David Baillie

Donna Lynn wrote:We bought an electric side by side utility vehicle as a prep for when gas becomes unavailable or just too dang expensive (which looms precariously closer....)  It plugs into a 110 outlet to charge, so I'd be recharging it during peak solar hours.  Or doing laundry, running a canner on an electric burner, vacuuming, using power tools, recharging the electric mower and chain saw, running the freeze dryer or dehydrator, baking stuff in the electric oven, using the infrared sauna, and so on.  

Although an actual solar sink to hold power would be something more along the lines of pumping water into a high tank or uphill pond to release later as needed to run a hydroelectric unit.  Or the compressed air others mentioned.  We bought undamaged Tesla car batteries from wrecked cars to store power, but they only hold so much, just like any other batteries.  So they can cover us for a cloudy day or two, but that's about it.  

hi donna, what is the model of the electric side by side?

John Weiland wrote:Thanks, David!   Can you tell me why this is not done routinely for LiFePO4 batteries?  Granted, a bluetooth version would be able to give you an estimate based on the battery management system display, but wouldn't one want to be able to 'real-world' test that capacity.  And even if the discharge curve for Li is flatter than that for legacy lead-acid tech, if one was detecting a 'fully discharged' status well before the amp-hour rating on the battery, this would indicate where power deficiencies may be located.  Finally, it seems from some videos out there that comparing LiFePO4 battery specs often involves validating the advertised Ah rating and so this often is done, albeit with shop electrical control units that appear more expensive and sophisticated than I wanted to deal with. Thanks for insights here....

John Weiland wrote:Thanks, David!   Can you tell me why this is not done routinely for LiFePO4 batteries?  Granted, a bluetooth version would be able to give you an estimate based on the battery management system display, but wouldn't one want to be able to 'real-world' test that capacity.  And even if the discharge curve for Li is flatter than that for legacy lead-acid tech, if one was detecting a 'fully discharged' status well before the amp-hour rating on the battery, this would indicate where power deficiencies may be located.  Finally, it seems from some videos out there that comparing LiFePO4 battery specs often involves validating the advertised Ah rating and so this often is done, albeit with shop electrical control units that appear more expensive and sophisticated than I wanted to deal with. Thanks for insights here....

Mart totally wins for geek wizardry! His own monitoring! If I want to test a lithium it depends in the quality of the inverter and the batteries. Those drop in replacements that dont need comms to inverter you would have to charge until it does not take charge, apply a known load and discharge till it shuts down; i dont like that. If its a solark, lux or eg4 ( rebadged lux) and a battery that does two way comms you have a state of charge meter and an app so its way easier. I can apply a known charge to it add in the system running load and watch the percentage go down. If it matches spec you are golden as it ages I would expect it to drop more rapidly. The batteries im installing today are less than 2 years and so far no change over about 12 systems. Here is a screen shot of the lux app: the website version is better. Eg4 and solark have similar ones. The cheaper  inverters not so great I dont install them as its too much call backs and confusing menus. There are other good ones of course.

John Weiland wrote:For those that use battery storage for home power generation or even powered small electric vehicles or appliances, do you check the capacity of your batteries annually or every few years?  I have a battery load tester to examine general battery health, but for deep cycle batteries that are rated in amp-hours, how to you test for how far off of the original "100%" that your battery capacity has declined?  General internet searches have revealed some rather sophisticated devices for which load, discharge rate, etc. can be programmed, but I was wondering if I was missing something that would be more low tech, but still give a duration measurement on when the battery was depleted.  Thoughts?  Thanks!.....

John, for larger lead acid deep cycle banks i used to apply a c5 to c10 load on the inverter and hold for 15-30 minutes with all inputs and other house loads off. I usually used space heaters. The speed at which the voltage dropped would give me an approximation of ability. You start fully charged with a good absorb cycle and repeat after say a year and see where they are in comparison. Its pretty time consuming and to have someone do it expensive so its kind of gone the way of the dodo bird. Add to that the switch to lithium and its a dying art. Ill still perform a test if someone asks me to evaluate a house they are buying or figuring out if they are going to make the winter.
Cheers, David

Mikael Korhonen wrote:Seeing your actual consumption data like this is really the foundation - Steve's right that it's what you do with the data that counts. Here in Finland we've taken it one step further by shifting heavy loads like water heating to the cheapest hours of the day, guided by the hourly price forecast. I plan tomorrow's loads each evening using this Sähkön hintaennuste page, and it's made a real dent in our electricity bills.

I've fallen off monitoring and posting after that first winter. The system works well in someways better that at first. We added an Ecobee Thermostat which automatically changed from heat pump to electric auxilliary based on outside temperature and time of day.
I looked at the site and its really interesting. What does a kWHr actually cost you once its delivered? Very few people in Ontario adjust consumption day to day as we do not pay spot prices.  We have various plans we can choose from either low, medium, high depending on time of day, fixed price per kwHR anytime, or ultra low night time and ultra peak rate. Its only adjusted yearly and honestly the rates we pay are low by world standard. I do adjust based on time of use somewhat. I'll turn on the electric boiler radiant floor at night to store low price electricity in the slab.
cheers,  David

Paul Grace wrote:

David Baillie wrote:On our worst day duty cycles was about 33percent.

David, thank you for the detailed conditions. Your written figures give a useful illustration: if the 1.2-1.35 kW running input and 33% duty cycle refer to the same measurement period, that works out to roughly 0.40-0.45 kWh per elapsed hour for that running load. That is quite different from budgeting the full running input for every hour. I would not extend that average to a whole night without the corresponding nighttime reading.

Does your heat-pump energy measurement include the indoor air handler/blower as well as the outdoor unit? That boundary would help when translating it into a battery budget. Your note that the winter totals exclude some supplemental resistance heating is also important: those totals cannot represent the house's complete heating electricity use.

The insulation and latitude context makes this useful, even though it is a larger house than a cabin. I would keep it as a well-described individual case rather than scale it to cabins by floor area alone.

That is a great point a out the air handler. In my case it adds 90watt hr per hour of runtime. I took a look at the site Paul. The company I used to work for had a detailed spreadsheet for calculating usage and peak watts. We would walk them through their load profile, build a model and custom design for them. It took time and we would charge for it. The pace has accelerated around solar since then. These days my clients seem much less interested in modelling and more in maximizing what we can deliver based on their budget. The site would be useful to them. I would like to see a much more populated library of loads though.
Cheers, David

Mikael Korhonen wrote:No AC here in Finland, so I can't add measured numbers, but one thing I'd stress for sizing is inverter overhead. Mine idles around 40W, so an all-night cooling run quietly tacks on another 0.3-0.4kWh that people often forget to budget.

Also, duty cycle matters more than rated watts. A small cabin AC mostly sips once the space is already cold, so pre-cooling during afternoon solar hours genuinely shrinks the nighttime battery number. If you're collecting real data, a cheap plug-in energy meter over a full week tells you more than any calculator.

That is such a great point Mikael; using the mass of your home  as a battery extension by over cooling your space in the high sun hours makes a significant difference.

Paul,
We heat and cool 2640 sq ft or 242 Sq M of very well insulated house at latitude 44.5 degrees using a heat pump central system. I am attaching three screenshots showing a yearly total, an hourly summary on a very hot July day (it was a record busting hot summer for us) and an instantaneous shoulder season heating scenario. The system uses a 2.5 tonne heat pump which when active consumes between 1.2 and 1.35 kWHrs per hour if it was running all the time. On our worst day duty cycles was about 33percent.  For the instantaneous reading shot I cranked the heating temp of the house up to 23 degrees with an outside temp of 13 The house is currently at 21 and I would not usually do that. That does not quite  duplicate what we see as a differential in summer time but its the best I can generate.  Average set point for daytime summer is 23, nighttime 21, winter average is 21 day 19 night. Heat pump heating totals in winter are not accurate since we use some radiant electric at nighttime on nights colder than -15C. Trying to peg down exact efficiency is a near impossible science as energy modelling of this house proved to be extremely inaccurate. Its an ICF build with triple pane windows and extra slab foam so did not fit well into the software so it outperforms. Hope some of this interests you and does not divert from the original question.
Cheers,  David

Which solarcalc do you maintain? There is an app, and a .net . Are they the same?
These days I am usually using the tonnage rating as a wattage determination and assigning it a duty cycle based on perceived insulation of the dwelling. We dont worry as much about it here due to our much longer summer solar hours creating a glut for off grid locations which is perfect for AC. Most people are doing heat pumps here so the fun part become trying to figure out how much they can use it during the shoulder seasons.  I do very little net metering mostly off grid.

thomas rubino wrote:I have been looking for some metal to finish the roof on the new battery shack.
Our boy removed some 100-year-old copper sheet from a demolition job in Butte a few years ago.
I thought that it might look pretty good as a roof.
When I asked for it, he couldn't remember where it was...
Seems someone noticed it in a pile outside his shed... apparently they needed it more than he did...

Several years ago, a fellow artist had given Liz some large sheets of new copper, remnants purchased from Boeing aircraft.
She had big plans for a while but ultimately did not use them. They have been sitting wrapped up in one of the outbuildings, waiting.
Yesterday, the waiting was over.  She reminded me that she had these and announced that she was not going to use them...
I was welcome to see if they might work as a roof for my battery shack project.

Holy cow, Batman!  It's like I ordered three perfectly sized sheets of copper!
I literally only had to trim one of the three pieces to have a perfect, flawless copper roof!
I ran out of roofing screws, but I had enough to get it in place,
I think it looks outstanding!
If I ordered this size copper sheet today, it would cost over $100!!!   SCORE!

Beautiful work Thomas. One thing you must absolutely understand about the onboard heaters. They ONLY work when there is a positive input into the battery whether from solar, a generator or the grid. This is consistent across every battery I has researched and installed. Lithium can discharge down to -20 C but can only charge above 5 to 7 degrees celcius. So when the solar comes back out you can waste precious winter sun at 300 watts as the internal heater brings the temp up to 5 degrees before it allows the full array power to come up. I've been installing a digital thermostat and a 200 watt heater in my boxes to keep it warm. When you stop and think about it it makes sense why the internal heater does not heat the battery with nothing coming in as it would discharge it down to zero.  
Cheers,  David