Energy meter for grid-tie solar system?

TonyC
TonyC Registered Users Posts: 3
I'm thinking of installing a 100 Wp grid-tie system for research purpose. I want to measure the long term actual output of the system instead of simply trusting the rated power and applying some modifiers to account for losses. This will be plugged to an outlet instead of being properly wired. Yes, I am aware that that is risky, but it's for personal research, and I don't want to spend lots of money into it and I want to be able to unplug it when I am done. And at 100 Wp the current should still be within the safety limit of the wiring in my house. (Edit: AND WITHIN LOCAL CODE. Checked. I'm fine as long as I stay under 100 Watt.)

Anyway, my real question is about measuring the amount of electricity gained. As I see in youtube it seems I can use any regular energy meter (e.g., Kill-A-Watt or any number of similar devices). But energy meters usually measure the flow of electricity from the outlet into the plugged device. I, on the other hand, want to measure the flow of electricity from the plugged device (the solar power system) into the outlet. Can a regular energy meter do it or do I need a special one?

Comments

  • Aguarancher
    Aguarancher Solar Expert Posts: 315 ✭✭✭
    Re: Energy meter for grid-tie solar system?

    While there are many grid tie gorillas out there, don’t expect to get much info here on furthering your potential illegal activities. Labeling it “for research purposes” doesn’t cut it. Any advice offered from the forum could have possible liability consequences attached to it. jmo (just my opinion).
  • verdigo
    verdigo Solar Expert Posts: 428 ✭✭
    Re: Energy meter for grid-tie solar system?

    If you purchase a grid tied or grid interactive inverter and have it net metered by you utility you will know how much you produce. What's to research?
  • Cariboocoot
    Cariboocoot Banned Posts: 17,615 ✭✭✭
    Re: Energy meter for grid-tie solar system?

    Note: in some circumstances if you do not have the proper meter on your utility your excess production will read as consumption to them and you will be charged for your contribution.

    But with 100 Watts, why even bother? You can make a bigger dent in your bill by turning things off. Really.

    Here's why: if the unit could maintain 100 Watts output for 4 hours a day (and don't expect more than 6 at the maximum) that would be 400 Watt hours. Compare that to your electric bill. It's like leaving your TV off for two hours of the day.

    Reverse the plug/outlet arrangement on the inverter and a Kill-A-Watt will read the energy flowing from it to any loads. Many small (off grid) inverters have outlets built in.

    Stick with off grid for your research. Do not trust any of those plug-n-play grid-tie inverters. You may be trusting them with your life. No joke.
  • Photowhit
    Photowhit Solar Expert Posts: 6,002 ✭✭✭✭✭
    Re: Energy meter for grid-tie solar system?
    Reverse the plug/outlet arrangement on the inverter and a Kill-A-Watt will read the energy flowing from it to any loads. Many small (off grid) inverters have outlets built in.

    Would you have to with alternating current?...
    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: Energy meter for grid-tie solar system?
    Photowhit wrote: »
    Would you have to with alternating current?...

    Good question. I've never tried back-feeding my meter (not a K-A-W) and I don't know exactly what is inside them. In theory the connection should be bi-directional. In practice ... theories often fall down.

    But for the sake of mechanical and safety considerations the supply should be an outlet, not a plug. This completely falls apart with a GTI where it produces nothing (we hope) without the sync signal of the grid and you certainly don't want the grid to be a plug! I'd recommend a double-ended plug, but even that can present a danger if it's in the grid outlet; live prongs dangling. There's always some risk.

    Now I'm curious about wiring the meter up backwards to see if it will work "wrong way around".
  • TonyC
    TonyC Registered Users Posts: 3
    Re: Energy meter for grid-tie solar system?
    verdigo wrote: »
    If you purchase a grid tied or grid interactive inverter and have it net metered by you utility you will know how much you produce. What's to research?

    The local utility does not have a net meter. There is no FIT. I am in Indonesia. Local conditions are not the same. Many data aren't available or unusable. For example, the panels that Northern Arizona Wind & Sun sells? Are not available locally. Pre-made mounting and cabling? Doesn't exist here. Energy tax credit? Not here yet. UL and CE certification? No such thing. Local electricity code was last updated in 2000 and has nothing about solar power or tying it to the grid. The few local sellers concentrate on the off-grid market, which is great for those who live in remote villages, but not so much for a city guy like me.

    I need to research almost everything myself. Right now my reference book is the Solar Electricity Handbook 2012, which is very useful, but getting help from you guys will be great.
    Note: in some circumstances if you do not have the proper meter on your utility your excess production will read as consumption to them and you will be charged for your contribution.

    But with 100 Watts, why even bother? You can make a bigger dent in your bill by turning things off. Really.

    Here's why: if the unit could maintain 100 Watts output for 4 hours a day (and don't expect more than 6 at the maximum) that would be 400 Watt hours. Compare that to your electric bill. It's like leaving your TV off for two hours of the day.

    Reverse the plug/outlet arrangement on the inverter and a Kill-A-Watt will read the energy flowing from it to any loads. Many small (off grid) inverters have outlets built in.

    Stick with off grid for your research. Do not trust any of those plug-n-play grid-tie inverters. You may be trusting them with your life. No joke.

    I am not sure how off-grid will help me when I am trying to determine whether solar power is competitive with grid power locally. I can't use American or European numbers to figure economic feasibility. I know the local power pricing (about US$ 0.11-0.13 per KWH), but I have no idea what the expected power production will be. I can find insolation data, but there's no weather data, so it's not adjusted for seasons or even clouds. Plus given the unfamiliar brand names, who knows what their actual efficiencies are?

    We are already reducing power consumption. We have started using LED lighting. We use fans instead of air conditioning during the day. We use a propane stove. But we can't switch to off-grid. The investment needed for a solar power system big enough to go off-grid is just too expensive. So I am instead trying to reduce billable KWH.

    Please be assured that I don't trust the plug-and-play inverters. The inverter will be put on a circuit that usually only has lighting. Additional circuit breakers will be installed around the inverter. There are no kids in the house. Given that we use 220V, the inverter should output less than 0.5 A, which is well within the safety margin of the outlet and wiring. If things goes well, the plug and play inverter will be ditched and the system expanded with more panels with micro inverters wired to the house's power entry point. But only if it's economically viable. To know that, I need to be able to measure and record the amount of electricity produced. Hence my question about those small energy meters.
  • Cariboocoot
    Cariboocoot Banned Posts: 17,615 ✭✭✭
    Re: Energy meter for grid-tie solar system?

    With your utility rates around $0.10 to $0.13 per kW hour you will not see any benefit from solar. Rates are about the same here where I am, and production from solar is 5-10X as expensive. I expect you also have the problem of high prices for any solar equipment, which only makes things worse.

    You can easily set up an off-grid system that will be safe (no connection to the grid) and see how much power you get out of it, but it will involve a battery. The main problem with off-grid is that the full power potential can only be realized when you have enough load to maintain full PV production when the batteries are near or at full charge. This is difficult to achieve and will never be at 100%.

    But the basic problem is that with even the most efficient production (standard grid-tie; no charge controller or batteries) the cost base of capital investment amortized over equipment lifespan and divided by kW hour production comes down to expensive electric. Even in the US with tax credits and cheap equipment and known insolation factors some installs have no payback at all due to low utility rates, and you already have those low rates.

    I don't see anything that wound indicate you benefiting from solar unless your grid is unreliable.
  • Photowhit
    Photowhit Solar Expert Posts: 6,002 ✭✭✭✭✭
    Re: Energy meter for grid-tie solar system?
    TonyC wrote: »
    I can find insolation data, but there's no weather data, so it's not adjusted for seasons or even clouds.

    Generally the insolation numbers are actual measured numbers over time. A good chart/graph or table should include this information, but some don't. Here's one site that states for 1983-2005

    I think you can do projections from what information you have. If your asking about solar panel efficiency when you state;
    TonyC wrote: »
    Plus given the unfamiliar brand names, who knows what their actual efficiencies are?
    Panels should run at roughly 77% of their panel label rate, you may find other standards in your region, but hope fully you can refer the manufactures test standards and compare them to the European and US standards. I suspect if they are made for world markets they will be labeled to the same standards.

    So you can multiply the hours of insolation x the rated panel number x 75%(an extra 2% off for inverter inefficiency) x 365 should give you an idea of how many watts you would produce.
    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.
  • TonyC
    TonyC Registered Users Posts: 3
    Re: Energy meter for grid-tie solar system?
    With your utility rates around $0.10 to $0.13 per kW hour you will not see any benefit from solar. Rates are about the same here where I am, and production from solar is 5-10X as expensive. I expect you also have the problem of high prices for any solar equipment, which only makes things worse.

    You can easily set up an off-grid system that will be safe (no connection to the grid) and see how much power you get out of it, but it will involve a battery. The main problem with off-grid is that the full power potential can only be realized when you have enough load to maintain full PV production when the batteries are near or at full charge. This is difficult to achieve and will never be at 100%.

    But the basic problem is that with even the most efficient production (standard grid-tie; no charge controller or batteries) the cost base of capital investment amortized over equipment lifespan and divided by kW hour production comes down to expensive electric. Even in the US with tax credits and cheap equipment and known insolation factors some installs have no payback at all due to low utility rates, and you already have those low rates.

    I don't see anything that wound indicate you benefiting from solar unless your grid is unreliable.

    We're getting off-topic, but eh, sure.

    The grid IS unreliable. Last Thursday there's a grid failure. Dunno why, they didn't say. And I live in a big city. Over at my parent's place in the boondocks, back in July there was 3 days of consecutive power shutdown each lasting over 8 hours. The reason? Not enough fuel to run the local diesel-based power plant. If everything works out eventually I'll go with a grid-interactive system, but that's for way later.

    Solar equipment prices vary. American-made equipment are more expensive due to the logistics involved, but Chinese, Japanese, Taiwanese, Australian and South Korean ones aren't. Several companies opened local solar panel assembly factories to take advantage of cheaper labor cost too. While the wafers are imported, the price is competitive at approx. $1-2 per Wp depending on brand and model.

    As for benefits, well, at this point knowledge is its own reward? I am very aware that this experiment will not make money. Period. It is geared for minimum initial investment and simplicity, not maximum power production. However, the budget for this experiment is less than $400. I can afford to lose it. I can even salvage and sell the components (probably not the inverter) and recoup some of the money later. Going with an off-grid approach and a battery will not save me money. The cost of a deep-cycle battery and charge controller plus the need of finding a suitable DC load will actually be more expensive.

    Power cost is going up. Solar system cost is going down. There is talk in the government of introducing Feed-In Tarifs and giving rebates for solar installations. I am not going to put too much money into this until the above happens, but I can spend $400 on a new smartphone or this, and since my current Android smartphone is good enough for the moment, well....

    EDIT: thank you Photowhit for the link. That matches with what I have and it's nice to have corroboration.