New to solar, Massachusetts

lasitter
lasitter Solar Expert Posts: 56 ✭✭
OK, so I'm a noob and not from Arizona, but I'll stick my nose in here anyway for a question or two.

Of course I'd appreciate any and all links to FAQs or particularly informative stickies, but I do have some specific areas where I know that I'm in need of education.

All my life I've wanted to try renewable energy, and now that I'm having to move from Rhode Island to Massachusetts (wife's new job) I think I have my chance.

I don't confess to understanding all the credits and rebates, but it seems that there are strong incentives for installing up to a 15kw solar system.

It's really easy to understand the concept of using solar as it's being generated or that of putting excess energy on the grid and in exchange getting even more credits. What I hadn't thought much on until today was whether it might make sense to store generated solar energy in batteries and then pull that energy back out of the batteries when it's dark.

So one of the first big questions I have is how many big batteries do you have to get and of what rating to push big inverters to supply xxx watts for so many hours.

So taking your typical home and applying whatever scenarios you would like, what do you see as a number of years break even point to string together up to four MS4124PAEs, panels, routers some Big Reds, etc., etc., and maximizing life off the grid?

I'm also looking at how all the other pieces of the energy puzzle go together. I originally thought of having a natural gas generator only for backup power, then I realized that running a big generator to power a light bulb might be kind of expensive.

So then I had the idea about getting big batteries that a generator could charge, and running everything off the inverters, thereby generating low duty cycle requirements for the generator.

But if you get really big batteries and a big solar array, maybe the generator itself becomes a "just in case" item.

Just in case there's a storm that knocks out power and covers the panels in frozen precipitation.

But what if you have "Autonomous Winter Solar Panel" which can melt snow (???).

Does this stuff actually work or is it all hokum?

It sure sounds great.

Comments

  • Cariboocoot
    Cariboocoot Banned Posts: 17,615 ✭✭✭
    Re: New to solar, Massachusetts

    Welcome to the forum.

    "whether it might make sense to store generated solar energy in batteries and then pull that energy back out of the batteries when it's dark."

    No, it doesn't.

    A direct grid-tie system is far less costly and far more efficient than any battery-based (off-grid) system. With off-grid you're looking at a difference of 2X the cost per kW hour for production (incentives aside) and about 25% less efficiency for production vs. grid-tie.

    How expensive per kW hour is grid power there? I bet it's not around $1, which is what it will cost to produce power with batteries. What's more those batteries need ongoing maintenance and periodic replacement.

    In terms of equipment grid-tie is PV + inverter where as a battery-based system is PV + charge controller + batteries + inverter.

    For back-up power a generator is nearly always a cheaper means.
  • lasitter
    lasitter Solar Expert Posts: 56 ✭✭
    Re: New to solar, Massachusetts
    "whether it might make sense to store generated solar energy in batteries and then pull that energy back out of the batteries when it's dark."

    No, it doesn't.
    Running some numbers here makes this sound like sage advice.

    kWh here is 14-15 cents.

    Natural gas spiked near $25 mcf back in August of '08, but now it's about $16 mcf. I'll use that number for my worst case scenario that follows.

    2011 Halloween nor'easter

    Three years ago some people near where I'm heading claim to have gone without grid power for two weeks. It was epic for these parts. Here in Pawtucket, Rhode Island, we were only without power for 24 hours, but that was a record for my experience in over 20 years here.

    Looking at a Kohler 20Resal, it consumes 127 cfh at 25 percent load and 281 at full load.

    That looks like a range of cost for a 14 day outage of $27 per day to $108 at full load. For two weeks that would be $378 to $1,512.

    For an event that happened once in 20 years, that makes it pretty easy to see that $8,000 in inverters and another $1,000 to $2,000 in batteries (plus other equipment) might not pay off.

    So how do you figure what it costs to store a kWh in batteries best suited for the task? The cost of putting solar panel energy into the batteries is either near zero, or the opportunity cost of what you would have realized in credits putting that same energy on the grid, isn't it?

    The inverter cost is really about getting a certain amount of energy back at a certain rate, isn't it? If you assume that you really wouldn't draw more than eight kWh continuous, that could be handled with just two inverters.

    It occurs to me that a key advantage of the batteries is redundancy and peace of mind. If the generator unexpectedly fails, and one would expect that failure to occur during an extended outage, the batteries could continue to supply power while waiting for mains power to return.

    And about keeping the solar array clear: 40' long broom?

    TIA
  • Photowhit
    Photowhit Solar Expert Posts: 6,002 ✭✭✭✭✭
    Re: New to solar, Massachusetts
    lasitter wrote: »
    For an event that happened once in 20 years, that makes it pretty easy to see that $8,000 in inverters and another $1,000 to $2,000 in batteries (plus other equipment) might not pay off.

    So how do you figure what it costs to store a kWh in batteries best suited for the task? The cost of putting solar panel energy into the batteries is either near zero, or the opportunity cost of what you would have realized in credits putting that same energy on the grid, isn't it?

    Now it sounds like your talking about a hybrid system, where your grid tied but have a battery back up?

    If your idea od a 15 Kwh array to offset your electrical expense, I would take a stab in the dark and say your battery bank numbers are off 10X!!!

    I off set a 4 Kwh winter load with a 4 Kw array, realistically you could likely do it with 2.5 Kw array, your array is 6x as large and will generate 3x as much energy if grid connected... That is a whole lot of storage!

    Off grid systems, start with an array 3x as large as a grid tied array, for the same usable energy. Only 50% of the energy is available once stored extra storage for cloudy days.

    So before we get into silly numbers, which off grid solar can be for a normal 'flip the switch' household, How many kwh's do you use a month, easy to find on your bill...
    Home system 4000 watt (Evergreen) array standing, with 2 Midnite Classic Lites,  Midnite E-panel, Magnum MS4024, Prosine 1800(now backup) and Exeltech 1100(former backup...lol), 660 ah 24v Forklift battery(now 10 years old). Off grid for 20 years (if I include 8 months on a bicycle).
    - Assorted other systems, pieces and to many panels in the closet to not do more projects.
  • Photowhit
    Photowhit Solar Expert Posts: 6,002 ✭✭✭✭✭
    Re: New to solar, Massachusetts

    On clearing the array, it can get dusty, mostly count on the rain to clear it, but for snow and long droughts, a 16 foot painters pole and 7 feet of reach and I can just get to the top of the panels.
    Home system 4000 watt (Evergreen) array standing, with 2 Midnite Classic Lites,  Midnite E-panel, Magnum MS4024, Prosine 1800(now backup) and Exeltech 1100(former backup...lol), 660 ah 24v Forklift battery(now 10 years old). Off grid for 20 years (if I include 8 months on a bicycle).
    - Assorted other systems, pieces and to many panels in the closet to not do more projects.
  • lasitter
    lasitter Solar Expert Posts: 56 ✭✭
    Re: New to solar, Massachusetts
    Photowhit wrote: »
    Now it sounds like your talking about a hybrid system, where your grid tied but have a battery back up?
    That's one alternative I'm considering. I like to consider lots of crazy things, and somewhere out there in all the alternatives you usually find the truth ...
    Photowhit wrote: »
    If your idea od a 15 Kwh array to offset your electrical expense, I would take a stab in the dark and say your battery bank numbers are off 10X!!!
    All I know is that various flavors of Big Reds are expensive, and I don't have any idea how many of them you'd need to deliver 4-8kw for say, 12 hours.
    Photowhit wrote: »
    I off set a 4 Kwh winter load with a 4 Kw array, realistically you could likely do it with 2.5 Kw array, your array is 6x as large and will generate 3x as much energy if grid connected... That is a whole lot of storage!
    I see this as a tricky area, from many angles. Like, what if you want to maximize your SRECs? The value of a megawatt put on the grid here is currently $270. But this is far from a static number. As I see it, this is the equivalent of a gold rush. As more people take advantage of the credits and put systems on line, SREC / auction values will decline. So part of this is figuring out how to get while the getting is good.

    It's also challenging to figure out how much system to build because you have to factor in the rapidly declining cost of solar panels, the marginal additional cost of a kilowatt added, how much energy your home will use, your local kWh rate, the value of redundancy for peace of mind, etc., etc.

    And if that's not enough, there are so many other things to figure that it can make your head spin. Since there's also a 30 percent federal tax credit for geothermal based system installs, how do you trade off money spent there versus the solar panels? What is the synergy like, derived from the fact that the solar will be producing the power that will be driving the geothermal heating / cooling / hot water?

    Even if all the credits / SRECs expire in 10 years, you still have the benefit of "free" power from solar to run your energy saving heating / cooling / appliances / whatever.
    Photowhit wrote: »
    So before we get into silly numbers, which off grid solar can be for a normal 'flip the switch' household, How many kwh's do you use a month, easy to find on your bill...

    Again, sage advice. I'm sure it's a complete different matter off grid where you're not going to be selling excess to anyone.

    And like you say, it's also a function of how much you want to store.

    My last 12 months electrical was 13,136 kWh, so I'm sure I'll benefit from whatever the array puts out. Electrical is too high because the gas water heater isn't putting out right, forcing the electrical tankless to take over. I make my living with computers, and I've also got some epic 24/7 computer power consumption.

    Look forward to doing better at my new place.
  • Photowhit
    Photowhit Solar Expert Posts: 6,002 ✭✭✭✭✭
    Re: New to solar, Massachusetts
    lasitter wrote: »
    It's also challenging to figure out how much system to build because you have to factor in the rapidly declining cost of solar panels, the marginal additional cost of a kilowatt added,...

    Solar panel may continue to decline a bit. Panel prices have been flat or perhaps a bit more expensive the last 3 years due to the tariffs. They represent a smaller percent of system costs and will/are running up to the material and shipping costs of the panels them selves.

    Something to consider is the federal tax credits may end for systems built after 2016, though I think there is enough support for credits to continue many have lost money betting on political whim...
    Home system 4000 watt (Evergreen) array standing, with 2 Midnite Classic Lites,  Midnite E-panel, Magnum MS4024, Prosine 1800(now backup) and Exeltech 1100(former backup...lol), 660 ah 24v Forklift battery(now 10 years old). Off grid for 20 years (if I include 8 months on a bicycle).
    - Assorted other systems, pieces and to many panels in the closet to not do more projects.
  • Cariboocoot
    Cariboocoot Banned Posts: 17,615 ✭✭✭
    Re: New to solar, Massachusetts

    Basic math.

    4kW for 12 hours = 48 kW hours. Gigantic quantity of power by off-grid standards.

    48 Volt system with zero losses (which does NOT happen) = 1000 Amp hours used.

    25% averaged DOD = 4000 Amp hour 48 Volt battery bank.

    Got $30,000 to spend on a massive bank of forklift batteries that are going to die over time whether you use them or not?

    The end-to-end efficiency of an off-grid system is typically 52%. This means the nameplate rating of the array times the hours of equivalent good sun (not just daylight) time 0.52 equals the number of AC Watt hours you can expect.

    Same process for grid-tie the efficiency is typically 77%, and you don't need as much equipment (lower cash outlay).

    The cost of power produced by either system is based on the capital expenditure to buy the equipment and the amount of power it will produce over its lifespan. Yes, lifespan; none of it lasts forever. Batteries in particular. As such you get numbers like $0.50 per kW hour for grid-tie and $1.00 per kW hour for off-grid. A long ways from $0.15 per kW hour utility.

    Having financial incentives to offset the initial purchase helps bring that down. The grid-tie then operates more efficiently because every Watt hour it can produce has someplace to go: the grid if not the load. Off-grid systems become more efficient if you can make use of their every Watt hour, but it is not as easy to do because as the batteries charge up the production potential is not realized unless opportunity loads can be utilized.

    As for back-up power, you don't try to run the whole house whether using batteries or a generator. You just try to run those things that would be a serious problem without power, such as refrigeration that would result in a loss of food and heating which could result in frozen pipe damage. This does not mean electric heat!

    Honda inverter-generator will run a long time on a few litres of gasoline. You don't need it running all the time either; cool down the 'frige, warm up the house, let everything rest overnight, start again tomorrow. You can even use it to recharge a small battery bank to give you power overnight and leave the solar for when the grid is up. The hybrid systems (grid-tie with battery back-up) cost more and are often larger than what is really needed.

    Solar power isn't cheap, and it certainly isn't free. Nothing is free.
  • Alaska Man
    Alaska Man Solar Expert Posts: 252 ✭✭
    Re: New to solar, Massachusetts

    When I had access to the grid I ran a chord from my brothers house to keep my batteries in float. The bank would supply my power when the grid went down, but we are not consuming anywhere near 8kwh I doubt any off-grid system is. Our average usage is between 10 and 12 amps. That's around 220 amp hours per 24. If you want to go off-grid you would have to down size big time. LED T.V. propane or inverter fridge, propane for cooking/heating water and wood heat just to start. We don't even own a microwave.

    You could have a small battery bank that runs critical loads during power outages, but a generator would do the same thing at a 10th the price. For the system I have in my signature line, plan to spend around $15,000 and you will still need to run the generator during cloudy weather, if there is no grid tie. With your Grid-Tie the generator run time is almost zilch, but you will still want a generator for backup.


    If I were you I would go grid tie to get the credits and take advantage of Government treats, but then get a nice inverter generator for back-up. Forget about the batteries/inverter/Charge Controller etc. Unless you just want to goof around with the stuff and money is not an issue for you? Expensive hobby.........
  • AuricTech
    AuricTech Solar Expert Posts: 140 ✭✭
    Re: New to solar, Massachusetts

    If you decide to install a grid-tie system (as Marc mentioned, battery-based PV systems are not cost-effective when grid power is available), you might want to consider the SMA Sunny Boy xxxxTL-US series of inverters. These inverters feature a "Secure Power Supply" 1500W outlet compatible with standard 110/120VAC outlets (I couldn't find the exact voltage for this outlet, but it's a standard three-prong outlet), which provides up to 1500W of AC power while the PV array is exposed to sunlight. That could give you enough power to run a critical load (such as a freezer), with some power available to recharge battery-powered devices.