June 8, 2015

Grid Tie Solar Generator

Solar panels to slow down your electric meter



TUCSON (A-P) — The simplest way to go solar is to hook up a grid-tie inverter to some solar panels. No batteries, no solar charge controller, and no permit needed if you don't put the panels on the roof. Just put in backyard facing south and run an extension cord from the generator to a plug. The panels make power and the grid-tie inverter turns the solar DC into AC, and it goes into your home wiring to be used. The solar power is free electric power not drawn through the utility's meter and so isn't measured. If the panels are generating 400 watts and your home is using 1000 watts, you're paying the utility for 600 watts instead of 1000 watts for a few hours a day. If you're only using 400 watts the meter will stop. If only using 300 watts, you will be giving 100 watts free to the power company to sell, but average homes use over 1200 watts on average, especially on hot sunny days.

The grid-tie inverters shut down if the power grid goes down to protect and workers who will need to fix it, so during a power outage you will have no solar power either. To have solar power you'd have to have a battery bank, a solar charge controller, and a different type of inverter. The solar panels could charge a battery bank or send the power to the home wiring, but not both at the same time. An off the grid system is much more expensive. The batteries would have to be replaced periodically. They might last 5 years while the solar panels will last 25+ years. The grid-tie inverter is the only part of the system that probably won't last 25 years. How long the inverter will last is an unknown. Maybe 1 year, maybe 10 years, maybe more years.

Bigger may be better, but only up to the point you are giving free energy to the power company, as unless they put a special meter on your house (and they won't unless you get a huge, approved, and expensive system) the meter won't run backwards. The electric company isn't going to pay you if you produce more power than you use.

A small system is a cheaper system. The grid-tie inverters go from a $90 250W inverter to a 1500W $470 one. The rated power output is a maximum one meaning a 250W inverter is rated to work with up to 250 watts of solar panels, but the inverter will likely last longer if not pushed to the max, so 200 watts of solar panels would be better.

The 200 watt rating is the maximum the panel will put out on a cold sunny day. When it is hot, panels put out less power, maybe 80% of rated power or 160 watts. The inverter itself may be 90% efficient, and the sun won't always be pointing directly at the panels, and there may be clouds or dust on the panels, and so a 200 watt array may be putting 125 watts into your home wiring when the sun is shining and 10 watts when it's cloudy. In Tucson we get about 290 days of full sun.

A 100W solar panel is about $150 for one, so a small 200W system would be $290 for panels + $90 for inverter + about $100+ in bits and pieces, not counting an extension cord or labor. A system of 4 panels and a 500W inverter which would be $570 for panels, $170 for 500W inverter, plus little stuff, say $850 in parts. Panels are the main cost. If 8 panels were used they'd cost $1,140, and a 1000W inverter would be $250, so you're looking at about $1,500 just in components.

If going solar is all about saving money, then going solar only barely makes sense as a long-term investment. A 400w system costing $999 will save maybe $60/year in electric, and will "pay for itself" in 17 years if nothing breaks assuming $0.11 kWh, or more like 20 years as the inverter will likely not last 17 years. The assumption is that electric prices won't go up and up and up. If electric cost is $0.16 kWh, then payback would be 11 years. In some areas electric cost is $0.50 kWh and payback would be less than 4 years and in 10 years don't be surprised if your electric rates double. Going solar is more than about saving money. It matters who you are paying for what. Going grid-tie solar and owning the panels is a step to going off-grid in the future as may be a better idea then.

A sensible plan would be to start small, and add more generators over time. If you move, take'm with you or sell them easy enough. Having more than one small generator adds up and not having all your solar power depend on one big generator is worth considering. If a 200W system costs about $2.50/watt and a 400W system costs $2.15/watt, so two 200W systems would be more for parts and involve more labor, but if one inverter failed the other system would still be working and $90 would get you a new inverter. An 800W system would be about $2.00/watt for parts, be less work, but if the inverter dies the whole system is down. Four 200W systems would cost more than one 800W system, would involve more labor to make, but you could buy an extra $90 inverter for a spare and have a much more reliable easy to fix system.

If 800 watts isn't enough, add 200W more for 1000 watts, or another for 1200 watts, or 1400 watts, and so on. The 200W generators could be lined up or scattered around. Three or four could share an extension cord. You wouldn't want to plug in two 1000W inverters into one circuit as you would overload the wires in a 15A circuit which could cause a fire. Best to plug the solar generators into several different circuits. The power will be available to all circuits, you just don't want to overload one circuit by putting all the panels on it.

Each 200W generator would have its own inverter which means each would need its own housing, which involves more materials and labor, but the redundancy of having 5 generators instead of one means there would never be a total system failure. Buy a couple of extra 250W inverters and never have any serious downtime. To go with one 1000W system would be putting all your eggs in one basket.

The generators can be plugged into a Kill A Watt meter ($18) which will tell you how many watts each is generating and how much a day, week, month, or year you are saving. This raises the question of how long it will take to pay for the systems from the money saved. Assuming in Arizona you're getting about 6 sun-hours a day average, and you're paying 11 cents per kwh, then the pay off time would be about 15 years at current prices. Solar isn't cheap, but the satisfaction of not paying quite so much to support your local power monopoly may be priceless.

The only certainty is that the cost of grid power will go up and up, so maybe the pay back period will be 10 years. If you got their permission to put in a huge grid-tie system on your roof, they'll make sure you pay for the privilage of being tied to their grid one way or another. The ultimate satisfaction would be to go off-grid and tell them to take their meter and shove it somewhere, but that would really cost a lot. At this time, a little satisfaction is obtainable.



RENOGY 100 Watt 100w Monocrystalline Photovoltaic PV Solar Panel Module 12V Battery Charging


250W 300W 500W 600W 1000W 2500W Grid Tie MPPT Power Inverter Converter for Solar Panel and Wind Turbine Generator System Stackable Pure Sine Wave USA (500W Solar Input 10.8v - 30v DC)


P3 P4400 Kill A Watt Electricity Usage Monitor


RENOGY® Branch Connectors Solar MC4 Connectors Y connector in Pair MMF+FFM


Odyssey 30A MC4 Solar PV In-Line Fuse Holder Waterproof w/ Fuse 30 Amp


RENOGY® One Pair of 10ft. Adaptor Kit Solar Cable PV with Mc4 Female and Male Connectors AWG 10 Connecting Solar Panel to Charge Controller, Perfect Match with Renogy Panels


Islandoffer 5 Pairs of MC4 Male/ Female Solar Panel Cable Connectors


A custom housing would be needed for each inverter to keep it dry yet well ventilated. Also needed would be nuts and bolts, and aluminium bar to hold panels together. A couple of support poles would attach at top of panels and prop them up. The bottom of poles would attach to a cement block sitting on the ground to keep wind from blowing the panels over. The angle of the panels should be adjusted three or four times a year so they point to the low winter sun or high summer sun. Otherwise they just sit somewhere. The 200W system would be about 47 in. x 44 in. and weigh about 40 lbs. It could be transported in the back seat of a car.

Detailed how-to-make insturctions will be given as this is a work in progress.


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