Hi
Anyone here interested in Solar Power for the home? We are getting into it for back up when the power goes off and also to help offset the cost of Electrical bills that seem to keep going up.
Charlie.
Go read the posted link. It is a good long discussion that is continuing. I need to get back over there myself.
When I designed our house, the roof angle was just right for our area to maximize PV and hot water production. The house was sited to maximize this as well. The problem was that PV cost too much to install to make money sense. I have been looking to install PV for over 30 years but it has never made money sense. We really wanted to install radiant flooring but the cost was too high to justify. We have to have a heat pump to handle AC and we have a wood stove to heat the house. Having a third heating option that would have cost $50-75 a month on a 30 year mortgage did not make money sense. It would be cheaper to run the heat pump for heat.
Solar PV prices have dropped dramatically because of oversupply and low demand. This is good for the consumer but one is going to have to be careful on which panel maker to buy since there has to be a consolidation in the market and many have already gone under. One of the big Chinese firms went bankrupt in the last week or two.
Now is a very good time to be looking at PV. Two years ago, I did some more research on PV costs, subsidies, etc. The cost per installed watt was around $8. The Journal of Light Construction just had an article from a MA PV installer who said they are installing at a bit over $4 a watt. In the previous link, a TBN said he installed a PV system himself for a bit over $2 a watt.
My local community college just had a small class for home owners regarding PV. It was very good, and while I know a fair amount on PV, there were some great lessons in that class. Check out your local community college to see if they have a similar class.
This website,
DSIRE: Database of Energy Efficiency, Renewable Energy Solar Incentives, Rebates, Programs, Policy, has quite a bit of information on government subsidies for solar. The Federal subsidy is 30% and NC is 35%. There are also power company programs that can be good or bad. The ones in NC don't look so good to me since they put you on a time of use schedule meaning that my power costs go from 10 cents per KWH to either $3.xx or $5.xx! Here in NC we are lucky that there is a great source of information in the NC Solar Center at NCSU.
Here are some limitations to PV solar power:
- Traditional solar PV uses a single inverter to takes the DC power from the panel and converts to AC. The panels will be wire in a string and for some reason the lowest performing panel will limits the power output of the other panels. There will be power variations in the panels which really should not be a big deal but if one panel is shaded then the power generation from all of the panels are limited.
- There is a new technology called microinverters. A microinverter is a paper back book sized DC to AC inverter that is attached to each PV panel. Since each panel has its own inverter, a shaded or poorly performing panel does not limit the power production of other panels. This is goodness not only because of power production but also because all wires after the microinverter is AC power which any electrician is familiar. The problem with microinverters is that they only work on a grid tied PV system. They provide no backup during a system outage.
- Inverters are designed to sense the grid, and if the grid is gone, the inverters will stop producing power during an outage to prevent back feeding the power lines. Thus no grid power, means your PV can be producing power but it will not show up at your outlets, unless you have batteries...
- If you want power in an outage you have to have batteries which require DC power so microinverters are not an option. Batteries increase your costs substantially and will cost you in the future.
- Power is lost from the PV panels to the power outlets. I have read as much as 65% which seems very high to me. One of the modeling tools says the loss is 77%. I just figure 75% since it is easier to remember.
What this means is that if you want 3,000 watts at your power outlets, you need 4,000 watts of PV. That is a substantial increase in cost that is not really apparent until you dig into the technology.
- PV power production is not from sunrise to sunset but when the sun is at a certain point in the sky. In our case, we have about five hours of power production a day during the year. Putting 4,000 watts on the roof gets us 20,000 watt hours of power generation but only 15,000 watt hours at the outlets. 4,000 x five hours not 4,000 x eight or twelve hours.
- Net metering may or may not work for you depending on the local regulations.
- Batteries like human comfortable temperatures to maximize their lifetime so having them stored in the house is a good thing.
Let me throw out more numbers...
I was hoping to net meter and be able to generate enough power to drive my power bill to 0. This is possible with the size of my roof, current PV power densities, and the cost of PV. However, the net meter details and the hassle according the class I just went too, suggest that producing 100% of our power would be a waste of money. We would end up giving the power to the power company for free. :shocked: This forces us to only generate the power we use during the five hours of energy production during the day. So how much power do we use during the middle part of the day?
For the last week or so I have been reading our meter and figuring out our power production during certain times of day. My first guess and the data seems to suggest that we should put 4,000-5,000 watts on the roof to meet our energy needs during the day. That would save us about $50 a month in the power bill which is a bit more than a third of our cost on average.
We want power backup but that requires batteries. If we get $1,200 world of batteries that last 10 years that means we will be spending $120 a year on batteries or $10 a month. So instead of saving $50 a month on the power bill it really is $40. Is it worth $10 a month for have power backup? $1,200 worth of batteries is not much backup and one could easily double that amount which would reduce your power bill savings to $30 a month. One battery company was saying their batteries had a lifetime of 1,000 cycles. A cycle is a draw down of 50% to maybe 80% of its power. The more power use the worse for the battery lifetime. Buying 10,000 watt hours of batteries means you really should only use 5,000 watt hours. My measurements are that we are burning about 1,000 watt hours at night and 3-4,000 watt hours during the day NOT including the hot water heater, washing machines, clothes dryer, and HVAC. A 10,000 watt hour of batteries allowing 5,000 watts of usage is expensive and does not last long. Of course in a power outage, one would REALLY clamp down on power usage, but these sort of numbers are not readily apparent until you start digging into the details. The question one has to ask and answer, is the expense worth it? I might say yes but you might say no. It really depends on each person.
Back to lifetime of 1,000 battery cycles. If you wanted the batteries to last 10 years that means you could use the batteries 100 times a year or once every 3-4 days which I doubt many of us would do who are grid tied. I also don't see getting more than one or two cycles per day out of the batteries. The batteries would be charged up during the day, hopefully, then drawn down at night. I could see the possibility of using a generator to recharge the batteries in poor sunlight which might get you to two cycles a day. The longest power outage I think we could expect would be two weeks or 14 days. IF we cycled the batteries twice a day during an outage that is ONLY 28 times compared to 100 for the year. So it might be possible to get more years out of the batteries.
In my previous research, I figured seven years on the batteries as a hopefully worst case lifetime. The instructor in our class has built numerous PV homes and they are still using the original batteries from over seven years ago. He figures they will get at least 10 years out of the batteries. It seems possible.
I have never liked solar hot water heaters. They are just too complicated but they can/should drastically reduce your power bill. In theory our power bill would drop by 20-30% if we had a solar water heater. What has occurred to me with the lower cost of PV panels is that it might be cheaper to just throw in a few extra PV panels to heat your water and put the hot water tank on a timer that limits power usage. In effect, the hot water tank is a battery. I asked our instructor about this idea and he said one would need to run the numbers but that it is likely to be cheaper to put up extra PV panels. He said the cost of the solar water heaters they used went from $4,000ish to around $6,500! :shocked: You can put up a heck of a lot of PV wattage for even $4,000....
Later,
Dan
