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Hello, I’ve been lurking and reading a lot from all these posts. I’m finally getting quotes from different companies around my area. I live in Southwest Florida and My yard is very sunny with no shade trees. I also have a large yard 2 1/2 acres and I am looking to do a ground mount system. The run from the system to my home is about 220 feet. My average monthly usage is 1,108 KWh. We are also in the process of installing a pool with a variable speed pump and an electric heater. I keep getting conflicting numbers for how many kilowatt hours to add to my system for the electric heater. I keep hearing the number 2000 kWh but is that monthly or yearly? I’ve also been advised to maybe complement my solar panel system with a solar heater to help with heating the pool rather than putting all the burden on the electric heater or build a larger array to help with energy consumption. The other factor that seems to vary greatly is the cost difference between companies. I’ve received quotes from $36,000 all the way up to $99,000. My biggest concern is what system size should I really be looking for? I want to make sure that I am not under the threshold I need to be at. I’ve had quotes for 9.4kw system, 11.4kw, 15.8kw and 11.6kw. All these builds would be using enphase is microinverters. Can anyone help with some guidance?
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Last edited by bnd063011; 04-12-2022, 10:49 AM. -
even though PV systems have multiple aspects you can simplify pricing comparison by converting total amount by total DC label power or AC microinverters sum. When you wrote 9.4KW most likely it meant nominal DC rating of selected solar panels. It is the common pricing model in the industry, even though it is not totally reflective of value to a consumer.
It is possible to model electricity consumption by your pool heater but since you are already in process of installing it you might be better off waiting until installation is completed and using actual readings. Temperature adjustments for colder months are relatively simple. Heater uses energy to bridge ambient temperature and target temperature. If consumption reading is for 10F delta it would be twice more if delta is 20F.
keep in mind that many electric utility companies do not allow installation of a system with expected electricity production exceeding prior history of consumption. If consumption level is expected to go up because of pool heater, EVs and so on, you might have to wait until it is reflected in several months bills. These rules vary greatly from state to state and I do not know FL rules.
A typical PV estimate gives rather accurate electricity production estimates for the next 25 years. You use your goals (highest economic efficiency, highest possible coverage of electricity consumption by solar and so on) to select a proposal that matches them as close as possible. Unfortunately you would need to wildly guess your future electric consumption (EVs adoption rates are wildcard) and expected electricity rates (very volatile lately). Also you need to estimate ability of solar installation company to stay in business for many years and their quality of service. One remarkable example is Tesla. Their prices are very low but service is almost non existent.
For EVs electricity consumption rough estimate you can multiple 0.25 by expected annual mileage, 0.25 * 10000 = 2500 KWh.
Economics efficiency of PV system goes down with size. Many times state incentives apply to smaller systems. If the goal is to have shortest payback time you would stay on the smaller size.
Theoretically increasing PV system size with microinverters is relatively simply by increasing number of branches. Enphase IQs have 13-16 max number of units in each branch. In reality extending existing system by outside installers might be difficult to arrange since companies would need to figure out what is already in place and utilities considering any change to the system requiring the same paperwork and fees as a totally new system. -
Thanks for your response! What i am most questioning is between 3-4 companies the prices vary greatly, the finances varies greatly, the estimated kWh production varies. Even tho the panels are relatively identical. Some are 440w panels and the others are 365w panels. Trying to make sense of all these quotes and what they offer is challenging because I’m still trying to grasp the differences in systems they’re building for me.Comment
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PV panels industry figured out a simple trick of increasing size of a panel with proportional increase in nominal rating. Most likely 365W panels are 60 cell (6 by 10) and 440W are 72 (6 by 12). This means that larger panel will produce roughly 20% power but also has 20% more footprint. Since panel power is higher it requires microinverter with higher limit. In the past 72 cell panels were mostly used in commercial installations but it changed in the last 5 years.
Since all of your proposals use microinverters it should be doable to compare them. Cost of PV system consists of panels, inverters/microinverters, permits, fees, racking, electrical supplies (wiring, conduits, combiner panels, cutoff switches and so on), monitoring controller (Envoy in case of Enphase), sealants for bracket attachment to the roof, labor, sales and profit margin. Most likely the last 3 vary the most from company to company. Somewhat unexpectedly some PV installation companies spend 25% of their budget on sales force.
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Specific to your pool heating situation: First, get an idea of what the pool heat load will be, noting that the loss will be more that through temperature difference between the air and the water, but a usually significant evaporative loss as well. Second, get a pool cover and use it. That'll kill a lot of the evaporative loss. third, get a solar thermal flat plate heater. Compared to PV, solar thermal pool heaters are close to dirt cheap and also DIY friendly.
1st approx. on pool heater array size is about half to 2/3 the pool surface area. Likely best slope for winter pool heating is about latitude + 15.
It'll be much cheaper up front per unit surface area than PV and, because solar thermal pool heaters are something like ~ 50+ % efficient at turning sunlight into electricity whereas PV panels are less that 20 % efficient, a lot smaller than a PV system that produces the same amount of energy to heat the water. So, a lot less $$ per area and about 2 1/2 more energy collected for that same area = less 44 and a smaller surface area for the same effect.
That's an example of why heating water with electricity when other methods are available, and especially for heating pool water is analogous to cutting butter with a chain saw. The more entropy is increased, the more expensive it gets. Get more for your energy $ by using an energy source that a loser entropy match to the desired result.Comment
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Having owned solar pool water heaters, one big note is that a solar pool water heater bladder will probably last you 1/2 to 1/3 the time that panels would last. Solar pool water heaters generally begin with small patch leaks after about 3 years, and by about year 10-12, you have more patches than good material. That's about when you have to consider replacing it. You also have to calculate the added electricity for a larger pool pump to lift the water 15 or so feet above the ground (maybe 30 on a two story). While you might think you don't need it year round, you still have to push water through it every few weeks to keep it clean and malleable. If you don't, you'll get a cess pool smell from your pool when you need to turn it on again.Comment
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With respect to flat plate pool heater, the term bladder is one I'm unfamiliar with.
Are you referring to the type of pool water heating collectors such as those marketed by FAFCO and others ?
If so, I too have owned and designed 3 flat plate pool heating systems over the last 40+years. I never had and odor or fouling problem, but I kept a pretty sharp eye on the water chemistry. The 2 back in Buffalo got drained in the winter and never had fouling or odor problems. The designs were such that they could be filled with a garden hose and so the pump size didn't need to consider elevation head - just added friction head from the heater and while it's not something that's well known, most pool pumps have more than enough excess grunt to handle the added friction and flow head. The pool heater in CA has run from 1997 and, although I no longer own it, it's still functional. That one was a DIY project with the HOA I lived in at the time.
In Albuquerque I had a motorized cover that was tight and dark brown. It served as a cover and also a pool heater that kept the water at 85 F or higher 10 months of the year with uncovered nocturnal cooling in the summer. Best pool heater I ever designed. I thought it was pretty elegant, but it was in an almost ideal solar climate even if it was cold(er) than SO. CA in the winter.
I've not done a LCOE analysis on a pool heater and I suppose I could, and maybe I'm wrong in this opinion, but if for no other reason than the enormous heat load a pool takes, and the disparity between the per unit area output of a PV system relative to the per unit area output of a reasonably well designed solar thermal flat plate pool heating system, my money's on the thermal pool heater for cost effectiveness. And, even though it's no more than an anecdotal opinion (like yours seems to be) I'm also pretty sure that well designed and maintained thermal pool heaters have a long service life free of leaks and fouling.Comment
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I’m debating leaving the pool solar heater out of my project for now. For 2 reasons mainly. 1. I still want to see real numbers with the PV panels and see how well we can run them pool and home included. And 2. I hate the idea of drilling into my roof. Maybe later down the road I’ll build a pergola style roof or aluminum style roof on the pool deck and install solar heating up there in the future if needed.
I was going over my quotes and the cheapest one comes from EnergyPal. Most of all these companies use the same installer it seems like (Urban Solar) in my area. Any who, EnergyPal is quoting me $35,672 for a 9.24kW system using 21 Aptos DNA 144-440W panels, enphase iQ8 microinverter, ground mount system. Financed through Sunnova for 25 years @ 0.99% interest. My average monthly usage NOW is 1,108kWh per utility company and EnergyPal is projecting my average annual at 12,500 based on a 12 month reading. EnergyPal is claiming these panels will produce 14,816kWh based on my area (Naples, FL). EnergyPal is claiming this size system should be able to handle my home and electric pool heater just fine and still turn out 119% energy offset. I’m still trying to understand how they get to these numbers but does this sound accurate to anyone? It seems TOO good to be true. All the other companies are offering me 11kW, 14kW and 16kW systems based on my home and future pool use. Any guidance from experienced members here? How much smoke are they blowing up my a**?
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Just panels and geographical location are not enough to estimate electricity production. You need orientation, pitch and shading (if any). I assume that ground mounting will allow ideal Southern orientation and spacing allows optimal angle. We cannot verify their calculations but most installation companies have written policy in the contact with guaranteed level of production. I do not think you should be skeptical of their estimates.
Price, $4 per Watt sounds high but since it is ground mounting a lot depends on how it is done. I am more familiar with pricing for roof mounting. Mounting has to handle wind strength required by your municipality. Mine had 105 mph requirement 5 years ago but changed to 120.
IQ8s are still a novelty and substantially more expensive than previous generation.Comment
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My biggest concern is under producing with this size system and the electric pool heater. Granted I won’t be using the heater all the time. But I have no idea how many kW to add to make the PV system run both pool and home with next to no energy consumption from Florida power and light.Comment
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With the price of 6061 aluminum plus concrete work, my ground mounts
cost more than the panels on them. I consider it a good investment. A
treated wood mount is cheap and works, but probably will not last as
long at the panels. Bruce RoeComment
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Does anyone know what the maximum length of a run from an array is? My property is long and skinny (hehe) 660’ deep. I was wondering about installing it in the back of the property. (approx. 400-450’) from the panel on the side of the house. I’ve heard that you can lose efficiency/watts if it’s too long. Is there any truth to this?
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Potentially you can use Alu wiring for a long run but I do not know if NEC code allows use of Alu wiring for DC.
The answer to the original question is that longer run will require thicker wire to control voltage drop caused by wire resistance. Twice thicker wire has 4 times lower resistance (roughly) so replacing commonly used for branch 10AWG wire with 1/0 is equivalent to reducing length 4 times. Unfortunately thicker Cu wiring is rather pricey. i think Bruce Roe is using remotely located PV system so his comment might be helpful.
One possible option is to run AC to remote location and place inverter by the array. If you are using microinverters running AC is the only option and will require doing Enphase calculations for allowed voltage drop. This calculation will drive wire sizing.Last edited by Will792; 04-15-2022, 11:00 AM.Comment
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My stuff on 5 acres is similar to your layout issues. You should plan rather
carefully just how much power loss in each section of the system, how big
the wire needs to be. Use ohms law and wire resistance tables.
Here loops of 10 gauge copper varying but up to 400 feet long, connect
individual strings of panels to a combiner box. Then each of 2 independant
systems feeds a 6 gauge copper pair through about a 500 foot loop to the
inverters. Operating at 400VDC, losses are around 1%.
My inverters in a shed, must feed a 600 foot loop, 60A at 250VAC (15KW) to
the house meter, for this net metering system. Initially the existing 4 gauge
copper was used. At 1/4 milli ohm per foot, a resistance of 150 milli ohms
conducting 60A produces 9V drop, times 60A is 540 watts lost to heating
that wire, or approaching 4%. Eventually 4/0 aluminum wire was burried,
to bring those losses under 1%. Remember 4/0 aluminum has about the
same resistance as 2/0 copper, but the larger equivalent aluminum is
WAY cheaper than the copper. Some aim for numbers like 2% loss, I
invested to do better.
You will find similar numbers for your ground array, figure them out before
you build. One thing that will become obvious, the more of the runs done
at high voltage DC panel voltage instead of lower voltage AC, the better
your losses/wiring cost tradeoff will be. Here I think a string inverter will
do best, optimizers will lower voltage and increase loss, micro inverters
will easily be the worst. good luck, Bruce RoeComment
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