Get a big battery

[Zwy]

Going on day 3 of no sun and no real PV yield. My battery is 54Kwh. First day with heat pump on we used 32% of the bank, yesterday used 28% ( I did see some charging for about 10 minutes) and this morning I just left the house and down to 31% but sky is brighter today. Official Loads Tester did one load in the washer this morning. Heat pump has been running the whole time heating the house. Pretty windy, sustained winds around 20 mph and above. I did turn the heat down slightly yesterday, no one was in the house all day except me for lunch.

I can't stress the importance of a larger bank. I think it is money well spent in most cases. Sun should shine tomorrow and I'll get as much as my array can put out. I doubt I'll get back to 100% SOC in two days but never know. We have 8480W of PV. My opinion is oversize on the battery bank, I like the 6 to 1 ratio of bank to panels. We are not in the house much during the day but do schedule laundry and dishwasher during the day. If we hit 100% SOC and it is sunny the next day I usually see battery charged back to 100% by noon. I actually could use more battery simply because I don't have much for dump loads and I'm not capturing that PV yield in the afternoon. I did size system according what I thought would be necessary for winter.

I'm currently weighing installing a system in my shop, that will be more power draw during the day and might make more sense to have a smaller battery to PV ratio. But I will still need a decent sized bank for several cloudy days in a row unless I decide to use some grid input.

What ratio of PV to battery bank size are you currently running?

 

[OffGridForGood]

I like the 6 to 1 ratio of bank to panels.

What ratio of PV to battery bank size are you currently running?

9.68 PV to 68.6 ESS = 7:1

Edit: 3.3kW PV and 15.5kWh cells on current order = 6.4:1 soon...

 

[Solarcabin Channel]

Sounds like my weather!

I recommend a propane heater and OD water heater for backups.

Just a 30# tank will run those for a week when you have low sunshine and your family won't freeze and can have hot water.

 

[Adam De Lay]

Same weather here. Lots of rain. I need to double both battery storage and PV.

 

[OffGridForGood]

R 32 walls, R 71 Attic insulation, tight building envelope.
Wood heat (with it's own combustion air supply) furnace.
I took out the Propane a number of years ago. too expensive per btu.
We have only made a small fire three times so far this fall, for three cold nights.
Only 21kWh yesterday, periods of rain and heavy overcast again today, sun in the forecast for tomorrow, ESS is sitting at 52% and November is still ahead...

 

[WolfbaneAries]

16kw.pv to 45kwh... 2.8:1.

Last winter I was at 4.6kw pv and 30kwh, so closer to 7:1 and I had to run the generator a little every day to keep things going.

My thought was that more than tripling the pv and adding 50% to the battery bank would allow me to get through the winter without needing to start the generator... however I'm thinking that I might a larger bank for those long stretches of grey weather we get here in the PNW, especially after seeing the size some of the banks people have around the forum.

So far the system hasn't gotten tested to the limit but considering I was pulling in 800w while it was raining a couple days ago I think that's a good sign.

I too have an Official Load Tester and she really likes her electric clothes dryer ? However for heat I built a hydronic system using an on-demand propane water heater as a heat source. My dream would be to switch to a heat pump and get away from the propane, but we'll see.

 

[JJT211]

Is it possible to expand your Solar array?

 

[HalfBaked]

What ratio of PV to battery bank size are you currently running?

5:1, but only charging at .1C due to 3 separate arrays at different angles and directions to maximize production on a single 150v/60a SCC. Room for improvement with another SCC, but will wait until the need dictates.

 

[OffGridForGood]

I'm thinking that I might a larger bank for those long stretches of grey weather

me too!

I too have an Official Load Tester and she really likes her electric clothes dryer ?

LOL yeah, I hear YA! two days of rain/cloud is clearly the BEST time to run the electric Dryer...NOT!

especially after seeing the size some of the banks people have around the forum.

+1 yeah - were talking about You @timselectric

My dream would be to switch to a heat pump and get away from the propane, but we'll see.

I took out the propane (or is it Pro-Pain?) a while back. I am committed to a ducted heatpump Sensville and will see what it can do in the shoulder months (spring/fall) and it will provide the bit of A/C we need in July/August. Summers keep getting hotter it seems.

My current plan is to keep building new DIY battery packs to 115kWh capacity, and expand the PV to 19kW, but this (like all our solar set up) will be done in stages, and looking like 2025 to hit those target capacities on PV and ESS. The EV is a great 'dump load' for summer, with the excess PV capacity. Next one will need to be V2L and will allow increase in the ESS without building more packs, ideally 200kWh+ total with an EV.
Oh look at that: the sun just showed up unexpectedly, maybe my OLT and ESS will not have a war today afterall!

 

[Shimmy]

6:1 on a system sized for net-zero is good, but I would rather have 6:1.5 to 6:2 (50-100% over-paneled for net-zero).

 

[Zwy]

16kw.pv to 45kwh... 2.8:1.

Last winter I was at 4.6kw pv and 30kwh, so closer to 7:1 and I had to run the generator a little every day to keep things going.

My thought was that more than tripling the pv and adding 50% to the battery bank would allow me to get through the winter without needing to start the generator... however I'm thinking that I might a larger bank for those long stretches of grey weather we get here in the PNW, especially after seeing the size some of the banks people have around the forum.

So far the system hasn't gotten tested to the limit but considering I was pulling in 800w while it was raining a couple days ago I think that's a good sign.

I too have an Official Load Tester and she really likes her electric clothes dryer ? However for heat I built a hydronic system using an on-demand propane water heater as a heat source. My dream would be to switch to a heat pump and get away from the propane, but we'll see.

I have high efficiency propane furnace, turned it on for a few minutes this morning to make sure it still works.

I will need it when it does get cold in January. The idea is to burn off excess PV power to heat the house. Last spring I used a pair of resistive heaters and would go thru 50Kwh per day on sunny days. Did not burn much propane in the spring. Heat pump is way more efficient, I see my furnace blower takes 300W to run, about the same running the heat pump but with COP above 3 I'm using that electricity more efficiently but certainly not getting the same BTU's.

I had 26 ash trees to cut down, some over 4 feet in diameter. I'm trying to decide what to do will all the wood. Nobody wants it because the Emerald Ash Borer is killing every ash tree in the area. Tree cutters are just hauling the ash away to a compost site. I might use it for heat in the dead of winter for quite a few years. Loads Tester rolls her eyes when I mention heating with wood.

I think in the end you will find a larger battery with the ratio closer to 6:1 works much better. Sun did shine for a few minutes before it became dark and cloudy again but I did gain 5% on my bank while running all the loads. I think it might be done until late in the day. I need 10% of battery bank capacity overnight.

 

[Zwy]

Is it possible to expand your Solar array?

Doesn't help if the sun never shines. Wednesday was a total of 0W came in. Dark, rainy.

I'm glad I have the battery bank I have, might even need to make it bigger for those dreary stretches of 3 to 4 days of no production.

 

[Zwy]

R 32 walls, R 71 Attic insulation, tight building envelope.
Wood heat (with it's own combustion air supply) furnace.
I took out the Propane a number of years ago. too expensive per btu.
We have only made a small fire three times so far this fall, for three cold nights.
Only 21kWh yesterday, periods of rain and heavy overcast again today, sun in the forecast for tomorrow, ESS is sitting at 52% and November is still ahead...

I'd run a heat pump this time of year and save the wood for when you need those BTU's. Wood supply lasts longer and so does the furnace.

Heating with wood isn't cheap, it still carries a cost. I grew up in a house completely heated by wood. Spent many days working with a buzz saw on a tractor. I have access to all the wood I want but I prepay on propane after summer fill and can actually make it thru on the 800 gallons for the house sitting in the tanks. Propane goes over $2/gallon, I'll think of switching. It's one thing to have to cut trees down and in the process gain a wood supply, quite another to go and cut it just for the purpose of heating with wood.

 

[Zwy]

5:1, but only charging at .1C due to 3 separate arrays at different angles and directions to maximize production on a single 150v/60a SCC. Room for improvement with another SCC, but will wait until the need dictates.

I'm of the camp that arrays should, if possible, be pointed directly at the sun at high noon. Sometimes that isn't possible due to shading or other issues but I think it's better to have a large battery bank and catch as much energy as possible when the sun is most powerful even if it takes more SCC's. Another 150V/60A SCC would put you up to 18Kw charging capability.

 

[Zwy]

Same weather here. Lots of rain. I need to double both battery storage and PV.

Last few days have been no sun but plenty of dark clouds and rain. I don't see the need for more PV on this system, I can recharge daily most days by noon. Battery? Yes, for the extended stretches of poor sun.

If I had a garage attached to the house, I could park the golf cart in it and run some cable to pull off that battery. Like some do with an EV. I wouldn't need the extra capacity in summer and the cart sits all winter anyway.

 

[HalfBaked]

I'm of the camp that arrays should, if possible, be pointed directly at the sun at high noon. Sometimes that isn't possible due to shading or other issues but I think it's better to have a large battery bank and catch as much energy as possible when the sun is most powerful even if it takes more SCC's. Another 150V/60A SCC would put you up to 18Kw charging capability.

While I do agree, and will do what is needed, I'm a bit of a paranoid hermit and like the disparate arrays because they have a smaller visual overhead appearance. The 2 arrays that point directly towards East and West are nearly vertical and live beneath large trees, therefore invisible from above.

 

[Shimmy]

Last few days have been no sun but plenty of dark clouds and rain. I don't see the need for more PV on this system, I can recharge daily most days by noon. Battery? Yes, for the extended stretches of poor sun.

If I had a garage attached to the house, I could park the golf cart in it and run some cable to pull off that battery. Like some do with an EV. I wouldn't need the extra capacity in summer and the cart sits all winter anyway.

It really comes down to your local weather; my worst day ever was 5kWh (0.05 percentile roughly) on an 8.3kW array. While 10kWh from doubling the PV won't run my house (30-35kWh average), it limits depth of discharge a bit and makes me well capable of easily covering the 2nd percentile days of <15kWh.

I have a lot of data from my system; I wonder if I can actually evaluate the "optimal" solution for my location...

 

[Solarcabin Channel]

I'd run a heat pump this time of year and save the wood for when you need those BTU's. Wood supply lasts longer and so does the furnace.

Heating with wood isn't cheap, it still carries a cost. I grew up in a house completely heated by wood. Spent many days working with a buzz saw on a tractor. I have access to all the wood I want but I prepay on propane after summer fill and can actually make it thru on the 800 gallons for the house sitting in the tanks. Propane goes over $2/gallon, I'll think of switching. It's one thing to have to cut trees down and in the process gain a wood supply, quite another to go and cut it just for the purpose of heating with wood.

Yep, I love wood stoves and used them for a long time but I don't have close access to wood now and buying it cut is not cheap and when you consider you need a truck to haul it, chainsaws, gas oil and a good strong back it is a lot of work. Then you have to clean the chimney and at 60 years old I can't get on a roof or split wood like I used to.

Propane is also a multi-use fuel and is considered a green fuel because no one drills for propane and it is a biproduct of gas and oil drilling that would have to be flared off if not used. It also burns very clean and 99.8% efficient in new appliances.

 

[G00SE]

Phase 1: 5.9kw panels 31kwh bank. (5:1)
Phase 2 next year: 11.1kw panels 80kwh bank. (7:1)

No clue if it’ll be enough, if not I guess we will keep playing Legos and expanding.

 

[ksmithaz1]

The problem with panels to battery is somewhat complex: Can your panels fill your batteries, and cover a load for a day? Will it be able to do the same for enough batteries for 3 days? 4 days? What is the longest stretch you will have without sun?

IMNSHO In a weak solar area your panel output:storage ratio is likely going need to approach 1:1, and your storage:backup time ratio is going need to be 1:[max no PV days in a row]. The former because you really need to fill your batteries maximally whenever you have PV. Thus the key is likely to be average daily usage vs days with no sunshine. Here in Phoenix I've had ZERO "NoPV" days, but some definite "LowPV" days. I think panels are cheap and fairly easy to deal with if you have a place to mount them, but also the biggest challenge to implement. Adding 200KWH of batteries to 8KW of solar that produces maybe 30-40KWH/day on a "normal" day is not going to help much. By building out your panels first you create a charging infrastructure, then you just add battery as you move closer to parity.

I have 18KW of panels, I have produced as much as 115-120KWH of output in a single day, though presently it's closer to 95. I have 30KWH of batteries, this gave out this morning at 0530, and I switched over to the grid until about 0800 when the sun charged things back up and the inverters turned back on. I obviously need more batteries.

To that end on a 'normal' weekday, the current 30KW pack is charges 100% by 1215, so I should be able to get near 100% to 60KWH of storage by end of sun. However, on the weekends my energy usage skyrockets. I'm usually charging a car and doing laundry, to the point where I often times cannot even charge the 30KWH pack. This means I'm likely to run out of battery reserve at night on the weekends, and I will have no way of replenishing until Monday.

Demand is a b*tch.

I'm going to build an outbuilding, and I'll be covering it with panels as well. There is a diminishing return (to the point of the exercise), because my demand curves are not really going to change, I just need to have enough battery to last through the night, and enough solar to get them charged during the highest daily demand. It is extremely unlikely I will ever have a Z day, so I'll probably be OK with just some extra panels when all is said and done, but I have had a 40-45KWH day. I'd create a spreadsheet / database, and start tracking solar output and daily usage to get a better feel for your area. I started tracking (some) usage last fall, so I'm just approaching a full year's worth of some data. As the year has passed I have increased the number of sensors and I'm now polling my inverters at regular (30sec) intervals.

Also remember Mr Murphey. Hit's me regularly, I had a partly sunny day, the two clouds that happened to be in Phoenix were directly over my house all day tracking the sun. I was home, decided to charge my car. Oops, didn't notice until like 1400. I got about 50KWH total that day, started the evening with a 50% charge. My buddy about 45min north with about the same capacity had a nice 85KWH day. You just never know, and THAT is the problem with any kind of Solar/Wind stuff.