{"id":455,"date":"2012-11-13T16:29:59","date_gmt":"2012-11-14T00:29:59","guid":{"rendered":"http:\/\/shirleyandchris.net\/blog\/?p=455"},"modified":"2020-10-04T17:50:09","modified_gmt":"2020-10-05T01:50:09","slug":"solar","status":"publish","type":"post","link":"http:\/\/shirleyandchris.net\/blog\/2012\/11\/13\/solar\/","title":{"rendered":"Powering Our Home With Solar Panels"},"content":{"rendered":"

We recently had solar panels installed on our home by Real Goods Solar<\/a> in March of this year. This post describes some of the process and analysis that went into the decision, the installation and tracking the results.<\/p>\n

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Background\u00a0<\/strong><\/p>\n

We are a pretty green family and try to minimize our impact on the environment.\u00a0 Chris has been very interested in energy use and the environment for a long time (including majoring in this subject in college and grad school and is currently working in the field).<\/p>\n

Solar electricity produces no air pollutants or greenhouse gas emissions during operation (there is some energy and pollution generated when the panels are made, but that is typically offset in a year or two).\u00a0 It also produces electricity during times when demand is highest which helps to alleviate stress on the electric grid.\u00a0 Peak electricity use in California occurs in summer afternoons<\/a>, when air conditioning use is highest.\u00a0 Since we don’t have air conditioning, the excess electricity that we generate during these hours helps to reduce demand during peak hours (which offsets electricity use from inefficient and polluting peaking power plants) and reduces strain on the transmission and distribution system.<\/p>\n

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Financial considerations <\/strong><\/p>\n

There were a couple of ways to get the solar panels: buying or leasing.\u00a0 With leasing, you don’t own the system and you pay the solar company instead of the utility for the electricity that the system generates, but the big benefit is that you don’t have to pay much (or anything) upfront to go solar.\u00a0 With buying, which is what we did, you pay for the system upfront, but then you own the system and we won’t have to pay PG&E or anyone else for electricity ever again.<\/p>\n

The net system cost after federal and utility rebates was $9500.\u00a0 A big question that many people have is how long will it take for the system to “pay” for itself through savings on our electric bill.\u00a0 The answer is, it depends.\u00a0 It depends because we don’t know what PG&E rates will be in the future.\u00a0 If we continue to use the same amount of electricity and if electricity rates stay the same in the future, then it’ll take about 20 years before we save enough money to pay for the system.\u00a0 If rates rise at 2-3%\/yr (the historical average), then our system will pay off slightly faster in 16 years.\u00a0 Basically, we have pre-paid\u00a0 our electricity bill for the next 16 to 20 years and our electricity will be free after that (hopefully another 20+ years).\u00a0 Solar panels typically lose about 0.5% efficiency each year, so after 40 years, the maximum output will still be (hopefully) around 80% of the rated power.\u00a0 16 year payback is equivalent to a 6% return on investment.<\/p>\n

One of the reasons why it takes so long for our system to pay for itself is that our system is relatively small, and labor is a big part of the installation cost.\u00a0 Another reason is that we are very efficient with our electricity usage (lots of Energy Star appliances, fluorescent bulbs, etc. . . ).\u00a0 PG&E has tiered rates and as you use more electricity, the price of electricity rises.\u00a0 If you are in the top tier, each additional kWh of electricity you purchase costs 33c\/kWh, whereas we only pay 13c\/kWh.\u00a0 If your solar panels can offset your usage of electricity that costs 33c\/kWh rather than 13c\/kWh, your system will pay back much faster.\u00a0Solar Hot Water Systems Installation, Repairs & Prices in Perth, WA<\/a> is another effective usage of alternative energy sources.<\/p>\n

It is unclear whether having the solar panels increases the value of our home (we recently had an appraisal for our refinance and the appraiser didn’t add any value due to the solar panels).\u00a0 However, it would be logical for a rational buyer to value the panels based on the present value of the expected electricity bill savings.\u00a0 (Sandia National Labs created a tool<\/a> to help estimate an appraisal value for a solar system and after plugging in the relevant stats on our system, it came out with an average value of $7837 for our brand new system).<\/p>\n

Gathering data and analysis<\/strong><\/p>\n

The previous owners of the house had solar panels on the roof.\u00a0 You can see from this satellite image on Google maps that there were 22 panels on the roof.\u00a0 When we bought the house, the panels were no longer there, though we are not entirely sure of the circumstances (it was a foreclosure, so the bank didn’t disclose much).\u00a0 Anyway, the panels were gone but the mounting brackets was still largely on the roof and in good shape.\u00a0 So when we bought the place, the idea that we could install some panels on the roof was fairly obvious. We first needed a Soft Wash Roof Cleaning Services<\/a> come out and clean the roof before we installed anything.<\/p>\n

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We contacted Real Goods Solar, who looked at our past energy usage and checked out the roof in order to determine the size and design of a system.\u00a0 (We went with Real Goods because\u00a0we’ve been to their store\/solar living center <\/a>a few times and their sales rep Justin was super helpful and knowledgable).<\/p>\n

Our electricity meter from PG&E is a smart meter so we have access to hourly data on our energy usage (both natural gas and electricity) since we’ve lived in the house.<\/p>\n

Chris used a web-based program called PVWatts<\/a> from the National Renewable Energy Lab to download representative hourly solar data for San Francisco in order to estimate the amount of solar generation we might expect on an hourly basis.\u00a0 Our climate isn’t exactly like San Francisco – we’re 15 miles away across the bay – but it is similar enough to get a decent estimate.\u00a0 If anything the estimates will be conservative since San Francisco is a bit foggier\/overcast in the summer.<\/p>\n

Chris put all the data into excel and ran a few calculations to aggregate the data in to monthly averages.\u00a0 This figure compares our average hourly electricity usage for the month of July 2011\u00a0 (red line) to the estimated solar generation in July for a system like ours in San Francisco (black line).\u00a0 You can see the electricity demand is relatively flat while solar generation peaks in the middle of the day and is much higher.\u00a0 Our system does not have batteries because we are still connected to our utility (PG&E). In essense, we can use the electricity grid as our storage system.\u00a0 Once we installed the solar panels and our system was approved and connected to PG&E, our system became “net-metered” meaning we would draw power from the electricity grid when demand was greater than supply (before 7am and after 6pm) and we would be feeding power to the electricity grid for others to use when our generation was greater than our demand (between 7am and 6pm).\u00a0 The meter keeps track of the net flows of power and keeps track of whether we had excess demand or supply in the month and that is the amount they will charge us for.<\/p>\n

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This next figure shows the same data but for the month of January.\u00a0 Solar generation is lower because the sun is at a lower angle and is out for fewer hours.\u00a0 Demand is a bit higher than July, mainly due to more lights and our furnace (which runs on natural gas to produce heat, but uses electricity to power the blower to move the heat around the duct system).<\/p>\n

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We typically use about 3300 kWh\/year (around 200 kWh\/month in the summer and up to 300-400 kWh\/month in the winter).\u00a0 This is about half of the average household electricity usage for PG&E (6500 kWh\/yr).\u00a0 Our system is estimated to produce a little bit of excess generation for the year (3600 kWh\/year, ranging from 160 kWh\/month in the winter to over 400 kWh\/month in the summer).<\/p>\n

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Installation<\/strong><\/p>\n

Here are two of the Real Goods installers on the roof.\u00a0 You can see the existing roof mounts, little metal brackets that attach through the roof to the roof rafters, that were left behind by the previous owners.<\/p>\n

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They are setting up some rails to the brackets which are then used to attach the panels.<\/p>\n

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Here are all the rails after they have been installed.<\/p>\n

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The crew had a cool method of getting solar panels onto the roof.\u00a0 We had 10 panels installed (225 watts each for a total of 2250 watts).\u00a0 Talking with the crew, they used to strap panels to their backs and climb the ladder.\u00a0 These panels weigh about 46 lbs each and are about 5′ tall x 3′ wide.\u00a0 But as you might expect, this is pretty dangerous since the panel will catch any wind and these guys are 30 feet off the ground.\u00a0 So the had a small electric motor and a pulley system at the top of the ladder to pull the panel up to the top of the ladder where one of the installers could grab it.<\/p>\n

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Placing the panels onto the mounting rails.<\/p>\n

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The finished installation (10 panels, 8 on top and two below).\u00a0 Of course it’s cloudy when this picture is taken (you can see the BART tracks and the San Francisco Bay in the background).\u00a0 Chris climbed the ladder to get a closer view of the solar panels.\u00a0 It’s bit scary being up 30 feet on a ladder.<\/p>\n

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Another view of our roof and some of the unused brackets.\u00a0 Here we have a view of the Berkeley hills in the back.\u00a0 We can always add additional panels in the future, which would be useful if we decide to get an electric vehicle (someday).<\/p>\n

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System Details and Performance<\/strong><\/p>\n

The system in detail<\/p>\n