hardware is here!

We have just received 10 200-W solar panels and the 4 kW inverter. I will post photos soon. We are aiming for installation the first week of December.

tax credits for Puerto Rico solar power installations

Prior to the passage of law 248, the Puerto Rico legislature created the Administración de Asuntos Energéticos (AAE) to monitor and regulate solar electricity installations in Puerto Rico.

I read law 248 of 2008 (in Spanish) last night. There are a few useful points to highlight.

1. The 75% credit was during Puerto Rico fiscal years 2007-2008 and 2008-2009.

2. The 50% credit applies for FYs 2009-2010 and 2010-2011.

3. After FY2010-2011, the tax credit is 25%, and this seems to extend for an indefinite period.

4. The credit applies to both the equipment and installation, although it also applies only to equipment that carries 5 years or more warranty.

5. The equipment must be installed and certified by solar-licensed electricians and engineers.

6. The tax credit can be carried over for up to 10 years, so if for some reason you cannot receive some or all of the credit in one year, you can carry it over to the next, for up to 10 maximum. This may be important, as the total available in tax credits for any given FY is limited.

7. The tax credit can be transferred once.

8. Apparently, the documents that are required for the tax credits must be submitted with one's tax returns for 6 years following the installation.

9. The sales tax (the famous IVU) does not apply to the acquisition of solar electric equipment.

Later, I will detail the process of applying for the tax credit.

finalizing specifications

Choosing a grid-tied system has its costs. The main one is that when the utility power goes down, so does the solar electricity. This is for several reasons. First, "grid tied" means what it says, tied to the grid, not to the house. It serves to mitigate some or all of the use of grid power, but the house still runs off the grid. Second, the house cannot run off power from the panels alone (inverted, of course). This is because of the fact of brownouts caused by clouds passing in front of the sun, or surges in demand. So a storage system is required as a buffer. This consists of a battery bank, which I decided against for reasons detailed below.

Our contractor visited with the solar energy engineer on Tuesday. They measured the estimated average daily production based on the hours of sun that can be expected per day. This measurement consists of first, a device that records the sky exposure of the site. Based on the annually integrated solar track, shadowing from trees, adjacent buildings, even our TV aerial, cloud-cover data for our location, and other parameters, it computes a number that they claim is quite reliable. In our case, we will get an average of 5.4 h/day of production. This comes to 300 kW-h/month, which is just over half of our energy usage.

We will purchase 2 kW in panels, but with a 4 kW inverter, so if we choose to add capacity, it means only additional panels. The panels are 200 W models from Canadian Solar. The inverter is a Sunny Boy 4000US. The reason to forego the batteries that would have given us a standalone system is mostly cost. The batteries are expensive and short-lived. In fact, I calculated that whatever we save in electricity costs, we will spend in replacing battery cells, which have roughly 5-year lifetimes.

Our contractor is PR Green Tech Corp. Julio Correa, the owner, is friendly and attentive, and appears to be quite devoted to his avocation. I hope this will serve us into the future as technologies evolve.

restart

After most of a year of delay, I have restarted my solar home project.

Yesterday (October 2), I gave a presentation on home solar power at a local parochial school, "Nuestra Señora de Carmen", in Hatillo, PR. I was very impressed by the abilities and interests of this group of 11^th graders. They asked a lot of interesting questions, and in this post, I will begin to address them. We start with anticipated power cost savings.

The simple calculation is to estimate how many kilowatt-hours per month my system will produce and how much electrical power will cost over the coming years. We are installing a 2kW system. We can reasonably expect to have full sun on the panels for 6 hours/day, 25 days per month, which adds up to 150 h/month. We currently pay 20¢ per kWh, so this will be worth $30/month. At this rate, we will reduce our electric bill by $360 a year, or $3600 over 10 years, and it will take about 20 years to pay off our ultimate construction cost, which is close to the 25-year 80% efficiency lifetime of the panels. (A total cost of $7200 includes the tax credit we expect to receive from the PR government.) In reality, it may take 25–30 years to pay off the system.

The above calculation makes a big assumption: that electricity costs will not go up. However, only a little over a year ago we were paying close to 30¢ per kWh, and this cost will increase in the coming years. The question is, by how much? This is a big problem to estimate, as electric power costs do not change with any predictable pattern. We can assume that these costs have bottomed out, given the state of the economy, the environment, and of known reserves of petroleum (see this link for estimates of future petroleum costs) (in PR there are currently no other sources of electricity). If electrical power averages 30¢ per kWh over the next 10 years, we will save $5400 rather than $3600.

I will do some more research on electricity costs. In future posts I will touch on changes in our plans, solar-thermal power, and wind power.

solar energy system components

My solar energy system is still taking shape, but here are the components I am looking at at this time, including some sample web sites that describe them:

1. Panels: Evergreen Spruce 195W — These are polycrystalline panels that we have chosen because of both their electrical and mechanical properties. I will try to spell these out in detail in a later post. We will mount them in sets of 3, to get 72 V and 585 W peak power.
2. Battery charge controller — The charge controller makes sure that the charging efficiency is maximized by regulating the charging voltage to the battery bank (48V) while minimizing power loss.
3. Batteries — These are a big issue, as we want to use the solar energy collected when the sun is down, but battery technologies are far behind the rest of the technologies we are considering, the costs are very high and stay high, as I estimate we will spend $800-1000 per year average to keep the battery banks at full strength. That is more than we expect to save from taking most of our electricity use off the grid.
4. Inverter — Inverter technology is very good these days. The inverter we have chosen is 4400W (model MS4448AE), which has 94% peak efficiency.
5. Automatic transfer switch

There are a lot of options on the market, which is very good. I am still doing my homework to compare systems and technologies.

My Solar Home

Web resources:
English:
Puerto Rico Incentives for Renewables and Efficiency

Español
Ley 248 del 10 de agosto de 2008
Carta Circular Rentas Internas 08-13
Resumen de ley 248

Introduction
In August of this year (2008) the government of Puerto Rico announced tax incentives for the installation of solar energy systems in homes and businesses. These include both electricity and water heaters. They pay up to 75% of the cost through June 30, 2009, 50% during the following year, and 25% thereafter. Costs that exceed the taxpayer's tax liability can be carried over to following years, up to 10 years.

My goal is to install a grid-tied solar electricity system to provide for most of my house most of the time. I hope to reduce my electricity use by 1/2, and I hope to sell a little back to the utility (at 10¢/kW-h). Here in Puerto Rico we have adequate to good sun all year, so this should work well.

My home has a solar water heater, and I have been considering solar panels since we began building in 2002. This tax incentive has inspired me to move forward, though I have been studying the options for some time. An internet search identified a handful of solar energy retailers in Puerto Rico, and I send out several e-mail and webform inquiries. I received a response from PRGreenTech.com, and most of what follows came from that communication. I also have visited Casa Solar, PR in Bayamón.

Julio Correa, of PR Green Tech, visited my home on November 21. I was concerned by the fact that there is a tree-covered hill to the east and many afternoons are cloudy, both of which may limit sun exposure, but Correa did not feel these were such important concerns. Sun will be on the panels by between 8:30 and 9:00, even in mid-winter, when the shading is worst, and we should typically have 4-6 hours of full sun. The fact that Puerto Rico is 18N latitude also helps.

Correa works with 48 V DC systems, and the panels are 195 W, 24 V. Rather than connecting to the charging system in pairs, producing 48 V in full sun, he uses the panels in sets of 3, which will produce 48 V even in some degree of shade. The panels are polycrystalline, which, though they are less efficient, have two advantages: 1. they are more durable, and 2. (I understand that) their "turn-on" light level is lower than for monocrystalline (I have to confirm this).

My house has a few items that produce heavy loads. We will exclude the one air conditioner, which will continue to connect directly to the grid. It is a 18,000 BTU/h unit, which is rated for 1950 W. That excluded, we still have the following:
1. A water (deep well) pump. We always use water from a 600 Ga reservoir, which is supplied from the aqueduct authority. This is because water supplies here are quite unreliable (we recently had 2+ weeks with no water during the day, and only a trickle at night). This pump is rated for 1500 W.
2. A microwave oven. Correa says these are among the biggest problems for solar inverters.
3. A toaster oven.
4. Blowdrier
Happily, our oven and cloths drier are both connected to gas. The solar water heater has an electrical backup, but if we are using that, it means there hasn't been sun for a while, so we will be running off the grid in any case.

In future blog posts, I will describe the process by which we choose our solar energy system. These are divided up as follows:
1. Total power output of the panels.
2. Specifics of the charging system (voltage regulation)
3. Battery capacity (in A-h), costs etc. (batteries are not covered by the tax incentive law, so cost is critical)
4. Inverter capacity
5. Grid-tie system
6. Questions:
- At what point in the battery depletion do we switch off the solar powered system and go to grid?
- How much solar panel capacity is needed to provide sufficient charge to the batteries to run until charging re-commences?
- How much energy consumption (A-h) will we need, and how to we convert that throughout the system?
- How do we make sure the system is expandable, so we can add capacity later for running the air conditioner?