to the point it’s out of the question. I’m not going to sell them power at mid-day for 3c/kWh and buy it back at damn near 30 at night. So the only real winning strategy here is the “ToU + battery time shift” and since the equipment needed to do that almost certainly has plugs for solar power, might as well put up some panels. Buying power at 7c/kWh in the early morning, generating your own power and not buying anything during the day while power is 11c/kWh, and then using the power you bought earlier when it costs 29c/kWh is the move.
This isn’t congruent with my understanding of how heat pumps work. Electric strips are going to kick on in extreme cold if/when the heat pump can’t keep up, or for defrosting the outdoor unit. Every heat pump I’ve used, unless they frost up, will happily heat a house to 80 degrees from 32 without kicking on the emergency heat until and unless it needs to defrost. I’ve never personally seen one kick on heat strips simply for increased Delta-T, not without manually putting it in EM-HEAT mode.
I don’t currently own a heat pump, I have an air conditioner and a condensing furnace. My long term plan is to have the air conditioner replaced with a heat pump, and keep the furnace for emergency heat instead of strips. I recently learned that in North Carolina, if a given heat pump system is calculated to keep the home up to a certain temperature on the typical coldest night in the county, backup heat is not legally required. Defrost will be achieved by running the unit in AC mode, so you’ll occasionally get a blast of cold air from the vents.
Neither my air conditioner nor my furnace run 24/7/365, both are duty cycle modulated, they turn on and off throughout the day and night to maintain temperature. Here in late September I actually have the system switched entirely off and my windows are open, because it’s a comfy 65F outside tonight. Spring and fall are comfortable enough that I just don’t run HVAC for 4 months a year.
partial_accumen@lemmy.world 3 days ago
I had already done the research I needed and was ready to put in a larger house-attached grid-tied system slightly before the current generation of portable battery/panel setup came out. For your situation, I agree you are taking the right approach.
Can I ask if the 14c/KWh is the rate you pay for generation only or the whole cost to deliver 1 KWh to your house (transmission,distriubtion,generation,customer connection plus fees). Put another way, if you consumed 1000KWh in a month would you have exactly a $140 electric bill?
Ouch, so even on the fixed rate power plan you essentially 4.67:1 net export (as in you have to export 4 KWh at midday to import 1 KWh any other time of day)?
Yep, in your state, I agree TOU+battery is likely the best way to go limiting import as much as possible.
For modern heat pumps your experience is mostly still applicable. The exception is the “comfort” settings most vendor thermostats incorporate. If a temperature increase is indicated by the operator above a certain set point, the system interprets this as a call for rapid heating and will run the condenser at 100% but also kick on electric strips to reach the called for temperature much sooner.
When we bought this house it had natural gas furnace too. Not only was the gas expensive, but during the warmer months the minimum require “connection fee” continued to get hit with price increases even when zero gas was consumed. When we finally replace the heat pump the connection fee was $40/month. My neighbors tell me its risen to $70/month now and none of that money goes toward consumed gas.
I considered a dual fuel setup like that, but the economics of the connection fee negated any value. I’ll be the first to say that my January and February electricity bills are very high, but all of the saving from not having natural gas, and being able to heat with solar generated heat pump in the spring and fall very much still make it financially worth it for this setup.
I can run my heat pump in AC Defrost mode too, but the **Wife Acceptance Factor ** goes way down doing that so we run electric strips for the defrost cycle.
Perhaps I wasn’t clear. I wasn’t suggesting my heat pump is running 24/7/365, quite the opposite. Rather, the thermostat is set to a single temperature and, unlike gas heating, there is no value in lowering the thermostat temperature at night or when the house is unoccupied. The opposite exists, when running a heat pump reducing the thermostat temp at night means the heat pump has to run harder and longer in the morning when you want the house back up to temperature. Its less efficient because the limiting factor is the volume of air that can be moved through the outdoor condenser to extract heat from. If the option to save energy is having the house uncomfortably cold for hours everyday, I consider that a failure of an HVAC design. This is, of course, just my opinion though.
I’m three states north of you and we’ve been running on our Cold Climate Heat pump for two winters now without any gas heating. This unit can still extract heat for the house when the outside temperature is -15°F, but its running pretty inefficiently.
captain_aggravated@sh.itjust.works 3 days ago
The price per kWh is set at 12.623c/kWh, which they then adjust up and down a few hundredths of a cent via “rider” for fuel costs, it tends to hover around 14c/kWh in my experience. To this is added a $14 monthly Basic Customer Charge, and then state sales tax.
So in a month where I consume exactly 1000kWh, the bill would be ($0.14c/kWh*1000kWh + $14)*1.07 = 164.78.
Something I just now learned reading documentation kinda buried on the website, during the winter months, even on a standard rate plan, it’s 12.623c for the first 800 kWh, and then 11.623c for each additional kWh. I’m guessing to go easier on folks with electric heat? I’ve never come close to 800kWh…I may have to look back.
They don’t allow you to grid tie solar panels on a fixed rate power plan. If you attach solar panels to the grid you HAVE to be on a ToU plan, and that deal is actually getting worse on New Year’s Day for those who plan to export power. I’m honestly struggling to understand some details about that, most literature about it starts saying “The bridge rate is being grandfathered out” and stuff like that without explaining what it’s talking about, so if you’re a newcomer to the discussion, fuck off back to kindergarten, child.
Yeah we’re definitely designing HVAC against different climates. Down here, we never see temps as low as -15F. I don’t think I’ve ever seen 0F. Heat pumps struggle more to keep up in the summer here, mine has failed to keep the house at 75 a few times every year I’ve lived here, and there’s no such thing as strips to help out.
I’m not getting rid of gas without a whole house system capable of running a heat pump for at least a day, for power outage reasons. We’ll have winter storms that’ll take down the lines, and then I’m heating my house with a Glo-Warm, since it requires no power, and the gas system around here…I’ve seen it fail once, because someone didn’t call 811 before renting a backhoe.